I was worried about those two/three years when I posted that.

 

I think I might have a problem with my fan clutch not engaging. I have replaced it twice, both with Motorcraft units, and I NEVER EVER hear it engage. During driving, the temperature usually seems fine; the needle rests right in the middle of the gauge most of the time. Other times, after driving for a while, the needle wants to creep up to the "A" on the "NORMAL" scale. The needle will come back down to the middle of the gauge, sometimes even below the middle of the gauge when I accelerate again. But if I sit at idle in the driveway in park, the needle is always right smack in the middle of the gauge! AND I NEVER HEAR THE FAN CLUTCH ENGAGE.

I don't really understand this. The top radiator hose is hot, the bottom hose is cool, and the coolant in the reservoir bottle isn't expanding as if the engine were getting hot. The center of the radiator where the fan clutch is located isn't all that hot. The engine doesn't seem hot, but at times the gauge says otherwise and I have NOT ONCE heard the fan clutch engage.

What gives? Is there a way I can check the fan clutch to make sure it is working when the engine starts to get hot?

 

On mine I can hear the fan engage in hot weather when the temp gets up to about 195. That's sitting in the driveway idling. But out on the road I never hear it - possibly because it doesn't have to come on due to air flowing through the radiator.

As for checking yours, someone suggested testing the resistance to rotation when it is cold and again after the engine has gotten hot, like up to A on the gauge. Obviously this means you'll have to be quick and not let it cool down after shutting the engine off, but you should feel a big difference.

 

Yes, described in post #7.

If you have a metal fan blade and like to live dangerously you can try to slow the fan using a rolled up newspaper while the engine is hot and running. If you can slow it down the clutch is bad.
Personally I prefer the engine off method.

 

Most of the working clutch fans I have had make a terrible noise when you first start them up in the morning(they are locked). As they start turning, the fluid makes it's way to where it's supposed to be and they unlock after a few seconds. If you don't get this every morning you start it, I would be suspicious it's not working. The GMC van I use at work does this same thing, and is always locked when I start it in the morning.

 

Good point Dave. Mine always engage when I first start with the engine cold.

 

Well if you have a centrifugal fan clutch it will never lock. Only the thermostatic fan clutch locks. You can tell the difference between them as the front of the thermostatic Fan Clutch has a spring, the centrifugal fan clutch doesn't.

Some things to check...

Check for blockages in the fins, etc...

Possible Faulty gauge or wiring, or air pocket in engine.

It's possible that you have a centrifugal clutch, or the thermostatic clutch isn't getting hot enough.

Another trick on testing thermostatic clutches is to take a piece of cardboard and block the radiator for a few moments and let the engine heat up slightly. Just do not overheat your engine doing this...

 

if your gonna go through the trouble to change the fan just go electric. it takes no power from the engine, more powerful, mounts right against the radiator, and in my opinion gives you a cleaner looking engine bay. electric fans will give you the most mpg and hp gain.

 

I have the exact opposite opinion on electric fans. I don't like them, and more trouble than they are worth.

Although it takes no power from the engine directly, you have to upgrade your charging system as the stock system will not have enough to power everything. I don't like the upgrading the charging system 3G upgrades either.

You have to retrofit the electric fans to work in these trucks. Some of these retrofits I've seen are, cut, tape, splice, zip tie, the things to the radiator. To me this looks very shoddy, and the electric fans look very out of place.

Clutch fan only requires four bolts and 10 minutes and you are done. Electric fans require several hours/days of in my opinion, jury rigging. Lot less effort to switch to a fan clutch, than to go electric.

With that said, I really do not like any non-factory equipped modification. If I wanted something with electric fans, modern gadgets, out of place modifications or electronics, I'd buy a brand new truck. So to each their own.

 

After I drive my truck for 20 minutes, the gauge will eventually end up on the "A" in NORMAL. I can turn the truck off and let all the needles go back to zero, start it right back up again, and the temperature needle will come back down to dead center of the gauge between the "R" and "M" within a few seconds and STAY THERE. I can let it sit there and idle for 10 minutes in the driveway, and the temperature stays right there. Yet I NEVER hear the fan clutch turn on!

I can take it for a drive again, and the same thing happens: the temperature wants to creep back up again to "A" and stay there. But if I accelerate from a stop, the needle will come back down to the middle of the gauge or even a bit lower.

When I shut the engine off, the fan continues to "freewheel" for a few seconds. But it does seem a bit stiffer hot rather than when the engine is cold.

I don't hear the fan clutch at all when I first start the vehicle, or when it is running normally. I have replaced the fan clutch TWICE with brand new Motorcraft units, each time with the same result. I can't imagine TWO being bad right out of the box. Are the original Motorcraft units quieter than aftermarket clutches?

I do have the correct thermostatic fan clutch; there is a spring on the front of it. The clutch just bolts to the front of the fan. The clutch attaches to the front of the fan with four bolts, and the fan attaches to the water pump with four bolts. The radiator is a brand new 2-core aluminum radiator. The sending unit has been replaced twice, both with Motorcraft units.

At normal operating temperature, the top radiator hose is pressurized and hot, and the lower one is much cooler, barely even warm. The center of the radiator where the fan clutch is doesn't seem all that hot either.

How do I check for an air pocket, and what can I do to fix it if I have one?

 

I won't try to analyze the condition of your clutch, I've had similar symptoms with different ones myself - 20 year old units doing the expected 'cold start roar' for 30 seconds then quietening; & also new ones never doing so.........but spinning smoothly, & never giving cooling problems either.

I eventually came to the conclusion that different clutches simply had different characteristics.

But when you are experiencing the 'overheating' symptoms you describe, I would use an infra-red thermometer to confirm what is really happening, & where (heads, below thermostat, above thermostat, top hose, bottom hose, etc).
The original gauges are really only any good for a very broad (& varying) indication.

 

X2! In reverse order, you really do need aftermarket gauges - at least a temp gauge. I fought what I thought were heating problems some time ago only to discover that the real problem was the gauge. And, I discovered that with an aftermarket temp gauge.

My fans don't roar right after startup unless it is really hot outside and the truck has been driven and the radiator hot. Then it does roar, but it should do. On the other hand, when the outside temp is hot and the radiator is up to temp the fans don't continue to freewheel for a few seconds when the engine is shut off - they stop pretty quickly. But, that is only in hot weather after everything is up to temp.

My guess is that there is no problem, but that is just a guess. Without good data that is all that can be done - guess. You need a real temp gauge on the truck.

 

Air pocket in the cooling system... Run the engine with the radiator cap off on a cool engine untill the thermostat opens should eliminate any air in the system.

The top radiator hose being hot, and the bottom being cool suggests that the cooling system is operating normally.


I would get a mechanical temperature gauge, place it where the temperature sending unit is located and let the engine warm up. If the temps are within spec, I would replace the temperature sending unit.

I suspect the only problem you have is with the gauge itself, wiring or the sending unit.

 

Does anyone know the parts/numbers/etc to get to eliminate using a fan clutch on and 80-86 ford 300-6 cyl ?
I am satisfied with simple old school stuff.

 

You would need the complete fan assembly and possibly the correct pulley also. That's going to be junkyard items. It may also depend on if you have the thread on type of clutch. If you do, you would need the older style waterpump also. I think I would just get a new clutch.