Overheating at HWY Speeds
 

My 96 Mustang GT runs hotter on the freeway than it does on city driving. Its an automatic. If I turn on the A/C it gets worse. It never goes hotter than the A on the N O R M A L range. The only mods it has are CAI, Flowmaster & UDP. I already installed a new water pump, radiator, 2 thermostats & its still doing it. I was thinking that maybe UDP might be the cause but from what I read so far UDP usually make the engine run hot at idle. Has anyone had a similar problem before.

U do realize the stock (gauge) isn't worth a ****? Overheating is defined as boiling over fluid in the overflow tank. If it isnt puking fluid could be.

collaping hose
defective sending unit (gauge)
Bad head gasket

Bad head gasket. The symptons you wrote about were the same symptoms i had when i discovered i had a blown head gasket. squeeze the radiator hoses when the car is at operating temperature. if they are flimsy then that gives me more reason to say the head gasket is broken.

I'd say you are having circulation issues (either a collapsed hose or clogged coolant passage somewhere).

flush your radiator and install a 185 F thermostat. stock is 195F

A/C should LOWER the temp because it makes the fans come on at a lower TEMP. sounds like a clog. flush it really good. also check your seal on your thermostat. when the engine is off sqweese the tubs and see if its pushing fluid on other ends.

It's the radiator. The 96's have well documented issues with the cooling system. My Mark VIII swapped GT ran HOT, like 235*F hot. Swap out the rad and you should be OK.

+1 I ended up putting a misimoto rad in mine it it helped a lot. also note that the 96 had a a/c condenser that the fins were closer togther that caused a airflow problem.

turning the air on woud not make the fans come on at hwy speeds.

Thanks for all your help. It has a new radiator. I think I should had put a 3 row instead of the stock design. I dont think its a head gasket because there are no other signs that would indicate a head gasket, its not loosing coolant & the compression is even betwen cylinders. Im going to bypass the heater core, switch to a 185F thermostat, install an aftermarket temp gauge, and install a transmission cooler. I will post what the problem ended up being when its fixed.

Im posting again on the problem Im having with my car. I bypassed the heater core, installed a tranny cooler, put a new thermostat, new water pump & installed a lower air dam which was missing. I feel that its running a little colder, but still gets hotter on the hwy than on city driving. 96meangreengt said it could be the radiator, but I didnt think so because it was new. Im starting to think its the radiator because the one i bought is only for 96 mustang gt/cobras & from 97-04 they use the same rad. Here are the Spectra part numbers (96 only) CU1775 (97-04) CU2139. So, that makes me wonder why it would be like that.

Ok. I finally found what was making my car overheat in the hwy. I replaced the stock radiator I bought a few months ago with a 3 row. That helped my car maintain cooler speeds in the hwy. Now my car runs below half in the hwy with the a/c on max & +100 weather. I think the radiators on 96-04 Mustang GTs isn't good enough & if it needs to be replaced might as well get a better than stock one.