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Non-M/C mechanical question - moisture in the oil

  • Thread starter Thread starter JMHJ
  • Start date Start date
J

JMHJ

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Forgive me for posting a regular vehicle mechanical question here, but I thought I'd throw it out there since a lot of you all seem highly knowledgeable about the mechanical stuff: my '89 GMC pickup (4.3 V6, TBI, about 190k miles) has had moisture on the engine oil dipstick for several years (starting probably 18-20k miles ago or so). It doesn't seem to be losing coolant to speak of, and I checked the compression (good) and changed the intake manifold gaskets a few years ago. It seems like the problem was better for a while, but maybe I was dreaming; in any case, it's there again.

It runs well, except that the rpms don't drop normally when off the gas, mainly when it's cold.

Sorry for the car post, and thanks for any ideas.
 
it could be condensation in the oil, and the rpms shouldnt drop off quick when its cold because it idles up higher to warm up the engine.
 
With that many miles I would be suspecting a head gasket. If all you drive is short trips, under 5-6 miles then that would contribute to moisture in the oil but again with that many miles, my money is on the head gasket.

Tom
 
Thanks. I wondered about one of the head gaskets too, but I thought the compression test would tell me that, if it was blown between two cylinders. Maybe it's a small breach. I don't think I'll be fixing that any time soon if that's it.
 
GM is famous for the intake gaskets going bad. Even tho you have replaced them It could be leaking again.
Just some of the crap they sell us, then we have to pay$$$$ to fix their screw ups.
 
leaking replace head gaskets..

leaking replace head gaskets..

on a gm you need to use coppercoat to seal the oem type metal gaskets.. felpro should not need it but you may want to ask a local gm mechanic what they do to seal the gaskets properly..

Joe
 
It could just be normal condensation -- older vehicles don't tend to go on long highway trips that would get everything up to temp and boil off the condensation. You're also most certainly getting more blowby past the tired old rings, so there's more gunk going into the oil and probably less opportunity for it to get boiled out.

You might also check the PCV valve and hoses -- when they get a little gunky, the engine might not slurp out the blowby as well as it should.

Heck, it could also be a head gasket. But you might as well check out the cheap stuff first.
 
bwringer stole my thunder... I lean towards the fact that engines that run on mostly short trips tend to build up a lot of condensation in the oil. The longer the engine runs, the better able it is to boil off the moisture.

It CAN be a gasket leak (I had to replace the intake gasket on my 96 4.3L Vortec V-6 last week for the same reason, but mine was leaking externally like a pig with a severed carotid artery) But I'm inclined towards the simpler explanation when the rest of the symptoms aren't present to point towards a gasket.
 
normal

normal

One of the byproducts of burning hydrocarbons is always water. Think of the water you commonly see dripping out of exhaust pipes. A little blowby is common in all engines. It is the job of the PCV (positive crancase ventilation) system to allow the evaporative byporducts in the oil to by consumed by the engine again. This needs the engine to be ran for a period of time long enough for these products (mainly water and gasoline vapours) to be evaporated out of the oil and back into the intake track. You could have a malfunctioning PCV system or it may be normal for your engine to have some water condensate, as long as your oil is not taking on a milky consistancy.
If you are truly concerned, check out http://www.fluidlife.com/
This place analyzes oil samples for major transport companies and will give you a breakdown via e-mail of all of the contaminants in your oil and can tell you if there is an unacceptable level of water in your oil. it can also tell you about oil life and other engine problems.
Tho check for excessive blowby, you can plug the pcv line and see if there is pressure on the dipstick tube.
 
:-k
Where do you live? If you are in the Northern states or Canada, it is not uncommon to get condensation in engines that do short trips during the winter. GM engines have a poor crankcase ventilation system. If you pull your valve covers you will probably find them covered with sludge. I would replace the ventilation valve ,PCV, and the hose that comes off it. If your model has the filter on the inside of the air cleaner, replace that too. Put a can of crankcase flush in and run it for a while, change the oil, put in the cheapest stuff you can find, with another can of cleaner, drive it around for a while, dump that oil, it will be disgusting. Replace your oil with mobil and keep replacing the pcv each fall, you will also want to take a long run each week do keep the condensation down.:-k
 
Thanks for the replies, I missed a couple of them. I guess my trips are usually 10 miles or less one way. I don't drive it alot either when the weather's good for riding. I haven't changed the PCV valve or hoses, but I've taken to leaving my dipstick unseated by 1/2" or so, which seems to have helped.
 
Most of the replies from other members are correct, the PCV system is probably the cause. A most common cause is not the PCV valve, but the vacuum supply at the front of the throttle body. The passages in the TB tend to carbon up real bad. The base gaskets tend to blow out with age also. To test the passageway, just pull the vacuum hose off (the one that goes to the TB) while the motors running.If its clear, the RPM's will go way up......Never had much luck cleaning it out good w/o taking the TB off the manifold. That carbon can be really hard.....BadBillyB
 
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