Runs hot at low speeds fine when moving on interstate.

Replaced t stat and water pump, think they were fine. Cleaned the radiator, a little dirty but not bad. Radiator seems clean on the inside. New fan clutch last fall.

1 The transmission was re-built last fall, could they have filled the system up with pure antifreeze and altered the mix enough to make a difference?

2 I can not hear the fan but if you put your hand by the engine you can feel the air blowing, any way to test? I read about getting it hot then shutting off and if engaged it would be hard to turn? Shop put on the computer and they said it was locked and working fine.

I have checked the stock gauge and it is reading correctly, over the weekend it almost went into the red pulling a 3k boat at 35, luckily made it over the hill then it cooled down.

I have had the truck since it was new and it has never gone more than a needle over 200. Not sure what is going on, any help appreciated!

 

Would help to know what truck we are talking about. Most low speed cooling problems are related to the fan. Do you still have the fan shroud on it? Are there any obstructions in front of the radiator? Have you had the system flushed? Unless your exhaust exits right by your window and you dont run a muffler, you should hear it when it is engaged. Also check your belt tension, I have seen them slip with the fan engaged and not make a sound.

 

Sorry. I thought it would come thru with signature. 2005 2500 4x4, 8' bed.
Bought the truck new. Cat back 6 years ago, original rusted off. Shroud if factory, sprayed out radiator with water hose, looked decent, not much in it. New water pump 3 years ago, leaking, thought it was slipping so replaced it, same. Replaced thermostat, same.

Last year the computer went out and took the fan with it. Seems like it would be the fan but I took it back to the shop and he put the computer on it and the fan was 98 locked I think, you could feel the air being pulled thru the radiator.
With the truck idling and the air on it kicks in and out every few seconds, air also get warm when you idle, great when you are moving, does the tie together?

 

You need to ground pin 1 on the fan clutch connector . Monitor fan clutch RPM and engine RPM. Chart shows what fan speed should be compared to engine RPM. If not in range replace fan clutch. Dealership scanner will be needed to monitor RPM of engine and fan clutch.

DIESEL

NOISE

NOTE: It is normal for fan noise to be louder (roaring) when:
•Fan duty cycle high. This may occur when ambient (outside air temperature) is very high.
•Engine loads and temperatures are high such as when towing a trailer.
•Operating conditions where transmission temperatures may be high
•Cool silicone fluid within the fan drive unit is being redistributed back to its normal disengaged (warm) position. This can occur during the first 15 seconds to one minute after engine start-up on a cold engine.

LEAKS

Viscous fan drive operation is not affected by small oil stains near the drive bearing. If leakage appears excessive, replace the fan drive unit.

ELECTRONICALLY CONTROLLED VISCOUS DRIVE - DIESEL





If the fan assembly does not free-wheel and a metallic grinding sound exists, replace the electronically controlled fan drive (Refer to 7 - COOLING/ENGINE/RADIATOR FAN - REMOVAL).

NOTE: The following test may take up to 15 minutes to perform.

The engine should be at normal operating temperature.
1. Set the parking brake and verify the transmission is in park or neutral.
2.Set air conditioner (if equipped) and blower fan to OFF.
3.Start and allow engine to reach normal operating temperatures.
4.Stop engine, connect the scan tool and select appropriate model year and engine option.
5.Check for and correct existing DTC's
6.Using Tool 6801, backprobe pin 1 of the electronically controlled viscous fan drive connector, with the harness connected located at the lower fan shroud to battery ground.
NOTE: The fan drive control coil is energized to 12 volts at this time.

WARNING: A spark may occur when connecting pin to ground. Be sure that no combustible material is in the area.

7.Using the scan tool, verify that DTC 0480 set. If it is not set, verify that a good ground is available.
8.Start the engine.
9.Actuate engine speed to 2000 RPM..
10. Go to the SENSOR screen and observe the fan speed.
11.Run the engine at 2000 RPM until the fan speed increases to 1850 RPM or more for 30 seconds.
NOTE: Fan RPM may ramp up slowly.

NOTE: It maybe take 15 minutes before fan speed increases.

12.The fan speed should be in accordance to the table below.
13.If fan speed does not increase, make sure that the jumper wire has a good connection. If so replace the electronically control viscous fan drive.
14.If the fan speed does increase and there is still a concern, refer to the appropriate Engine Electrical Diagnosis Section to diagnosis the electronically controlled viscous fan drive control circuit.

ELECTRONICALLY CONTROLLED VISCOUS FAN DRIVE SPEEDS
ENGINE RPM FAN RPM (Min)
1000 950
1500 1420
2000 1850
2500 2230

 

I too, had some moderate heating issues. Nothing real bad just around 210 - 215 in bad traffic. Tranny around 220. Took it to a local diesel repair and was told not to worry until it went over 240...hmmmmm. Shuffled it to the back burner. Then I noticed that the ac at idle was not too cool. It worked fine at speed... hmmmmm off to the back burner it went (I don't use ac much, it is just when my wife rides along). A friend at work noticed I had a birds (lots of chirping) under the hood at idle... this could be something so it got priority. I started poking around and saw a thin strip of my serpentine was wrapped around the fan shaft and there was an odd metal piece sticking up from the bottom rear of the radiator upward into nothing. It was sheared at an angle and had 6 wires in it... hmmmm front burner time. The first thing I wondered was where the other end of this bundle of wire was and why didn't my truck realize something was wrong. After several trips to the computer and the shop manual I realized it was the wires for the fan clutch. Well I just got done replacing the fan clutch, idler (for the birds), and belt. Things seem to be much better now. I will know more as time goes, but I do think the heating issue was because of the fan clutch.

 

Drove from TN back to Ohio, truck temp goes from about 220 to 180 up and down the hills running 75. Truck will get hotter if at slower speeds but will cool down if allowed to idle. Could still be in the fan but both high and low speeds are fluctuating more than normal.