Overheating but okay on pressure and sniff test?

[Trystan92]

Hi all,

The Bongo ('95 2.5 diesel - 122000 miles) overheated the other day idling in traffic - bubbling over from expansion tank. Pulled over and bottom radiator hose was cold...fan didn't turn on...Front heater was blowing hot air. Only has the 'standard 11 o'clock' temp gauge. Had a bit of coolant dribble out of expansion tank the day before at the top of a long hill (assumed due to hotter than normal engine) and was on my way home to bleed in case of an air lock, but didn't manage to make it home.

AA man did a Sniff test - no colour change from blue to yellow in liquid suggesting no exhaust gasses in coolant. He did a roadside positive pressure test, held its pressure so I guess a sign of no leaks. Revved the engine during the pressure test which he said could test if the water pump was working and there was no deviation in the pressure needle on heavy revving...so likely a faulty water pump?

Changed the water pump yesterday and refilled the system and started bleeding, quite a lot of bubbles coming out of the funnel in the bleed hose even after 40 minutes of idling and sea sawing and the bubbles seemed to be getting bigger and more frequent rather than less. Level in the expansion tank never dropped either which is concerning. Engine got to temperature and after heavy revving (almost 1 hour in total spent bleeding) bottom radiator hose was still cold but top radiator hose was too hot to touch. Heater was blowing cold air. Then I noticed in the heavy bubbles what looked like oil residue on the surface . So It looks like cylinder/gasket failure but why did the pressure and Sniff test suggest otherwise after the Overheating incident?

I flushed/changed coolant 18 months ago (50/50 mix), and replaced the thermostat (with genuine mazda) and properly bled the system. No coolant system issues in 18 months/15000 miles. Checked coolant level in the expansion tank regularly - never needed to top it up and no evidence of any coolant leak over this period so this issue seems to have come on quite suddenly.

Another thing which may or may not be related. I changed the timing belt a week before...but drove 200 miles afterwards without any issues. I also did an oil and oil filter change the day before the overheating...BUT I hadn't noticed the O-ring from the old oil filter had remained stuck to the engine and when I screwed on the new oil filter over the old o-ring and turned the engine on, after 20 seconds oil started spewing out of the oil filter/engine interface as the old O-ring failed (lesson learnt check the old oil filter for the o-ring). I quickly turned the engine off and refilled the oil level (and replaced the oil filter), but I feel this may be related to the engine failure the following day...

Hope there is enough information here, My next step is to take to a garage for diagnosis, but wondering if there is anything to check/try before that. I've read many other posts and the helpful factsheets, but I am a little stumped by the results of the pressure/Sniff tests...maybe they are not 100% accurate..

thanks,

Trystan

[g8dhe]

If the bottom hose is staying cold it suggests that the thermostat has failed and hence no cool water is being introduced into the flow hence all sorts of problems with over heating are possible.

[haydn callow]

Agree with the above….remove stat to test in hot water

[Trystan92]

Thanks for replies. Tested thermostat in water and opened at 82 degrees as normal, when I reinstalled it I found a small pebble blocking one of the pipes in the thermostat housing. Not sure how on earth it got there or if it may have been the source of the issues. Refilled and bled system but a lot of bubbles were coming out o the bleed hose constantly throughout, even after the bottom radiator hose had been hot for 20 minutes and lots of revving. Radiator fan never came on either, even after restarting the engine. Cabin heaters were working mind.

Topped up the coolant in the header tank the next morning as it had dropped a fair bit and drove it over Haldon hill to the MOT centre. Didn't overheat on this journey so I thought I may have made a breakthrough, but when I got to the garage the bottom radiator hose was warm but rock solid like it had built up a substantial amount of pressure.

Failed its MOT as needs some welding ( ), and on the way back from the garage it overheated and had to call out the AA. It's at the garage now getting its welding done so I've asked to see if they can help diagnose the overheating issue but they aren't Bongo specialists. Someone said to flush the radiator incase it was blocked but I did that last year and very little crud came out, plus the radiator is only a few years old.

So in short: excessive of pressure building up, no coolant loss or signs of a leak, and radiator fan doesn't seem to be turning on even when overheated.

[g8dhe]

That's rather odd, given that the thermostat has been tested, but the engine is still overheating. I wonder if there is still something blocking the radiator cold coolant flowing ? Which pipe was the stone blocking on the thermostat housing? Could there be more stones in the pipes/radiator ?

[Trystan92]

Hi.

Garage got back to me, said they changed thermostat (just incase), flushed radiator, bled the system and it idled okay but after 20 minutes the temperature gauge started to rise above 11 oclock so problem still persisting. They also noted that there was a lot of pressure building in the system causing it to overheat even before the thermostat opened and the bottom radiator hose warmed. They said that the radiator fans were coming on as normal and that after flushing the radiator, not a lot of crud came out really (radiator is less than 3 years old anyway) suggesting a blocked radiator was unlikely to be the issue. I haven't tried replacing the expansion tank cap (where the coolant is spilling out from during overheating), but the coolant hoses are so rock solid to the touch when engine is at temp that I think the cap is functioning as it should.

Their assessment is a head gasket failure but after speaking with ADS services in Bristol they recon that 96 % of the time its a failed cylinder head rather than head gasket. I guess I could get a second opinion from another garage but my gut feeling is telling me to book it in for the engine to be dismantled and looked at...

Any suggestions from anyone for a Bongo friendly garage in the Exeter area?

cheers

[Bob]

To be honest be it head or gasket the head has to come off, so if the head's good it can go back on, if not there’s little extra labour to replace it.

Re Exeter garages, since Allan's retirement Doone has recommended a couple near Plymouth. A search of her posts will find them.

[Ian]

Spinners near Newton Abbot specialise in Bongos. Their details are on Facebook at https://www.facebook.com/Mazdabongorepa ... wtonabbot/

[Trystan92]

thanks for suggestions. Van is at ADS in Bristol now - they confirmed a cracked head and proceeded with fitting a new one. However they just rang me to tell me it hasn't solved the issue so they recommend an engine replacement for the tidy sum of £4500. Debating now whether to scrap the thing (I doubt we'll get much for it with a shot engine) but since the engine has already been taken apart and we're £2k in, might be worth just seeing this job out until the end... I didn't quite get down to what the issue still is, will catch them properly on the phone tomorrow. £4.5k seems quite a lot for an engine replacement though?

Trystan

[Bob]

Rotten luck.

Impossible to know what’s best.

[g8dhe]

I had a similar problem with my V6 a seized engine, however after checking around I did come up with a new engine at a fair price. This was put in and I was able to sell the van with no problem ( I had already started replacing the van before the engine turned up!), the van is still going strong 4 years later no problems.

[davetheshrew]

thats incredibly expensive for an engine swap in a bongo, they are a doddle to swap over, an afternoons work with competent people and a good used engine on ebay wont cost you more than 1k usually with a free gearbox bolted on. Id do it on my street for 500 . Totally understand overheads etc but 4.5k for a pretty standard garage situation is quite a bit over the odds in my opinion, id get a couple of quotes before pulling the trigger on that deal.