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General Automotive General automotive discussion. This is intended to be a discussion about other not VW and Diesel cars you may have or interested in.

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Old June 13th, 2018, 13:11   #1
Wallace
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Default General engine advice, Mazda diesel.

Just been reading Whitedog's "Talk me off the ledge" post and I think I too am almost there. I have a vehicle which I don't think will be known in the US but some general advice about temperatures, engineering and cooling systems would greatly help me out, and maybe off the ledge, the good way
The vehicle is a Mazda Bongo MPV converted to a camper. These were originally produced for the domestic Japanese market only but as they don't keep older vehicles they quickly filtered out to loads of other countries. Ours is a 2.5 TD Auto with 4WD and is now 20 years old but only 40,000 miles.
they seem to have become somewhat notorious for overheating issues, I always thought we were immune as it's low mileage and well maintained, you can probably guess what's coming.
One burst pipe and total coolant loss later, I cannot get it back together and despite changing hoses, thermostat, radiator and so on it just will not bleed all the air out.
There is a process on the owners Forum/You Tube as ti how to do this, i have followed it to the letter, also checked and re-sealed everything in case it is drawing in air when running. It will however hold pressure or vacuum, so there shouldn't be any leaks and there is no visible coolant loss. There are also none of the normal head gasket issue signs and it doesn't seem to lose coolant when running.
The heads seem to trap air easily, so I have been monitoring the temperature with a laser gauge, it is frequently about 90 degrees but has been over 100, at which point I normally switch off as I think that's too much, but is it? To be honest I am not sure how hot a normal cylinder head gets, so this would be my first question. how hot is reasonable for an alloy head on a Diesel engine?
Forums seem to suggest it is likely I have a Head gasket issue or a cracked head. I have to say the quality of mechanical information and knowledge of owners of these vehicles is not as good as VWs and there's a guy just now who was advised he needed a head, a job which he duly undertook, to find ther is nothing wrong with the head. So for me no outward signs of head trouble and I am struggling to accept I may need to remove the head. It has never had a full overheat situation, it has got hotter than I would like at times but we have pretty much treated it with "kid gloves" and with the low mileage as well, I just can't accept it, am I wrong?
I am not a mechanic but I have worked in cars as a hobby all my life, now 56 I have a fair knowledge and set of tools and like to think I am not stupid and can usually think my way out of a problem but this ime, it's looking less and less likely. Why, Oh why, didn't I just buy a rusty T4? Basically any advice, thoughts would be great, bearing in mind I am already on that ledge
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Old June 13th, 2018, 23:45   #2
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I drove a Townace for many years and a fellow owner migrated to a Bongo, so am well versed in overheating problems...

100c isn't a problem at the head, and might well relate to 90 at the return hose. Your radiator cap is probably about 1bar, which means the cooling system may me expected to reach 120c.

Holding pressure or vacuum is half the battle. Next direction for me would be to tee a pressure gauge into the system semi-permanently. Starting at zero pressure when starting the engine it should only start to build pressure as the coolant warms (many minutes) so if you see an immediate spike up to towards 1bar a head, gasket, or EGRcooler issue is confirmed. If all is good when started then load the engine up rapidly and look for the same pressure rise.
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Old June 14th, 2018, 09:42   #3
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Thanks for that, surprised to find someone knowledgeable about Bongos, wow!
Where about in the system would you put the gauge? The reason I ask is for me there is one obvious place where I have already created a T and blanked it off. This is on the small pipe under the expansion tank which I believe is the thermostat by-pass pipe. I don't have a gauge I could do this with so may have to buy one, any suggestions where, would be appreciated
Caps are 1.1 bar and seem fine but I have wondered about renewing them but it's a bit of a case of where do you stop, some of the smaller hoses I haven't done, metal water pipes, Water pump, heater matrixes, list is getting shorter at this end though
Update today; we beld it again last night and took it a short run, it didn't overheat. On return home I tested the head temps and they were over 100 degrees but no fans on, no coolant being pushed out, stat open, heaters warm, all looking good, so we switched it off and left it. Tonight we did much he same but a longer run, head temps were lower 90-101 approx and everything else fine. We will try it again tomorrow, maybe longer run again and I will report back,signs seem good though, fingers crossed
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Old June 14th, 2018, 22:30   #4
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sounds fine tbh.
yes, the smaller hose coming out of the exp tank would be good for a gauge.

something like this:
https://www.ebay.co.uk/itm/50mm-DIAL...N/122135257492
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Old June 15th, 2018, 13:43   #5
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Bad news, took it out tonight, 9km later gauge shot up out of the blue and it spat all it's coolant, what do I need to do to get this thing to run properly, it's so frustrating!
Cheers for the info, will look into that, not tonight though, need a break from the whole thing
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Old July 6th, 2018, 04:38   #6
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Sorry for the delay getting back. I am still working on this and enthusiasm is waning a bit.
I will try to keep this brief and as up to date as I can, so I bought a pressure gauge but only really had a chance to try it yesterday. We changed some more hoses, just in case and at the last bleed it was badly air-locked around the Thermostat to the point it wouldn't open, which didn't help. So to be on the safe side I had decided to remove and check it, change the hoses and radiator/expansion caps. This stat is the brand new Mazda part, which was working when fitted and still is (which is why I am so sure now it was an air-lock), so it's back in and all built back together and we followed the bleed process as per the Bongo club videos on You Tube. Thermostat opened this time, I was ecSTATic (sorry coudn't resist) for about 2 minutes, then without warning, as we thought we should be coming to the end of the process the radiator fans suddenly came on and there seemed to be loads of air through the funnel, almost though like coolant was virtually boiling and we had to switch off and abort the mission.
All this time the pressure gauge never moved and I had been warching it most of the time, so in hindsight I am thinking this would really only work with the caps on? At present it wouldn't run for very long with them on and I couldn't be certain the coolant would be circulating through the entire system until I can get at least most of the air out.at least that's what I am thinking.
Anyway I had another try later on once it had cooled a bit, similar result but not so dramatic, this time it was like the stat wasn't going to open, then it did, loads of air through the funnel, then the fans came on and I decided enough was enough, rightly or wrongly.
So does any of that make sense to anyone, I am either nearly there or a mile off but then I have been thinking this for a while now.........
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Old July 6th, 2018, 05:19   #7
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why is it airlocking at the thermostat? there should be a bleed hole/jiggle pin to let it through...
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