Overheating when towing

[73powerstoke]

I just bought a 99 F350 SRW. It appears to be the late model 7.3. Date on engine is 12/9/98, looks like the bigger turbo and has 3" intake. I have only had it about a week, and have had no problems, other than towing today. I can go down the highway at 70-80 mph with no problems and have been since I bought it, but I hooked up a stock trailer and towed a couple horses today and it started overheating after about 20 minutes at 65-70 mph. It cools down into the normal range as long as I stay at about 55 mph. After I unhooked, I drove it and had no problems, then hooked up to flat bed trailer with a round bale of hay and same overheating problem happened again. Any ideas on what the cause might be? Thanks!

[Dietoremain]

These trucks have efficient cooling systems for sure.. How does the coolant look? Is the clutch fan kicking on? Id say the radiator is do for a good cleaning and a coolant flush couldnt hurt either..

Secondly, does it have a CAT? and a stock muffler? If so chop em both off, they are nothing but restrictive in these trucks.. they run much better with more air in and more air out.. simple as that. Hope that helped a little..

[73powerstoke]

Could use a coolant flush, and does still have cat and muffler. I was just worried because it's not a lot of weight, but seemed to have made a big difference. Thanks for the info!

[ttyR2]

Is the ECU and 02 sensor affected by the cat delete?

[Zander's 5.8]

Originally Posted by ttyR2

Is the ECU and 02 sensor affected by the cat delete?

These trucks dont have O2 sensors, and no the ECU is not affected.