area for a direct read rather than the factory gage and sender. Check the compression and compare results to factory. Check cooling system for exhaust gases due to leaking head gasket and oil in the coolant or coolant in the oil. Check engine vacuum at idle and at 2000rpm shoul be about a very steady 19 to 20 Hg and increase about 1 to 2 Hg at 2000 rpm. The important thing here is the needle should be STEADY no vibs at a steady rpm.
Do you use oil or coolant?
If you are not a mechanic you are going to have to rely on one or some friend who is mechanically inclined.