I just bought a 98 12V the other day. The temps here in Ohio have been in the 20s (Not THAT Cold).

Anyways, the engine temperature on my 12V "seems" to take forever to get going. The heater finally starts putting out some good heat after about 10 minutes or so.

The Coolant Temp Guage stays around 165F after sustained (10-30 miles) of Highway driving. The seems VERY low IMHO.

I know Diesels are real finniky about fuel/timing issues, but I'm guessing it "may" be in need of a new Thermostat.

Ideas ???

 

my 82 does the same thing with 183 thermo. 2 new ones from cummins. if u find the answer i would really like to know. a thermostat is only supposed to start opening at its rated temp. so it doesnt make sense to me.

 

You have to remember that when you fire up the engine there is a whole lot more mass to heat up than a gasser. You also need to keep in mind that a diesel by nature does not generate much heat when idling. A diesel is like the furnace in your house. The more fuel the more heat. That doesn't mean you go out and stomp it to the floor cold, just that you need to work a diesel in order to get them warmed up properly. Another thing to keep in mind is the radiators seem to be somewhat oversized for our application unless you tow heavy quite a bit. Mine heats up to about 180* and then the guage drops to about 150* but the heat that comes out of the heater will actually burn your hand.
Tom

 

Cummins says,

THE COOLING SYSTEM USED ON THE CUMMINS DIESEL ENGINE EQUIPPED VEHICLES PROVIDES THE CAPACITY AND PROTECTION OF THE HIGHER GVWR AND GCWR RATINGS AVAILABLE ON THESE VEHICLES. OWNERS SHOULD BE ADVISED OF THE NORMAL SLOWER WARM UP AND LOWER ENGINE OPERATING TEMPERATURES ASSOCIATED WITH DIESEL ENGINES.

THE COOLANT TEMPERATURE GAUGE WILL FLUCTUATE ON DIESEL ENGINE EQUIPPED VEHICLES. IT IS INFLUENCED BY VEHICLE LOAD, OUTSIDE AMBIENT TEMPERATURE AND EXTENDED IDLE TIME. THIS FUNCTION IS CONSIDERED NORMAL

 

i understand longer warm up because of less use of fuel of the diesel. i do not agree with running cooler all the time at lite loads. the thermostat is not supposed to START opening until the engine reaches stamped thermo temp. i called cummins tech line the gentleman i talked to agreed with me. he did say the temp swings are normal. i deal with 4 ctd trucks only my 82 will not heat up even in summer. oh neither of the 4 trucks do the temp swing thing.

 

One thing to keep in mind about the temp swing, how much is the temp really changing? Sure it may look like a significant amount on the gauge but without a real gauge with real numbers we do not know exactly how many degrees it is swinging.

IMHO The temp swing is normal. Every CTD I have owned and driven has done this.

 

I would question the accuracy of the factory gauge, in my 99 the gauge read around 160 yet when I shot the cyl head at the tstat housing with a lazer it was 177 so I suggest you check the temp via another source.

 

i did have temp swing with an after market thermo but i change to cummins and it corrected the problem. ac thermometer in water coming from thermostat housing 95 degree day was 165 degrees after driving hard for 20 miles. i am not trying to argue with anyone i am hunting an answer. i have been in the repair business for over 40 years and will admit most out there are smarter than i am. that is why i ask questions. when weather warms up will be checking with a different type thermometer.

 

I have an oil temp gauge and it stays constant when the coolant temp swings. This indicates to me that the engine temp isn't effected much by the swings.
I feel worrying about something that is considered normal a waste of time.