Funky Fan Clutch

[BuffaloGuy]

Here's something to think about.

I've got a '93 with the '97 cooling mods and a Heath (I think) upgraded fan clutch. My radiator is pretty clean inside and out.

Saturday I was hauling a bull in a trailer (total weight of load 6000lbs) and it was 75F out. After getting loaded and back to pavement I just put 'er to the floor to see if I could get it hot.

It took awhile but after about 5 miles at 80 mph the coolant temp started climbing and when I had to pull out of it it was about 220F and still climbing. The fan clutch never kicked in until I let my foot off it and the truck slowed down. Then the fan kicked in and pulled the temp right down.

This happens all the time. If I run over about 70 mph the fan clutch doesn't like to kick in. The heat must be at the radiator since it kicks in as soon as I slow down.

My theory is at high speeds I am not getting the proper wind flow through the radiator. With an 80 mph wind you'd think that would push the heat through but it's not.

The next time I pull a load like this I am going to plug the 2 holes in the bumper that feed air to the radiator with an old feed sack or something. Perhaps at high speeds the wind coming in these 2 holes creates enough of an updraft ACROSS the radiator that it blocks the wind from going straight thru and hence keep the fan clutch from getting the heat.

Anyone else have given this any thought?
Ken

[JohnC]

The fan clutch is activated by the temperature of the air coming off the radiator and is only indirectly related to the water temperature. At 80 mph the air may be going through fast enough it doesn't get up to the right temp. At slower speeds less air flows and that that does gets hotter.

Another possibility is that at the higher speed the engine speed tends to overcome the lockup of the clutch.

Don't plug up the holes in the bumper. They're there for a reason.

[CareyWeber]

I have had fan clutch engagement issues too with my 180

[ucdavis]

How are the fins on your AC condenser? If they're clean but all bent over, you may not be getting enough air thru and fan only kicking in when coolant gets too hot & transfers enough heat to the too little air flow. Maybe space between condenser & radiator is plugged; condenser & rad can look fine but this space can be filled retarding airflow. I just unbolted my condenser to check & its got too much accumulation for comfort while both exposed surfaces looked great.
Or it could be a collapsing hose- temp guage reads @ crossover or @ block, so a collapsed hose would retard coolant flow, therefore heat flow to clutch.
Could be bad clutch- try spinning fan by hand w/engine off, it should be real stubborn.

[CareyWeber]

I also clean the bugs/junk out of my radiator/AC condenser and oil coolers annually.

[Journeydog]

Hay Buffalo Guy...(I really like that name...sounds like a new Kevin Costner film)...I had to go find a pic of an early year p/u to see where the holes in the bumper are since I have a motorhome...which needs all the holes it can get. Without any knowledge of what your under hood looks like, here's a thought for you. Does your setup have an air dam or a big plastic plate or baffle or whatever under those holes to keep incoming air from being sucked under the engine and around through the fender wells? If it doesn't, the faster you go the more likely that the airflow under the chassis is creating a vacuum and pulling the air away from the radiator. I know my m/h does not have such a baffle, but it will soon. Just a thot...

-Al

[Journeydog]

Hay Buffalo Guy...(I really like that name...sounds like a new Kevin Costner film)...I had to go find a pic of an early year p/u to see where the holes in the bumper are since I have a motorhome...which needs all the holes it can get. Without any knowledge of what your under hood looks like, here's a thought for you. Does your setup have an air dam or a big plastic plate or baffle or whatever under those holes to keep incoming air from being sucked under the engine and around through the fender wells? If it doesn't, the faster you go the more likely that the airflow under the chassis is creating a vacuum and pulling the air away from the radiator. I know my m/h does not have such a baffle, but it will soon. Just a thot...

-Al

[Journeydog]

Sorry about the double post...turns out all you have to do is hit the browser's back button and off you go again...got nothing to do with cooling tho...

[BuffaloGuy]

Thanks for all the response. Since the fan kicks in very nicely at slower speeds I can be sure that the heat is there (no collapsed hoses or stuck thermostats etc.) and the flow thru is fine (no plugged radiators or bent fins, I checked too). If a 60 mph head wind pushes the heat thru and engages the clutch shouldn't an 80 mph wind do so better?

A couple of your thoughts seem to be possible explainations. I leaning toward the air flow issues from under the chassis and maybe the clutch not having the strength to engage in an 80 mph headwind.

For a couple of weeks I was missing the rubber flap that plugs the space between the fender well and the top ball joint. I really noticed the fan clutch didn't engage so well then. In particular, I was on the Interstate hauling a load with a cross wind and it just wouldn't kick in. Then, after I turned off and the cross wind became a head wind the clutch worked fine (at lower speeds).

Thinking back to the old 195f fan I had the same problems with it. Of course, it wouldn't want to engage until later. The new 180f fan is better since, when it works, it does engage much sooner.

Perhaps at 80 mph the wind is coming under the bumper and creating a positive pressure area between the motor and the radiator. This is easy to test. I'll just block off these areas with some rubber and watch my coolant gauge like a hawk.

A concern is that this area is possibly designed as the outlet for the air from the radiator. By blocking them off I am forcing the air over the motor and out by the firewall, which may be not as it was designed. I have a remote temp. sensor that I can put under the hood and do a before and after test.

What a pain in the neck. An air dam would be an easy solution (as one of you all said) but I'm scared the off road use would wipe it out. Does anybody make an air dam for these trucks?

Of course, another easy solution would be not to drive 80. But being as I live in the land of the wind where days of 30 mph + winds are common and if luck makes it a head wind then I'm driving 50! Of course, when it's a tail wind it works great.

Anybody know what the designed exit path for heated radiator air is?
Ken

[Kennedy]

There's too many forces at play here to really give accurate speculation, BUT it is possible that increase in the flow rate of air through the rad is causeing the resultant airtemp to be insufficient to engage the clutch.

There is also a potential radial "flinging" of the air that could put the coil in a vortex of sorts...

Then there is the idea that the air is just stalling in front of the rad, and cannot get through so It goes around.


Additionally, unless it is my clutch or I am missing something, you will have a 190

[BuffaloGuy]

Thanks John,

No, the fan is the upgraded 180f from Heath (I looked it up). Not yours but still a good outfit I believe. Actually, I had the same problem with my factory fan just at higher temps.

I've heard the radial vortex idea bandied about before. I guess how that would work (or not work actually) is that an column of air right in front of the thermocoupler is kinda stuck in a little tornado at higher rpms. The air in this vortex is "old" air that was put there before the radiator got hot and is still cool so it won't activate the fan. Then when the rpms or maybe the road speed changes the vortex breaks up and allows the hot air to reach the center. I've never really thought that one thru till just now. Sounds like a stretch but who knows. Sometimes the hardest mysteries are solved by the simplest of ideas.

Seems that any easy test/solution would be to add a fin of some type to the radiator right between the radiator and the fan clutch about as long as the thermocouple and its' housing. Make it just a simple vertical or horizontal fin, firmly attached to the radiator, that comes as close as is safe to the thremocouple on the fan. This should destroy any vortex in this area.

This I will do. I like it. Simple and cheap and, if we're right, a good solution.

Sorry for the rambling. I guess I was "typing out loud" (AKA thinking out loud)!

I'll give an update later.
Ken

[Marty Lau]

Ken;

Just my own not so humble opinion but I think your are DRIVING WAY TOO FAST TOWING!!!!!!
65-70mph is plenty fast so what if it takes 15-20 minutes longer on a trip.
1. You burn less fuel
2. Your safer to yourself and the poor unsuspecting fools who might be in your way if you have a couple of blow outs and lose control at 80mph plus.
3. Your truck runs the way you want.
4. Your truck is telling you SLOW DOWN!!!!!

again just my IMNSHO the view expressed are my own and do not repersent the view of the DP or any of it's sponsors given that it does make sense.

[autocrosser]

The clutch on the fan won't lock up as soon as you reach 220 deg. I take a little bit for the hot air off the radiator to heat the clutch up. I have seen that several times even when my 96 was new. I didn't like the engagement temperature so I tweaked the spring a little to move lock up down to around 200. I can't get it over that temp even with a 8500lb trailer going up serious mountains in NC. I just wish it had a little more power but the big exhaust and upping the boost helped a lot. Exhaust temps never seem to climb above 950 deg

[AJ650]

65 is too slow to tow with my truck, it's an absolute dog at that speed and heats up on every hill and sucks fuel like crazy. at 75-80 it pulls strong and stays cool. I've yet to hear my fan engage at any speed, so I believe the clutch is not working correctly. Anyone know of an electric clutch that you can lock on demand?

[BuffaloGuy]

Yeah, 80 is pretty fast in some places but in others it's normal. Like no one on the road and a big hill coming makes 80 just about right. We are 40+ miles between towns and lots of wide open spaces. Not like back east. Normally I run about 65 loaded because I get better mileage.

The real problem is that if I'm bucking a head wind I have the same problem as 80mph on a still day. Somethings not right and it bugs me. With a 30 mph headwind on a 100 degree day I have trouble doing 60! (not for power but for heat problems because the fan won't kick in)

As for the fellow who said he never hears his fan kick in - somethings wrong. They really move some air and make some noise when they kick in. Pulling a load, especially up hills, these motors get hot and need that fan. I'd get a new fan clutch from one of the outfits here on the DP. They are pretty cheap for the benefit you get. I have read about some guys usinga Duramax setup of some sort and really liking it.

The more I think about the vortex idea the more I think that may be the whole problem. Seems like when I pull the mountain passes in lower gears but higher rpms (like 3000) I think I was having the same problems.

It really maybe an RPM issue instead of a headwind/wrong pressure issue. The times I had problems bucking a 30 mph wind on 100F days I think I was in 4th gear instead of overdrive and that would put the rpms back up to about 2800-3000.

Hmmm. Maybe the higher rpms can create a sufficiently strong vortex to inhibit the thermocouple on the fan clutch. Maybe wind speed/road speed has nothing (or very little) to do with it. I will construct a simple fin, mount it to the radiator to break any possible vortex and report back.

Later.
Ken

[rustypig]

The DMAX fan is a no-brainer. If you've got a 97+ fan clutch it will bolt right on. You may have to trim the fan shroud a bit (1/8" to 1/2"). It's lighter than steel blades (composite material), nine blades vs six, and really seems to pull air much better. I like the fact that it seems to pull more air at slow speed or idle even when the fan clutch isn't fully engaged. Just my .02

[Dimsdale]

Here is a link to an article on an electronically controlled viscous fan clutch that GM is going to begin installing on some cars and trucks.

http://www.atra-gears.com/gears/2002-10/2002_10_64.pdf

Maybe we will get lucky and they could be retrofitted onto our Diesels!

[Kennedy]

Originally posted by The Buffalo Guy:
Thanks John,

No, the fan is the upgraded 180f from Heath (I looked it up). Not yours but still a good outfit I believe. Actually, I had the same problem with my factory fan just at higher temps.

Ken

Interesting. Considering that Hayden isn't making these clutches and Borg Warner is, I'd be curious to know if it really is 180

[Kennedy]

Originally posted by rustypig:
The DMAX fan is a no-brainer. If you've got a 97+ fan clutch it will bolt right on. You may have to trim the fan shroud a bit (1/8" to 1/2"). It's lighter than steel blades (composite material), nine blades vs six, and really seems to pull air much better. I like the fact that it seems to pull more air at slow speed or idle even when the fan clutch isn't fully engaged. Just my .02

Here's what the expert had to say reference 20 9 wing steel vs. 21" Dmax :

There is no clear winner across the board.
With proper fan tip clearance to the shroud (.75" is normal for GM) the
15992650 is probably a little better at idle and low vehicle speeds, and
the 15010202 is probably marginally better at speeds with more ram air.
But, remember our previous discussions. It is a mortal sin to put an
alternative fan on a fan drive after initial development. A fan drive is
developed for a specific fan, and if a different fan is introduced a new fan
drive should be developed. The fan drive that BorgWarner released for you
was developed for a 15992650 fan.
The C/K Diesel fan drive is not appropriate for the GMT800 (15010202) fan.
The GMT800 Diesel fan drive is not appropriate for the C/K (15992650) fan.


Bear in mind that the test data he referenced had the 21" Dmax blade swinging at a full 21" diameter and not trimmed down...

[BuffaloGuy]

Originally posted by Dimsdale:
Here is a link to an article on an electronically controlled viscous fan clutch that GM is going to begin installing on some cars and trucks.

http://www.atra-gears.com/gears/2002-10/2002_10_64.pdf

Maybe we will get lucky and they could be retrofitted onto our Diesels!

Hey dimsdale. When they get the bugs worked out of that I'd try it. I suspect it will be a couple of years yet and then since mine is a '93 and I don't have a computer to run most things it may not work after all.

Maybe the "vortex breaker" (sounds kinda silly) will do it. Gonna be a while since I don't have any heavy pulling planned right now.

And John, I'll be checking out what you wrote.
Ken