Alright guys I'm new to the mustang world and am not great under the hood but I have buddies that are and are willing to help
I have a 03' Mach1 and its over heating and coolant is leaking but only when the engine overheats.

I'm thinking I need a new thermostat... what do you guys think?

 

It could be a thermostat

um ins't your quote backwards I thought it was supposed to be

"It's better to die like a tiger than to live like a *****"

 

Well I wouldn't just toss parts at it until I knew what was wrong. To see if its the thermostat start the car let it get hot. You should wait till the gauge is in the middle of the heat rang. Then go and feel the upper radiator hose, it should be very firm and hot. If it isnt that means the thermostat has failed and isnt letting water go to the radiator. So do that and see how the upper radiator hose feels. Also is the cooling fan turning on when the car is at this temp as well?

 

I havent had much of a chance to do more trouble shooting but I appreciate all the great info guys!

 

alright well looks like the thermostat is working, checked the upper hose and it did get hot and the fan is working...

 

Since that engine is 5 years old, and you most likely have not had it flushed, you should take your car to a radiator shop and have them access the problem. Most likely a good system flush and a new thermostat plus fresh anti-freeze solution will take care of the problem.

 

i want a mach1...

 

Sounds like you need a new radiator.

 

UPDATE:
Well after checking everything I ended up Burping the cooling system, i was suprised as all hell that it worked. So just incase anyone ever has a overheating problem give burping a shot.

 

Glad you solved the problem.

 

Looks like you had some air stuck in there.

 

wow im suprised that it didnt burp befor it overheated

 

Reviving this thread...

I'm having similar issues with a new build. Car runs fine but won't stay cool. Installed a new HyperTech T-stat but still no go. Anybody want to describe in detail the "burping" process?

 

the above was in ref to a "burpping" a DOHC engine, not a SOHC....
is the aftermarket thermostat correct for a Modular? wahts the temp? is it installed correctly? coolabt fan comming on? what was done to your engine? need more info.......

 

Hey Randy, how's it goin'? Thanks for piping in here, the stuff you sent me seems to be doing great!

Here's the poop:

98GT, teksid (coolant passage drilled in driver side deck), dry sleeve 3.700 bore, PI Heads and Intake, VT StageII NA, 160 Hypertech t-stat.

But, I have other issues as well. I just found a connector that we missed. It's 2 white wires that are covered with BK/O insulation that terminate into a single lug. At first I thought it was a ground but it's way too clean to have been on the bottom of the motor for 9 years, lol. I'm thinking it may go on the post on the side of the fuse box. Which leads me to the question... how many lugs go on that fuse box post? 1 from the pos battery term and ???

I took a ton of pics when we took this thing apart back in May but I just don't have clear pic of this particular connection.

 

Solved the electrical thing... starting new thread.