what is the risk in driving a vehicle with a bad head gasket? I am looking at buying a used 740 turbo wagon that the owner believes has a bad head gasket. He says it doesn’t use any anti-freeze, but the cooling system becomes “pressurized” when driving and the expansion tank “hisses” after the car is shut off. Could this just be a bad radiator cap? I want to buy the car and drive it for a while before pulling the head because it is too cold here to do any work right now (garage temperature is around 10 degrees F). Do I risk doing further damage by driving the car (100-200 miles per week) until warmer weather arrives?

The last time I looked, there was no radiator cap per se on a 740. I suppose it could be the cap on the expansion tank.

Few quick checks for a bad headgasket: Pull the spark plugs. Do any of them have a "steam cleaned" look, i.e. does one of the plugs look cleaner than the others? Is compression significantly lower on one cylinder? Coolant contaminated with oil or vice versa?

Please post back and let us know what happens.

-Jim

If you can get a pressure gauge hooked to a radiator cap you
could tell pretty quick. If it builds up pressure before the
engine gets warm, that is a bad sign.
A leaking headgasket would also probably make the antifreeze dirty
or oily, or at least put an oily film on top of it.
--
George Downs Bartlesville, Oklahoma

My question is, am I going to damage the car further by driving with a bad head gasket? The car runs great and it is to gd cold out now (0 degrees) to work on it.

Apparently neither Jim nor I are convinced that you have a bad head
gasket. If you are NOT getting any oil or slime into your antifreeze,
and you are NOT using any antifreeze, it is OK to drive and your headgasket
is probably good.

The dangerous situation is when antifreeze starts getting into the oil.
It tends to make some compounds that greatly reduce the oil's ability to
lubricate, and can even be like sugar in your oil. If your oil doesn't look
milky and your antifreeze doesn't look oily you are probably pretty safe
from at least this problem.

This comment is made as a free service in a spirit of helpfulness.
It carries NO authority nor responsibility for damages that may ensue.
--
George Downs Bartlesville, Oklahoma

As a first step I replaced the cap on the expansion tank. It was making a hissing noise, and the prior owner told me this was a symptom of a bad head gasket. The old cap must have been cracked or something because now there is no hissing noise. I bought the cap at the dealer for $20 (seems like a rip-off) and am somewhat concerned because it really doesn't look much like the old one. Do you know if Volvo changed the design?

I checked the p/n in my Volvo Parts Quick Reference (Feb 1999 issue). 240 series all 4 cyl and B28F have the p/n 1357775-4. Other models, 700, 900, 850, more, have p/n 9445462-6. You may have been given the wrong p/n by the dealer.

Good Luck,

Bob

:>)

Thanks for your advice. It is too cold today to do a compression test, but I hope to be able to do it next weekend and report back to you. I sure hope it isn't a blown gasket.