Temp Gage Reading For 91 Fox

Discussion in 'Fox 5.0 Mustang Tech' started by NFLjunkeez, Jul 8, 2013.

  1. Can somebody PLEASE tell me what their 1991 stang runs at with regards to the temp gage. I've been dealing with overheating issues since I bought this car several years ago and have just recently got aggressive in attacking this problem. When looking at the gage you'll see the word "NORMAL" going up and down. My needle kept going up to the 3/4 mark covering the letter "N" of the word NORMAL causing my coolant to flow out of the reservoir (overheat).

    Since I removed the 4 cats (1 was clogged) and replaced them with 2 magnaflow cats the reading now gets to the letter "O", still at the 3/4 mark. What should the NORMAL reading be for this type of car?

    Things I've done so far:
    * upgraded Alternator to a 3g.
    * upgraded to dual electric fans
    * upgraded to a 4 core radiator
    * upgraded battery cables
    * removed 4 stock cats (1 was clogged). Upgraded to 2 magnaflow cats
    * removed stock mufflers and went to flowmaster 40's

    My next and last guess is the Head gaskets on the left side as this is the side that gets the hottest. this was also the side that had the clogged cat. Maybe the gasket was put on backwards or is blown in some manner. I don't have aluminum heads so the chances of them being warped is slim.

    So again, what should the NORMAL reading be on this type of car?
  2. should be about dead nuts in the middle. between r and m. time to test that cap.
  3. The stock gauge is inaccurate. I've seen them all over the place on cars with normal temps.

    The operating temp on my autometer gauge is 188-190 degrees
  4. 1. the stock gauges on mustangs are terrible and would not advise using them as anything close to an accurate assessment
    2. your car will run normally run anywhere from 180-200 depending on where you live and the stat
    3. puking coolant out the overflow is not normal and needs to be addressed. Running the car when the car is overheating will lead to broken parts
    4. First thing to do is go rent an exhaust gas coolant detector from Autozone, It will tell you if you have a blown head gasket.
    5. are the hoses good? a collapsed hose will cause overheating problems
    6. Test the radiator cap
    7. Is the overflow tank clogged and is the hose working
    8. Have you checked to see if the thermostat is working properly
  5. Been there several times. Annoying to say the least. Personally I'd check these first:

    Air in the line.

    1) Replace that darn radiator cap - Could be letting air in.

    2) Change the thermostat or throw the one you have in boiling water and look for it to pop open. Another way to tell - Are those radiator hoses getting hot? Do they have fluid running through them? Check the top one - If it ain't hot and you're up to temp, you need a thermostat.

    3) Air in your closed system WILL cause the antifreeze to pour (or shoot) out and the car to overheat. Park on a slight upgrade. You'll find a kit at your local parts store that allows you to take the hose going to the heater core and splice in a screw on cap. May have to drain some antifreeze. Splice it in, refill antifreeze. Then open that cap *slightly*. Let the c ar run for 20 minutes. Watch for bubbles. Listen for air seeping through the cap. Make sure that cap is as level to the ground as possible. I'll have to look at mine or my buddies car later. You can do the same thing with the radiator cap but it doesn't work as well. If that doesn't work start looking for cracks.

    I have had a lot of air in my lines before and it literally took 3-4 times letting it bubble out the radiator cap before I bought said kit. The kit worked the first time. Better spot and high up so the air will travel there to those heater hoses. Leave the heater on.
  6. Just faced a very similar issue. Check your thermostat and for air in the line. In my case, I believe it was air in the line, as when I went to remove the old thermostat, the previous owner had left it out. Replacing the thermostat only takes about 30 minutes and costs about $6-$15, biggest pain was the lower bolt, but it wasn't bad at all. If you do change it out, try to get the gasket with the one adhesive side, if not, use a piece of fishing line hold pressure on the thermostat so it doesn't slide when installing (not my idea, got it from someone on this forum). As for temps, before installing the new thermostat, my car would heat to about 250 then drop to around 190-210. After draining the system and installing a 180 tstat, it now heats to about 200 and drops to a normal temp of around 185-195. I have a single electric fan.
  7. You can also use blue RTV sealant on both sides of the gasket. Fishing line... Smart.
  8. My 1991 ran on the stock gauge between the r and the m. I put on a aluminum radiator and went to the junkyard and ripped the electric fan out of a ford contour, put it in my car (almost perfect fit btw) and it ran at the a. It is very true the stock gauge is very inaccurate so shortly after I put in a autometer one. It never gets past 190 unless im beating on it and then it quickly cools back down. I do highly recommend the Dual fans out of a ford contour!

  9. Half the stuff you've done doesn't address overheating at all. Before you do anything I'd feel your coolant hoses, squeeze them after they warm up (with engine running) and see if they feel thin and flimsy. If they are they should be replaced.

    Whens the last time you changed ALL of your coolant? During the radiator upgrade? Did you purge the system of all the air? If not, like others said, air in the line will cause random spikes in the temperature. Burp the system well with the engine running and at operating temperature.

    Some things are so dang inexpensive it's better time spent just replacing them instead of testing them. Thermostats and radiator caps won't break the bank so just replace them with new.

    Did you install your fans correctly? Fans should pull air into the engine compartment, not push it out.

    Lastly, get a real temp gauge and their inexpensive too (like $40 for autometer, even less for sunpro)

    Lastly, if you have a bad head gasket you're plugs would be able to tell you if you're lean or like somebody else said, get the coolant testing strips.

    Good luck.
  10. Do you have access to a infrared thermometer gun? Harbor frieght sells them pretty cheap.

    Another thought to check your factory coolant guage is to get a 10 ohm resistor from radio shack. Pull your coolant gauge sending wire. Put one end on connector and other to engine ground. Guage should show hot (270) with a 10 ohm reisitor place. 74 ohm resistor would equal cold(130) reading.

    My guage is pretty close to my infrared gun.
  11. infrared gun on the upper hose is a great idea and has worked for me many times when finding things like dead cylinders and overheats due to a t-stat not opening. here is how i install a t-stat in a fox I will test/ boil the t-stat while monitoring temps to unsure at what temp it opens anything within 5 degrees is fine anything more then 6 I will warranty out for another and test again if I have 2 failures in a row I go to the next temp down and retest. once I get a working t-stat i will install the t-stat and leave the upper hose off the water outlet until just before I'm ready to fire up the car. with the radiator full and everything but the water outlet/ hose hooked up i will pour boiling hot water inside with the t-stat and let it sit for a few minuets to open the t-stat then quickly hook up the upper hose and leave the radiator cap off and start the car and it should burp itself shortly there after. also lets not forget the intake coolant leak that is also common a good pressure test will be required for this.
  12. I've had the coolant changed flushed twice. Once when I upgraded the radiator, and again just a couple weeks ago to ensure everything was out. It was purged both times during the burping process.

    I've replaced the thermostat 3 times now and still no improvements. The cap was just changed out a couple weeks ago as well.

    Fans are in correctly

    That leaves the heads and or head gasket. :(