Fan clutch not working when cold?

[The motor guy]

Occasionally I've noticed the ac quits blowing cold if it sits and idles for 5 minutes or so. I left the house this morning, then went around the block and came back becaise I forgot to add oil and wanted to check the transmission fluid. Coincidendly I noticed the ac started blowing hot and that the fan wasnt spinning all that fast. Pretty sire the truck was warmed up at that point. Not sure what was up. Shouldn't it still work on a cold truck? I dont think their is anything electronic about these fan clutches. Its not good for the ac at all. Came home today and it was spinning plenty fast.

 

[The motor guy]

Vehicle in question is a 1999 dodge ram 2500 diesel

 

[clinebarger]

I would start with making sure the entire cooling stack is clean......
*24V/VP44 trucks have the crankcase vent in the front & oil vapor will cause a build up of dust on the radiator core
*Condensers tend to get beat up on these.

 

[The motor guy]

I would start with making sure the entire cooling stack is clean......
*24V/VP44 trucks have the crankcase vent in the front & oil vapor will cause a build up of dust on the radiator core
*Condensers tend to get beat up on these.

Does not explain why the fan wasnt working good this morning though. I'll check and make sure the condenser is clean though. This truck leaks like a sive. My 07 dodge cummins does not leak.

 

[clinebarger]

The fan clutch needs to sense the heat coming off the condenser. If you're not working this truck....You could have a pretty good airflow restriction & not know it based off engine coolant temps.

 

[The motor guy]

The fan clutch needs to sense the heat coming off the condenser. If you're not working this truck....You could have a pretty good airflow restriction & not know it based off engine coolant temps.

Makes sense

 

[The_Jeff]

Every fan clutch I've ever had locks up when cold (i.e "works great") then loosens up and works normally when warm.

 

[FowVay]

Every fan clutch I've ever had locks up when cold (i.e "works great") then loosens up and works normally when warm.

That's how the ones that I've had worked. They'd make a hugh whirring sound when you'd rev the engine cold. The fan was almost a direct drive to the input pulley. As the oil in the coupler warmed the fan speed would slow and eventually the incoming air across the clutch fins would regulate the fan speed. Vehicles mentioned were my 1980 280ZX Nissan/Datsun and my 1999 BMW 3-series.

My current Nissan Frontier uses a viscous coupled fan clutch but it's much less noisey than the older vehicles. I believe a failing fan clutch will have very little resistance when cold. You can spin the fan around when the engine is not running and feel the drag on the coupling.

 

[The motor guy]

That's how the ones that I've had worked. They'd make a hugh whirring sound when you'd rev the engine cold. The fan was almost a direct drive to the input pulley. As the oil in the coupler warmed the fan speed would slow and eventually the incoming air across the clutch fins would regulate the fan speed. Vehicles mentioned were my 1980 280ZX Nissan/Datsun and my 1999 BMW 3-series.

My current Nissan Frontier uses a viscous coupled fan clutch but it's much less noisey than the older vehicles. I believe a failing fan clutch will have very little resistance when cold. You can spin the fan around when the engine is not running and feel the drag on the coupling.

I forgot about that trick. I think constantly shutting off the engine wears them out imo

 

[kschachn]

Every fan clutch I've ever had locks up when cold (i.e "works great") then loosens up and works normally when warm.

And then can fail completely locked up, hot or cold. My old BMW had a test for the clutch which involved using a rolled-up newspaper.

FWIW, the difference in cost for a new one is typically due to the fluid being used in the coupling. Cheaper ones will use a silicone or hydrocarbon fluid whereas the more expensive ones use a perfluorocarbon or fluorosilicone fluid.

 

[The motor guy]

Now it blows like the wind when you first start it, then it rappers down once the engine warms up....I dont get it. Maybe its intermittently working and I just don't know it.

 

[Sumboodie]

Every fan clutch I've ever had locks up when cold (i.e "works great") then loosens up and works normally when warm.

They normally spin easy when cold and get harder when warm.

Should spin easy when cold and can easily stop the fan when the engine is running. (don't recommend doing, but just saying). Least that's the case on the similar year Dodge and Ford diesels sitting in my yard right now.

 

[The motor guy]

They normally spin easy when cold and get harder when warm.

Should spin easy when cold and can easily stop the fan when the engine is running. (don't recommend doing, but just saying). Least that's the case on the similar year Dodge and Ford diesels sitting in my yard right now.

What do you mean spin easy? Mine does not spin by maybe 1/4 turn spinning it with the engine off. I thought that was good. A bad fan clutch spins easily by hand

 

[Sumboodie]

What do you mean spin easy? Mine does not spin by maybe 1/4 turn spinning it with the engine off. I thought that was good. A bad fan clutch spins easily by hand

Not much resistance when cold and it locks up as it gets hot. Best way to test that the clutch is ok is check that the fan doesn't spin easy after going for a drive on a warm day.

 

[The motor guy]

Not much resistance when cold and it locks up as it gets hot. Best way to test that the clutch is ok is check that the fan doesn't spin easy after going for a drive on a warm day.

So what does that mean when the engine runs? I guess i need to check again when hot and cold to see what's its doing.

 

[Sumboodie]

So what does that mean when the engine runs? I guess i need to check again when hot and cold to see what's its doing.

The fan is near freewheel when the engine is cold and the clutch locks up more as the air on the clutch warms up (IE engine warms up).

Here, way easier than me fingering all the letters on my phone to write it out...

 

[The motor guy]

The fan is near freewheel when the engine is cold and the clutch locks up more as the air on the clutch warms up (IE engine warms up).

Here, way easier than me fingering all the letters on my phone to write it out...

Thats the opposite that mine is doing.

 

[Chris142]

A fan clutch should still move enough air when cool to keep ac working. If it's not it's bad.

 

[The motor guy]

A fan clutch should still move enough air when cool to keep ac working. If it's not it's bad.

Thats what my 07 dodge does when it fails. The electric part of the viscous fan quits working. This 99 is 100 percent viscous. Ive just been shutting off the ac if I stop for anymore than a few minutes. The ac can still cool just fine with the head pressure through the roof and youre thinking everything is still honky dory. I learned that lesson the expensive way

 

[kschachn]

Now it blows like the wind when you first start it, then it rappers down once the engine warms up....I dont get it. Maybe its intermittently working and I just don't know it.

That’s how the one on my BMW behaved. When it was cold the fluid was viscous, but it quickly shear heated as it warmed up. When you turned the fan by hand it moved, sure, but at higher RPM it turned the fan at engine speed. It literally took less than a minute for the fluid to warm up and the roaring stopped. I never gave it another thought.

When it was broken broken it roared all the time.