Overheating on highway past 65mph!!

hallowsleeve · May 21, 2008

Ok guys and girls, I'm back on the Fox Body scene and this 91 GT I just got is pissin me off. So it takes for ever for it to heat up first off, which I didn't see as a problem. But after it gets up to temp, it would continue to climb if the car was not moving. Also, on the highway if I got on it hard the needle would climb, and if I stay above 70mph it keeps climbing till I slow back down again.

Now I got the Black Magic Extreme yesterday and put it in, and sitting is no longer a problem. The real test though was the highway drive home. I got on it hard for a testing and it went up pretty quick. I eased off as to not kill my engine and it calmed down. I can't figure it out!! HELP!!

Here's a list of answers to common questions on this issue so you guys can just give input and not ask me for many other details:
- All new hoses
- New 3-core copper/brass radiator
- 180* T-Stat
- New stock waterpump
- New e-fan from above
- Using stock cluster temp gauge
- No air deflector under front bumper (I've seen this mentioned in other threads I've searched. What is the purpose?)
- Crappy Red coolant that will be flushed in another day or so and replaced with green.
- UPR underdrives on crank, alt, & waterpump

mustangfan1990 · May 21, 2008

I would say it is possible that your gauge is wrong. Stock gauges are crap anyway. I would try hooking another gauge to compare with. I would def have had my system flushed before I would have added all the new parts. If there is rust and corrison in there doesnt matter what new parts you put on it. Underdrives also will make a car run hotter. It slows the water pump down so the water pump doesnt flow as much water and will run hotter. Also does it run this hot no matter what speed you are going if you are dogging it. If so Iwould think you could have a leak from your combustion chamber to your coolant (blow head gasket) but that is a small chance. I would try the gauge and change that water pump pulley back to stock if it was me. You arent really going to make a big differnece with underdrives anyway and if you cant race it why want more HP

Joey7508 · May 21, 2008

Make sure the water pump is the right rotation, new doesn't always mean correct. Also check stuff like timing. Doesn't seem like it will do that but if you have to much timing and lean fuel at a steady rpm it will run hot.

millhouse · May 21, 2008

You have the classic symptoms of not having an air deflector. To fix it…put it back on. It re-directs the air flow at speeds to circulate through the radiator.

Sicarius428 · May 21, 2008

The air deflector creates a low pressure area behind the radiator which sucks air through the radiator at speed. Without having that and the Underdrive pullies are both working against you. Red radiator fluid sucks but you already knew that and what is the condition of your radiator cap? Might want to look into another one if it is old. For every lbs of pressure that the cap can hold, it raises the boiling point of the radiator fluid/water mix by 3 degrees. So if your cap can hold 15 lbs, 45 degrees is a significant difference. Another thing is what is your mix of water to radiator fluid. Water cools better than radiator fluid. The radiator fluid is there to lube the waterpump, keep down corrosion and keep the fluid from freezing at very cold temps. You may want to add a little more water to raditor fluid mix. I run a 2 parts water 1 part radiator fluid in my car but here in the Bay Area the weather stays pretty much the same year round.
Kevin

RYC CUKR · May 21, 2008

As others have explained the problem probably lies with no air deflector. I had the same type of issues with my 91 when I lost the air deflector somehow.

hallowsleeve · May 22, 2008

Thanks for all the input guys. I kinda figured that the stupid little piece of plastic was the problem. Well, its on order with a new water pump pulley, we'll see if that fixes it. The coolant flush worked out great today though. That with the new e-fan had the needle just sittin there at idle now, and getting off the highway after the slow overheating, the needle actually starts to drop. Thats from the new coolant alone though cause it didn't do that too well yesterday after the e-fan install. Hopefully this deflector really does the trick, then I can start with the not so serious issues and just enjoy driving in the meantime. Thanks again everyone. I'll chime back in a few days from now with a follow-up post of how it all turns out.

satanas · May 22, 2008

I had the same problem. with my stang, i cleaned out the radiator but didn't seem to help. Thy told me i was really clog even though I saw water circulating. Then I changed my radiator problem solved..

hallowsleeve · May 29, 2008

Ok, quick update. So, I had a coolant flush done and all new green fluid. I installed the air deflector today and the pulleys will go in on saturday. Now the air deflector is on but the car still does the same crap on the highway, especially if I get on it even for a little. It doesn't skyrocket but it moves. Now keep in mind the pulleys are still crappy underdrives. Could the pulleys be it? Is the water pump not turning fast enough? Am I not getting enough power to the e-fan for it to spin fast enough and draw enough air? I mean I guess I'll find out on saturday after the install, but I figured I'd ask cause I really thought the air deflector would solve the problem and the pulleys would just help me run even cooler.

HISSIN50 · May 29, 2008

hallowsleeve said:
Ok, quick update. So, I had a coolant flush done and all new green fluid. I installed the air deflector today and the pulleys will go in on saturday. Now the air deflector is on but the car still does the same crap on the highway, especially if I get on it even for a little. It doesn't skyrocket but it moves. Now keep in mind the pulleys are still crappy underdrives. Could the pulleys be it? Is the water pump not turning fast enough? Am I not getting enough power to the e-fan for it to spin fast enough and draw enough air? I mean I guess I'll find out on saturday after the install, but I figured I'd ask cause I really thought the air deflector would solve the problem and the pulleys would just help me run even cooler.

I'd atleast get a 15 dollar mechanical temp gauge installed so you can really see what's going on. The trend you're seeing on the stock gauge may or may not be misleading, but no one knows. The gauge was never intended to be precise enough for diagnostics.

If the stat used isnt balanced, you could have a bad one (even if it was new). Unbalanced stats can suffer from hysteresis, especially at higher engine RPMs.

67coupe · May 29, 2008

HISSIN50 said:
I'd atleast get a 15 dollar mechanical temp gauge installed so you can really see what's going on. The trend you're seeing on the stock gauge may or may not be misleading, but no one knows. The gauge was never intended to be precise enough for diagnostics.

If the stat used isnt balanced, you could have a bad one (even if it was new). Unbalanced stats can suffer from hysteresis, especially at higher engine RPMs.

+1

You said it takes a long time to warm up. How long exactly? My cars at full operating temp within 5 minutes (driving).

You might have a thermostat that stuck partially open. How old is the thermostat?

ninety15.0 · May 29, 2008

I agree with everything the last two people have said. My car warms up fairly quickly now that we are into warmer weather. Oil temps might not be up to normal in 5 min...but the water temps sure are.

Now...you definitely need to get a more accurate gauge on there. The stocker isn't worth a crap. Also the next time you buy a thermostat...but a nice balanced unit and then test the thing on your stove in a pot of water. Put a thermometer in the water and note the temp at which the tstat opens. A nice tstat is only a few bucks more than a crappy one.

If none of these things work...i would suspect a partially failed head gasket. What happens to the temps when you get on it at low speeds...like WOT in 1st and 2nd repeatedly.

What happens if you just run it at really high rpms but dont load it up. Like cruising down the highway in 3rd at 4000+ rpm? Also do you have a nice 3g alternator?

2000xp8 · May 29, 2008

Get a mr gaskets 180 t stat. Some chain stores even have them. The std chain store cheapos are garbage.
Also as said above get a better temp gauge.
An autometer or equivalent is almost a must on foxbodies, the stocker is junk and that's putting it nicely.

I've seen alot of mixed results with the BM fan, some cars it works on, others it's worthless. But since you are ok when sitting, i'd say the fan is not the problem.

Sicarius428 · May 29, 2008

At driving speed it shouldn't be the efan. The general rule is if the car is moving and you are overheating, your radiator is the culprit and if the car is stopped the fan is the issue. Granted that is just a general rule but I would start looking there. How old is your radiator, tstat and waterpump?
Kevin

Overheating on highway past 65mph!!

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