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MG MGB Technical - emulsified oil in valve cover

Hi all,

I have just got my car registered and after the first outing noticed that there was some emulsified oil inside the valve cover. Suspecting that there might be a head gasket problem I took the car to the garage for them to have a look at. They say that there is not a problem with the head gasket since the only emulsification is in the valve cover not in the main oil. They say the problem is with the inlet gasket which is leaking.

My question is how will a leaking inlet gasket cause emulsification of the oil? I'm having difficulty thinking how this could happen.

Thanks in advance

Billy
William Beattie

Sounds like anti freeze is in the oil. Can look mayonaise like and just be on the filler cap.
Dennis Pantano

I don't see how a leaking inlet gasket can cause scum in the rocker cover either, maybe they were just advising you of another problem and not the cause of the one you asked them about. There should never be any scum in an MGB rocker cover, particularly after 1964 with the positive crankcase ventilation. You can check this by letting the car idle when warm and removing the oil filler cap. There should be a slight change in engine revs, and if you put the palm of your hand over the hole you should feel slight suction. If so the ventilation is OK, you just need to be sure you have a vented oil filler cap. They are a service item and cheap, so just replace it anyway. If there is no change in revs and no suction then you need to check the ventilation plumbing, which varied over the years.
Paul Hunt

If an engine has been used predominantly on short runs where it hasn't warmed up fully, then "mayonnaise" in the rocker cover is not unusual - especially in cold weather.

One of the by products of combustion is water and this will find its way into the sump. If the oil never gets hot enough to boil this water off, then the oil's emulsifiers will trap it in the "mayonnaise".

Remedy - take her for a good hard run and get the engine up to temp - then the breating system can remove the water vapour.
Chris at Octarine Services

Apart from the water from the combustion process as Chris mentioned, the air is damp so when you switch off, the saturation point of the air inside the engine will lower, along with the cooling down. The air will contract, pulling more air into the valve rocker, which then condense out. For any machine or tank that doesn't have a regular splash of oil (or even fuel) around the topside of the tank, then rust and corrosion will start which will drop minute particles into the oil.
As above, change the filler cap (they should be done regularly), and, as Chris said in another post, change your oil, run the car for a few miles, and change the oil again with a fresh filter. This should help get rid of any residual nasties in the oilways that may not have drained out in the first go. Also, has the car has stood for a while (I assume from your first post) then the double oil change will help for definite.
My Austin 1300 had a crankcase breather pipe that ran up to the carb inlet, and the little cannister used to choke up over a few years with this mayonnaise.Martin
Martin

This thread was discussed between 05/11/2003 and 06/11/2003

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