You said you replaced the radiator when you put the new motor in? Did you buy a 2 row or 3 row radiator? Maybe the radiator is too efficiant.

I don't think the radiator size makes a difference - I mean, if the thermostat was stuck shut it would overheat eventually. The thermostat should be able to regulate the temperature consistently, even if it has to open just a little in very cold weather. Throughout the posts, this has sounded like a heat regulating problem - there are very few items that cause a vehicle to run cold (faulty gauge ;) ) or a faulty thermostat.

Maybe you 351 guys have an easier time of the t-stat. On the 302, it's very close to the water pump, and that lower bolt is a little difficult to get to. I did mine while the intake was out!

It sounds like I have another bad t-stat. I think we'll switch brands and make sure we test the next one before putting it in. I just wanted to make sure I had explored all possibilities before I took the truck back in. I'll let you know how it goes.

Thanks!

maybe your clutch fan is not working properly

If you bleed it again, make sure you trip the thermostat as much as you can, or justtake it out. You might have a weak thermostat, that when presuure gets put on it, it pops open, but with little pressure, its closed. Maybe a new thermostat. But if its happening with the Japser motor, I'd get the rad cap tested. Since coolany boils at a lower temp with no pressure on it, it might be boiling, and thats why you needed to fill it those 2 times. I'm not a colant expert in any way, so just wait for a few more posts, but it could be the cap.

Interesting thought on the pressure causing the t-stat not to work properly. I won't be home for another week, but I figure I'll put a new rad cap on when I get a chance to hit the auto parts store to just make sure that's not part of the problem.

Hadn't really thought of the clutch fan... I would think it's doing it's job since the engine doesn't overheat while idling. I guess it could not be releasing, hence the slower warm up times. I can't imagine that the fan makes much of a difference at 70 mph. How do I check this?

I I knew how a clutch fan worked, I'd tell you. But I don't. Something about heat, like a T-stat I believe

By any chance are you from Cape Breton, or do you have relatives up towards Nova Scotia sfitzgerald?

if you clutch fan sounds like a plane under the hood then its time for another one. or try and spin it when its cold. it should spin but only half rotation or more. if it wont spin at all then that is your problem

I've heard at highway speeds, it makes no difference to the cooling if the fan is running or not. To check: Stone cold with the engine OFF, the fan should turn easily by hand. Hot, right after the engine is turned OFF, it will be noticeably stiffer to turn. In the cold weather, it may not warm up at all. The normal failure mode for fan clutches is for the fluid to leak out, leaving a dirty spot in the middle of the fan clutch on the coils. Then there is no additional cooling action whatsoever, and the vehicle runs hot at low speeds/in traffic. It could fail "on", but when you're moving it won't make a difference.

Based on what everyone has said I doubt I have a bad fan clutch. It does spin easily when cold (just replaced a noisy serpentine belt last week). I'll double check the next time the motor is warm to see if it's firmed up. But since I'm not overheating around town I doubt it's broken.

As for Nova Scotia, I don't have relatives up there. I did visit Cape Breton this year for a week. Drove up from Boston. What a beautiful place. I've been to almost every corner of North America (see http://home.comcast.net/%7Estf351/Alaska/ for a big trip I took a few years back) and I have to say that Capre Breton is one of my favorites. The best bonus were the beaches with 75 degree water. Who knew?! Coming from Mass, where the ocean is DARN COLD I was surprised.

A fan clutch works by shearing a viscous fluid, the drag from which couples force from the driving shaft to the driven hub. The clutch consists of two sections, a fixed drag section that provides a minimum level of torque and a variable drag section controlled by a bimetal thermostatic coil visible from the outside.

Fan clutches will fail when the viscous fluid leaks out(it's like heavy gear oil). Usually you won't notice it because it is not a lot and it spins off of the fan. But once enough of the fluid leaks out, the fan will not spin fast enough it idle to cool the motor, and it will overheat. However, once you get back on the road, the air will cool the motor back to operating temp. You can check the fan clutch for lack of fluid easily - just spin it when the motor is cold and turned off. If it spins around freely, then there is no oil in it and is bad. Imagine spinning something that is immersed in gear oil. When it is cold, it would be hard to spin, but when hot, it would spin easily.

As you should be able to see now, none of this has anything to do with cooling at highway speeds. The fan clutch has nothing to do with highway speeds, except to cause the fan to "slip" and not waste engine horsepower. I have never heard of a fan clutch going bad and spinning with full force all the time, although I suppose that it could happen. However, if it did, I do not think that it would be enough to cool the motor any more than it is already being cooled from the cold air rushing over it from driving.

Hope this helps.

Damn, because almost half the people up there are surnamed Fitzgerald

Because I was curious I just went outside to look at the fan clutch. It's about 40 degrees out and the fan spins about 1/8 of a turn. It certainly feels like there is fluid in there. I also verified that I'm still at the same fluid levels: full rad and overflow bottle is right at the cold mark. I have paper's the write, some finals, and a couple of job interviews so the t-stat probably won't get changed for at least a week, but I'll keep you all informed.

The Wreck of the Edmund Fitzgerald