pressure in header tank when engine is stone cold

[racing green rover]

Hi Iv had a problem with water loss and slight misfire when engine is cold whet I press the accelerator quick I was thinking inlet manifold gasket was leaking first but when I unscrewed the header tank cap this morning there was a hiss and the coolant was on MAX this time I'm wondering if the pressure has raised the level when cold the engine doesn't overheat it usually reads around 88 degrees when running car otherwise runs fine apart from above problems the oil and water are clean no sign of any mixing I can't smell any exhaust gasses in the header tank either
car in question is a 1.8
Thanks

[racing green rover]

I'm just going to leave it as it runs fine with no overheating and put a new inlet manifold gasket on

[Saga Lout]

Originally Posted by racing green rover

I'm just going to leave it as it runs fine with no overheating and put a new inlet manifold gasket on

It needs looking at for sure..That hiss is a pressure build up from something, mine blew a hose in the end...

[ProfDave]

are you sure u don't have a leak

when my coolant rail was leaking then in the mornings there was a hiss of incoming air rather than pressure build up

obviously coincided with coolant loss

[kaiser]

If you have overpressure at cold, your head gasket is gone.
So make sure your diagnosis is right!
If it is, repair.
http://www.the75andztclub.co.uk/foru...d.php?t=214880

[SD1too]

Originally Posted by racing green rover

I'm just going to leave it as it runs fine with no overheating and put a new inlet manifold gasket on

Good idea Pete. Don't forget to let us know the outcome.

Simon

[racing green rover]

It sounds weird as it runs fine with no overheating and heater stays warm so I'm at an undecided guess if the headgasket had gone as it would airlock the cooling system with exhaust gases and overheat but mine doesn't. The noise when undoing the cap sounded like a straw in an empty bottle with someone sucking on it like a gurgling noise. There isn't no bubbling up of the coolant with the engine running and cap off even when I rev it I have also noticed water around the rim of the header tank leaking cap maybe? Although its only a few month old

[kaiser]

If your rubber pipes are under pressure (swollen), then exhaust gases, if not,- not.
Over pressure would certainly result in water loss as well.

[SD1too]

Originally Posted by racing green rover

... I'm at an undecided guess if the headgasket had gone ...

Guessing is never a good idea Pete. Let's look at the evidence you've given instead:

• Some coolant loss, traces around rim of expansion tank.
• Slight misfire when cold & accelerator pressed quickly.
• Gurgling noise when expansion tank opened.
• No mixing of engine oil and coolant.
• No bubbling in coolant, even when engine revved.
• Running temperature 88°.

All of that sounds like an inlet manifold gasket which isn't sealing properly. I think that you should stick to your original proposal to renew it. Before starting work, drain the cooling system fully and afterwards refill and bleed it by following the official MG Rover procedure here.

I would urge you at this stage not to attach too much prominence to any hissing when the expansion tank is released. I know that some argue on the basis of theoretical physics that this must mean head gasket failure, but others have reported that after a complete bleeding session the hissing stopped. Another member currently has a KV6 with rising coolant level but, like you, there is no associated evidence of head gasket problems. So stick to your plans Pete. It's a fairly easy job, I understand, to renew the inlet manifold gasket and it should put your mind at rest.

Simon

[kaiser]

I have learned the hard way that physics and math you don't argue with.
You understand it and behave accordingly.