What could cause this overheating. Water pump failure?

[Tony x]

Cheers again Northern Bongolow.
I will replace the temp sensor and I'll have a go at testing it first just in case it's ok and there's another problem causing the fans to trigger and the sensor is ok. Can't think what other problem would cause this unless something was causing the area near the sensor to somehow get hotter than it should relative to the rest of the system.
I didn't do the fan test like you say - but I have that planned as part of my final test before I take the Bongo further than pushing distance from home.
Cheers again and thanks for the advice regarding sensor types to buy and what they're responsible for.

As a further tip to any other readers, when we first got our current Bongo I thought I'd bleed the system thoroughly. I kept going long after I would have normally stopped. No harm in that you might think - well, yes there was - the coolant started to boil over and it basically had to be bled again from cold. All that was gained was a scolded hand from plugging up the bleed pipe.

[Tony x]

Hi
I see Blueprint make a fan temperature switch for the Bongo - it's substantially cheaper than the Mazda one £13.50 as against £39.
Blueprint is where I usually go for stuff like oil filters and the like and the quality is generally regarded as good.
Do you think it would be a suitable alternative to the Mazda one?
Part number is B593-18-840A
Here's a link https://www.buycarparts.co.uk/blue-print/2898596

Cheers
Tony

[phil 1]

Hi
I see Blueprint make a fan temperature switch for the Bongo - it's substantially cheaper than the Mazda one £13.50 as against £39.
Blueprint is where I usually go for stuff like oil filters and the like and the quality is generally regarded as good.
Do you think it would be a suitable alternative to the Mazda one?
Part number is B593-18-840A
Here's a link https://www.buycarparts.co.uk/blue-print/2898596

Cheers
Tony

Hi,
I change that sensor the last time i change the coolant as a bit of routine maintenance. I fitted a new blueprint sensor as other blueprint parts i have fitted over the years have been ok.
However when I came to beed the bongo the cooling fans kicked in to soon and before the thermostat had opened making it impossible to bleed i tyred several times but same thing happened every time. So bit the bullet and got a genuine mazda one and bleed first time no problems. Now i might have got a dud sensor or possibly a air lock but i also had problems when I fitted a blueprint thermostat a few years back fitted a genuine one everything was fine. So when it comes to the cooling system with my bongo it's genuine all the way.
Good luck
Phil

[Tony x]

Mazda temp sensor it is then.
I'm still considering what caused the initial problem. I think it may have been a combination of leaking water pump and faulty fan switch.
I recall the fans coming on a few weeks ago at a low engine temperature (according to the TM2) and it's odd that they then go off as the engine temperature rises further.
Finally I generally note when the fans come on and I can't recall them being on when the overheating occurred and they certainly weren't on when we pulled over and turned the engine off.

[Northern Bongolow]

thats why i like this forum, we bat the thing about a bit whatever the problem is and usually together we all get there. .

sometimes its the little sentences that someone recalls later that make you think. im just wondering now on something you said a couple of post up, - - - - - your wondering if anything else around the sensor could cause this local hotspot. now dont panic yet but the heads usually fail around cylinders 2 or 3 on the exhaust side which is around the area of the fan sensor. but the sensor is on the inlet side so thats one good point, and you seemed happy that it bled all the air out when you bled it so thats another good point,i think you said earlier that you did a exhaust gas check on the coolant and non was detected so thats another. sorry but i had to mention my thoughts.

a few years ago myself and steve widdowson did loads of tests for ian at fury on these sensors and stats and wishbone ball joints, even a cylinder head, we cut em up with a grinder, tested new and old of the sensors and stats, the differences in performance and manufacturing quality varied quite a bit.

bet its a duff fan switch or a copy.

[Tony x]

Hi.
Thanks again. I need to hear all thoughts good or not. Would it be obvious if the head has failed? The engine sounds OK and the coolant didn't look or smell any different in the funnel when bleeding.
Tony

[Tony x]

Hi again.
I see I can test for a cracked head by starting the engine from cold and seeing if the top hose gets harder in the first few minutes of running. I'll do this Sunday plus if I keep the engine running I'll see if the coolant level expands excessively.

[Tony x]

Well, I think the head has a crack in it....
I ran the Bongo this morning for the first time with the cooling system sealed up - all the other runs have involved bleeding.

I checked the top hose for hardening as suggested and it did get a bit harder to squeeze in the first 5 minutes of running. I wan't exactly sure what I was looking for here never having done this test before on a healthy or otherwise engine.

However, at around 66 deg on the TM2, which is around 6 deg below the temperature the thermostat opens, coolant came out of the header tank overflow. The top hose was notably swollen, the bottom hose was cold, the fans remained off (I had previously unclipped the fan sensor and clipped it back on to clean the connection)

I can't see any other explanation but I'm open to suggestions...

I don't think it's the header tank cap (although I see these can go) as this doesn't explain the swollen top hose.

Again, thanks for everyone's help.

I guess one learning point is, if the fans come on early, then this might be an indicator of a crack in the head as Northern Bongolow theorized.

[teenmal]

Well, I think the head has a crack in it....
I ran the Bongo this morning for the first time with the cooling system sealed up - all the other runs have involved bleeding.

I checked the top hose for hardening as suggested and it did get a bit harder to squeeze in the first 5 minutes of running. I wan't exactly sure what I was looking for here never having done this test before on a healthy or otherwise engine.

However, at around 66 deg on the TM2, which is around 6 deg below the temperature the thermostat opens, coolant came out of the header tank overflow. The top hose was notably swollen, the bottom hose was cold, the fans remained off (I had previously unclipped the fan sensor and clipped it back on to clean the connection)

I can't see any other explanation but I'm open to suggestions...

I don't think it's the header tank cap (although I see these can go) as this doesn't explain the swollen top hose.

Again, thanks for everyone's help.

I guess one learning point is, if the fans come on early, then this might be an indicator of a crack in the head as Northern Bongolow theorized.

A normal thermostat for these engines should have an opening temperature of 82,did you fit a lower temp thermostat.

[Tony x]

Hi teenmal.
The TM2 temperature reading is a little off the true coolant temperature as it's mounted externally on the cylinder head. Thermostat is stock.

[Northern Bongolow]

get one of those cheap infrared laser temp guns, they are cheap, get some accurate temps from the hoses, rad, stat housing etc, and a new cap before you start thinking its dead, it maybe hotter than you think and the rad is partly blocked and the fans arnt working till late.

ive not found the hard hose trick reliable, on rest the cold bongo sits at minus 1 pound, thats why it sucks in air when cold if there are leaks, it doesnt take long to get to positive pressure when the engine is started. i fitted a min pressure gauge and a max pressure gauge to mine and constant pressure gauge and studied pressure for years on mine, they go poss in about 3-4 mins of normal running.

ive also made a exp cap tester out of an old exp tank, when tested over half the caps i tested at the big bash failed, they blew off too early usually under 1 bar.
normal running for a well run warmed up bongo while still moving is around 10 pounds the fans come on at around 13 pounds. its very near to the 1.1 bar cap blow off point, especially if the cap it opening at under 1 bar. the only weird thing is the cold bottom hose.????.

if you still think its the head remove the glowplugs, get on of those cheap flexible tiny cameras and have a look in the cylinders you should see wet dark stains maybe even water if its cracked, a healthy cylinder look completely different to a cracked head cylinder.

[Tony x]

Hi.
Thanks again Northern Bongolow - yet more valuable information.
The information on the pressure of the system is particularly useful.
When I ran the engine the last time before today I bled the cooling system and sealed it up whilst hot.
When it was a fair bit cooler (but not cold) I opened the expansion tank just to check the level. It was fine.
If there was a suction type leak have you any idea what volume of air the system would draw in?
I ask because when I ran the engine today a lot of coolant came out. Around 2 litres at a guess.
I'm sure the engine wasn't that hot when I ran it today. The top hose was significantly cooler than the bottom hose gets when the thermostat opens and it didn't radiate heat or smell hot.
Please correct me if I'm wrong but the only explanations I can think of are either a completely shot expansion cap or the head.
One thing that niggles me is that I've read many times on the forum that, should the Mazda temperature gauge go past 1 o'clock (like ours did) then the head will go. Whilst I hope to find another explanation I keep wondering if I'm just kidding myself that the head could be OK.

I think I will get a new expansion tank cap and make a pressure testing device from the old one.
If a new cap doesn't fix things then maybe the camera down the glow plug hole and / or a sniff test but this time when the coolant is hot.
However I'm open to suggestions as to what to do.

[Northern Bongolow]

just to be sure get one of these so you can put figures to each pipe and head etc.

https://www.manomano.co.uk/thermometer- ... gIzY_D_BwE.

a small leak sucking in will only pull in a very small amount of air each time the system cools down, once it reaches zero poss and neg pressure it will just drip water out then the level will drop.

have you done a cold and a hot pressure test on the system since you have rebuilt it.

[Tony x]

Hi.
IT doesn't take much to persuade me to buy a new tool. I've just ordered the temperature gun.
I was planning on further pressure tests but I'm a bit concerned I might cause damage by forcing fluid through any cracking in the head and down into the cylinder.
Again I'm being drawn to conclude the head is the issue.
I know the stat is ok and there is no evidence of any leaks and yet the coolant overflowed when the engine was up to temperature. I've considered a faulty expansion tank cap but the amount of coolant that came out appeared excessive.
I'm going to fit a new expansion tank cap, replace the stat again ( just in case) bleed and then run the engine with the coolant system sealed up as normal and taking readings of the temperature of the top hose and various other places. I'll also flush the system and check for blockages prior to this.
I'll post up the results which will either point to the head or else something I've not thought of, overlooked or incorrectly thought was ok previously.
Thanks again
Tony

[mikeonb4c]

If its any consolation, my head went at 125k miles approx, and despite the best of attention to my coolant system. I wondered if it might simply be linked to a known vulnerability and fatigue caused by mine being used every day for 9 years for short commuting runs, taxying kids etc so that it had done a lot of thermal cycles. The onset was slow and hard to spot (steamy start ups and running from cold, slight loss of coolant, i think hoses a bit hard) and if i'd wanted to stay in denial i might have for a while. But i didn't want the doubt so we decided to strip head off and test and sure enough there was a hairline crack (between cylinders 1 and 2 i think as per classic failure?). I got new waterpump, sensor, thermostat done at the same time and a nice spin-off was the engine has since been quieter as rocker clearances got adjusted up). Two and a half years later and she's remained perfect and never needed a coolant top-up.