Overheating

Tiny
JIM52
  • MEMBER
  • 1995 CHEVROLET TRUCK
  • 5.7L
  • V8
  • 4WD
  • AUTOMATIC
  • 113,000 MILES
Silverado 5.7 liter 350. Replaced radiator, thermostat, water pump and gauge sensor. Engine temperature runs at 190 at idle. At 2000 rpm temperature runs to 250-260. Have checked thermostat in boiling water and it works. No sign at all of blown head gasket with emissions, power, smoke, etc. Will idle all day long at 190. Seems to be a flow problem somewhere? Could it be new water pump?
Fan and clutch good too.
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Saturday, April 8th, 2017 AT 12:30 PM

6 Replies

Tiny
CJ MEDEVAC
  • EXPERT
Maybe a radiator hose is sucking flat? Or tight bends?

Used to, all of them had internal anti-collapse springs, you seldom see them now. In fact, I have pulled them out of old hoses and reinstalled them on the new!

How did you check the fan clutch?

New radiator has the same or more rows than the previous?

This is something to look at should the normal stuff fail, see my last answer in this old post.

https://www.2carpros.com/questions/1961-pontiac-other-1948-6-cl-getting-too-hot-215deg-just-blocks-driving

I am not the only one here, others may jump in with other solutions!

The Medic

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Saturday, April 8th, 2017 AT 5:35 PM
Tiny
JIM52
  • MEMBER
Checked fan by hand. Not loose, no play, spin good. Of course fan on while idle and temperature remains normal at about 190. Once on road or putting about 2000 rpm still, gauge maxes out and check gauge light comes on.
Hoses seem fine and appears I have flow, but have not checked them while increasing rpm. Since I know thermostat is good, should I pull it regardless to see if it still runs hot?
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Saturday, April 8th, 2017 AT 6:26 PM
Tiny
CJ MEDEVAC
  • EXPERT
Fire it up

'Listen to fan'

It is sort of freewheeling. Fan rpm is much slower than engine rpm.

Let it get to operating temperature.

'Continue to listen to fan'.

When the radiator gets to the right temperature it will activate the fan clutch (if it is working).

The fan will suddenly get a louder roar to it (it is easy to hear!).

When it cools the radiator back down, the roar will stop, and it is back to the freewheeling mode.

This cycle will continue over and over.

If you are doubting this, listen to someone else's vehicle that has a fan clutch.

If you never get the "strong roar", I would say the fan clutch is not working like it should.

Of course, the mechanical, part (not much or no resistance while turning by hand, floppy, wobble, locked up) would also deem a clutch as 'bad' too.

The Medic
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Saturday, April 8th, 2017 AT 6:41 PM
Tiny
JIM52
  • MEMBER
Thanks, I will check the fan out tomorrow again as well the hoses.
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Saturday, April 8th, 2017 AT 6:58 PM
Tiny
JIM52
  • MEMBER
Ok car medic,
Installed new HD fan clutch today and it does gear up when truck reaches certain temp. New HD radiator, water pump, thermostat, and temp gauge relay. Ran at idle today for about 45 mins with cap off to re burp. Put another 1.5 gallons anti freeze in it and went for a drive. Still remained at 190 when warm at idle but at 2000 rpm, temp shoots back up to 240-250. Not showing any sign of blown head gasket but that seems to be only answer left I can think of? Any thoughts? And hoses fine too
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Saturday, April 15th, 2017 AT 10:46 AM
Tiny
CARADIODOC
  • EXPERT
Hi guys. As I was reading this, I was remembering this problem on my minivan. It was caused by corroded and rotted cooling fins on the radiator. Since you replaced the radiator, the next thought is HOW did you determine this is not due to a leaking cylinder head gasket? That isn't a common failure for this engine, but if combustion gases are getting into the cooling system, that can cause the thermostat to close. Thermostats have to be hit with hot liquid to open. Hot air won't do it. Once they open, air getting in SHOULD go to the reservoir, but when engine speed is a contributing factor, the volume of gas could overwhelm the thermostat.

The clue to this is a 200 degree radiator hose will be too hot to hold onto for very long. If the thermostat is closing, and the engine gets to 250 degrees, you'll still be able to hold onto the upper radiator hose. If that hose is much too hot to hold onto, feel the lower hose. If that one is also real hot, the heat is not being given up by the radiator. Possible causes of that are the fan shroud was removed, an excessively enthusiastic butterfly collection stuck in the AC condenser, the rubber seal along the front edge of the hood is missing, or there's unplugged holes in the core support. That's the sheet metal with the opening the radiator sits in. Any of those things can let the hot air from the radiator go around to the front and right back through the radiator again.

Removing the thermostat is not a valid test. Doing that can actually cause overheating because the hot coolant doesn't stay in the radiator long enough to give up its heat. If this happens, you won't have reached a valid conclusion.

You should also confirm the engine really is getting that hot. If you can still hold onto the radiator hose when the dash gauge says "250", it isn't. You need a scanner to view live data and see what the Engine Computer is seeing for coolant temperature. The computer uses a two-wire coolant temperature sensor. The dash gauge uses a different single-wire sensor. Both have an extremely low failure rate because there's just one component inside them, but if a sensor's readings suddenly shoot up faster than engine temperature can, I'd expect to find the sensor has a problem.
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Sunday, April 16th, 2017 AT 1:20 AM

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