Stumped on fan clutch operations

boogie_man · December 07, 2019, 01:28 PM

Had my radiator start leaking at lower tank. Pulled-re-cored did thermostat, belts hoses factory water pump and changed the fan clutch too (factory GM). Upon buttoning everything up, I noticed the fan clutch wasn't engaging "howling" when motor up to temp or when revved. The motor at idle you can see the fan is barely turning/free spinning. Pull GM fan clutch and went with a aftermarket one. Fired it up and it howls when it's cold but as it warms up it stops engaging causing it to heat up to 3/4 as the fan just free spins. Stumped here.. 86 P30 454 gas

Rickf1985 · December 07, 2019, 04:35 PM

That is how a thermostatic fan clutch is supposed to work. At first start the viscous oil is stiff and needs to circulate and loosen up. This is the engaged fan you hear at first and then it drops out. It will not reengage unless the radiator gets too hot and the sensor coil on the front of the clutch senses the heat and then it will engage. Traveling down the road at 60 mph you are ramming a lot of air through that radiator so the fan is not needed but f you start climbing a steep hill with your foot mashed down you will hear it kick in, big time! If you are sitting at idle in the summer for a long time you will hear it going in and out. It will only stay engaged as long as it takes for cooler air to hit the fan.

boogie_man · December 08, 2019, 03:48 PM

thanks for the reply Rick. Understand how it works as I'm trying to pass it thru smog and at idle the temp gauge is going past 1/2 to 3/4s hot as we're concerned with it overheating when it needs to run at 2500 rpms during it's test. The shroud is off of it to make sure it's all buttoned up with no leaks but as it gets over 1/2 to 3/4 hot the fan clutch isn't kicking back on to cool and you can see when you rev the engine the fan spins/coasts barelt spinning and won'tre-engage which is strange as we've installed a factory GM clutch then a A/M clutch with same result. Hmmmm

Froggy1936 · December 08, 2019, 04:16 PM

N:( The shroud is very important for proper cooling ! And 3/4 May not be too high Get a infrared temperature checker, to see what is really going on , An inaccurate gauge Is a very possible thing ! Frank

tmsnyder · December 09, 2019, 08:38 AM

Sounds like it's working perfect.

There's three parts to this.

The first part is getting the heat out of the engine _as_needed_, and the thermostat controls that. The thermostat is trying to maintain the engine temp at its set point. A 195f thermostat is pretty standard. Below that, it's closed. Blocking coolant from leaving the engine brings the engine up to temperature quickly from a cold start. Above 195f, it starts to open and passes hot coolant to the radiator to be cooled. By doing that, it allows the same volume of cold coolant from the radiator into the engine to bring the temperature down. Meanwhile the water pump is recirculating the coolant through the heads and the engine, round and round in a loop. Some of it gets pushed to the radiator as the thermostat opens. The higher the coolant temperature is at the thermostat, the more the thermostat opens until it's wide open allowing the maximum coolant flow to the radiator.

The second part is getting rid of the heat at the radiator. It's a water to air heat exchanger. As the temperature in the radiator increases above ambient air temperature, that DeltaT is the driver for heat to transfer from the metal surface of the radiator to the air, heating it while it cools the metal, which cools the coolant. Air is a lousy heat sink, it can't absorb much heat without its temperature rising to equal the temperature of the radiator, so it takes a lot of air movement to remove the heat created by the engine.

This brings up the third part, the fan equipped with a thermostatic clutch. The clutch is soaked in air that has been heated by the radiator. If the air is hot, it causes the clutch to engage the fan. This pulls air through the radiator, increasing the heat transfer rate from the coolant to the air. It should sound like a small airplane trying to take off under your doghouse. It will also make this sound when you first start up, it takes a little while to loosen up for some reason. Once the air soaking the clutch is cooler than its setpoint, it will start to release the fan. It may seem almost like an on/off type of control, where the fan is either running full blast or seemingly not at all.

If you have to run this for some period of time in order to pass emissions, you should see the thermostat bring the temperature up to operating range fairly quickly (5-10 minutes) and then you may start to hear the fan engage and disengage , cycling to dump off the excess heat from the radiator. If you hear that happening then everything is working properly.

Another way to test this is take it out and drive up a long grade with it. You should see the temperature go up a little, but not overheat, and you should hear the fan cycling.

Good luck with your emissions test

Rickf1985 · December 09, 2019, 10:29 AM

The fan shroud is very, VERY important because without it the fan will be pulling air from the sides at the back of the radiator more than through the radiator. You need to get the shroud back together. Proper placement of a shroud is to have the blades halfway exposed from the shroud. Something else to consider is the fact that the higher the difference in between the ambient temp and the heat of the radiator the faster it transfers heat out of the coolant. Kind of hard to explain but at 200 degrees it will take longer to cool at 50 MPH wind trough the radiator than it will at 240 degrees. Factory dash gauges are total garbage, you cannot believe them at all. Mine barely comes off of the bottom of the scale but when I check the thermostat housing with a temp gun it is at 195. The best thing you can do is to put in aftermarket gauges for oil pressure and engine temperature. You can get modern digital gauges nowadays that are very accurate and visible.

boogie_man · December 09, 2019, 03:15 PM

"If you have to run this for some period of time in order to pass emissions, you should see the thermostat bring the temperature up to operating range fairly quickly (5-10 minutes) and then you may start to hear the fan engage and disengage , cycling to dump off the excess heat from the radiator. If you hear that happening then everything is working properly"

This is exactly what it's NOT doing as the temp climbs the fan loosely spins/coasts and doesn't spin with the motor. Going to put the shroud on it to seal the cooling system correctly and update this post with the outcome.

Guys. As always, thanks so much for the input and help you're the best

Rickf1985 · December 09, 2019, 04:21 PM

The fan will not engage until after the thermostat opens and the temp of the coolant reaches probably 200 degrees. I put a super heavy duty one in mine and it is always engaging as soon as the stat opens, what a pain and you can feel the power drop as it engages too. Mileage went to crap. Unless it is boiling over or a temp gun on the radiator shows over 200 don't worry about the freewheeling, that is what it is supposed to be doing. If you really want it to roar all the time and give you 3 MPG get a centrifugal clutch fan. I can assure you that you will be changing it out very quickly.

tmsnyder · December 10, 2019, 08:05 AM

The operating temperature on the factory gauge is just what you said, half to 3/4 on the scale. If it's in the highest quarter it's a bit hot, and if it's pegged you're probably blowing steam through the radiator cap, overheating. It will get pretty high on the factory gauge before the fan even engages. Like Rick said, the factory gauges are terrible.

Just idling in a parking lot, the engine is doing zero work, so very little heat is produced compared to pulling the rig up a mountainside. So that fan isn't going to run much just idling, even at a high idle. Not enough heat to kick it on.

They do this to save gas.

Fix the shroud and try it out.

ClydesdaleKevin · December 10, 2019, 06:17 PM

You can also consider adding aftermarket electric fans that go in front of the radiator. On our old Holiday Rambler Imperial, 1989 with a 454, it came stock with two electric fans in front of the radiator...in addition to the big engine driven fan with a fan clutch. We ran that thing to well north of 130K miles, never overheated...and would probably still be driving it if the transmission didn't fail catastrophically when the drive shaft exploded last winter.

Kev

boogie_man · January 03, 2020, 04:51 PM

*** Update*** installed fan shroud, checked for leaks and all is working as it should be !! Woot !! Thanks so much for the input and help, this board rocks !

Took to smog yesterday as it failed on the idle portion as it was too rich. It is a rebuilt Rochester that has worked and passed smog no problem in the past. Not sure I want to fiddle with the adjustment screws on this carb as I hear they can be temperamental as I might just make an appointment to a smog and repair station to get it to pass. Again thanks for your help guys.

Froggy1936 · January 03, 2020, 08:47 PM

Yep they can be temperamental, But you should be able to check for any hose vacuum leaks, With a carburetor cleaner spraying on any suspected hoses ( Have a fire extinguisher very handy

) Also check that the choke is operating correctly (opening all the way ) Make sure air filter is clean. These are things you can do. As far as working on the carbh best to see someone who knows them ! Frank

Rickf1985 · January 04, 2020, 09:31 AM

With changes in gasoline formulations it is common to have to adjust for emissions. All you need is the tool for adjusting the idle screws although getting to them is a lesson in contortion and pain. And if the tool slips out of your hand it will spring back into the fan. THAT will get your attention real quick!!!

D:oH!

udidwht · May 01, 2022, 11:56 PM

Quote from: tmsnyder on December 10, 2019, 08:05 AM
The operating temperature on the factory gauge is just what you said, half to 3/4 on the scale. If it's in the highest quarter it's a bit hot, and if it's pegged you're probably blowing steam through the radiator cap, overheating. It will get pretty high on the factory gauge before the fan even engages. Like Rick said, the factory gauges are terrible.

Just idling in a parking lot, the engine is doing zero work, so very little heat is produced compared to pulling the rig up a mountainside. So that fan isn't going to run much just idling, even at a high idle. Not enough heat to kick it on.

They do this to save gas.

Fix the shroud and try it out.

Pretty much what I see on my dash gauge in my 94 Southwind Storm 454 TBI. When I first start up (cold engine) I'll briefly hear the clutch fan engaged. But within 30 seconds it subsides to where your hear no fan. When climbing a grade say 4+ percent grade the dash gauge will be at the 3/4 gray area before the full roar sound. Then the temp is held steady at 230-240. One thing that will kick in the clutch fan sooner during grade pull...pull foot off accelerator briefly then reapply. The heat soak moment will kick in the clutch fan quicker.

With this era RV it's rarely 3rd gear during a grade climb (4+ percent). You'll be in 2nd more than likely or even 1st given the overall grade percentage and distance of it. Move to the right lane and enjoy the view. Keep the rpms at roughly 2000rpm or so. That equates to generally 20-30 mph.

Another way to verify good flow thru the radiator is at first start (cold engine) quickly go to the front of the RV. What is the auxiliary fan doing? Is it freewheeling? If it is, that is a good sign of no obstruction/s between it and the radiator front-side (clean flow). On mine I can finger stop the aux. fan and when I let go it will start freewheeling again. Continue to watch it and as the engine warms and the silicone fluid in the clutch fan thins the aux fan will slow then no longer freewheel. At this point the aux fan will be off until either the AC pressure reaches a certain point or the coolant gets to approximately 221F. Then the aux fan cycles on.

Quote...

"Just idling in a parking lot, the engine is doing zero work, so very little heat is produced compared to pulling the rig up a mountainside. So that fan isn't going to run much just idling, even at a high idle. Not enough heat to kick it on."

An exception/s to this would be 'waste heat'. After a highway run and/or grade pull the temp will rise due to waste heat. Especially with the 454. The dash gauge will reflect that

udidwht · June 05, 2022, 07:22 AM

Quote from: Froggy1936 on January 03, 2020, 08:47 PM
Yep they can be temperamental, But you should be able to check for any hose vacuum leaks, With a carburetor cleaner spraying on any suspected hoses ( Have a fire extinguisher very handy ) Also check that the choke is operating correctly (opening all the way ) Make sure air filter is clean. These are things you can do. As far as working on the carbh best to see someone who knows them ! Frank

TBI has no functioning choke mechanism on the body. If it is running rich it is very likely the cooling temp sensor that needs replacing. I'd also replace the O2 sensor.

eXodus · June 05, 2022, 03:55 PM

I've improved under-hood aerodynamic. Put in a piece of foam board insulation from the underside of the maintenance hatch - across over to the top of the radiator.
Prevents air from going up and above the radiator and directs it better into the radiator.

Now the fan clutch hardly kicks in at all.

Thinking about channeling that even better -maybe two boards on both sides of the rad.