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1992 Silverado overheating
02-26-2014, 02:08 PM
Post: #1
1992 Silverado overheating
I have a 1992 Silverado 5.7 V8 350. I replaced the thermostat and drained the coolant out and its still running very hot and blowing cold air, I have no idea why it's doing this
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02-26-2014, 07:18 PM (This post was last modified: 02-26-2014 07:19 PM by Rupe.)
Post: #2
RE: 1992 Silverado overheating
Feel the heater hoses. If they are cold when the engine is hot then the system is not full. This will also cause the engine to run warmer than usual.

Since you already know the engine has gotten warm at least once then remove the radiator cap while it's cold, fill the system, then let it run for several minutes with the cap off. Keep filling it a little at a time. When it stays full for a few minutes and the heater blows warm then install the cap. At this point fill the overflow tank to about half way or a bit more and go for a ride. Recheck the fluid level in the morning again when it's cold to see if it needs a bit more. (common) Top up the rad and the tank as necessary then see how it goes for a few days.

This presumes what you drained out was clean and there is not a blockage in the system. We can talk more about that if the problem continues.
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02-27-2014, 11:44 AM
Post: #3
RE: 1992 Silverado overheating
(02-26-2014 07:18 PM)Rupe Wrote:  Feel the heater hoses. If they are cold when the engine is hot then the system is not full. This will also cause the engine to run warmer than usual.

Since you already know the engine has gotten warm at least once then remove the radiator cap while it's cold, fill the system, then let it run for several minutes with the cap off. Keep filling it a little at a time. When it stays full for a few minutes and the heater blows warm then install the cap. At this point fill the overflow tank to about half way or a bit more and go for a ride. Recheck the fluid level in the morning again when it's cold to see if it needs a bit more. (common) Top up the rad and the tank as necessary then see how it goes for a few days.

This presumes what you drained out was clean and there is not a blockage in the system. We can talk more about that if the problem continues.

The hoses were hot while the engine was hot, would that mean that there is a blockage somewhere? I am going to be doing a coolant flush through my school to see if that helps today.
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02-27-2014, 12:04 PM (This post was last modified: 02-27-2014 12:08 PM by Rupe.)
Post: #4
RE: 1992 Silverado overheating
You may want to flush the heater core while you have the system open just to get any old coolant out of there.

Back to the heater hoses being hot when the engine is hot: If that's the case then you proabably have coolant flowing so the next step would be to have a look at the various blend doors within the heater case. This will require listening and feeling for the air out the dash vents, floor, and defroster, plus what happens when you move the selector from cold to hot. If everything seems to be headed out through the defroster on top you likely have a vac hose issue under the hood. (this is a safety default) If some things change but others do not then it's time to crawl under the dash to see if the vac pots are doing anything. They are mounted on the outside of the case and are subject to both wear and big feet over the years. Sometimes the linkage falls off or gets kicked off. The least likey issue would be the vac rotory valve within the heater control itself. I haven't seen one of those fail since the 70's.

Back to the vac issue under the hood: There's a vacuum tank out front, usually on the inside fender or down low just behind the radiator. The newer style is a round black plastic thing and a bit bigger than a softball. The early style looks like a black painted coffee can. You can also pull off a hose and use your finger to feel for vac with the engine running. The hose goes to a tee fitting. One end goes to the engine and the other feeds through the firewall near the heater. Follow the hoses and look for damage. I usually find one is broken near the engine due to heat. Sometimes it's mice chewing on things.

Edited to add: Going from memory here so I might be off by a few years. If you have the "push button" heater system with the green indicator read out mounted directly below the radio then you may want to check all of your fuses. This system is electric as well as vac operated.
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03-05-2014, 04:55 PM
Post: #5
RE: 1992 Silverado overheating
some where else to look is your fuse block and check for blown fuses for the heater control or if it is over heating that much it is a far stretch but could be water pump

help where i can leave the rest up to the everybody else
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