91 Mustang GT 306 Running Pretty Hot! - Mustang Evolution

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Old 10-07-2009, 05:05 PM   #1
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Exclamation 91 Mustang GT 306 Running Pretty Hot!

I have a 91 GT 306 and I wanted to know what is the normal operating temperature for the motor in 90-100 degree weather? It's been running at or around the second the last hash mark (second one above half or over the "o") and depending on how long I drive or idle(usually for a while) it will either slooowly go higher or if I'm lucky go down. It has an electric fan....when I say "an" electric fan I mean one electric fan. The guy installed a pretty big single electric fan and a bigger radiator. The electric fan always seems to be on...even if it's not half way on the temp gauge.

I took it to a shop and they found out that the Flex-a-lite Radiator and Electric Fan kit that was put on my stang wasn't pulling enough air through the big radiator with an A/C condenser and Transmission Cooler....I notice I run around 230* or over the "o" on cluster gauge. An IR gauge was used and it showed 230* and when a very small fan was placed in front of the car it dropped to 210-220*. He says it should about 10* higher than the temp of the thermostat. I have a 180* stat.

It has UD Pulley(s). It's also been pressure tested and had the fan modified to suck and pull more air through by moving the fan itself more inside the shroud.

I tried to test the thermostat today during the hot day this time. I started it after driving 8-9 miles from work to hom with the gauge showing on the "0" whether or not it's there I dunno. I'm about to install a new gauge. I checked the upper radiator hose as soon as I parked and the hose was sort of stiff and hot....dunno if it was from the coolant or from the engine. It was squeezeable and was hot last night when I had it sitting for 30 minutes. I took the cap off after 20 minutes of being home...and the hose was squeezable right before I took the cap off....wierd. The coolant was just below where the cap's pressure spring would sit. I started the car and the coolant dropped to the first fin from the top...so about maybe 1/2" to an 1" dropping of coolant level. I ran it for 20 minutes and saw some very very very small bubbles come up every now and then...dunno if it was from the vibration or air pockets. I also noticed the lower radiator hose was hot, but not as hot as the upper was, and sort of squeezeable. As the engine was running I turned the A/C on since I do not have my heater setup. The gauge showed at the "M" for most of the time and then went up to nearly halfway "R". Again it has a 180* T-stat and a big aluminum radiator with an electric fan.
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Old 10-07-2009, 11:04 PM   #2
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Re: 91 Mustang GT 306 Running Pretty Hot!

210 is the normal temp range. on elec. cooling fans the size doesn't matter as much as it's CFM rating you cna have two fans that are the same size and one can flow twice as much air as the other.

one easy way to tell if your not flowing enough air through the rad. or if your engine coolant flow isn't enough.
start the car and let it idle tell it starts to run warm. with the cooling fans running hold the idle at 1500RPMs if this brings the temp down, then you need to look into a high flow waterpump. If reving the engine does nothing and the only way to drop the temp is to put a fan in front of the rad. or take the car for a drive, then you have a air flow problem . You need to get a better cooling fan.

another thing you can do is replace the thermostat with a 195*. what this will do is hold is hold the coolant in the rad. longer allowing it to cool more before entering the engine. (this works best if you have a air flow problem)
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Old 10-07-2009, 11:13 PM   #3
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Re: 91 Mustang GT 306 Running Pretty Hot!

I understand 210* is normal but with my engine running hotter than that it's not so normal. I've pretty much exhausted everything I can think of. I'm going to change the temp gauge to an aftermarket one tomorrow to see if I get a better reading. I bought a pretty fancy multimeter today that has a thermometer build in and no matter where I stick the probe it shows 160-200. Putting on the Thermostat housing gets me closer to 200*, but when I put i on the radiator I get around 175...this is after I drive it for a couple miles (3-4).
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Old 10-08-2009, 09:05 PM   #4
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Re: 91 Mustang GT 306 Running Pretty Hot!

ran the car with the radiator cap off from somewhat cold for 30-45 minutes and the coolant just rose up in the filler and stood near spilling, even spilling every so often. The gauge read at 1/4 pretty much the whole time. I had the A/C on full blast and even revved the engine a lot throughout and nothing. The upper hose never became hot enough to keep me from squeezing and holding for at least 3-5 seconds.

The coolant never went down during the whole 30-45 minutes of running with the A/C on full blast and revving the engine quite a bit throughout.
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Old 10-21-2009, 03:54 PM   #5
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Re: 91 Mustang GT 306 Running Pretty Hot!

Well I put a cobra water pump pulley on today and the first thing I noticed is that I can drive a little farther with out the temp going up as quick. Nonetheless, the temp still is high. It notw rides on the "R" and it's been in the 50* at nights to maybe 80* during the day...mostly in the mid to low 70s.
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Old 10-21-2009, 04:04 PM   #6
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Re: 91 Mustang GT 306 Running Pretty Hot!

i would install a real temp gauge (real good on eas stock sucks) and see if it opens/closes as suggested by the T-Stat info
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Old 10-21-2009, 04:48 PM   #7
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Re: 91 Mustang GT 306 Running Pretty Hot!

I have one installed just not hooked up since I accidentally broke the the electrical connector on the temperature sensor for the aftermarket gauge lol.
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Old 10-22-2009, 08:41 PM   #8
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Re: 91 Mustang GT 306 Running Pretty Hot!

I would look at the fan first. A lot of the aftermarket fans are crap. Consider getting a fan off of a Taurus or Mark VII. They are cheap and move a ton of air.

My car runs around 200* with a Taurus fan, a 3-core brass radiator from O'Reilly and a 180* thermostat.
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Old 10-22-2009, 09:01 PM   #9
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Re: 91 Mustang GT 306 Running Pretty Hot!

No I dont think it's the fan now. I have a mark viii fan..though not installed yet. I noticed the a/c clutch turning whenever the engine is running regardless of whether or not I turn the a/c on. I did however figure out that one of the wires was wired wrong and would turn the compressor on when the fan is turned on......I may have found my problem with my cooling....
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