Overheating - Looking for troubleshooting steps

[Diplomat]

I've found a way of getting the bung in without scalding and without letting air back in.

For all recent bleeds I have been using a bucket style yogurt container as the bleed reservoir and seesawing above and below the header tank level until I am satisfied there is no air in the system. An added bonus is that the handle of the bucket can be hooked over the handbrake lever much of the time while revving the engine etc.

When it's time to put the the bung in, using pliers to grip it lightly I stand the bung, on its flat end, in the yogurt bucket, below the level of the hot coolant and carefully lower the hose onto it but only push hard enough for it to stay in the hose well enough to be pulled out of the hot liquid and then push it home properly in free space.

As the cap is not on the header tank at that stage the plug won't blow out in the crucial few moments.

Last did it only a few days ago after dealing with a leak in the heater feed from the cylinder head.

Frank

[haydn callow]

I always use workman’s gloves when bleeding. I find it best to bend the bleed tube back on itself to cut off the flow and then replace the bung with no hassles,

[surfkernow]

I've found a way of getting the bung in without scalding and without letting air back in.

Thank you Frank and Haydn, much appreciated. Sorry for the delayed replies. I am working a lot at the moment and am seriously lacking any free time to look at my Bongo. I am going to give it another go in the next day or so, we have had torrential rain for weeks now.

I am trying to flush the system as the moment.

I put some uv dye in the system when i was troubleshooting a few weeks/months back and that has turned the current blue dye green anyway. I posted on FB about blue triple QX as I think I might have some lying around from my Volvo days. I might add that tomorrow at this rate.

Haydn, thank you, I will bend the tube back on its self when I next give it a go and cable tie it whilst I get the bung in

[surfkernow]

I gave up on flushing the coolant and resorted to the 2 year blue coolant garage had used. I managed to bleed the system in just over an hour, and this time I did not require a trip to A and E to treat my burnt hands. I actually adapted Haydn's idea and used a G Clamp before putting the bleed stop in.

I have taken the Van for a short test drive but the inevitable has not happened, yet. I have a Cylinder Head Temperature alarm, a coolant alarm and now a new set of rubber pipes from Mazda Bongo spares so it is a waiting game. I will take her to the garage in the early new year so the cooling system can be pressure tested again. I might try and adapt my own pressure testing kit, as per an earlier suggestion but my patience is thin at the moment, i was going to joke about my blood pressure but collecting my first batch of medication for that next week !! I wonder whether my Bongo ownership and sudden Blood Pressure problems are linked !!

But, I did sort out the smoke at start up today after I swapped all the glow plugs, no smoke and no rough start-up so that is a big positive.

I will update this thread if there are no more overheating problems in the next few months, or earlier if there are

Thank you for all the input and help thus far

[Bob]

Thanks for the update.

Sounds good so far.

[surfkernow]

And there she spurts. Lasted a few days and a couple of one hour journeys but today that Bongo overheated in almost the same scenario as last time. I had gone for a bike ride a few minutes drive from home. I went cycling for an hour then drove the few minutes home up a very steep hill and we hit 105 and lost about a ton of coolant below the expansion tank. There was still coolant left in the expansion tank.

One of the things I noticed on the journeys i had made after replacing all the pipes and bleeding the system was the lower radiator hose did not get hot. Even when I went on a 1.5 hour drive with an a static temperature of 92 for most the journey on a dual carriageway, the lower radiator was not hot. Nor was it hot after the return journey. I guess this means the thermostat did not open?

The thermostat was replaced at the garage with a genuine Mazda one a month or two back, so before I go pulling it out and testing it. Would a thermostat stuck in the closed position cause the problems I am facing?

Thank you for your help

[haydn callow]

In this weather it would not surprise me if the stat didn’t open under normal driving conditions with air passing through the rad. Could be time for a new head.

[surfkernow]

Hi Haydn, thank you for your reply. A new cylinder head is a possibility, it has always been my hunch that it is cracked. I need to make sure I am as confident as I can be so I don't drop a new head in and still have the same issues and crack the new head.

At present I have no other identifiers that the head has gone. There is no white smoke, no ice cream in the oil filler cap, no oil in the coolant and no bubbles in the coolant when the engine is running when I look down into the expansion tank.

I am going to bleed the van again tomorrow and see if I can get it to a local garage for another coolant compression test. I cannot see where it could be drawing in air, i have replaced all the pipes that I thought might be leaking. I will do another round of checks in the next few days

The issue I have is that there is rust to contend with. An entire sill is going to have to be replaced before the next MOT so I need to make sure I am fixing something that will last a few more years

[mikeonb4c]

Hi Haydn, thank you for your reply. A new cylinder head is a possibility, it has always been my hunch that it is cracked. I need to make sure I am as confident as I can be so I don't drop a new head in and still have the same issues and crack the new head.

At present I have no other identifiers that the head has gone. There is no white smoke, no ice cream in the oil filler cap, no oil in the coolant and no bubbles in the coolant when the engine is running when I look down into the expansion tank.

I am going to bleed the van again tomorrow and see if I can get it to a local garage for another coolant compression test. I cannot see where it could be drawing in air, i have replaced all the pipes that I thought might be leaking. I will do another round of checks in the next few days

The issue I have is that there is rust to contend with. An entire sill is going to have to be replaced before the next MOT so I need to make sure I am fixing something that will last a few more years

Agree its a tricky decision how much to sink into it. Out of interest (to save trawling through old posts) has it had a new radiator fitted?). Also, are you confident rad fans are coming on when engine hot from working hard?

[surfkernow]

Hi Mike, thank you for the reply, yes the radiator, water pump and thermostat were all changed. BUT

Today when I went to bleed the Van, it over heated and threw out a load of coolant out of the expansion task whilst I was bleeding it.

It happened after about 40 minutes of bleeding, all was going well, most of the bubbles had gone, i was revving the engine to get it to about 85 when It started to climb about 1 degree every 2 seconds. I let it rise as I had seen it at 92 and wanted to ensure the lower radiator pipe was going to get get hot, when it just kept rising, at about 94 I heard gurgling, looked at the bonnet and it had emptied the expansion tank ,and coolant was gurgling up.

It got to about 98 , i filled up the expansion tank and watched the air it must have sucked in come out through the bleed pipe for about 30 seconds then everything went back to normal with the bleed process except the temperature was about 98. At that point I stopped as there seemed no point to bleed it ...

A cracked cylinder head sucking in air over the 40 minutes I was bleeding it? Then the thermostat opens and the accumulated air pushes the coolant that was in the radiator out of the expansion tank leaving no coolant in that part of the system and causing the system to suddenly over heat.

Do you guys think that is what is happening?

[g8dhe]

That isn't what one would expect, the thermostat is at the "cold" input to the engine, once the coolant that is flowing back to the input side is above the thermostat temperature then the thermostat opens and allows additional cooled coolant in from the radiator to reduce the input temperature. Normally what happens when the engine overheats is it pushes coolant out of the engine into the de-gassing tank from which it then overflows/vents when the pressure rises. Best to refer to Steve Widdowson's diagrams and animations;

[Doone]

Originally the old rad was blocked and the water pump was leaking, which was why it originally overheated.

The ststem pressure tested OK.

The system was completely flushed and the rad was replaced, along with the thermostat and water pump.

It then bled easily and ran perfectly.
It was OK for several long journeys over a couple of weeks.

Then it overheated / over pressurised after ticking over for a couple of hours. Which is when a new leak was found in a hose. You've addressed that problem.

You haven't found any other leaks but it's overheated again while you're working on it.

It does sound like there's air in the system.

If you're sure there's no airlock, maybe it's time to test the head again, as its overheated a couple of times now?

Do I remember Ady (Northern Bongolow) posting a way of testing the head yourself? Someone will know.
Or your local garage could do it for you.

[Northern Bongolow]

I don't know of a reliable head testing method, I always start from a pressure test of the entire system, if it isn't air/ pressure tight then there is no point attempting to bleed it. There are certain times when it's airtight but as the head or gasket get hot they may let gasses into the coolant.
If you bleed via the 3 vid method my wife filmed you can get a really good idea of what should happen and when, they all bleed up the same way so any early signs of things not happening when they should should ring bells.i always bleed to the point where it takes no more coolant into the system then put the cap back on and let it pressurise to max then let it tick over till the first speed rad fans come on knocking the temp down quickly, maybe do this several times, up to very hot ( the fan control temp) then down again. Then if your feeling confident you can test it to near destruction by getting the fans on to second (high) speed but this takes a lot of revving and balls of steel.

[surfkernow]

Thank you for all the replies :

g8dhe - thank you for the diagram, that is helpful

Doone - thank you for your reply, is there any way to know that you have an air lock? I bleed for 40/50 minutes and a lot of air bubbles passed through my funnel, but things were just starting to calm when I heard the gurgling in the expansion tank and realised it had shot out all my coolant. It also asks the questions, how is the air getting back in?

NorthernBongolow - thank you for your reply. I do use the method you outline in your video. I am tempted to get this pressure tester : https://www.ebay.co.uk/itm/254334550550?ul_noapp=true

The only question I have is you only tested the fans at the end of the video to check whether there was hot air coming out, does that means you should not have the hot air fans A/C running as you bleed the system?

The radiator fans were spinning as the coolant was being thrown out of the expansion tank.

[mikeonb4c]

Thanks for the update surfkernow and phew what a business! Bongos can be really baffling. The only other component that comes to mind and that I have read experts on here (widdowson?) say is an integral/critical part of the Bongo cooling system is the heater radiator. Given the main rad was blocked, is this one also ( and are there indicators when it is). I've always found it hard to believe the heater rad could be a critical part of the cooling system on any car but its all I can think of (apart from cracked head stuff) so maybe those more techie than me could comment. Also, on the issue of blockages (which i assume happens when a system has experienced prolonged neglect - maybe in its earlier life), can the channels in the block etc end up clogged? And of course, check all hoses for condition.