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Overheating

Tiny
DCKY320
  • MEMBER
  • 1999 GMC JIMMY
  • 6 CYL
  • 4WD
  • AUTOMATIC
  • 170,000 MILES
Recently after doing an engine flush my vehicle started overheating when the rpm's are maintained over 2000. During normal running when the rpm's are below 2000 the temperature stay around 180 degrees, but when running and the rpm's stay above 2000 like going up hills as such the temperature will just keep going up as long as the rpm's are over 2000 until the truck overheats. It takes a little while to do it. E.G There is a five mile stretch going to work that is an all up hill run. The rpm's usually run around 2400 doing sixty mph up the hill. With the temperature starting around 180 degrees it will usually climb to around 230 degrees by the time I reach the top of the hill. I can idle the truck all day or run it with the rpm's below 2000 without and issue.
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Wednesday, May 17th, 2017 AT 8:34 AM

4 Replies

Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
Pressure check coolant system for a head gasket leak. These engines leak to the outside.
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Wednesday, May 17th, 2017 AT 9:43 AM
Tiny
STEVE W.
  • MECHANIC
  • 13,419 POSTS
180 degrees is a low temp for the 4.3. They normally run around 200-210. 180 sounds like you may have a bad thermostat that is stuck just slightly open. When the engine coolant flow has to be higher due to the extra rpm the flow can't rise to meet the demand. I would check it first.
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Saturday, May 20th, 2017 AT 9:27 AM
Tiny
DCKY320
  • MEMBER
  • 17 POSTS
The thermostat is new, replaced it in March. Though it is only a 160 degree thermostat which is what it calls for. Found the actual problem to be a clogged radiator. Found that out when the return side of the radiator failed and split wide open. After replacing the radiator 2 days ago haven't had any issues with cooling.
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Monday, May 22nd, 2017 AT 12:53 PM
Tiny
STEVE W.
  • MECHANIC
  • 13,419 POSTS
The OEM temperature thermostat in the 4.3 is 195 degrees.

Clogged radiator will do it.
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Monday, May 22nd, 2017 AT 8:19 PM

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