once every 5 months or so, my volvo will turn over just fine, but no sound of possible combustion, just the engine turning over. It ocurrs during the first start attempt of the morning. Once in summer, temp 80 degrees, and most recently, January, temp 18 degrees.

I took it to a shop,and after 2 hours, and determining that 3 out of the 5 cylinders had very poor compression readings, the mechanic pulled the plugs, added some oil to the heads, turned it over a few times, cleaned the plugs, reinstalled them and the engine started just fine, compression readings returned to normal on all 5.

Recently (January) it happened for the second time. I repeated the mechanics proceedure myself, and successfully started the motor.

How do I go about trouble shooting this. The motor burns no oil. There is no apparent contamination(gas) in the oil.

Help :)