the car will randomly overheat sometimes driving down the highway, stop-and-go city traffic or idleing.
it happens maybe 1 in 10 trips, but the other 9 could be for 100 miles with no problems.
it has a very slow leak, i havent noticed any water actually coming out but i notice a drop in the resorvoir from time to time, i dont know if this could be from the car getting so hot it evaporates or not.

i have replaced the thermostat, and i think they had a pressure test done on the radiator and a compression check on the cylinders, however im not sure about those.
it does not produce any smoke out of the exhaust but people have suggested it could be a cracked head.

any ideas?

 

What year is the car? Early 3.8's suffered head gasket problems.

 

x2 is it a 94- mid 96?

 

sorry about that... 95 mustang with the v6

let me interject this is my sister's car.
my only cars were a 78 camaro and a 92 eagle talon
i had a problem with the head gasket on my camaro before and it clearly let me know that was the case with the white smoke from the exhaust
we thought about it being a head gasket a couple times with her mustang but no smoke??

any cheap easy way i can tell if this is the problem?
and why is it so random?

 

Does the fan come on when the car is sitting at a stop with the A/C on, check this, that happened to my 98 and caused me to overheat on my way one day to school, so park your car, rev it up till the temp gauge hits the middle, and keep this up with the hood down and see if it starts to get "HOT" if the gauge passes just a little more than mid way, pop the hood and quickly raise it, and see or listen for the fan, if it doesn't come on, you need a new fan, if it does come on, may be the head gaskets.

 

fan kicks on... whats the easiest/cheapest way to check if it is the head gaskets?

 

There is a block test kit you can get from pretty much any good parts store. BUT, you have to follow the directions TO THE LETTER. It's complicated, but it WILL tell you if there is a problem. In my experience, just cus there is no white smoke, doesn't mean there isn't a prob. I've seen some with white smoke, some with oil in the antifreeze, some with antifreeze in the oil, some with cross conmtamination of the oil and cooling system, and a few with none of those symptoms, that had a loss of power. All had either blown head gaskets, or a head cracked.


EDIT!
There is one other "easy" test thet MIGHT tell you. If you have a bud that is a smog tech, take it to him, and CAREFULLY pop the rad cap. Have him position the tailpipe sniffer over the opening of the radiator. Be sure the engine is at running temp. With the engine running, ask him to sniff for HydroCarbons. If there are HydroCarbons present, that confirms either a cracked head, or a blown head gasket. If not, there may still be a problem. This test doesn't always tell for sure.

 

i replaced the head gaskets in my 95 3.8 last fall. first had symptoms similar to what you are saying, random overheating, water loss. mine began running shi*ty too. it ran differently when cold vs hot, as the expanding heads when hot often sealed the leak up (in the beginning). lots of pinging too. i also had NO white smoke in the tailpipes. i think they most often leak externally, so you may be able to see coolant leaking from the block/head if you get under the car. often will leave a white trail if dried up. like mentioned above, your oil will look milky as water/oil dont mix very well. there may be exhaust bubbles in the water, however i myself don't safely know how to check that with a hot engine. it was a 900$ fix for me. get it fixed sooner than later, as running it too much with a gasket leak my cause your engine to seize with water getting onto oiled surfaces