Coolant Reservoir Overflowing - 2.5 diesel

[James6666]

Been putting off looking into this over winter but a few months ago my bongo broke down and I had to get towed back, the coolant was overflowing (pressure release) out of the reservoir.

Obviously there's a few possible causes, I have replaced the coolant cap on the reservoir and have bled the system for at least a few hours using the see-saw method however was still getting bubbles when moving the funnel up and down with the engine idling? However since I had spent so long on it I decided to run the bongo (stationary) anyway to see if the coolant overflowed again. First time I ran it (up to normal temperature) it was okay however checking the coolant level once it had cooled down it had definitely increased in the reservoir (now above the max line). I have just come in from running it again and this time about 10 minutes after getting to temp the radiator fan came on, a few minutes later I turned off the engine and coolant dribbled out the overflow, so problem certainly isn't fixed... The temp gauge didn't go above 11 o'clock (ish) position.

My main fear is that the head gasket (and of course possibly head itself) needs replacing, however there are no other symptoms, no residue in the oil filler or on the dipstick, coolant is clear and red. Exhaust smoke is non existent apart from a bit of white smoke within the first minute or two of starting? I can't find any leaking pipes however other than looking for puddles on the ground I'm a bit unsure how easy this is to check for...

I have a low coolant alarm fitted however the issue is never a lack of coolant in the reservoir (far from it!) so this has never gone off in anger. I'm sure it's air in the engine block, either expanding or leading through the head gasket.

Does it seem likely to be the head? Am I missing something when I'm bleeding the engine, or is there something else I can check?

[g8dhe]

The regular mechanics that deal with these problems rarely find that it is the head gasket
The sensor for the temperature display is at the top of the engine just before the outlet pipe, hence if there is combustion gas getting into the coolant it pushes the normal temperature coolant up first as it expands hence the gauge doesn't increase to start with but the coolant will be pushed out of the de-gassing tank (its NOT a reservoir tank, its a sealed system and the tank just allows gas to come out of the pressurised coolant and to remain out of the coolant flow path at the highest point).

Its well worth reading thru these threads where a lot of work was put in by Steve Widdowson, if you want to understand the situation;
Basic fan operation https://www.igmaynard.co.uk/bongo/forum ... =3&t=48872
Cooling system diagram https://www.igmaynard.co.uk/bongo/forum ... =3&t=35902
Coolant flow - (follow up to cooling diagram) https://www.igmaynard.co.uk/bongo/forum ... =3&t=36433
Pipe - expansion tank to heater circuit return https://www.igmaynard.co.uk/bongo/forum ... =3&t=49505
Mazda thermostat - A few observations https://www.igmaynard.co.uk/bongo/forum ... =3&t=39193
Water pump - opinions please https://www.igmaynard.co.uk/bongo/forum ... =3&t=47381

[James6666]

Thanks for the topics, just having a read and look at the diagrams now. Thanks for the correction regarding the expansion tank! But you expect it as quite unlikely to be head/head gasket related?

I recently (6 months ago) gave it a pretty thorough service (fuel/air/oil filters, timing belt and oil), but not the waterpump, I did buy a new waterpump, there was a reason we didn't do it but can't remember what it was now ... Don't know if that is of any relevence.

The thermostat I think is working okay as when I was bleeding it I was able to get that lower pipe on the radiator to heat up.

Edit. Just been out to check, expansion tank is still very much full to the top...

[g8dhe]

The two most common items are a crack between the ports in the head as in the diagrams I linked to above, the other is a pin hole leak in a pipe which squirts vapour/coolant out when under pressure and then draws in air as it cools down, this then builds up until you get an air lock and the pressure builds up as the coolant flow stops and the sir expands pushing the coolant out of the tank.

[Winniebongo]

Hi, I hate to say it but your symptoms sound very much like ours, which then turned out to be the cylinder head (cracked). I had bled the coolant about a year before, no issues and it ran fine after that, then we broke down one night and it was pushing coolant out the reservoir. we got recovered home by the AA. I bled it again, thinking I knew what I was doing (dangerous), I actually lost count of how many times we bled it and Halfords started to look funnily at me due to the amount of coolant I was buying, I think they thought I must be drinking it. My Wife also became an adapt Bongo bleeder, we took advice online and from mechanics several, checked there was no exhaust fumes in the coolant, all OK, changed temp sensors, thermostat etc etc etc, still issues. the mechanic we eventually used did it all over again because he is a real mechanic and didn't know if I had done it right, I mean my wife had hand in it but still it had issues, so he decided it must be the head, removed it nothing to be seen but we got another one and fitted it and to cut a longer story short, that fixed it.
So what's my advice, do all your checks, do your best to bleed it as per the instructions (assume you have seen the YouTube videos) but don't waste too much time before passing it on to the experts and you do want someone with considerable Bingo experience, not just someone with general mechanical experience (extensive or not). I hope I am wrong but putting this down on here makes me feel like a Kiljoy, so I hope I am not doing so lightly, all the best

[Hazzobongo]

I cracked the head on another diesel import, like yours there was no cross contamination and no symptoms while driving the only thing I noticed was the level in the radiator dropped about a centimetre after a twenty mile run so I got tired of topping it up and went leak searching with dyes and torches, new rad caps and coolant by the gallon for six months all the while driving it as my daily without it losing power or anything else.

Finally I took this two ton truck to its limit both up a four mile incline and down again, parked it up to check the levels again when cold and took a look the following morning, sure enough slightly more coolant had gone from the rad, so topped up again to head to the shops and it wouldn't start/turn over, it was hydrolocked.

I did the speed test on the advice of a forum 'expert' who was changing heads regularly for other members, it was then I admitted I had been deluding myself about the head going. I bought and fitted my own which saved me a lot though I did spend extra on an extra tranny oil cooler and some numerical temperature guages so I'd know for certain when the temps were increasing. Hope this helps, don't do what I did but have it professionally pressure tested by your garage then make the decision as constantly trying to diagnose the fault while you're in denial can get expensive too.

[Winniebongo]

Yep we had all of that, I had actually forgotten about the joys of "Hydrolocking"............thankfully

[Hazzobongo]

There were several factors came into play in my case, number one being these Japanese market vehicles aren't designed for towing and I was dragging 3 tons of fully loaded six berth tourer which was no problem for the 3.0 litre engine itself but it wasn't actually being cooled sufficiently because the viscous fan they used on that vehicle had dried out the oil inside which operates the grip mechanism on the shaft from the engine, so althouth the fan was merrily spinning it was doing so because it was on a rotating shaft but not turning hard enough to properly cool the radiator and in turn both the transmission oil and the engine, the cylinder head being the weakest point in the system then cracks and usually between the same cylinders these ones pop at.

The difficulty in recognising the head has gone rather than a gasket is due to these cracks being hairline which open up during heat expansion and close when the motor cools so basically a very small amount of coolant enters the cylinder and burns off as steam which is visible during cold winter months as 'white smoke' but you see very little in the summer.

I just thought there was a pinhole leak in the pipework or rad somewhere and as the surf had the same type of rear heating controls and pipework as the Bongo I spent an age looking for the leak which wasn't even there.