Pressurising cooling system.

[Hettiherald]

Hi all
I'm sure these cars have a cruel streak built in. Just booked in for extensive body work and respray, ( the car) and i think the head gasket has blown. System pressurises as soon as it starts from cold, but pushes a small amont of water out, then maintains the pressure when hot and is switched off. Almost like a one way valve. Am i missing anything or is my assesment of gasket failure correct? Uses no oil, no water in oil, and no excessive vapour from exhaust. Help.
Dave.

[Staggard]

Hi all
I'm sure these cars have a cruel streak built in. Just booked in for extensive body work and respray, ( the car) and i think the head gasket has blown. System pressurises as soon as it starts from cold, but pushes a small amont of water out, then maintains the pressure when hot and is switched off. Almost like a one way valve. Am i missing anything or is my assesment of gasket failure correct? Uses no oil, no water in oil, and no excessive vapour from exhaust. Help.
Dave.

If the cooling system pressurizes straight after start up, I would say you have diagnosed correctly. sounds like combustion gasses are blowing straight in to the block water jacket.

[flying farmer]

If your cooling system is still under pressure when cold then it is definitely head gasket failure, but this will depend on the system having no other leaks.

Gas from the combustion chamber enters the cooling system far more easily than water finds its way back through the same fault into the cylinder.

It is very rare to get oil and water mixing when Stag head gaskets fail, the only access for water to enter the sump is either the timing chain cover or the drain from the camshafts at the back of the heads.
Neil

[Hettiherald]

Thanks for the replies, i was just making sure i hadnt missed somthing. Dont you just love these cars
On another point, the engine was rebuilt about 16 yrs ago, done around 20,000 miles so i can be fairly certain that the heads have been shaved. Do the shims for the heads work ok, or or they a bit iffy? Ta
Dave

[Staggard]

Thanks for the replies, i was just making sure i hadnt missed somthing. Dont you just love these cars
On another point, the engine was rebuilt about 16 yrs ago, done around 20,000 miles so i can be fairly certain that the heads have been shaved. Do the shims for the heads work ok, or or they a bit iffy? Ta
Dave

Cross that bridge when you come to it. When you pull the heads they may not need skimming and you can use thicker head gaskets anyway.

[Hettiherald]

Thanks for that advice. Keeping everything crossed now untill i can pull the heads. Have to be after the bodywork is done as its all booked in. Watch this space!!
Dave

[flying farmer]

The heads don't always warp. The gaskets can eventually fatigue fail and provided the engine hasn't been allowed to overheat it can be a straight replacement gasket job.

This is what happened to the first Stag engine I built, it took 70,000 miles before it occurred so I decided to do a total strip down and replace any worn parts. As it happened everything was as good as the day it was first put together, so a full gasket set was all that was needed.

More than likely the heads have not been retorqued hence the gasket failure, but when you do have them off put a steel ruler over the back of the block and check the cylinder block face has not sunk where the rear waterway is. I find about half the blocks I have looked at have sunk here.
My first Stag came with a history file that showed three sets of head gaskets were fitted in 15,000 miles. When I had to strip the engine following jackshaft failure I found the head faces were perfect but the block faces needed skimming by 8 thou due to the aforementioned sinkage, not surprising the gaskets kept failing!
Neil

[wilf]

Thanks for that advice. Keeping everything crossed now untill i can pull the heads. Have to be after the bodywork is done as its all booked in. Watch this space!!
Dave

Be careful, you don't want to leave your car for an extended period of time with water in one or more cylinder bores, you can wreck it like that.

[Hettiherald]

Words of wisdom neil, thanks. Dont worry wilf, not leaving it for long, and thankfully no water is getting into the cyls(yet!).
Dave