2004 D2, 144k miles.

New: Radiator, Water pump, Hoses & Pipes, 180 degree Thermostat, Fan & Fan Clutch, Flushed and Filled with Prestone Green plus Water wetter.

These temperatures are from my Ultra Gauge, without the AC on, and outside temperature between 65 and 80 degrees:

• Highway: 185 degrees
• Neighborhoods: 200 degrees
• Idling for more than 10 seconds: >210

I feel the low speed and idle temperatures are too high and from what I’ve read here in the forums, I shouldn’t be seeing 200+ at all given what I’ve done.
The odd thing is, if I’m at a light and the temps get into the 210+ range, if I put the truck in neutral and rev it to around 2000 RPM’s, the temperature goes down immediately to the low 190’s. Could this be a coolant circulation problem?

Thoughts and input appreciated.

Thanks.

 

You don't mention your coolant bleeding procedure. Could be as simple as a little air remaining in the system. And yes, that could make this much difference. A quick way to check is to open the bleed screw when the engine is stone cold. If the coolant is not right to the top, you have found some air as this is the high point bubbles will migrate to it. If you find air, just top off through the bleed hole with coolant. Check again for more bubbles the next time the engine is stone cold.

 

I'm in the same boat as you. Just rebuilt my engine, new radiator, new water pump and a 180 stat. Fan clutch assembly is the same though. Idle temps are 217-221. Highway speeds my temps are 197 to 212. When I get home I am going to test the fan clutch assembly and bleed any air out of the coolant system and see if that makes a difference. If bleeding doesn't fix it or the fan is bad, I will likely convert to an electric fan. Looking at these guys on ebay but have no experience with them.

Electric Fan Conversion

 

I second the bleeding steps. also check belt tension and if PS pump or something else is leaking fluid on the belt.

 

Thanks Dave. I went out and opened the bleeder screw and looked in. I could see fluid but it wasn't near the top. With the screw off, I raised the coolant reservoir up high until fluid began pouring out of the bleeder opening. While the fluid was coming out, I put the screw back in.

I then went for a long drive and here is what I observed:

• Highway: 185 degrees { no change }
• Neighborhoods: 190 degrees { -10 }
• Idling for more than 10 seconds: 200 { -10}
• Idling for 2-3 minutes: 206 {it never went higher}

I think that was it; air in the line.

Thanks again Dave.

 

open the screw tomorrow morning with a cold motor and pour in distilled water or coolant until full. do this a couple more days in a row and you should be golden.

 

Thanks Ben. I'll check it again in the morning.

 

I went to bleed the coolant system this morning. The good news is there was air in the system when I bled it this morning using Disco Mike's method. The bad news is that I am still running between 217-221 during idle and not much better than that under load. Ironically, if I have the AC on full blast while driving on the highway, I can get the temps down to 197. So my question to you all is, what about running the AC full blast is dropping my temperatures on the highway? Why doesn't it help during idle? What's the next place I need to look?

 

Looks like you saw some improvement with the bleed procedure. Keep an eye on it though. Personally I would think your temps should still be lower in neighborhood and idle temps. What kind of thermostat fan clutch did you get?

Once I did the inline thermostat mod and hayden HD fan clutch I never even saw 190 degrees ever again, idle or highway.

 

Probably the fan clutch. The hayden HD fan clutch is power house for cooling. You'll need a 99-02 fan should you go that route.

Also the 180 grey t-stat while an improvement over the stock one can be hit or miss. The inline thermostat mod is truly the way to go on these trucks. You get cooler temps on the highway because air is cooling down the radiator. Your idle temps are too high probably because of the fan but thats just my guess.