Engine 95 Gt Fine At Idle Overheats At Speed


New Member
Mar 7, 2016
Hey guys,

Relevant upgrades: TFS aluminum heads and stage 1 cam, recent downsize from my 3rd 3 core aluminum fluidyne radiator to a 1 core O'Reilly (Lifetime Warranty), also a 160* thermostat(down from the initial 180* recommended by the guy I purchased the car from, but having chronic heat issues and a recent head gasket replacement i wanted to play it even safer.)

What all is new (>100 miles): 160* Thermostat, radiator, water pump, coolant hoses, coolant temp sensor, heater tube and heater tube hoses.

I only recently finished an almost full rebuild on my 95 mustang GT with the WC T-5. This was my first rebuild and unfortunately i attempted things in the wrong order, hence almost. I resurfaced the cylinder heads and installed them before taking a look at the crank and I ended up having to have it machined.

So I went through all the work without pulling the pistons having the block machined/checked/fluxed and the cam bearings replaced ( I was told it had around 10k miles on the block when I bought it ~5k ago).

Since the rebuild she has been running well but she has been getting quite hot, the M in normal which my IR thermometer reads as 233*. Yesterday she idled for a solid 10~15 minutes at a significantly lower temp around the R. But as i went to drive home (1-2 miles) she started heating up which was when i was able to get the 233* reading.

What I get from all this is that everything is working fine at idle but under load the cooling system is incapable of getting the job done.

Any and all help greatly appreciated and Happy Fourth of July!
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I didn't really have an issue with the stink...
SN Certified Technician
Mar 2, 2015
Aluminum heads transfer heat to the coolant faster than stock heads. The radiator may be too small. Is all the air out of the system ? Is the fan functioning properly ?


Mod Dude
Apr 6, 2011
Hillsborough county
In any efi system the ecu is expecting to see warm engine temps. 160* the Stat is not enough. Period. The fans on your car (assuming the ecu controls them) won't even turn on until 205-210* then they typically shut off around 185*...... your thoughts t-stat doesn't even get a chance to close.
My recommendation is to put a stock thermostat back in the car (it's not carburated.... "most" efi dont even achieve closed loop control until 180*.)
Check and see if the air dam (plastic piece under the radiator core support) is in place it should bend forward slightly, if it's damaged or nonexistent that's a problem as well.


A little massaging and it went right in
Mod Dude
Feb 18, 2001
I agree. Lowest tstat I'd run is 180, and to be honest I'd stick to the stock 192 degree tstat. All a colder thermostat does is cover up a problem, and sometimes it makes things worse. The thermostat could be always open and coolant could potentially flow through the radiator too quickly and not be cooled properly. Modern EFI engines need to run in the 190-200 degree range.

I also agree that a 1 core is probably two small. I'd also check to see if the plastic deflector is mounted to the underside of the radiator support along with the other various plastic deflectors inside the engine bay.