Blown head gasket on '91 740 Turbo???

I have recently purchased a '91 740 Turbo, it was a one owner and meticulously maintained! I pulled the oil dipstick out recently to check the condition of the oil and found the end of the stick to look like it had been dipped in a chocolate milkshake! I assumed it was a blown head gasket. I drained the oil and it looked perfectly fine. I changed the oil and continued to drive the car for another week and looked at the dipstick again, another chocolate milkshake!! I put the car in the basement and decided to replace the head gasket. Again I drained the oil (after having changed it a week ago) and the oil looked perfect?? I am very confused. The milky substance seems to only be located in the dipstick tube, and not in the oil itself. How could this be? I am mechanically inclined, and have changed 4 cyl. head gaskets in the past (although never on a Volvo), but the quality of the oil being drained has me very confused! What could be causing this milky substance in the dipstick tube and not in the oil itself? Also, the motor does not and has not overheated, and shows no other typical signs of a bad head gasket. There is also no water or steam or any other type of irregular exhaust coming from the tailpipe. What is this mysterious milky substance in the dipstick tube? I will be very greatful for any helpful information I receive

 

These engines are pretty sturdy, so although head gasket failures have
occurred (mostly with serious overheating) they are not that common.

I have a thought about the dipstick tube, though. If the crankcase
ventilation plugs up oil is forced out of the dipstick tube (at least in my
'85) and I'm wondering if the tube extends not so far in your engine so
crankcase vapors can be forced out the dipstick tube instead? If so,
condensation could account for the glop you are seeing.

In any event, it is a good idea to check the ventilation. The system is
really no more than a hose that runs from an oil/air separator box under the
intake manifold to the turbo inlet duct, sometimes with a "Y" to the
throttle body. The separator box is held down by two screws, but if you
elect to remove it many people favor just buying a new one with the two
O-rings it uses. You can do a confidence check by pulling the hose off the
inlet duct and removing the oil filler cap. When you blow into the hose it
should feel like you are blowing through a 3/8 inch hole instead of like a
soda straw. (Now wipe that silly black ring off your mouth.) In my case, I
never suspected the large ventilation hose could plug up, but given enough
time it sure did.

Mike

 

That's exactly the issue my 740 Turbo had, and the reason it was only
$500 instead of the $4K or so it would have otherwise been worth at the
time.

In my case the only thing I could ever come up with is the O-ring on the
dipstick was missing so moisture must have got down in there. I've put
over 50K on it the last 6 years and the problem never came back.

 

Change the thermostat (and gasket) and check that the radiator hasn't
developed a leak between coolant part and transmission cooler part. Check
radiator by looking at transmission fluid via gearbox dipstick. If ATF is
red and pleasant smelling radiator is usually okay.

A monthly "Italian Tune-up" is recommended if you do a lot of short journeys
where the engine does not have the time to get up to it's running
temperature.

All the best, Peter.

700/900/90 Register Keeper,
Volvo Owners Club (UK).

 

As winter comes on short trips cause moisture build up in the oil so a good
warm run or the "Italian tune up "read rev it out hard, will rid the oil of
moisture .I once ran a mini 998 through thick fog at low revs for hours in
high cattle country at night ,my s-HELL oil was like milk the next day .This
was extreme for sure but it shows what can happen .Congratulations you have
a great car there use synthetic oil turn up the turbo and enjoy .We have two
an 88 and a 90 .