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1992 Chevy 1500 Runs Hot

I have a 1992 Chevy 1500 5.7L V8 with 167,000 miles that is running hot. When I drive the vehicle the temperature quickly rises to just about 250 degrees and hovers just under the “red” zone. It never fully overheats, even on longer drives (50+ miles). It seem to run just fine otherwise. It is not leaking coolant and I have not had to fill the radiator. My first thought was that the thermostat was bad, but wouldn’t that be an “all or nothing” issue? Where should I start looking for the problem? It has been going on for about 3 weeks, and I want to get it resolved quickly. Thank you.

No more than a thermostat costs why not try that first and if no difference have the system checked before you ruin the engine.

On a truck that age ( much like my 80 Bronco ) a good cleaning is in order too.
Clean off the greasy sludge that no doubt covers the entire engine by now. That acts as an insulating blanket and heat can not dissipate well anymore.
Clean the radiator fins of accumulated bugs , grass, and debris. Use a radiator fin comb ( Santch # MT1030 - Murray # 59145 ) and you’ll also create nice new airflow through what are probably numerous bent over fins as well.
And another age related gunk issue is INSIDE the radiator. What do you see just looking in when the cap is off ?
A flush may be in order . . or . . if these cleanings don’t fix it . . a radiator shop can rod out a crusty old radiator.
While looking in the radiator neck, check for coolant FLOW when the stat is open.

A T-stat is not an “all or nothing” device. A 5.7L V8 with 20+++ years on it needs all the water passing through that the system was designed to provide. A T-stat partially stuck could easily cause hot operation.

I also agree with Ken’s comment. And in addition to a good cleaning, I’d take an infrared thermometer and scan the radiator with the engine at running temp. Cold spots will mean you have blocked tubes, and that reduces the ability of the radiator to dissipate heat.

It’d be a good idea to change the hoses too. They’re made in laminated layers, and the inside layer can collapse and restrict flow. Frankly, at this advanced age, the elastomeric parts are probably deteriorated too, so I’d add emphasis to my suggestion to change them.

Let us know how you make out. We do care. :relaxed:

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You didn’t say what you used to measure the 250 degree temp with… If it is the truck’s gauge, I would doubt that reading in an instant.

Note @the same mountainbike’s response… read the radiator temp with an infra-red temp device to get an accurate number.

First I’d read the temp with a IR thermometer and replace the thermostat.

If I remember right these also have a fan that is run off the crankshaft pulley. If so, the fan clutch could also be allowing the fan to free wheel.
This would make the fan look as though it’s working ok, but in all reality it’s not spinning as fast as it should.


Good point @Yosemite!

These trucks have a fan clutch mounted between the waterpump and the fan blades. On the front-side of the clutch, there is a coil-spring that is a bi-metal thermostat the engages the clutch. If it is broken, the clutch won’t engage and the truck will tend to overheat in traffic. Highway speeds should keep the temperature down even if it is broken.

Thank you all. I’ll start with the cleaning and then replace the thermostat. The hoses were replaced by the previous owner about 5-6 years ago so I am going to leave those on. The fan seems to have good resistance when I try to spin it so I think the fan clutch is still OK. At what point should I be worried about the water pump?

You can run a flow test on the water pump. Only until you have the results of that do you have to worry about the water pump.

See if the dealer parts guy can offer a flow spec for your engine’s pump. By providing a constant supply, like with a garden hose with the thermostat removed, you can use a large volume-marked vessel to actually measure the output of the pump. It’s a bit messy, and you may want to cleanse the system of coolant and leave only fresh hose water in there before testing to prevent groundwater contamination, but it works.

NOTE: I’ve seen engine water pump test procedures, but none that I’ve liked. If someone here has a better one, I too would love to hear it. And I mean that sincerely.

Be sure you don’t leave the engine with plain water after you’ve tested the pump. My preference is a 50/50 mix of coolant and distilled water ($1/gallon at the grocery store).

[quote=“fkoski, post:8, topic:93955, full:true”]The fan seems to have good resistance when I try to spin it so I think the fan clutch is still OK. [/quote]That’s not a valid test. If nothing else does the trick, replace the clutch.

Agree with @NYBo You would have to have the clutch hot enough to engage or flip the bimetal spring off its retaining tab and spin it. Or start the engine… it will sound like you have a helicopter underhood. They really are noisy when engaged.