CAT C15 Running hot at idle

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by Ilyalis1993, Jun 21, 2022.

  1. Ilyalis1993

    Ilyalis1993 Bobtail Member

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    Hey guys got a CAT c15 and had a coolant hose blew out, I replaced it topped her off with coolant everything runs fine and back to normal. Running temp stays 185-190 for the most part. But for some reason standing at idle it gets up to 200… any idea why? I’m thinking maybe air bubble in the cooling system since I lost a good bit and then added. Thanks I’m advance.
     
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  3. lester

    lester Road Train Member

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    That's perfectly normal. My C-15 will get right up to 217 at idle if I don't have the fan on manual (217 is temp ecm kicks fan on for engine temp)
    At idle you are still making heat and there is no air moving across the radiator.
    Whenever I am idling RPMs are kicked up to 950ish and engine fan is turned in manually.
     
  4. Ilyalis1993

    Ilyalis1993 Bobtail Member

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    Wanted to add after running the fan and getting temp down it’s stays about 188 or so. So not sure if the thermostat sticking or like I mentioned earlier just an air bubble
     
  5. lester

    lester Road Train Member

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    Still completely normal. Thermostats are probably right around 190 degree stats..and again mine does the same thing, kick the fan on and will cool it down to 188 and usually stay right around 180-195 at idle with fan running manually
     
  6. Lazer

    Lazer Heavy Load Member

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    Nothing to worry about. I have been in many Internationals with Cummins, that have no manual fan switch. Truck will idle all day(theoretically) right at the point of fan kicking in(215-220), fan kicks on just long enough to drop below 210, then the cycle starts all over again. When using pto off loading, fan will be on-off-on-off-on-off………..
     
  7. God prefers Diesels

    God prefers Diesels Road Train Member

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    Normal here too. 2007 Cummins, 180 stat. Every part and piece of the coolant system is new, including the fan clutch and hub bearings.

    It will run at 180 and not budge with the manual fan on. Even running uphill loaded. But without the fan running, it will slowly creep up to 209 at idle until the fan kicks on. Rinse and repeat.

    So whenever I stop, or am in heavy traffic, I kick on the fan. Keeps it nice and chill.
     
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  8. Rideandrepair

    Rideandrepair Road Train Member

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    You’ll find out soon enough if there’s a large air pocket. Once it works it’s way out, coolant will be lower. Leaving my cap loose, or off, and vent on top pipe open while idling helps. Newer closed systems may be different. May overflow. I don’t really know. I have had air pockets that take hours to get out. Sometimes adding as much as 2 gallons. Once I had to top mine 3-4 times in 5-6 hrs. while under a load, after flushing it.
     
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