Head Gasket

[maynard]

Although I know I need to do a compression test, it will be a week
before I can get around to it, but I thought I'd raise the issue.

A couple of weeks ago, while on the tollway, I blew a radiator
hose. I pulled to the side of the road before it overheated and
had it towed to a shop I know, where they replaced the hose.

They said they thought I might have a blown head gasket because it
took a long time for the bubbles to stop after they refilled it.
This despite telling them the car has to be bled the correct way.

Anyhow, I have been paranoid about it overheating and have been
checking the coolant religously. I have had to had a little bit
every time, but have attributed it to improper bleeding. THe
reservoir always had air in it, but the crossover pipe was always
close to full.

Today, after the car has been sitting for a couple of days, I went
to check the coolant. When I opened the cap, fluid squirted out
under pressure. It hadn't done this before.

The car is not overheating, and there is no sign of coolant in the
oil or at the breather.

The overflow is clear, though I didn't hear any bubbling when I blew in it.

Any ideas?

 

[jessebogan]

Try connecting a radiator pressure gauge to the header tank, with the car stone cold, and run the car up to temp. The pressure should rise gradually, but if all is well with the cooling system should stop well below the 15-16 psi that the caps blow off at. When the car cools, the pressure should drop to 0 or perhaps a slight negative. If you do not get a big, fast pressure increase, check the caps carefully. The other thing to do is to have the shop take a co sniffer, and hold it over the open header tank. The presence of combustion gases in the coolant means that a headgasket is leaking. If you have no other symptoms, try re torquing the heads. This is a bit of a project, but nothing like replacing the gaskets. If it turns out the the worst has happened, it is still well within the abilities of the home technician. Just do yourself a favor, and make or purchase the head pulling tools. I have never bought a tool that saved me so much time on a job.

 

[roger_abbott]

Before proceeding any further, I suggest you read Kirby Palm's book on the Jaguar V-12. His web site is https://www.nettally.com/palmk. Diagnosis of heating problems in a V-12 is very difficult. It took me two years to figure out, more or less, what was causing mine to exhibit symptons similar to yours, and it was not a blown head gasket.

 

[maynard]

I've read his book, in fact I've printed it out.

What was the cause of your problem?

Thaks

 

[Michael J.]

Read the section on "bleading" air from the V-12 when filling the radiator.

If not filled correctly, you will have trapped air in the heads and will have an overheating problem.

I suggest your doing that before you drive the car much.

 

[roger_abbott]

Maynard, I apologize for not keeping up with this thread. The problem with Palm's book is information overload. However, following the theory that the factory knew what it was doing when it made the car, I started looking for any missing parts involved with the cooling system. The first missing part I found was a one-way valve that was supposed to be installed in the overflow tube leading from the central filler neck to the radiator. The tube itself is bigger at one end than the other, so simply replacing the tubing won't work. You need the factory part. Next items were the thermostats - they weren't the correct kind. They have a small disk on one end that serves to cut off water flow through the cross pipe once operating temperature is reached. The lower hose was hard to reach so I waited until it split to replace it (!). Fortunately, it decided to split in the parking lot at work. I continued with all the ususal fixes and finally, overheating became an occasional problem: 100+ ambient temperature, 80 mph now seems to be the start of overheating - about as good as any other British car I have owned.

This was a car I bought when it had 21,000 miles and was four years old. It had always been serviced by the local Jaguar dealership according to its records. You can never be sure that your car has all its parts.

I am pretty sure I have some problems with the left head due to overheating. Eventually, I plan to pull the heads, check the amount of space between valve seat inserts and the head and hope that I can do something constructive with the heads. My local machine shop tells me that an overheated head loses its temper and can't be milled or machined, which means the valve seat inserts can't be replaced.

On filling and bleeding, I found that parking the car pointing uphill seems to work better than dead level. I still have to add a couple of pints every so often.

Good luck.