Mitsubishi Repair: Hi! I drive a 95 Mitsu..., mitsu eclipse, coolant leak

Question
Hi!
    I drive a 95 Mitsu Eclipse RS that recently was in the shop for a new radiator and thermostat because of overheating; it continues to overheat!  What do you suggest?
    Also, the shop that looked at my car seems to think that there is a leak around the head gasket; granted, there has been a minor leak for many years, I don't notice any performance problems.  Are there any things I would notice if there are problems with the head gasket?  A mechanic-friend who has worked on my cars mentioned putting something under pressure to determine any leaks (I think.)  
    Would the overheating have anything to do with the leak?  
    Thanks for your advice.
Peace,
Jeanne

Answer
Jeanne,
Leaking coolant is the main reason for an engine to overheat.  The most obvious signs of a leaking head gasket are continous loss of coolant, and white sweet-smelling steam coming out of your exhaust.  For a test, drive your car around until your engine reaches its normal operating temperature (that's when the temperature needle reaches the middle of the dial).  Then, park the car with it still running and walk around to the back to see if there is white smoke coming from the muffler.  You can also have some one watching the muffler while you're revving the engine.  Keep an eye out for white steam/smoke.  You can also tell if coolant is leaking outside the head gasket if your engine is warm, you open the hood, and you see steam coming out from the engine.

You won't notice any major performance difference if you have a coolant leak.   If the leak is bad enough, you could loose compression, and then your engine may not run at all.  But if left as it is to leak, you will continue to overheat and possibily warp you engine block and engine head.  

There are 2 tests that a mechanic should do to check for a leaking head gasket.  The first is a compression test.  A compression test makes sure your cylinders are producing and maintaining enough pressure to ignite the gasoline as it enters your engine.  If there's is leak, compression will be too low to ignite the gas, and your pistons will not move; hence not allowing your car to move.  

If the compression test shows there is lack of compression, then your mechanic should then perform a "leak-down test".  Most mechanics get this confused with a compression test, or never heard of a leak-down test.  Make sure the mechanic you use knows the difference between the two tests.  The leak-down test will determine exactly where the leak and loss of compression is coming from.  The compression test will only tell you if there is a compression loss.  Have the car tested and get the coolant leak fixed.
Good luck!