Cooling System High Pressure
 

OK, so I thought I’d start a new thread for this as the original one had become a bit befuddled due to its length.

So, in brief, the story so far (and my thanks to all the members who have helped me up to this point)…

Had a misfire on one cylinder at start up. Lasted just a few seconds to start with, but started lasting longer and longer before it cleared. Changed plugs, and no. 4 was black. New plugs made no difference to the misfire. Cooling system showing signs of over-pressurisation - hard hoses, losing coolant from expansion tank filler cap when warmed up. Gentle release of the coolant filler cap produced lots of hiss, then a flood of pressurised coolant.

Changed inlet manifold gasket. Old one showed clear signs of coolant ingress into no. 4 cylinder. New gasket made no difference. Checked plugs after a few days, and the new one in no. 4 was black (again), and I could see damp on top of the piston. Assumed that the new gasket had failed due to the high coolant pressure.

In case it was a failed thermostat I dialled in the temperature mode in the on-board diagnostics, warmed it up then took it for a spin. Temp fluctuated as I drove, but stayed within the 97 to 104 degree range. Got back and checked hoses - rock hard and bulging. Left overnight, then checked pressure. Virtually no hiss as I opened the expansion tank cap, but I suspect that the high pressure has opened up a small leak somewhere which is slowly releasing the pressure once it's switched off and cooled down.

So, today I started the car with the coolant filler cap off to see what happened. Within a minute or two the level in the expansion tank began to rise and soon overflowed the top of the tank. Some bubbles present, but not many.

So, I guess it has to be head gasket failure. Am I wrong? Thanks.

All the signs are there unfortunately :(

Oh dear. With 125k on the clock I need to think long and hard whether to keep it. Shame, because it runs really well, and I like it very much. However I bought it with high mileage and it was therefore always going to be a gamble! The clutch is very heavy too, so that also has to be viewed as a potential failure before too long.

Rather than trying to get everyone to diagnose the problem by telepathy and basing the car's fate on that you need to get to someone who knows the 1.8 engine to look at it then make a decision. I'd send shiner, the regional secretary for your area, a PM and ask if he knows anyone local who could look at it for you.

Gawd give me strength :duh:

Andy will be on the phone tomorrow after reading this.

If the hoses are as tight as a drum when the car is running, it's almost certainly as a result of combustion gas entering the jacket water.

You have covered most of the bases such as inlet manifold gasket, but the pressurisation of the hoses can be caused by only two things.

Air in the system from incorrect filling procedure

Leakage from the fire rings of the gasket

Best of luck

Brian :D

Thank you, but hardly telepathy, I would hope. I've tried to work through this issue as logically as possible, and present the findings as they've presented themselves to me in the hope that people who know more than I do can give me an informed opinion. I have worked on cars a lot in the past, but my knowledge is 40 years old and things have really moved on since I last worked on my old Minx. :}

Yeah, I've bled it correctly, so HG it is. Thanks Brian.

Update - I've had the head skimmed and a new HG, water pump and thermostat fitted, and changed the inlet manifold gasket. The system is still over-pressurising. I'm at a bit of a loss as to what to do now! Any thoughts people? Thanks.

Did you check the liner heights to see they were not below the block face. & interesting article in PC mag. this month about K series engines.