Getting hot on highway
 

My truck has been havving issues running hot when on the highway. Seems to creep up to the third line if I stay at 70mph, if I drop to 62-65 the needle will stay in the middle unless I climb a hill.

Seems that keeping speed below 2200 rpm allows the fan to kick on and cool it down. If I climb a long hill at 55 the truck will heat up too.

My info is telling me fan clutch but my experience with cars tells me that the fan shouldn't even be needed when going 70mph. So is the fan really needed that much on the first Gen or do I need to look elsewhere.

Radiator is newer, water pump is new, thermostat is new(cummins OEM), coolant is new. I added a second Gen intercooler up front but it did this before the intercooler, IC is unhooked right now. Cruising EGT is about 850-950. Climbing hill at 55, EGT is 1000.

Tell us a little about your truck. Auto or stick? any mods? Pulling something?

Im sorry, I could have sworn that I filled in my sig.

Truck is a 91.0 non intercooled. 727, 3.07, reg cab, 4x4.

factory height tires, pump is turned up very slightly, I had turned max fuel up a whole turn and I have taken out all but about 1/8 to 1/4 turn. Smoke screw is in a turn, and fuel pin is turned to the deepest cone area.

This problem is there when empty but is definitely more pronounced when loaded. Right now I have a 700lb quad in the bed and it even makes a difference.

Drop your transmission pan and empty it. Now go add some tractor hydraulic transmission fluid.

This tightens up the converter and transfers less heat into the stock system. The mileage bump is an awesome side effect.

Part of me was looking at that heat exchanger and wondering how much heat is coming from the transmission. I don't have a trans temp gauge on it yet. Thanks for the tip. I have seen some talk about the tractor fluid but didn't know it would have that effect. The other forum that I am on it is common to run that stuff in the 3 speed front wheel drive transmissions.

That tranny generates a lot of heat under load, and it transfers to the engine coolant. What would probably cool it down very good is a frame mounted fan cooled transmission cooler. My 93 with an A518 has one, and it keeps everything well under control, even when stomping up the mountains pulling a double trailer setup.

I don't know about the tractor fluid bit, but a lower stall torque converter goes a long way toward running cooler. Trade off is you give up some start up grunt as you have to give away some torque multiplication ratio to get the lower stall.

My goal is to swap in an nv4500 so I am trying to avoid spending any money on the automatic unless I have to. I checked out converters at one point and that's what lead me to thinking about at manual swap. I could easily spend 3,000 on either, but the auto would still leave me without overdrive and still no lockup. Thanks for the help guys, I am going to give the tractor fluid a shot, if that doesn't work I might throw a couple hundred at a trans cooler. I am also checking into an alternative to our small metal fan, It's a plastic 9 bladed fan from a modern truck.

My plan before another long tow is to add a stand alone cooling system for my water to trans fluid cooler to completely remove that heat load from the engines cooling system...

But it sounds like you have some issue with cooling b/c there should be no issue cooling an unloaded or even slightly loaded as you described truck...

Like he ^^^ said. A few bees and grasshoppers in the fins, or a thin coat of clay dust can wreck havoc on heat transfer. goodies like a bug screen (loaded) or a front mounted spare tire also.

Along those lines, is the rubber air seal along the top of the radiator in place?

As my 91 (with the same specs) got into the 200k range it started doing the same thing. Didnt have ic but all other maint. items were kept up on. Clutch fan would stay engaged at speed trying to cool it. Never figured it out myself but others may be on to something with the older tranny heat gen issues.

One thing I know is that with age and corrosion, the copper fins come loose from the tubes in these radiators. It isn't obvious until you pull it to get it cleaned and put your thumb through a few.

Between the fan cooled transmission cooler and the Mishimoto high performance radiator, I'd burn down the smoke stack before the cooling system would overheat.

One thing that I do to see if the engine is overheating or not, is stop, or slow way down, and if the temp goes down. it is not overheating. I was pulling my boat down to Mexico a few years ago and the temp started creeping up on a miserably hot day, (common here [duhhh]) I pulled into a rest area and the temp quickly started dropping. I stopped worrying and cruised on. That said, if your rise in temps is tranny related, you should probably listen to the AT experts...Mark

It does cool down right away as soon as I slow down, also even when towing it never goes out of the "normal" range.

That is good and certainly points to drag on the engine, like the AT, as mentioned above...Mark

Not sure why I didnt make the connection but today I realized that the truck only gets hot when using A/C. I guess I've been using the a/c so much lately I didnt notice. This morning it was 62 on the way into work and the temp was staying right in the middle with no issues. I kicked on the defrost and almost instantly it started to rise. I turned off the a/c and it slowly went back to normal over the next mile. So could this still be a clutch fan issue?