Hello all,
I hope you can help me.
I'll try and be as thorough as I can with my description.
The Bongo is a 2.5 diesel - year 2000 (not the one in my avatar)
We were queuing to leave an event this Sunday (Motocross of nations as it happens). It was stop / start stuff for around 1 1/2 hours to move about a mile - just the sort of thing to get an engine nice and hot. However, we'd done it last year where the weather was much hotter and the queue was longer by about an hour and we got out just fine.
I did all the sensible stuff - turning the engine off when I could but the engine appeared to get a bit hotter than I expected (I have the Haydn TM2 with a temperature sensor and low coolant alarm). I then turned the heating on and no hot air came out. A bit of panic set in and, just a couple of seconds later the low coolant alarm went off and I noticed the Mazda temp' gauge was at 1 o'clock. As you might expect I pulled over.
Fortunately I had some coolant with me and a funnel. I'm not sure how good a job I did but I topped up with coolant and bled the system. Heat now came out of the heater and we set off again. About 10 minutes later I heard a gurgling sound from the front - the header tank I thought - and then the coolant alarm went off again. Time for the AA.
They did a sniff test on the coolant - all was ok indicating no exhaust gasses in the coolant.
They also did a pressure test on the coolant system - again ok
The very sound AA chap said it could be a coolant leak that only happened when hot, it could be the head gasket, it could be the water pump.
A long time later having got home on a flat bed I changed the thermostat (testing it worked first), topped up the radiator, header tank and bled the system.
The Bongo appeared just fine except for one thing. When I bled the system I noticed that, after the few initial and large bubbles in the funnel, no others came through. I usually bleed the cooling system twice a year and, normally, you get a few small bubbles coming through but, this time, there were none at all. Not even tiny ones. I also noticed that, on revving the engine whilst bleeding, the coolant level in the funnel didn't drop much at all. It did drop a bit but not by much. there wasn't even the usual glug when the thermostat opened (at about 70 deg' on the TM2)
It was like a perfectly bled system should behave like. In any case everything worked fine, front and rear heaters, temp' gauge back to 11 o'clock.
Although the Bongo appears fine I put the old thermostat in boiled water and, annoyingly, it opened.
Along with the lack of bubbles when bleeding, the Bongo passing the sniff test and coolant pressure test could this be a water pump failure?
The water pump belt is ok. I did try leaving the heating on full to see if it got colder (thinking that if the coolant wasn't circulating the heating matrix would cool down and the air would get cold) I've no idea if this is a valid test but the heating stayed hot for the 5 minutes I tried this.
Finally the coolant system is in good nick I thing. I flushed it out thoroughly about 4 years ago and it had a new radiator about 6 years ago.
We've never had cooling issues before.
Your thoughts and help much appreciated.
Thanks,
Tony
What could cause this overheating. Water pump failure?
Moderators: Doone, westonwarrior
Re: What could cause this overheating. Water pump failure?
the heaters allways hot as soon as engine gets hot,its the flaps descide if hot air comes into cabin
waterpumps leak from bottom and can be hard to spot,you said rad was done 6 years ago,waterpump if older i would change anyway
waterpumps leak from bottom and can be hard to spot,you said rad was done 6 years ago,waterpump if older i would change anyway
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Northern Bongolow
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Re: What could cause this overheating. Water pump failure?
how was a pressure test done,? what method was used. was it a vac test or a positive pressure test. ive found that some water pump leaks leak at operating temps and pressures but seal again when tested up to 1 bar. take a dentist mirror and torch to shine into the mirror, its awkward to see the underside of the pump coss the belts are in the way, if you do it right and the pump is shot there will be a coolant (clean) slug trail at the 6 oclock position on the casting. ignore the tell tale hole at the 3 oclock position on the passy side, they dont tend to show leaks there but the 6 oclock tell tale hole is slightly nearer the seal on the shaft so show there first.
if during the bleed (using the video method) the funnel doesnt drop its level when the engine is revved there may be air in the system, this air stops the circulation of the system so that even the water pump cannot overcome the air lock. this applies in the following way depending on where you are in the bleed process,when the coolant is relatively cool at the start of the bleed it takes little revving to empty the funnel, as the process goes on and the coolant gets hotter the amount of revs and the duration of the rev time increases until you reach a point where the stat opens and the revving of the engine actually reverses the flow into the funnel causing it to fill when revved.
during the bleed did you manipulate the top hose and bottom hose to feel if water was present, squeezing them has the effect of manually priming the system as the pulse shifts air around towards the outlets.
putting the heaters does nothing to save the bongo other than to see if the heaters are hot, if they are hot you have coolant circulation, if they are on hot but are blowing cold then circulation is lost and a boil up imminent. the way to cool a struggling bongo is to put on the air con, this puts the front fans which cools the rad. also if stationary rev the engine up, this cools via the waterpump, the stat should already be open so it dumps the hot coolant into the rad to be cooled. if driving push the hold button to lock in a lower gear or select a lower gear to increase the speed of the water pump.
you didnt say the fans came on so i would swap the fan switch the one over the starter motor, these can get the end broken off or loose and affect the trigger point of the fans. use a gen mazda one not a cheaper copy they are twice the price but still cheap in the grand scheme of things. replace the pump.
replace the stat if not genuine mazda.
when you bleed it up again get the bongo as hot as you can after all the air is out, then fit the exp tank cap and bleed pipe bung then rev the nuts off it until its as hot as you can get it (in a healthy system the fans should still not be on) then turn the engine off for 2-3 mins then turn the engine back on and this will trigger the fans as all the hottest coolant is stuck in the head, they should run for about 2 mins then go off, this proves they work correctly before you need em in anger on the road.
good luck.
if during the bleed (using the video method) the funnel doesnt drop its level when the engine is revved there may be air in the system, this air stops the circulation of the system so that even the water pump cannot overcome the air lock. this applies in the following way depending on where you are in the bleed process,when the coolant is relatively cool at the start of the bleed it takes little revving to empty the funnel, as the process goes on and the coolant gets hotter the amount of revs and the duration of the rev time increases until you reach a point where the stat opens and the revving of the engine actually reverses the flow into the funnel causing it to fill when revved.
during the bleed did you manipulate the top hose and bottom hose to feel if water was present, squeezing them has the effect of manually priming the system as the pulse shifts air around towards the outlets.
putting the heaters does nothing to save the bongo other than to see if the heaters are hot, if they are hot you have coolant circulation, if they are on hot but are blowing cold then circulation is lost and a boil up imminent. the way to cool a struggling bongo is to put on the air con, this puts the front fans which cools the rad. also if stationary rev the engine up, this cools via the waterpump, the stat should already be open so it dumps the hot coolant into the rad to be cooled. if driving push the hold button to lock in a lower gear or select a lower gear to increase the speed of the water pump.
you didnt say the fans came on so i would swap the fan switch the one over the starter motor, these can get the end broken off or loose and affect the trigger point of the fans. use a gen mazda one not a cheaper copy they are twice the price but still cheap in the grand scheme of things. replace the pump.
replace the stat if not genuine mazda.
when you bleed it up again get the bongo as hot as you can after all the air is out, then fit the exp tank cap and bleed pipe bung then rev the nuts off it until its as hot as you can get it (in a healthy system the fans should still not be on) then turn the engine off for 2-3 mins then turn the engine back on and this will trigger the fans as all the hottest coolant is stuck in the head, they should run for about 2 mins then go off, this proves they work correctly before you need em in anger on the road.
good luck.
Re: What could cause this overheating. Water pump failure?
Cheers Northern Bongolow,
It was a positive pressure test using the header tank.
I'm not sure what the pressure was but the AA man said coolant should be pouring out if there was a leak. However the test was only for a couple of minutes and the Bongo was barely warm by this point.
The initial roadside bleed we did was probably not so good as we pulled over on quite a slope. Also the funnel I had was tiny. At the time it was all we could do.
When bleeding the system at home I squeezed the bottom hose but not the top one.
Reading your post and having thought more about the issue I've decided to replace the water pump. I'll check the leak points where you suggest but my current thinking is the coolant isn't circulating. A new pump and bleeding the system thoroughly should sort everything unless there's a physical blockage somewhere.
The fans are fine I think - they were a week ago but I gather overheating can damage the temp' sensor switch.
I'll fit the water pump, this time manipulating every hose I can see and then test the fans.
I should have made it clear in my original post, when I said the heater was cold I meant that it blew cold air even when turned to the hottest setting indicating a coolant free heater matrix and, yes your right, the boiling over soon follows.
Finally, when bleeding, the engine sounded fine. I can't road test it until the cooling issue is sorted.
Thanks again for the prompt help,
Tony
It was a positive pressure test using the header tank.
I'm not sure what the pressure was but the AA man said coolant should be pouring out if there was a leak. However the test was only for a couple of minutes and the Bongo was barely warm by this point.
The initial roadside bleed we did was probably not so good as we pulled over on quite a slope. Also the funnel I had was tiny. At the time it was all we could do.
When bleeding the system at home I squeezed the bottom hose but not the top one.
Reading your post and having thought more about the issue I've decided to replace the water pump. I'll check the leak points where you suggest but my current thinking is the coolant isn't circulating. A new pump and bleeding the system thoroughly should sort everything unless there's a physical blockage somewhere.
The fans are fine I think - they were a week ago but I gather overheating can damage the temp' sensor switch.
I'll fit the water pump, this time manipulating every hose I can see and then test the fans.
I should have made it clear in my original post, when I said the heater was cold I meant that it blew cold air even when turned to the hottest setting indicating a coolant free heater matrix and, yes your right, the boiling over soon follows.
Finally, when bleeding, the engine sounded fine. I can't road test it until the cooling issue is sorted.
Thanks again for the prompt help,
Tony
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Northern Bongolow
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Re: What could cause this overheating. Water pump failure?
squeezing the top hose out of the head towards the rad is on some bongos crucial, this is because the trapped air in the head cannot or doesnt want to go down hill towards the rad, air always wants to stay high above the coolant/liquid.
this what is often called the design flaw in the bongo, on most other engines but not all water leaves the head and goes level into the top of the rad but in a bongo it has to go down hill towards the axle then up. this area of air holds the coolant flow back until the air is pushed down manually then to the rad and out, the water pump wont always do it for you.
there is another place on the system that this happens, this is the front heater. the heater is pretty much one of the highest points on the system, the trapped air here is often hard to shift or is at least easy to loose flow, this is why a leak in the system is often detected here as a cold heater, no flow or air locked. i always manipulate the front heater pipes under the bonnet to push out any air trapped here during the early stages of the bleed process.
i can tell from your description of what you have done that you understand whats going on so these other bits of info will make sense to you.
this what is often called the design flaw in the bongo, on most other engines but not all water leaves the head and goes level into the top of the rad but in a bongo it has to go down hill towards the axle then up. this area of air holds the coolant flow back until the air is pushed down manually then to the rad and out, the water pump wont always do it for you.
there is another place on the system that this happens, this is the front heater. the heater is pretty much one of the highest points on the system, the trapped air here is often hard to shift or is at least easy to loose flow, this is why a leak in the system is often detected here as a cold heater, no flow or air locked. i always manipulate the front heater pipes under the bonnet to push out any air trapped here during the early stages of the bleed process.
i can tell from your description of what you have done that you understand whats going on so these other bits of info will make sense to you.
Re: What could cause this overheating. Water pump failure?
Cheers again Northern Bongolow.
I got the water pump off - there is evidence of a leak from the bottom hole and the bearings feel a little stiff.
All I need to do now before the new pump arrives is to scrape off the old gasket. This is not proving easy.
As a tip I always rub oil into gaskets before fitting. This doesn't mean you can reuse them, it just means they're easier to remove.
There was one odd thing - one of the upper bolts that held the pump on was covered in what looks like engine oil. No oil is coming out of the hole it goes into however. I hope it was put in like that...
If anyone is looking at replacing the water pump you could just about do it from the top but you can't really see what's going on. I did it from the top and bottom removing the extractor fan to give me room to use my favorite tool on the four water pump pulley bolts - an 18v impact socket driver.
I'll post again when done or if I find anything other readers might find of value.
I got the water pump off - there is evidence of a leak from the bottom hole and the bearings feel a little stiff.
All I need to do now before the new pump arrives is to scrape off the old gasket. This is not proving easy.
As a tip I always rub oil into gaskets before fitting. This doesn't mean you can reuse them, it just means they're easier to remove.
There was one odd thing - one of the upper bolts that held the pump on was covered in what looks like engine oil. No oil is coming out of the hole it goes into however. I hope it was put in like that...
If anyone is looking at replacing the water pump you could just about do it from the top but you can't really see what's going on. I did it from the top and bottom removing the extractor fan to give me room to use my favorite tool on the four water pump pulley bolts - an 18v impact socket driver.
I'll post again when done or if I find anything other readers might find of value.
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Northern Bongolow
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Re: What could cause this overheating. Water pump failure?
if you put some planks of wood down on the floor drive the bongo on to them, then slide under with your crawl board you can put a cushion against the fan to rest your head while you do the pump. 
. is the black stuff on the bolt belt dust and water mixed maybe.
can you post a pic of the snail trail on the casting for others to view on this post later please.
. is the black stuff on the bolt belt dust and water mixed maybe.can you post a pic of the snail trail on the casting for others to view on this post later please.
Re: What could cause this overheating. Water pump failure?
Hi Northern Bongolow
I couldn't embed the image of the snail trail for some reason - I kept getting a forbidden message despite resizing.
Here's a link to the photo. I marked the trail with a bit of tissue as I'd wiped the actual trail off with my finger.
The pump is oily from a leaky cam cover gasket
The oily bolt is definitely oil, at least according to my nose.
Cheers again for your help
Tony
https://imgur.com/a/T10bZ
I couldn't embed the image of the snail trail for some reason - I kept getting a forbidden message despite resizing.
Here's a link to the photo. I marked the trail with a bit of tissue as I'd wiped the actual trail off with my finger.
The pump is oily from a leaky cam cover gasket
The oily bolt is definitely oil, at least according to my nose.
Cheers again for your help
Tony
https://imgur.com/a/T10bZ
Re: What could cause this overheating. Water pump failure?
Do Not Panic if you see a slight trace of coolant coming from the Vent Hole, this is P&P of the water pump operation ,it uses Coolant to lubricate the mating/running surfaces .
Re: What could cause this overheating. Water pump failure?
Cheers teenmal - I'd heard to expect something along those lines when fitting a new pump.
Well, I'd finished removing the old gasket and I was just reconnecting the bottom hose thinking I could legitimately have a break as there would be nothing more to do when the postman hands me a new water pump.
Once everything was reassembled I squeezed all the hoses having filled up with coolant and did a cold bleed.
I then did a proper bleed with the engine running and, I could be paranoid but I'm unsure if all is ok.
To begin with all went as expected - the coolant dropped when I revved the engine and big and little bubbles came up. Excellent I thought - all is as it should be.
However, as I continued, two odd things happened. The first was I noticed the coolant in the funnel was stone cold, not warm as it should be.
The second was the two radiator fans came on. The temperature gauge was at it's normal 11 o'clock position, the TM temp gauge was showing around 50 - a few degrees lower than it shows when motorway cruising and the bottom hose that leads to the thermostat was still cold.
Still, I persevered and, after another odd moment when the TM started to go down the bleeding process then started to resemble what I'm used to. The fans turned off, the coolant in the funnel was now hot and the TM gauge started to rise. The lower hose was also well and truly hot now. Bubbles from the funnel were now much smaller and started to get less and the fluid level hardly dropped as I revved the engine.
All the other hoses were hot
I'm concluding all is ok and I must have had a fair amount of air in the system which caused the anomalies. However I feel a little uneasy and may well bleed the system again to see how it behaves from cold.
One useful tip for anyone changing the water pump is to put insulation tape on the edge of the hole under the seat. Otherwise you'll end up with loads of scratches.
Again thanks to everyone for their help.
If I do have further problems I'll post again
Well, I'd finished removing the old gasket and I was just reconnecting the bottom hose thinking I could legitimately have a break as there would be nothing more to do when the postman hands me a new water pump.
Once everything was reassembled I squeezed all the hoses having filled up with coolant and did a cold bleed.
I then did a proper bleed with the engine running and, I could be paranoid but I'm unsure if all is ok.
To begin with all went as expected - the coolant dropped when I revved the engine and big and little bubbles came up. Excellent I thought - all is as it should be.
However, as I continued, two odd things happened. The first was I noticed the coolant in the funnel was stone cold, not warm as it should be.
The second was the two radiator fans came on. The temperature gauge was at it's normal 11 o'clock position, the TM temp gauge was showing around 50 - a few degrees lower than it shows when motorway cruising and the bottom hose that leads to the thermostat was still cold.
Still, I persevered and, after another odd moment when the TM started to go down the bleeding process then started to resemble what I'm used to. The fans turned off, the coolant in the funnel was now hot and the TM gauge started to rise. The lower hose was also well and truly hot now. Bubbles from the funnel were now much smaller and started to get less and the fluid level hardly dropped as I revved the engine.
All the other hoses were hot
I'm concluding all is ok and I must have had a fair amount of air in the system which caused the anomalies. However I feel a little uneasy and may well bleed the system again to see how it behaves from cold.
One useful tip for anyone changing the water pump is to put insulation tape on the edge of the hole under the seat. Otherwise you'll end up with loads of scratches.
Again thanks to everyone for their help.
If I do have further problems I'll post again
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Merlot man
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Re: What could cause this overheating. Water pump failure?
hello Tony
I'm following this tread with interest as we all need to get to terms with the "special " cooling system in our buses !
I hope and suspect that it is now all sorted but either way please keep us informed .
Thanks
Brian
I'm following this tread with interest as we all need to get to terms with the "special " cooling system in our buses !
I hope and suspect that it is now all sorted but either way please keep us informed .
Thanks
Brian
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Northern Bongolow
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Re: What could cause this overheating. Water pump failure?
some bongos are just more difficult or stubborn than others, i think its just how the air locks settle in the system or what work has been done prior.
i do a non running bleed to get as much into the system before heating it all up, squeeze as much pipework as you can, you can then still hear the air flying about if its in there.
then i do a ticking over bleed and again spend loads of time squeezing, filling and see sawing the funnel.
then short bursts of revs to empty the raised funnel, then drop to fill, repeat repeat.
if the funnel doesnt empty quite quickly go back one step. the short revving shifts some stubborn trapped air but not always all.it also slowly builds the temps towards the stat opening temp. as the stat opens the funnel fills with revs not empties, but sometimes can shut again as the stat gets a rad full of cooler coolant so keep a close watch on things.
one thing i always do is keep in the back of your mind the volume of coolant going in should equate to the volume of air coming out in bubbles, if your getting loads of bubbles out but the coolant level/volume is static somethings wrong. its either making its own air
or theres a blockage, you do tend to get a good feeling as to whats going on especially on your own motor.
i do a non running bleed to get as much into the system before heating it all up, squeeze as much pipework as you can, you can then still hear the air flying about if its in there.
then i do a ticking over bleed and again spend loads of time squeezing, filling and see sawing the funnel.
then short bursts of revs to empty the raised funnel, then drop to fill, repeat repeat.
if the funnel doesnt empty quite quickly go back one step. the short revving shifts some stubborn trapped air but not always all.it also slowly builds the temps towards the stat opening temp. as the stat opens the funnel fills with revs not empties, but sometimes can shut again as the stat gets a rad full of cooler coolant so keep a close watch on things.
one thing i always do is keep in the back of your mind the volume of coolant going in should equate to the volume of air coming out in bubbles, if your getting loads of bubbles out but the coolant level/volume is static somethings wrong. its either making its own air
or theres a blockage, you do tend to get a good feeling as to whats going on especially on your own motor.Re: What could cause this overheating. Water pump failure?
I remember reading somewhere to raise the front of the vehicle to help with the bubbles to rise up. When I took mine into Ian Taylor to bleed his mechanic had my front up on ramps whilst bleeding.
Re: What could cause this overheating. Water pump failure?
Some good tips on bleeding there.
Well I bled the Bongo again using the tips given and all appears ok.
The fluid in the funnel got warm with the engine, the bubbles weren't to big and got fewer as the bleed progressed.
The only oddity was the radiator fans again came on before the bottom hose got hot. It was only a short while before and I'm not too concerned (should I be?) They went off after a little while so I figure the fan temperature sensor cooled as the thermostat opened.
There were no leaks that I could see and only a little extra fluid needed to be added.
Of course I can't be 100% it's ok - the waterpump was leaking but there could be another leak that happens only when hot.
I'm not sure if you can do a hot pressure test - one where the thermostat is open.
It's been such a busy week- arriving home very late Sunday night on a flatbed, sorting loads of muddy camping stuff out, bleeding the Bongo, fitting a new water pump and bleeding it twice again - not helped by having to work two 12 hour night shifts and a 9-5 between the Sunday night and now (Thursday night)
I still very much like the Bongo - in the past when a vehicle goes wrong it has at times ended up with me disliking it.
The only thing I want to do now is simulate the conditions that caused the initial problem (although not 100 miles away from home this time) and to see which happens first, the radiator fans coming on or the thermostat opening.
I've got all I need to bleed and fill the cooling system in the back of the Bongo but this feels like the common Bongo cooling paranoia rather than through real concern.
Again thanks for all the help and, again, if I discover anything useful to other forum members I'll post again.
Tony
Well I bled the Bongo again using the tips given and all appears ok.
The fluid in the funnel got warm with the engine, the bubbles weren't to big and got fewer as the bleed progressed.
The only oddity was the radiator fans again came on before the bottom hose got hot. It was only a short while before and I'm not too concerned (should I be?) They went off after a little while so I figure the fan temperature sensor cooled as the thermostat opened.
There were no leaks that I could see and only a little extra fluid needed to be added.
Of course I can't be 100% it's ok - the waterpump was leaking but there could be another leak that happens only when hot.
I'm not sure if you can do a hot pressure test - one where the thermostat is open.
It's been such a busy week- arriving home very late Sunday night on a flatbed, sorting loads of muddy camping stuff out, bleeding the Bongo, fitting a new water pump and bleeding it twice again - not helped by having to work two 12 hour night shifts and a 9-5 between the Sunday night and now (Thursday night)
I still very much like the Bongo - in the past when a vehicle goes wrong it has at times ended up with me disliking it.
The only thing I want to do now is simulate the conditions that caused the initial problem (although not 100 miles away from home this time) and to see which happens first, the radiator fans coming on or the thermostat opening.
I've got all I need to bleed and fill the cooling system in the back of the Bongo but this feels like the common Bongo cooling paranoia rather than through real concern.
Again thanks for all the help and, again, if I discover anything useful to other forum members I'll post again.
Tony
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Northern Bongolow
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Re: What could cause this overheating. Water pump failure?
in the standard system with everything in good order the fans should never come on before the stat opens, its not designed that way, i would take a good look at the fan sensor, theres a fair chance its gone out of plonk with the previous overheating episode, or the end of it is loose or the wires are dirty etc. the switch works on resistance, so if you raise the resistance by the above you may get oddities. is it a copy sensor, or does it wobble slightly where the plastic end attaches to the brass part. ive tested the resistance of these in a cup of water, the temp related resistance readings are in the manual, and if you wobble the joint you can get odd readings.
if it were mine i would replace it anyway as its the main ecu sensor for the glow plugs, egr,cold start solenoids, and the fans. fit a gen mazda one too as they are far better than the intermotor ones. you wouldnt fit cheap parts to control your house boiler at home would you.
just keep telling yourself, the more times i bleed the bloody thing the better i get at it.
just another thought, did you continue after you were happy with the bleed to cap everything off and run it up to fans on temp to test that they came on and went off when everything is really hot.(the ultimate test).
if it were mine i would replace it anyway as its the main ecu sensor for the glow plugs, egr,cold start solenoids, and the fans. fit a gen mazda one too as they are far better than the intermotor ones. you wouldnt fit cheap parts to control your house boiler at home would you.
just keep telling yourself, the more times i bleed the bloody thing the better i get at it.
just another thought, did you continue after you were happy with the bleed to cap everything off and run it up to fans on temp to test that they came on and went off when everything is really hot.(the ultimate test).