Engine Diagnosis

Can someone help me determine if I have a head gasket issue...The symtoms are this (99 Alero V6).

1. Start engine and it runs rough, engine light flashed for a while and then stops after it warms up - told this could be a slight amount of coolant leaking into engine when cooling down and runs rough on start-up until it burns off???

2. Often temperature builds up prior to thermostat opening (have changed thermostat and bled coolant often). Assume air bubble trapped at thermostat. However prior to the thermostat opening I have taken of surge tank cap and have seen the level rise in the tank from normal to overflow. I assume air is being forced into coolant and taking up volume pushing liquid level back to surge tank...when the thermostat opens up the air is then purged out through the vents...but often not until after coolant has spilled out of the tank...testing afterwards shows more air in the line so I have to bleed some more....

3. so I am assuming head gasket leak...HOWEVER a compression test showed good compression in the cylinders (~175-185 lbs) and I have noticed no loss of power either...

So thoughts on what is going on...???? Could it be anything other than head gasket and if so why is compression and power still good??

Thanks for your input!

Another method of checking for bad gaskets is to run a cooling system pressure leak down test. Your compression figures look real good. Another possible cause would be the infamous lower intake manifold gaskets which were revised around 2003. Many of us have the new LIM gaskets installed.

Thanks for the reply.

I had the LIM gasket replaced (although perhaps not fixed!) just recently...but not sure how an issue there could cause the symptoms I outlined? eg. why would system surge tank level and pressure build up?

Leak-down test is good idea, but have started to tear down engine so can't do too easily now.

I guess you can rule out the LIM gaskets for now.

Based on your symptoms and working with members in Alero and Grand Am forums it appears it may be a head gasket issue. Coolant blowing out the reservoir, varying level, and bubbling are classic symptoms. Since you are doing the tear down be sure to use the GM revised LIM gaskets or the Fel Pro kit. Also, I would check the cylinder heads and LIM for warpage before putting it all back together. Good luck!

Thanks again...so if it is a head gasket, which I kinda think it is, is it common for compression test to be so high, and power okay?

Just to close the loop on this...I got the 2nd head off this weekend and can confirm that it was indeed a bad head gasket seal. Just goes to show you can have a bad head gasket and still have high compression and not be billowing white clouds of smoke.

Hope this helps others that may have similar symptoms.