Fan clutch ?

[Hudsonaj36]

Hi first post here,

I have a 68 gmc c15 that was original a 6 cylinder but at some point has been swapped to a 350 that I think is a 70's Gen 1 with a short water pump. It currently has a flex fan and a shroud but I would like to put a fan with a clutch on it. Right now it doesn't overheat but in turn it fluctuates temp from 150 to 190 depending on what I'm doing. My thought is a fan with a clutch will help stabilize the temp.

So will any fan and clutch do or are they year specific? Or does anybody have a recommendation? I was thinking about running down to pick and pull and yanking one from a 350 but don't want to get the wrong one.

Thanks

[truckster]

I was pretty sure at least the SBC fan clutches were interchangeable, but I just looked up a 72 and an 82 on O'Reilly's website and different numbers came up. I still think they're interchangeable, but now I'm not so sure.

[70LonghornCST]

Hello Hudsonaj36! Welcome to the site!

The fan clutch will be the same for 350 engines from the late 60s and well into the 80s, and maybe up further. I know someone will be along to answer this for sure for you. Your thinking is correct, in that a fan clutch will help regulate the temperature, reduce engine energy, and in turn help to run your vehicle a bit cooler. There are two types of fan clutch: one is a thermal and the other is an automatic. The automatic runs based on the rotation speed of the fan, whereas the thermal is based on the temperature of the engine. I have known many to remove a fan clutch in the summer. I hope this helps.

I'm sure others will be along to continue to try to help you out. Enjoy the site!
-Richard

[Hudsonaj36]

Thanks for the input, I think the thermal is what I'm looking for. How do you tell the difference?

[70LonghornCST]

I'll move this into the Engine and Drivetrain area where it can get more attention. I'll try to locate a picture showing the difference between the two.

[Hudsonaj36]

Oh ok thanks, didn't see that area

[Stocker]

http://www.aa1car.com/library/cooling_fan_clutch.htm

There are two basic types of fan clutches: thermal and non-thermal (also called "torque limiting"). Thermal fan clutches have a temperature-sensitive bimetal coil spring on the front that reacts to temperature changes. When the air coming through the radiator is hot, the spring expands and opens an internal valve that reduces clutch slippage. This causes the fan to spin faster for increased cooling. As the air cools, the spring contracts and closes the valve. This increases the amount of clutch slippage, allowing the fan to slow down and decrease cooling.

I would only use a thermal fan clutch. As posted above, most 350s are probably the same. To make sure, take some measurements (bolt pattern, fan diameter, and distance from mounting plate to center of fan blades) before going to the boneyard. You'll probably need an 18" fan diameter. When mounted, the fan blades should be located about halfway into the end of the fan shroud.

My K20 with factory A/C has a 7-blade fan, which I would recommend, but a 6-blade might do as well. The shaft in the clutch unit should not have any noticeable slop in it. Also, you should be able to rotate the fan by hand, but it should have some resistance, as if it's turning in molasses.

[Hudsonaj36]

Great info thanks, started the evening messing with the fan ended up with the valve covers off to see what kind of heads I have. A little A.D.D. I guess. Ended up being 3998991.

[storm9c1]

Yep, but I would suggest a NEW clutch. Hayden and Imperial make fan clutches. I would install a Heavy Duty thermal clutch. On tow rigs, you can even install a Severe Duty version. All still available in their catalogs (online PDF, if you need the link, let me know). These part numbers can usually be ordered at local parts chains like Advance and AutoZone. I also recommend a 7-blade fan. Fan blades have different pitches. A steeper pitch fan will move more air. Get one from an A/C car or truck to get the steepest pitch. The clutch bolts on separately and GM and Mopar used the same bolt pattern for decades. The way to tell a thermal clutch is that it will have a little 1" bi-metallic coil on the front of the clutch. A non-thermal is pretty flat on the front. Most stock factory applications came with thermal clutches. The non-thermal ones aren't that common in stock form, but were used as replacement clutches as a cheaper alternative.

[rfmaster]

Tom

Would you be kind enough to list part numbers and corresponding applications? I have been running non-clutch setup in my square for years, but warm up can be long on cold mornings.

//RF

[burnin oil]

Swapping the fan might help but odds are that it is the thermostat. Cheaper thermostats more or less just pop open and the temp drops. Then the thermostat closes and temp climbs again. The Stant super stat is a gradual opening tstat that will give you a nice steady coolant temp. My truck has the factory straight fan and the temp is rock solid. I plan to swap to a clutch fan one of these days myself.

[rfmaster]

Well, did a bit of research:

Hayden Automotive 2797 Premium Fan Clutch

Need to find corresponding fan

[storm9c1]

+1 on the Super Stat. They are much better than the lower priced stats. Some Super Stats even already have a hole and check ball installed where I usually drill one myself!

As for the fan clutch, here are some links. You can look up by year/make/model.

Operating guide -- explaining the differences between the clutches:
http://www.haydenauto.com/upload/Hay...TS_6980012.pdf

Imperial Catalog:
http://www.haydenauto.com/upload/Hay...n-clutches.pdf

Hayden Catalog (they used to have a clutch-only catalog, which I have saved somewhere, this is their entire catalog):
http://www.haydenauto.com/upload/Hay...alog_FINAL.pdf

[Hudsonaj36]

I was considering changing the stat as well and will look into the super stat. I think I'm going to get a fan from the junk yard and a new clutch at the parts house.

[rfmaster]

Originally Posted by rfmaster

Well, did a bit of research:

Hayden Automotive 2797 Premium Fan Clutch

Need to find corresponding fan

Super STANT Part # 45358 for my 75 C20 (180F)

[burnin oil]

Did the 195* myself. This motor likes being warmer. The plus is the defroster works alot better.

[Stocker]

Originally Posted by burnin oil

Did the 195* myself. This motor likes being warmer. The plus is the defroster works alot better.

Yep

[Hudsonaj36]

Well a little update, replaced with a 6 blade fan, thermal clutch, and thermostat. Now I am running at a fairly consistent 190. Thanks for the help.

[imjeff]

I like the clutch idea, but your thermostat shouldn't allow your temp to drop to 150.

[Hudsonaj36]

My old thermostat was stuck open so with the cold weather it was dropping the temp. Seems to be all good now.

[imjeff]

Sweet!