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Mustang whoas

I have 1995 mustang with a problem. when the engine has ran for 20 minutes or more the engine overheats and boils out the antifreeze from the overflow tank.a new thermostat was installed and didn’t help.

a local mechanic said it could be a blown head gasket but he hasn’t seen it yet. could this be it and how can you tell if it is?

What engine ? 3.8 V6 or 5.0 ? The symptoms you describe does sound like a failed head gasket. What happens is the hot exhaust gases get pushed into the cooling system and force the coolant out.

What you can do is, on a cold engine remove the radiator cap, start it up and look for bubbles in the coolant. If you see bubbles and the coolant starts pouring out of the radiator its the head gasket.

If its the 3.8 it is a well known problem with this engine.

Also make sure you are not getting coolant into the oil as it will destroy a motor in a very short time.

I agree. If the motor oil looks like coffee with cream, do not drive it anymore. This needs to be fixed, and if you continue to drive it, you’ll ruin the engine.

Maybe the cooling fan is inoperative. With colder weather here, if you run the Defroster and the radiator cooling fan is inoperative the vehicle can overheat.
Knowing if the overheating occurs with both city and highway driving could help provide an answer.

If a head gasket is suspected, you could try this quick test. This is by no means the final word but can be very helpful.
After the car has sat all night and is stone cold, loosen the radiator cap and release any remaining pressure in the system. If you hear a pressure release then you may not have a head gasket problem at all.
After that, retighten the cap, start the engine, and allow it to run for a minute. Shut it off and quickly loosen the radiator cap. If you have a head gasket bleeding into the cooling system you will probably hear a “hiss” sound when you loosen the cap. If not, the head gasket(s) are probably fine.