tricky problem on my 94 gt

[Tyler16]

Ok I'm going to try to explain this the best I can.
My 94 gt will overheat only when the AC is on. I have replaced radiator,waterpump,thermostat 180*, and pulled off my underdrive pulleys. I also just fixed a code 564 with a new ccrm which was my high fan not coming on. I do not have milky oil, and no water out tail pipes or bubbles up from radiator neck or exhaust gas's out of neck. Also my overflow is not overfilling.

I also have a voltage problem. I can drive all day without ac and voltage seems fine with 14.1 volts coming from the alternator which is new. After running AC for about 15 minutes volts drop to only 12.4 on the alt and the overheating begins. Also voltage on both high and low fan seem to be the same. I am thinking that when the ac comes on it is slowing my fan down. The AC blows cold but could it still be causing a big load on the car that could cause the problems? Any other suggestions would be great b/c I have no idea at this point.

Also it must have been doing this for a while b/c when I bought the car the kid thought the alt needed to be replaced and he also gave me a new cooling fan motor.

 

[toyman]

Ok I'm going to try to explain this the best I can.
My 94 gt will overheat only when the AC is on. I have replaced radiator,waterpump,thermostat 180*, and pulled off my underdrive pulleys. I also just fixed a code 564 with a new ccrm which was my high fan not coming on. I do not have milky oil, and no water out tail pipes or bubbles up from radiator neck or exhaust gas's out of neck. Also my overflow is not overfilling.

You may not be overheating if you are just relying on then dash gauge. You will need to confirm the actual temperature. Problem may be a bad sender, connection, gauge or battery to engine ground.

I also have a voltage problem. I can drive all day without ac and voltage seems fine with 14.1 volts coming from the alternator which is new. After running AC for about 15 minutes volts drop to only 12.4 on the alt and the overheating begins. Also voltage on both high and low fan seem to be the same. I am thinking that when the ac comes on it is slowing my fan down. The AC blows cold but could it still be causing a big load on the car that could cause the problems? Any other suggestions would be great b/c I have no idea at this point.

Also it must have been doing this for a while b/c when I bought the car the kid thought the alt needed to be replaced and he also gave me a new cooling fan motor.

I would check the battery to engine ground. Look for corrosion either at the battery terminal or the engine grounding stud and nut.

 

[Tyler16]

Yes I really do need to get a real gauge setup in there. I have used a wire brush on the batt to engine and engine to frame grounds as well replaced the sender. I also pulled the belt off and my compressor spins freely and clutch has some resistance on it but spins fine.


I'm gonna try hitting the condenser with a power washer and find a fin comb to see what that does.

 

[ProKiller]

so your only basing the overheating off the factory gauge going up? this is no where near an accurate way to to determine engine temp. is the car over heating to the point that you are blowing coolant out the overflow? is the high speed fan coming on? if no to the first and yes to the second then you are probably fine. car just gets hotter with the increased load of the A/C

 

[Tyler16]

I think you're right and i'm going to take it somewhere that has one of them temp guns and see what its reading. I haven't had coolant come out of the overfill and I finally got my high speed fan to work. I do have one concern though.

I put one of them speed cals on due to my 4.10 gears and thats a setup that fixes your speedometer but does not change the speed sensor gear. So the ecu may think I'm going 50mph but in reality I could only be going somewhere around 35ish mph and causing the fan to cut off early. Regaurdless though it still shows very hot while traveling 70 mph down the highway.

 

[Chythar]

You could have several things going on here. For your engine temp, you could simply have a bad sensor. There are two on our cars: the CTS and the ECT. The CTS feeds the gauge only; it's in the lower intake manifold just to the right (driver's side) of the distributor. It has one wire leading to it with a right-angle connector plugged on to it. The ECT is what the computer uses to determine the engine temp, and it's plugged into the metal heater tube on the other side of the distributor from the CTS. If either one is bad, your gauge will read wrong.

When you start the car, the computer is in warm-up mode and will adjust timing/burn more fuel to bring the engine up to operating temperature. But with a bad ECT, the computer will never see the engine is at temp and will keep trying to heat the engine. I had this happen once, and the engine nearly overheated several times. To troubleshoot these sensors, you need a code reader that can read PIDs (engine sensor values, essentially)

As for your volts dropping on the fan, I do know when my cooling fan kicks in (low-speed), my voltage gauge noticeable dips and then goes back up almost to where it just was (don't know the volts). The voltage regulator on your alternator should bring your voltage up fairly quickly after the fan turns on. also be aware that the stock fan has a known problem of frying itself. I'm wondering if your fan motor is dying or shorting out internally.

 

[Tyler16]

Ill get a new sensor for the gauge. I just replaced the one for the ecu a couple days ago.

As for the alt if I check the voltage at first start up of the day it shows 14-14.3 volts but after driving 20 mins and I see the gauge has dropped dramatically I recheck it and it only shows about 12.4 volts. Its a new alt and I had replaced my old one b/c it was doing the same thing. I always thought an alt should run around 14 all the time to keep the battery charged up. This only happens if I run the AC but if not it will keep good voltage the whole time. So I'm wondering if my AC is draining to much and causing all my problems or should I find a beefier alternator

After driving and checking voltage my battery shows 11.5-11.8 with key off but then will recharge it self I guess over night and will be back to a 12.5 or so. So either there is a drain or these stock alternators just suck lol. I had a 95 gt a few yrs ago and it already had a 200 amp alt with a redtop and never had the voltage go this low so maybe this is just how they are stock I dunno. This battery in it right now is just a 650cca duralast.

 

[Tyler16]

well disregaurd my speedcal theory. It just got hot going 70mph. Also I got a infrared temp gun it's showing 199* on the upper hose and 215* on the thermostat housing. I'm not to happy about 215* on aluminum heads. I have no idea what to do.

 

[toyman]

215* is not particularly hot. Over 240* is when you want to be a little worried.

 

[Tyler16]

Yah I thought it had to have been around 230 but I guess 215 isn't that bad. I'll keep messing with it. It runs nice and cool at night so maybe ill look for a better radiator to get it to drop 15-20* and call it day.

 

[Chythar]

If memory serves, 220* is when the stock cooling fan turns on (the Cobra turns on a bit later). If your stock gauge is working correctly, that should be a little past halfway. On the freeway however, you should not be getting that hot. This has jiggled a memory here - I had a similar overheating problem on an old GT (I've since sold). The car overheated because the coolant system could not hold 16lbs of pressure. If the system won't hold pressure, it will get hot faster than normal. If you can rent a coolant pressure tester, especially one that can test the cap, would be good. On my GT, I had several cases where the hose clamps seemed tight but wouldn't hold enough pressure. Once I got them all tight, my cooling problems went away.

Don't remember where you live, but if you're in Los Angeles somewhere I can lend you my coolant pressure tester.

 

[Tyler16]

Thats a good idea. I bought a new cap but never thought of pressure testing the system. I live in texas though but I think the parts store should have one for rent.

 

[toyman]

Low fan on temp as per my Ford CD service manual is 220* and stays on until the temp falls to 200*. High fan is on at 230*. Radiator cap pressure spec is 16 psi.

 

[Chythar]

Low fan on temp as per my Ford CD service manual is 220* and stays on until the temp falls to 200*. High fan is on at 230*. Radiator cap pressure spec is 16 psi.

Obviously my brain is not working ATM; thanks for the correction. I've edited my post so someone using search won't get bad info.