Tried to do a compression test on the engine before it comes out but don't think there is enough life in the battery as result were all over the place 50-125psi and the turnover speed wasn't great.

I only wanted to have a quick check to decide whether or not to change the head gaskets while the engine is out. Do I spend time messing about charging the battery or shall I just do the gaskets to be safe?

charge battery up. Takes alot out of it turning it over.

So I assume all plugs out and throttle body flaps open is the best way. Any other things to do on the 300 when testing?

Takes a hell of a lot less effort and expense to charge the battery than strip the heads off and replace gaskets

Charge the battery up to full as this will effect the results, also bring the car up to temp before doing the test.

 

If the compression is low it may be caused by valve problems, damaged piston rings etc... so just changing the head gasket won't help. Better to get it tested before you strip it down. That way you'll know what needs to be done.

 

:)

Redo it with charged battery. You also really want to run it cold and warm, and with and without a few drops of oil down the plug hole.

 

If you still get low results then its worth running a Leak down test, after the compression test - to determine the source of the compression lost.

 

Low compression can be down to more than just Head gaskets; ie. Pistons, Bores, Rings and Valves.

I guess I'm just wondering whether to just do them anyway?

Charge the battery up to full as this will effect the results, also bring the car up to temp before doing the test.

 

If the compression is low it may be caused by valve problems, damaged piston rings etc... so just changing the head gasket won't help. Better to get it tested before you strip it down. That way you'll know what needs to be done.

 

:)

 

Too late, I can run it up to temp now as all the top end wiring/water/boost/air hoses are out as well as the rad!