Running cool

youngsamuel · Dec 11, 2009

First off thanks again to Greg and Dave for the advice on my sensor. I just replaced it I haven't checked to see if it works yet. I wanted to find out if it is normal for my engine to idle at 120 degrees and below. The problem is I have no heat in cold weather unless I am moving. As soon as I stop the temp falls quickly and I have no more heat so idling at night in very cold weather is not an option. I tried covering the radiator but that did not work.

highway star · Dec 11, 2009

Are you using your cruise control to bump the idle up?

youngsamuel · Dec 11, 2009

highway star said:
Are you using your cruise control to bump the idle up?

Yeh I tried that as well still nothing.

davekc · Dec 11, 2009

Not sure of what engine we are talking about but IF you have cardboard in front of the radiator with the idle bumped up and no rise on the temp, then it is the temp sensor (should throw a code) and if not, replace the thermostat.
That is assuming of course there is pressure in the system. If not, you have a pressure loss somewhere. Maybe something as simple as a bad cap.

moose · Dec 11, 2009

davekc said:
Not sure of what engine we are talking about .

Maybe this one ?

2000 Freightliner fl60
8.3lt Cummins

smokn72ss · Dec 12, 2009

I would say thermostat is stuck open .... have you tried a infared temp sensor on hoses to make sure gauge is right ? you can check the resistance range of sensor too ... to see if it is within spec

Slo-Ride · Dec 13, 2009

Keep in mind we are only guessing for you,,not being there no one can give ya correct answer just possibilities..
I assume sensors are working because you say heat falls off at idle only but comes up at road speed.. check the following things

Low coolant level
Stuck thermostat
fan clutch stuck on
plugged heater core or water lines partial turned off

Worst case,,,cracked block or head.
blown head gasket.. for the worst case ya should be seeing other signs tho,,oil and coolant mixing with each other,,air bubbles in coolant ,or coolant tank overflowing.

A bad water pump should give ya problems at all times so I think your safe there
G/luck with it

greg334 · Dec 13, 2009

OK Sam, what is cold?

If you are having problems with it under 15 degrees, then OK there is no real problem - it idles cold and there isn't much you can really do about it.

If it is happening when it is 30 out, then there is a problem - your thermostat needs to be replaced.

Sometimes when the thermostat is going bad, in warm weather (70) the engine will idle at a high temperature.

The problem with closing off the radiator is if you are driving it, then the charged air cooler can't do it's job and you may end up with engine problems because of the heat going into the engine being too high.

guido4475 · Dec 13, 2009

smokn72ss said:
I would say thermostat is stuck open .... have you tried a infared temp sensor on hoses to make sure gauge is right ? you can check the resistance range of sensor too ... to see if it is within spec

That is excactly what happened with my cummins 8.3. It had 2 smaller thermostats, right next to each other, and the pin that it rides on to open and close was bent,not allowing it to open/close properly.Same with my Cat C-15.Did the same thing yours is doing.Happenened to a freind of mine, also.Greg is correct, cardboard in front of a radiator is not a good thing.If the cooling system is operating properly,heater core is good, antifreeze mixture is correct, then you should not need to block the radiator for heat, no matter how cold it is outside.

youngsamuel · Dec 14, 2009

Yeh it idles cool at 30 degrees. I had one thermostat replaced last spring but I did not know there are two. Maybe that is it. Fluids are fine there is no mixing of oil and what not. Fan does not stick and I had a pressure test done also in the spring and everything tested fine. I am thinking it may be that second thermostat. I will replace that and advise. Thanks

Also I replaced that coolant sensor and no more check engine light. Thanks again.