design - Land Rover section


Land Rover FAQs


QUESTION - I have found a chocolate brown emulsion on my engine's dipstick or the underside of the valve cover. Do I have a cracked head?

ANSWER - It is uncommon for a cracked head or blown head gasket to open a passage between the engine oil and coolant. The common head crack failure mode creates a passage between the water passage and a cylinder. Blown head gaskets commonly create a passage between adjacent cylinders or between a water passage and a cylinder.

It usually takes a crack in the engine block to mix coolant and oil. When this happens you get lots of steam coming out all over. It is very noticeable. Or at least it was the one time it happened to me.

Your most likely cause:

Hot air is less dense than cold air. This means that when an engine is at operating temperature there are less molecules of air inside the engine than when the engine is cool. Hotter air can also carry more water vapor molecules than cold air can.

As an engine cools, the air inside the engine block cools down becoming denser. This creates a slight vacuum. Air is drawn into the engine block to equalize the air pressure.

If the air sucked inside the engine is moist and the engine gets cold overnight, a dew can deposit water from the air onto the inside surfaces of the engine.

If you drive the car long enough for the engine to come up to full operating temperature, the deposited water goes back to being a vapor then gets "burned" out of the engine.

If you do not drive the car long enough to "burn" the water out of the engine during periods of high humidity days and cool nights you get a build up of moisture in the cooler parts of the engine such as the valve cover and dip stick tube. This moisture combines with the oil creating a chocolate brown emulsion.

A normal product of engine combustion is water vapor. A little gets forced through the rings from the combustion chamber aggravating the condition.

Basically you are looking at a normal condition that occurs during certain weather conditions, usually in cars that are driven short distances. The additional moisture in the crank case will hasten the formation of acids in the oil.

The appropriate response is to change the oil and filter a little more frequently and wipe the emulsion build up off the dipstick to keep it from rusting.

Back to the FAQ contents

Return to page top


If you would like to discuss any of the contents, or just say hi, please feel free to .


© 1997, 2001, 2017TeriAnn Wakeman. All rights reserved.