dewclaw

This is probably a no brainer ..but.... do these trucks tend to run cold ?

I have a '99, 4X4.

When I run my truck in cold weather, going downhill on a long grade , no throttle, the coolant temeprature pegs out LOW. Cold.

Is this normal or do I have a stuck thermostat ?

(I am STILL impressed with the massive cooling system in these trucks.)

Thanks in advance for the input.

DEW

klx650a2

Do you have your radiator blocked off? Yes, these trucks run cold when not worked. When I had my 2000, I ended up replacing the thermostat. If you do that, only buy a original Cummins part, expensive but they work.

DIESELWRKS

you said 99 but below says 98.5. but anyway. if you have never replaced the thermostat or dont know if it has I would for safe measure. normally there is a 180 or 190 degree one. but if your going up and down I-5 up by like shasta with cold temps I can see a little colder but shouldnt be moving the needle drastic. check with the thermostat and go from there.

dewclaw

Yea, its a 98.5, just rounding it off a bit. And you are right , Shasta / Trinity area.
My radiator isnt blocked off. This thing just should not peg out low , yep its probably stuck open a bit. I will go with Cummins a part.

Out of curiosity, what is the down side of of it running cold other than my cab heater puting out cold air ; ) Any performance issues ? I have seen big-rigs with their radiators covered so there must be perf problems when they are too cold ?

Dinner

Diesel engines are more efficient when warmed up to the proper temp. Everything is seated properly and the fuel/air is being compressed and burned properly. It's also easier on parts to have the engine all warm and cozy.

WestTN

When coasting downhill you are burning NO fuelat all. The engine is just pumping air through. So, it has to cool down some.

1-5-3-6-2-4

yes true. at no throttle coasting theres no fuel injected at all. but with low cylinder temp when you do inject fuel it is not a complete burn you will eventually glaze the cylinder wall. which will be bad. burning oil, loss of compression.......you just dont want that.

dewclaw

I just ordered a new 'stat' from Cummins West. (180'F)

Dodge dealer wanted $72, ???????? Thanks but no thanks Dodge.

Cummins sold it to me for $33, shipped to my house.

bamadzl

This thread caught my eye. Mine's always run cold like that. I replaced the tstat and it performs the same. Either mine just runs cold or the sending unit or gauge is off.

Brad

jrv15

so whats a good temp? mine runs about 160

forwardho

190-200 on my truck is normal.

dewclaw

put a 180 in mine. Found that the old stat had one side of the 'perch' that holds the spring, cracked in half . Holds solid at 180 now. It does seem to run more efficiently now.
By the way, I just turned 300K miles on the truck today ; )

jrv15

ok im scared now... my truck usually runs just above the 145 mark all the time. is this bad?????

nickg

throw a new thermostat in and all should be golden, usually if they run cols the thermostats opens too soon, engine is more efficent when up in the 180-190 range. mine runs 190+ all the time except in extreme cold temps does it cool down,

jrs_dodge_diesel

3 possibilities come to mind:

1- you are driving short trips and the engine does not have time to warm up.

2- If the radiator is not blocked off, it will take longer for the engine to warm up (do this when it gets cold and stays cold outside)

3- you might have possible thermostat and sensor issues

1 and 2 can affect each other. Short trips, cold air, and an open radiator will definitely make the engine take a lot longer to warm up.

Try this, drive your truck around for about a 1/2 hour and see if it comes up to temperature. Even when it is 40ºF outside, my truck will come up to full temperature with an open radiator (takes a little longer but it will).

If it still does not warm up then start looking into possible thermostat issues.

If you have never blocked off the radiator, it's pretty easy. I personally use a large sheet of cardboard, and slide it in between the intercooler and radiator. Works good, and I've been able to use the same piece of cardboard for 2 years now.

Good luck, and let us know what you find.