Overheating and Possible Causes

Every Summer it becomes a highlighted point on the mailing list I’m on about 3rd gens and overheating problems. I never thought much about it until my engine rebuild last winter. This summer I started experiencing the dreaded overheating problems. So after exhausting all possible possibilities, I finally found my problem. I thought I would write a report on different things to check in case your thirdgen is overheating. I started with easiest and moved to the harder/more expensive possibilities….

1. Is the black air dam still in place?
   Get down on your knees in front of your car and make sure you still have the hard black plastic flap hanging down. Is it in good shape. It isn’t bent back is it? If you can’t figure out what I"m talking about, find another 3rd gen in a parking lot and check it out. New from GM they cost about 20 bucks. Symptoms of this would be the car overheating while driving and cooling OK when the AC is on or the fan is running.
2. Water pump recently replaced or is it leaking/bad?
   Is it leaking? Do you see good flow coming in the heater return line? Is it the wrong rotation for your car? In 88 they went to a full serpentine system on all F-bodies. The full serpentine setups spun the pump the opposite direction due to belt routing. If yours is a full serpentine(aka one belt) setup, and you just had your pump replaced….and now you have overheating problems. Look at the pump. Does it have extra bolt holes in it for what looks like mounting accessory brackets? If yes, you quite possibly have a 87 and older model. This is flowing water, but not quite enough to keep the motor cool. Also, I’ve heard of water pumps spinning the impellar on the shaft. This might be happening too.
3. Timing? Is it set to factory spec?
   If the timing is off too far, it can cause overheating
4. Is the car running lean?
   For this you’re gonna need a scan tool or a Air/Fuel gauge. If the car is running WAYY lean, it can cause overheating. This can also cause surging at cruise speeds. I don’t know what you would do to fix this…but it is a possibility. Too much EGR flowing can cause a surge too, but this is another issue.
5. Are the fans operating properly?
   Are the cooling fans coming on when they should. My IROC has 2 electric fans. The drivers side one will come on when the A/C is on or when the coolant reaches upwards of 236 deg. or so. The drivers side one is controlled by the switch in the head. It comes on at 225 or so. Make sure they work. If they don’t, track down the culprit. It also helps to get a lower temp fan switch for the head, but in a high performance motor, the chip will have to be changed to get the drivers side fan to come on at the right time. This is what I had to do to fix my problems.
6. Is the lower heater hose collapsing?
   Get the car good and hot, then stand and watch the lower radiator hose with the car idling. Grab the throttle linkage and rev the engine a coupla times. Does the lower radiator hose collapse some? If it does, replace it…preferrably with one with a wire in it.
7. Is the heater core leaking?
   If the heater core has a pin hole leak, it may be leaking just enough antifreeze to keep the system from building pressure, but not enough to cause a smell. This can cause mysterious overheating problems. If you are losing coolant, this could also be a culprit/symptom of your overheating problems. I have never personally experienced this and my car leaks some coolant…but so far, no overheating problems with my fans fixed.
8. Replace the radiator cap.
   If the cap is original, the spring may not be working properly which would keep the car from building enough pressure and causing it to boil over.
9. Is the radiator clogged?
   Have the radiator flushed. The shop can tell you if it’s up to factory spec on cooling. AutoZone sells a good 3 core all metal radiator for 140 bucks or so. Call around, prices on that radiator can fluxuate between stores. I think the price difference between 2 stores…20 miles apart was 20 bucks.