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Here's some final thoughts (long) (archive)

[ Follow Ups ] [ 5-series (E34) Message Board ] [ Msg. Board FAQ ]

Posted by EM on April 09, 1999 at 21:28:09:

In Reply to: OH NO! There's oil in the coolant. posted by MJKHAN on April 09, 1999 at 15:11:52:

The head separates three different systems in the car: the oil, the water, and the combustion chamber.

The oil travels through the oil passages in the block up through the head, then back into the block again into the sump and through the oil pump. There's pretty much the same process for the water except it travels through the radiator. The head gasket keeps "the lid" on the violent explosions that occur in your combustion chamber and keeps the water in the water passages and the oil in the oil passages (How did you think all that oil got to the top of the motor to lubricate those valves anyway :)?

Among other things, if the gasket fails, the oil and water can (a) get into the "other" system, or (b) breach to the outside and make a mess all over the side of the engine and your garage floor.

The failure you've described (water in the oil) is a nasty mess, gunks up all those *really little* passages in the radiator, reduces the ability of the cooling system to work and is a classic sign of a blown head gasket. Oil does not do a great job of cooling the engine either (unless you're a Porsche, of course). However, oil is a better coolant than water is a lubricant. So if you're going to have a problem, its better (realatively speaking, of course) to have oil in the water than have water in the oil.

However, I would have to disagree about your feelings regarding water in your oil if you find the oil level going up unexplainedly. Unless someone's sneaking out at night and putting oil in the filler, there's water getting into your crankcase and that's why the oil level is "increasing". There's water in the bottom of the pan that the oil's "floating" on, thereby giving you an erroneously high reading on the dipstick. Check the end of the dipstick. Is there anything other than pure, clean oil on it? Any streaky stuff? Any white stuff? Anyway, there is a possibility that you're measuring the oil level when the oil is cold, then measuring it again when the oil is hot and reading that it went up -- if so, see the segment on thermal expansion earlier...

Here's a trick..., when the car is at operating temperature, stop the motor and take off the oil filler cap. Put your ear right up next to the opening and listen carefully. Amazingly enough, when a head gasket is blown, sometimes you can hear a "steaming" or wheezinging sound from the filler hole as the cooling system cools, depressurizes, and sucks the oil into the water (or the other way around). Just don't let your neighbors see you do this or they'll think your nuts.

Another trick..., does the car start to crank over, then stop hard, then start cranking normally, then start? This can be due to "hydrostatic lock", a.k.a. water in the cylinder. Being that water is *not* compressable, as the piston goes into the compression stroke and tries to compress a cylinder full of water, it kind of hits a brick wall and stops turning until the water squeezes out past a leaky valve or past the oil/compression rings. Here's another fun way to impress your neighbors. If you have h/l, take out the plugs. Crank the motor with the plugs out and you can shoot water over your neighbor's house. I've done it, and other than the fact that you just confirmed a head problem, its a riot.

Good luck on Tuesday,

EM


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