Truck heats up on the highway and cools down in town.... ????

[Black6.5L1TON]

Well I just got my truck back on the road after installing an injection pump, glow plugs and glow plug relay. It say for 5 months because I didnt have the money to fix it and I bought it last october so I never have driven it in warm weather befor. I took it out for a long drive today and while I was doing down the highway it slowly heats up to a little over 210. But as soon as I slow down it drops back to 180ish. I bought the truck to pull my cars to the drag strip and shows. But the way this thing heats up on the highway there is no way I'll be able to pull a trailer with it. Its a pretty much stone stock 98 3500HD auto 4x4. The only modifications are an FSD cooler and a #9 resistor and 285/75/16s that I know of. Im not sure if the 98s had the dual thermostats from the factory or not but my truck does have them. If anyone could help me out please let me know. If there is any other information you need just ask. Thanks everyone.

Jeremy

[3bals]

I have a 98 also and have had high heat issues too. To solve mine, I pretty much went with Walt's advice.

First I replaced the thermostats (yes there are 2 on the 98) with new ones from Walt. At that time I also flushed the cooling system and replaced the OEM orange coolant with good old fashioned green stuff.

I still had heat issues, but only while fully loaded with a 11.5ft slide-in camper. I then cleaned the outside of the radiator from the engine side out to get any bugs and/or dead birds out. At that time, while I had the shroud off, I also replaced the fan with an upgrade from Walt.

That was an improvement but I stiill had high heat issues, especially traveling accross Utah in July. On my return, I ended up replacing the radiator on Walt's advice. I haven't had a heat issue since, but I haven't been to Utah since either. At that time, Walt didn't sell radiators, so I had to get one somewhere else. Too bad, because now Walt sells them and he even offers a HD copper core one. I surley woud have purcahed one of those.

Jody

[Black6.5L1TON]

Thanks very much for the reply. Im going to follow your advice. First Ill start by cleaning the front of the radiator off. I looked through the grill and didnt see many bugs or birds :P Ill pressure wash it when the truck cools down real good. I think it has already been switched over to green coolent but Ill check it out. I was thinking that maybe the clutch might be bad in the fan and slipping too much at the higher RPM my truck turns on the highway with the 4.10 gears. Hopefully I can get it straightend out soon. Thanks again for the help.

Jeremy

[3bals]

Be careful with the powerwasher. Hold it a good distance away from the radiator. High pressure can bend and/or break the fins. Not good.

Jody

[w_huisman]

You might also want to clean the area between the AC condenser and the radiator. That place tends to get an amazing build-up of bugs, grass, road debris, and about anything else you can imagine.

Best to completely remove the radiator when cleaning, best time is when you are changing the coolant. Use a good coolant system flushing agent before refilling system with new coolant.

I think, however, you will find the most dramatic improvement from installing new thermostats. Only install OEM ACDelcos or RobertShaws (Prestone). Every other brand is "hit or miss" at best.

[Black6.5L1TON]

Thanks again guys! Im gonna do the coolent change over this weekend. I wasnt sure befor what coolent my truck had in it but I figured out that it has the pink dexcool. So Im gonna clean the rad, condensor and aux coolers and install new thermostats when I switch over the the green coolent. What is the best way to get all the pink dexcool out of the block, hoses and heater core? Thanks alot guys for the help.

Jeremy

[UTexas]

I had the same problems with my 95, the truck ran fine until I hooked on to one of my trailers then I had to fight the high engine temps. I have installed the cooling system upgrade and had even added a water injection for cooling purposes. Even after all this I still wasn't getting any cooler. I talked to Walt about these issues and he toldl me that the aluminum core radiators that come on these trucks only have a life expectency of 10 years, even if they are serviced every 2 years. He said that they can't be cleaned out like the copper core ones. He said the best thing to do is replace the radiator with either a HD aluminum or HD copper. I did, and it made allot of difference. I had tried everything under the sun to try and make my truck run cooler when pulling and nothing worked until I replaced the radiator. Now I can run down the hwy pulling my travel trailer and my truck hasn't got about 210, as soon as it gets there the fan clutch kicks in and cools it right back down to about 180. Before it would run about 225-230 and the fan clutch would cool it down to about 210. NOT GOOD. Needless to say, it made a world of difference.