1988 – 89 Chevy GMC Pickup Engine

Reader Question: Some 7.4L TBI engines in 1988-89 Chevy/GMC Pickups (mine is a 1988 K3500 with automatic Trans), which run too hot – 240 degrees on hot day, 250-255 when towing.

The exhaust manifolds glow bright red. All of that heat overwhelms the cooling system. I have a larger radiator and auxiliary fan. All new parts from radiator thru tailpipe.

Fuel pressure and timing all on spec. All work performed at GM dealer, who is stumped.

I am looking for a way to cool this beast.

Thanks for any response you may have.

Roger

Hey Roger,

To me this really sounds like an ignition timing or compression type of problem more so than a cooling system type of problem. Since you say the exhaust manifolds are red hot, I would consider this an internal engine problem and not the ordinary engine overheating because of lack of coolant, restriction in a radiator type of overheating problem.

With those types of problems, you usually just see steam from the engine or radiator, overheating, hissing from the radiator due to overheating, belching of coolant from the overflow bottle because of overheating. This seems to be a problem with ignition timing, specifically late ignition timing, and the engine is laboring to power itself, or a compression issue in the valve train or cylinder heads.

I would triple check my ignition timing, check to see if the harmonic balancer has not slipped and has thrown off the timing marks, check timing chain slack to make sure timing chain has not “jumped” a tooth, and check each cylinder compression.

I have a feeling you are going to find a variance in the compression numbers and removal of the cylinder heads for a valve job or timing chain and gear replacement is going to be the “fix”.

But please keep me posted as to what you find so I can update this issue on my website to benefit the next person.

Blessings,
Austin Davis