Can you avoid a head gasket change...

[Cathryn]

We still have the major issue looming over us with the head gasket, which was most likely caused by the radiator not being replaced when the gasket was last done 18 months ago (pre our ownership).

As far as I can tell so far from the limited info I have, it's not losing water was but it is pressuring. I spoke to a mechanic thus morning who said you can put anti pressuring bits (sorry not very technical!) on but he couldn't recommend as a mechanic, but he said they do work.

Has anyone avoided a head gasket change in this way? Does it really work or a waste of money? The mechanic is going to test it this weekend so should have more info then.

Am I clutching at straws?

[Driver+Passengers]

Perhaps time to take it (or have it transported) to a Bongo-savvy garage... if you're in any doubt, advice may be to not drive it. Not trying to scare you, but consider it as an option.


In a healthy system, removing and replacing the header tank cap when stone cold so that the system is unpressurised, and then bringing it up to temperature should result in the system being pressurised. This happens because the coolant will expand as it warms up and squeeze the air inside the header tank itself. (The header tank cap is designed to withstand pressure up to 1.1 bar, or 16psi, at which point it will let air a little air out to maintain pressure at or below that 1.1bar).

I had an issue a couple of years ago which was resolved by replacing the head gasket.

In my case, the head gasket was letting combustion gas (exhaust) into the coolant system, but did not appear to be letting coolant leak back the other way (or allow coolant to leak into the oil ways, which is another possibility - ie mayonnaise on the oil filler cap). I was not losing coolant. However, if exhaust gets into the coolant then, apart from creating carbonic acid which can begin to dissolve metal (!), it will increase the amount of gas in the sealed system. Because there is the same amount of coolant in the system, but more gas (air and exhaust mixed), it will run at a higher pressure. If the exhaust gases circulate around the system in operation, they should end up in the header tank, where the air/exhaust mixture will be vented by the header tank cap in order to maintain the maximum pressure of 16psi.

I did coming on for 3000 miles with this happening. The exhaust gases are hot, and raise the overall temperature of the coolant, and therefore the operating temperature of the van, not in itself a grave thing but not ideal. Provided they are "degassing" correctly in the header tank and "being got rid of", then the van will continue to run. The danger is that the exhaust gas being introduced into the cylinder head will settle above the coolant, causing an air bubble, which if it grows significantly large will cause an air-lock, stopping the coolant from circulating, causing the head temperature to increase, eventually causing boiling of the nearest coolant to that point, which will expand to steam and cause all of the air in the header tank, along with a load of coolant to be ejected via the header tank pressure cap and overflow hose, at which point all bets are off.

I had a pressure gauge monitoring coolant pressure all this time, and was able to determine that if I was very light on the accelerator, then the van was "fine". However, accelerating down slip roads, overtaking or otherwise loading the engine, then the pressure would rise - I assume by overcoming the weak seal provided by the head gasket.

If there is a hairline crack in the cylinder head, then the same symptom may occur... nothing lost while cold or lightly loaded, becoming more of a problem when hot or working hard - obviously there is a spectrum of failure types - exhaust into coolant, coolant into cylinders, coolant into oil, happening all the time, or only happening under load... I was lucky.

There are a few tests which can be done.

On startup from cold, check how well it starts and what comes out of the exhaust - ie is there coolant sitting in the cylinders.

A cold pressure test - get a spare header tank cap and remove the spring, leaving only the top seal - effectively opening the overflow pipe - attach a valve to this and use a bike pump with pressure gauge to artificially pressurise the system to 10psi or so, leave it and watch for pressure leaks over some period of time.

A hot pressure test - as above but with everything hot - you don't want to remove the header tank cap when the system is pressurised, or you'd want to be extremely careful doing so, so you can remove the header tank cap and let it idle/rev it to bring it up to temperature unpressurised. Then repeat the "inflate with pressure gauge and watch for pressure drop test".

Gas analysis - attaching the right kit to the header tank opening and run the vehicle up to temperature - if exhaust gases are being introduced into the coolant and being degassed in the header tank cap, then you should get a positive reading for exhaust gases. Note that with my van, the exhaust gases only escaped into the coolant under load - I was unable to cause a pressure increase with my right foot while stationary, and only saw the pressure increase under driving load - I did not have a gas analysis test done, but suspect it would have shown no problem even if I had.

Cyclinder head test - once removed, heads can be pressure tested off the vehicle - often less useful if done cold, not all places have the facility to test it hot - a fail is a fail, but a pass doesn't necessary mean that the head is not a problem.

Thermostat - when cold, lift both front seats - squeeze the main coolant hose out of the head (drivers side towards the front-top of the engine) and listen for the jiggle of the jiggle pin in the thermostat over on the other side (somewhere middle-middle near the turbo). Run it up to temperature, feeling the bottom hose of the radiator (about a forearm's length behind the bumper - just to the right of the numberplate). It should be cold and soft to begin with, become pressurised and still cold up to 85-odd degrees and only then become hot (too hot to hold for long) when the thermostat operates. A genuine thermostat is only about £20, so worth doing.


I'm not sure I can advise, but hope that some of that helps you understand what may or may not be going on.

[francophile1947]

Read your other threads - pressurising is normal so, unless you're losing water or overheating, it's probably normal.

[Cathryn]

I have read them. Since spoken to three mechanics and it's with one specialist who say if it's pressuring then it's probably already gone. Just gutted we are in this position as we wasted our saving buying this thing and will now prob have to sell it for less.

[Cathryn]

Clearly I'm a good example as to why you should not buy privately and if you do take a mechanic unless you know your stuff anyway lol

[ThisIsTheSea]

I have read your other topic on your concerns about your Bongo.

From the sound of things, you haven't lost any water and the Bongo hasn't overheated. As others have told you - the cooling system is supposed to be pressurised - that's how it works. So why are you worried? If you bought it from people who live just round the corner from you, I'm sure they wouldn't have the nerve to sell a lemon to someone who lives so close to them.

[Driver+Passengers]

It depends how soon after startup it becomes pressurised and to what extent - if with temperature, as in a healthy system, then that sound normal - if pressurising quickly while still fairly cold then not so good - or in my case, pressurising only with engine load, more difficult to detect and still not good, though there's nothing to suggest this one - just relating my experience. That it's apparently not losing coolant nor has it boiled and been driven successfully are all good sign, but mine only boiled once in nearly 3000 miles of driving with a failed/failing head gasket.

We're going on just a few relayed words from someone at the garage, (ambiguous to begin with, without all of the facts and circumstance). It still warrants a second opinion from a savvy garage perhaps, rather than seeking clarity from the first.

[Dodgey]

if it's pressuring then it's probably already gone. Just gutted we are in this position as we wasted our saving buying this thing

what's "probably already gone" ?

If you have to replace your head gasket it's not a big job. In fact, it's a much better outcome than a lot of other people have with Bongo cylinder heads.

Step back and realise you probably have not bought a lemon, but you have bought a car 2nd hand with advisories. That always entails sorting out a few bits the previous owners didn't get done. If you bought the same car with no advisories, from a dealer, it would have cost you £5k ...