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Monday, 4 February 2013

Jeep CJ-7, Water Problems


Question: I've got an '84 CJ-7, 258 straight six. There is quite a bit of water-oil mixture in the valve cover. I've notice just a tiny bit on the dip stick. But, when I drop the oil there is no water. Also, there is lots of water-oil accumulation in the air cleaner. And I notice the radiator is short on water about every two months. I get the feeling I have either a cracked block or a blown head gasket but the engine is actually running under temp during normal operation.?

A:There's no need to get physical. I don't believe that you're cooling loss is related to the watery-oil problem in the valve cover and air cleaner. It's not uncommon for a vehicle of that age to have small leaks that could account for the loss. The accumulation of water-oil in the air cleaner is a good indicator that the Positive Crankcase Ventilation (PCV) system is not functioning properly. Next, you're going to ask, "Where did the water come from that's in the engine?"

Have you seen condensation on a glass of water? Well, the same thing happens to engines. With temperature change, moisture will condense and collect inside an engine. But, that's only a small part of the picture. The greatest source of water in an engine is the combustion process, the burning of gasoline. How do you get water from gasoline? Gasoline is a hydrocarbon (HC). When gasoline is mixed with oxygen and heat, a thermal-chemical reaction occurs, it burns. Am I scaring you yet?

As the gasoline (HC) and oxygen (O2) burn, they break apart and re-join becoming water (H2O) and carbon dioxide (CO2). Of course there are other chemicals but these two are the main players. The remains of combustion (exhaust) H2O, CO2 and other chemicals are supposed to exit the tail pipe, but that doesn't happen. A portion of the combustion gases leak by the pistons in the engine, into the crankcase.

The job of the PCV system is to pull these gases H2O, CO2, and other chemicals out of the crankcase so as not to contaminate the engine oil. If the PCV system is not operating properly H2O will collect in the valve cover and be forced into the air cleaner assembly. Cold weather will make matters worse.

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