01MGGT

So my car has neve ran hot in the 2 years I have owned it. Not when the ambient temp is say 85+ degrees if I sit idle for more than a few minutes, like today waiting on a buddy, the temp hand goes to 3/4 with the AC on. Once it reaches the 3/4 the a/c goes hot and the engine bogs for a few seconds then the A/C goes cold again like normal and the engine idles fine but temp hand is way up there at 3/4 still. This is the second time it has happened and it seems turning off the a/c makes it go away and cool back down. I have already drained and refilled the coolant and the thermostat seems to fuction perfect as far as giving heat in the morning only when it's warmed up and not like it is sticking closed or open.

I have been hearing about the CCRM that controls fan speed. I am not sure of an easy way to test it but I know it should be good as when I am flashing a tune with my tuner the fan comes on loud as hell. And it feels like it's blowing pretty damn good when it was running hot. I have smelt coolant on a few occasions but can find no leaks or loss of coolant in the bottle or anywhere else. Level seems to stay fine. I let the car run till normal temp with the cap off to try and get any bubbles out. When it over heated today I did notice some drops of coolant on the radiator plastic right around the cap. So I plan to replace the cap tonight and see if it goes away.

Any other ideas guys and gals? I need to fix it before temps hit 100+

01MGGT

I should add I have noticed no over heating at hwy speed with a/c on

69MustangCoupe393cid

Can't say for sure, but I would say stuck thermo. Can't hurt to replace it.
Also do you have UDP and have you always had them?

Kerns

Check to make sure your fan is turning on.

uberstang1

I suspect the fan, these cars are equipped with a two speed fan from the factory. The hi sped for the fan ONLY kicks on when the motor is hot AND the a/c unit is turned on. The fact that it gets really hot with a/c is probably because the fan is beginning to fail. The reason you don't notice at highway speeds is because the airflow is keeping the rad temps down.

Crazycarnut

+1 I've had this same problem on a past car. It was the fan. My advice is to change it before it stops all together. That is what happened to me.

01MGGT

I replaced cap and it's still overheating but taking longer to do so slightly. And yes, when the car bogs the A/C will blow hot air. And I only see one fan correct me if I am wrong. I just am not sure if I need to be looking at the fan or the CCRM that controls it and both look pricey so I am weary of throwing parts at it. I honestly can;t tell if the fan is going into the second speed or not. I know it's on but I think it may be running only in the lower speed and I don't know which part to replace first.

01MGGT

Ok guys I jumped the red wire to the fan for low speed op and the fan came on connected directly to battery. I did the same with the blue/orange wire for high speed operation and the fan also came on. With the car running and at normal range on temp gauge with a/c on I tested both low and high speed wires going to the fan from ccrm (i guess) and both were showing 12 volts at the same time. Is this correct? If so it's telling me the ccrm and fan SHOULD be good. Perhaps my blower just makes to much heat under the hood in the hot ait with stock cooling system? I can only assume my thermostat is good or I would not be having normal heat correct? Also my hoses appear to be in good shape also.

01MGGT

One other detail...back when it first over heated I topped off coolant and left the car running to normal temp with the radiator cap off. Coolant ended up starting to bubble all out with the cap off. Have since refilled coolant of course. I mean it bubbled alot. What is the proper way to bleed the air on these cars. I will probably replace thermostat this weekend.

01MGGT

OK I am going to change the thermostat and flush out the radiator tmrw and put in yet more fresh coolant in a 50/50 mix. Any other ideas I am desperate. I still am not sure I can rule out the fan. Its hard to tell a difference between the low and high speed. If I jump the blue and orange wire from the fan this should in theory put it into high speed mode right?