1981 F150, 302 (factory AC truck but AC removed, direct-drive fan with no clutch), C6.

Here in Texas it doesn't get too terribly cold, but I've noticed that when the temperature drops, my water temp on my truck doesn't really go up much. Short trips around town, the water temp doesn't get much past 100F. If I'm pulling a load or on the highway it gets around 150F.

I suspect the thermostat is stuck open. I bought a "fail-safe" 180F model to replace the stuck-closed 195F one I had in there before. Fail-safe mode for these units means that if it's heated past its rated opening temp, it will stick open to keep you from overheating til you can replace it.

When I first installed it, the truck heated up past 180F very quickly, within two minutes. Around 200F the thermostat finally opened up, temps dropped, and I didn't notice any problems. At least, til the weather got cooler.

I'll be going ahead and dropping in a new, non-failsafe 'stat over the weekend...but just out of curiosity, what do you guys run as far as winter operating temps?

EDIT: Pulled the radiator cap off just now and started the truck for the first time today. With the engine cold, I see coolant flowing through the radiator. When I started the truck, it shot a little out too. So this means I have a stuck-open thermostat, doesn't it?

 

Same as summertime (in general).

After the engine has sat overnight, remove the radiator cap and start the engine.

Look in the radiator - if you can see water flow, the thermostat is stuck open.

 

I dont have a real guage, but summer not towing it's "M" and winter not towing it's "R"...lol

 

Just checked it, saw water flow.

Looks like I know what I'm doing tonight after work!

And lol. I've pegged out the factory gauge before, though I don't think I was overheating the truck. I did get it up to 250F later on flat-towing a friend, but no damage was done and I promptly changed that bad stat out...

I hope the new stat actually lets me have the right temps. lol

 

When you get to the "L" is when you have to start worrying...

 

Yeah, the engine should run at near the same temp, regardless of outside temp. Of course, at higher outside temps, the radiator doesn't get quite as cold, so the incoming coolant isn't as cool, so the temp can be a bit higher.
Blocking air thru the radiator is a patch. Typically, the problem lies with the stat not working correctly.
Failsafe stats are a good idea, but in the real world, they can be problematic. All it takes the engine getting a bit too warm one time, and the stat hangs open. Resolving the issue that caused the engine to heat up doesn't return the stat to a functioning unit.

 

Naaah, that's just making full use of the incoming fuel mixture, going for that complete burn. That and it makes the heater work sooo much better...

 

'86 F-250 lifted on 35" tires with 460 at ~400/550 hp/tq according to DD. Coolant system is using a Edelbrock high flow pump, high flow fail safe thermostat 180*, stock radiator, clutch fan (7 or 8 blade?), no shroud. Winter temps it's lucky to soo 165* after a highwasy run, around town and whatnot it's 155*-160*. Temps are more like 170*-180* in the middle of summer. Pulling my boat at 5500+ lbs it's 180*-185*, on a 100*+ day in traffic towing it'll get up around 190-200 and stop there, dropping to 180 as soon as I get rolling.

No shroud on this as it broke when I broke a motor mount (something about torque) and I haven't got to repairing it. I need to fix the shroud and reinstall to keep more stable temps in summer towing in traffic and maybe go to a lower flowing thermostat to keep temps up.

 

Mine used to get between the M and A towing a 10,000 lb 5th wheel in the middle of summer with the AC running and a 190 stat. The clutch fan would sound like one of NASA Langley's wind tunnels till you gut between 45-50, then it would drop off. Never had any problems with it. Winter it stays around R.