I posted this in the Bump forum but I know some of you may not venture over there and wanted your thoughts as our trucks are very similar.

I appoligize now for the book below but I'm baffeled. Let me start by saying I plan to use my 1970 F250 2wd Crew Cab for towing. It is equipped with a 390 2bbl, a C6 and a tranny cooler. I will be towing a camper when loaded will weigh about 6500lbs.

I finally had the my mechanic install the new brass/copper 3 row High Effecient radiator along with a new 160 high flow Robert Shaw thermostat. See post https://www.ford-trucks.com/forums/1246396-buying-a-radiator.html for radiator info. The water pump was removed by mechanic and he thought it looked brand new and he compared it to another he had and said it was the high capacity model and we reinstalled it. I have a good shroud and a mech fan positioned properly inside the shroud. H filled the radiator with a 50/50 mix of antifreeze and water.

My mechanic drove it around with the A/C on to test it and was happy. I drove to pick up our new camper (5850lbs dry) about 40 minutes, through traffic short highway, truck ran cooler than ever even with the A/C running. I towed the camper back, still nice and cool, got into town with some traffic and the temp gauge moved slightly, start moving and it moves back. I got to the camper storage and idled around the lot and it started getting warm, stopped to back and it stayed warm, parked the camper and let it idle but didn't seem to help. By the time I unhooked and secured everything the truck had cooled down.

I spoke with my mechanic and he thinks it had an air lock. I checked the fluid level and it is normal.

I've heard of air locks happening before when an entire cooling system was drained so I know that is a possibility.

Is the mechanical fan I have OK or would the 19" clutch I see available at O'reily's along with a thermal clutch be better?

I had planned to install a Lincoln Mark VIII fan but was by Be Cool and Griffin to keep my mechanical fan for towing applications. I was baffeled by this but since they could have tried to sell me a fan setup I thought maybe they knew more than me.

What do you guys think?

 

I don't have any direct experience with the truck per se, mine isn't on the road yet, but I wanted to chime in. I'm a veteran technician and the brand of cars I've worked on for a 1.5 decades all use an electric auxiliary fan out front in addition to an engine driven fan. The aux fan only runs with the a/c on, or during engine overheat situations.

I think an auxiliary pusher fan out front that runs with the A/C on would fix you right up. Additionally it would probably make your A/C more efficient and a bit colder as well. It wouldn't need to that big either, I wouldn't go no more than about 1/2 the size needed if it were an electric fan only install.

 

It is possible that the water is going through the radiator too quickly to cool it properly.

I called BS on this one myself years ago until I did it. A 160* stat opens pretty quickly, you said it was high flow as well as a high capacity (never dealt with it myself) water pump. The coolant has to be in the radiator long enough to cool, otherwise the temp will just slowly rise when under load.

A cooling system that moves too much water winds up with the same symptoms as one with a restriction.

 

Sounds like it did fine on a roll and got warm idling. How warm? If it is not over 210-220 idling with AC on in hot weather I wouldn't worry as long as it cools off when moving. My dent with clutch fan gets a little warm with long idling in 95+ temps but doesn't overheat or boil. It cools of when moving so that's OK with me. A really big electric fan with big alternator to run it would improve idle temps... but may not be necessary.

I think a 160 stat is a bit low but that shouldn't contribute to the problem you are seeing. I like at least a 180 stat and run the OE spec 192 or so on my dent. Low stat temps make the bores cool which promotes condensation of gas, oil wash and bore wear.

 

the water pump is the high capacity model, if you look on o'reily's site you'll see a standard pump and a high capacity pump, I wondered about the 160 opening too soon, tomorrow i'm putting a guage on it and will have some numbers