How can you tell that cylinder head has been over skim?

warped block or cracked head

You didn't say what your compression readings were. If you do another 2 compression tests and note down the figures..

The first test is a dry test as per normal. Prior to the second test - the 'wet test', spray some some penetrating oil into the cylinder, spin it on the starter to get rid of the excess oil.

The second, wet test, allows oil to get in between the piston and cylinder wall.

If, on the wet test, your compression readings go up significantly this points towards ring/piston damage or excess wear .. a worn engine. This will give you a good indication as to whether it is easier just to fit a second hand engine instead of doing the cylinder head.

If, after doing the wet test your compression readings don't increase by more than 10% compared to the dry test, this suggests that the pistons/cylinders are okay.

Remember that an alloy cylinder head must be skimmed before refitting. Cylinder heads warp because of heat and become 'banana shaped' - raised in the centre. Failure to have the head skimmed is likely to cause head gasket failure very quickly.

If you're going to repair the cylinder head you should change the thermostat as a matter of course. It's good practise, that's all.

I would say that you used Holts because of a leaking head gasket. You should be fitting a new head gasket so there should be no need for the use of holts.

Well did you replaced the thermostat?

Hi, did you recently skimmed the cyl-head? if so, then cyl-head is skimmed till last capacity, so you need to get the thicker cyl-head gskt. If not skimmed, remove cyl-head and skim it. it might be corroded or wapped.

The car may have overheated to the point where you might be needing to skim the cylinder head.if the upper hose gets bulgy when the car is running it might be signalling some problems with the cylinder head.

Check what head gasket was used . I suspect that an after market gasket was used. If that is the case there will be holes in the block and head thet have no matching holes in the gasket thereby causing the problem

Hello,Got into the same situation and my mechanic explained to me all the "root-cause".Car driven with overheated engine because of water pump failure.Or cooling liquid gelling inside the radiator and blocked the cooling system.That could also have caused the water pump failure.
Anyways, my car is under repair as I am sending this e-mail to you.Mechanic said he will replace the gaskets after skimming the heads, then replace the water pump, then flush and clean the radiator and replace the thermostat.He will change the T-Belt as well (car has 75000 km).6 months warranty for this work.USD 1300 in total.
Hope this will solve my overheating problem.
Please tell me how did you went out from this? What happened?Id be very grateful if you/we can share this experience.Thanks in advance.
StanRelocated to Maputo/Mozambique

Unfortunately there's no way to tell until you pull the head off. if the gasket has failed you'll nee to get the head checked for cracks and flatness anyway (and possibly skimmed flat) and if the head comes off you have to replace the gasket anyway.

With overheating, the most likely situation is that the head has warped slightly causing the gasket to fail. If so, the head gets skimmed flat before fitting a new gasket. Note that on many modern engines it's vital to use new head bolts upon reassembly; your Oldsmobile dealer can tell you if this applies to your model.

waterpump? No movement of water/coolant, engine overheats. Engine overheats, warp heads. Next time you rip a head off, check gasket to see if head gasket failed or if there is a different cause to car overheating.