Internal oil/coolant leak. How to determine?

Just rebild the top end of a YZ426.

There are no external collant/oil leaks so far.

How do I know if there is an internal leak (between the cylinder and head / between the cylinder and crankcase)?

As far as I know there may be two scenarios:

Oil in coolant and coolant in oil

How to determine? (without taking apart the engine)

What can happen to the engine if there is an internal leak?

In the event of cross-contamination, you can see it visually. You will find oil in the top of the radiator, and/or coolant in the oil. In the latter case, the oil may become foamy and "milky", looking somewhat like a rather gross milk shake, and there may be actual coolant at the drain plugs when they are opened.

Coolant in the oil almost totally eliminates the oil's ability to lubricate anything, so you can imagine what happens. It also attacks wet clutch linings.

Coolant can also leak internally from the head gasket or a crack in the head/cylinder and go straight to the combustion chamber without entering the oil supply.

It is normal for the coolant level to drop to about the top of the radiator core due to expansion/contraction.

What makes you believe you have a leak?

Thank you very much for the complete info on this.

What makes you believe you have a leak?

I've installed a used head gasket :p The base (cylinder) gasket is brand new.

I've installed a used head gasket

That was not wise.

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now