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/1...-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?

 

Make sure coolant level is about 1 1/2" below cap.
My opinion on cooling, would be to go with an electric fan set-up. It doesn't rob the engine of horse power comes on when temperature is at 195* or what ever you choose and turns off when temp drops to normal.

 

well abyars i dont think i have your answer but just to brain storm.

90% of the time its the thermastat

FEs i dont think have air lock problems much at all, it would of pushed the air out after high RPMS. but im not an FE guru

do u have a radiator return reservior hooked up?

ive seen many threads on muscle car sights where people complain about there new (mostly aluminum) radiators fluctuating heat like that when they dont have a return reservior connected. im not sure of the brands. but u said your fluid lvl is fine so.

your problem happened to me but the hose on the inside of the reservior cap fell down/off so none of the fluid could return when cooling. when cold before and after the problem accured the fluid lvl looked the same.

probably not your salution sorry

 

Not sure why you chose old copper brass technology when big aluminum radiators are available? Aluminum radiators will ALMOST ALWAYS out perform C/B radiators. Didn't help yourself there IMO. And a properly set up mark viii fan will work just as well if not better than a mechanical fan.

 

I have a coolant recovery tank in place and seems to be working. I put in a 160 to ensure things would be cool, I think I shot myself in the foot there. I will switch it to a 180. I'm going to add a guage so I can have some numbers.

I debated going to alum radiator but went with a C/B in case I had a damaged radiator in the middle of nowhere while on a camping trip. I thought it would be easier to find a shop to fix it.

I'll let you know what happens after I change thermostat and put a gauge on.

 

switch to an electric fan , they are better

 

I'd remove the drain plugs on the sides of the block and flush all the sediment out of it's cooling passages. 180 is better. Make sure lower rad hose has a spring in it so it can't get sucked shut.