I am lost. I have replaced the t-stat, fan clutch, raditor, hoses, coollant temp for eec, collant temp sensor for the guage, and I have flushed the system. It still over heats while in traffic with the ac on. On the hiway it is fine. The water pump does not leak and I have not replaced it. The heater core is cloged. Could it be my problem?? Any ideas would help. I am out of them.

1991 F150 Reg Cab 5.8 E40D 3.08 gears
I live in Fort Worth TX. It has been over 94 the past few days.

 

Since you've done everything else and the only thing you can identify that is still definitely not right is the plugged heater core, fix that. I may be an unlikely culprit, but who knows? It can't hurt.

 

Fan shroud still intact? Even though you flushed the radiator it may be partially plugged.

 

Still looks new not cracked to broke anywhere. Flushed the system then installed the new raditor

 

Sorry I missed that. Was the replacement radiator listed as Heavy Duty cooling? You are in the worst case scenario. Might suggest to check the timing too.

I have also seen a few water pumps where the impeller was almost completely rusted away.

 

It is listed a super cooling and was twice as thick as the oem one. And no its not brass. Its plastic and alum.

 

You seem to have the bases covered on this one except the water pump and plugged heater core (which should not be a problem).

 

Then check the AC , is it working allright , may have a problem on the discharge side , condenser overheating ????....Lew

 

You might be on to something. The AC was working fine but when it overheated the other day the ac clutch started smoking. I have not drove or worked on it since.

 

I would start with the ac problems... If you are starting to lock up a pully it will put more load on the engine and slow your fan down... You might want to take your serpentine belt off and check the resistance of your pullys. Smog units like to lock up and slow the belt down too... Heater cores are cheap and easy so I would get that fixed too... It takes only 20-30mins and they are right behind the glove box. The other thing you might want to try is the E-fan conversion. My buddy put one on his 90' 460BB and he says it keep the engine cooler than before. He has a after market water temp guage so it's a matter of reading the guage and not so much just his opinion...

 

Well I tested the truck last night. It does not overheat with the ac off. What can make the condensor overheat and the ac clutch start smoking?? It was working just fine untill I put the new radiator in and let it run for 30 min with the ac on to see if it overheated it did, and the ac clutch started smoking right after I hosed the condensor and radiator down with a water hose to cool it off.

 

I have never seen an A/C problem cause engine overheating, but there is always a first. Quick checks are to check the center vent temperature. It should read between 34 to 40 degrees with the A/C set to Max, windows closed, A/C running for at least 10-15 minutes. If the ambient temperature is high (90+) your vent temperatures will be higher.

It would also be advisable to check the high and low side refrigerant pressures. If the clutch is smoking, it must be under quite a load.

 

Drove it again today in traffic. With no ac it never overheated. I never knew an AC system could make a truck overheat.

 

Sounds like your compressor is ready to seze up , that with hi condenser temp dosn't help ...Lew

 

Burp the coolant system! Start cold w/ the radiator cap off, allowing it to come to normal operating temp. You will observe air bubbles & the level drop as the thermostat opens. Keep topping off w/ coolant as needed during this time. After the level stabilizes, re-cap it and fill overflow to proper level. A clogged heater core could be problematic, because the hoses give air a place to collect in the system. Ideally, you want maximum flow though the heater core when doing this procedure. Also, as mentioned, the A/C compressor is very suspect! If that is the problem, "burping" the entire National Anthem won't help! (you probably have sufficient Freon, or the low pressure cut off switch would not allow compressor operation to begin with!/ but I'm not sure how it would handle an "overcharged system! Added Freon lately???)