Cooling system pressurising, but passed sniff test

[hurststeve]

Opening the pressure cap with engine cold after a run releases pressure from the cooling system with a hiss and a gurgle, but I've just had a sniff test done and it failed to indicate exhaust in the water. It's not simply an airlock as it was fine previously and no work's been done. Engine runs fine and keeps its temperature under control in hot weather.

Any ideas?

[TVR Beaver]

Is it air going in??

Water rises at temp and pushes air out... then cools and creates a partial vaccume if your cap has an 'out' valve only...

Remove the cap.. and air is pulled in?.. have a check

[hurststeve]

Even when the engine is stone cold, pressure is relieved by air escaping (or I thought exhaust gas, before the sniff test) when it's opened, so the sytem is pressurised, even when cold, to a pressure higher than atmospheric. Where can this pressure come from? Oh, only the combustion chambers. Sniff test. No colour change.

Back around the same circle.

[900T-R]

Had the same. Two weeks of mucking about and finally got confirmed that we did have a headgasket problem after all (they ended up connecting a pressure gauge to a purpose-designed coolant cap 'replacement' before running it on the rolling road again).

Why the initial sniffer test gave no result, I don't know. Admittedly it only spilt its coolant out of the header tank when at full bore on the rolling road for longer than a few seconds at thne same rpm, but surely that would've been enough to detect combustion gases in the header tank afterwards, no?

Edited by 900T-R on Thursday 26th July 13:15

[TJC46]

hurststeve said:

Opening the pressure cap with engine cold after a run releases pressure from the cooling system with a hiss and a gurgle, but I've just had a sniff test done and it failed to indicate exhaust in the water. It's not simply an airlock as it was fine previously and no work's been done. Engine runs fine and keeps its temperature under control in hot weather.

Any ideas?

All sounds quite normal to me When cold mine too will make a hiss and a gurgle, dont know if its air going in or air coming out. Car and temp behave as they should, as does your car, so you have nothing to worry about.
Check the coolant level in the bottom of the expansion tank when cold, they vary a bit but about 25mm to 50mm of coolant in there is correct. Take her for a spin if the temp is fine especially when stationary,with fans kicking in and out etc and everything seems ok, then head back home and let her cool down fully, for a couple of hours or more. Now check the level in the expansion tank and if its the same or similar before your drive, then you have no problems.
Keep an eye on everything over the next few weeks, checking coolant levels etc, just to be sure.
There is an age old saying....."dont choose trouble, until trouble chooses you".....Relax and enjoy your car, especially in this weather.

[hurststeve]

Yes, I think I will choose to let it develop, and maybe it's nothing. You're probably right about not looking for trouble, and indeed it does seem to behave itself in terms of temperature control.

But then again....

(I'll probably be back a few weeks moaning about having had to call the recovery service from the midst of a cloud of steam.)

Thanks.

[Mr MXT]

Did you get anywhere with this OP?

[Steve_D]

Mr MXT said:

Did you get anywhere with this OP?

6 years ago.....he's likely sold the car by now.

Steve