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DIY Fan Clutch mod

mfgguru

mfgguru

Makin' it better!
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Location
Winkler, MB, Canada
A while back I read a post by gmctd about how to adjust the kick-on temp of the stock fan clutch.

Quote:Remove the RTV glob from the slot - pull the angled section of the bi-metal strip outta the slot, gently straighten the angle, bending to conform to the rest of the coil, leaving a very small lip that will fit in the slot - re-RTV the stip (strip tip) in the slot, let cure, and voila!!!!!! - yer clutch now engages at lower temps............. By: GMCTD

I had to do a big(to me it's big) tow this weekend, hauling an 8x10 shed on a 30ft goose neck flat deck about 100 miles. Previously while towing my camper, the temps would come up just over 100 deg cel. and then go back down. Didn't want to spend the money on a new clutch just yet I though what is there to lose? I spun the fan assembly off and pulled out the RTV, gently straightened the tab out and made a new tab about 3/16 further down the BI METAL strip. I re RTVed it in place and put it back on. WHAT A DIFFERENCE! My truck, pulling the shed, the big wind sail it is(stupid thing pulled really hard), was WOT in 3rd to get 60 mph for 1.5 hours and the temp never went past 95 C. Boost was at 10-12 and fuel pressure at 2.5 PSI with an after market carter LP. I am thouroughly impressed. I would have Defueled for sure without that mod. I plan to make a little less agressive adjustment next time, for it came on a bit early, but the results are undeniably fantastic.

Will take pics when I make next adjustment.

PS, from what I have described, how much difference would a reflash make?
 
Last edited by a moderator:
Great info. I'll modifiy mine too and report info. So you recommend maybe pulling it out 1/8th inch?

What temps did it kick on at? Shut off ok?
 
That is the thing, it kicked on at about 90 C and was on almost constant, so I would go 1/8", should be good. It would shut of, but only for a very short time.
 
1000x better than running too hot. Is it easy to make 2nd and 3rd adjustments, or is each adjustment made that much closer to it breaking?
 
Matt Bachand said:
1000x better than running too hot. Is it easy to make 2nd and 3rd adjustments, or is each adjustment made that much closer to it breaking?
Click to expand...

I would think bending it more than once in the same spot would increase risk of breakage, I would think that 3/16 is a bit much, 1/8 or slightly less should be perfect.
 
So what your saying is you pulled the tab out of the slot, bent it in the direction of the coil, then rebent the tab 3/16" beyond where the original tab was? Great idea, I was wondering if something could be done like this.

Steve
 
Good job Mike

I read GMTD's post awhile back and it's on my to do list as well

Leo
 
Photos please! Great idea. I just got home from a hot mountain drive. Running too hot. I've got to bleed the air outta that upper hose.
 
Good input - been doing that trick since the viscous clutches began showing up back in the '60's - I'm firmly not a believer in electric primary fans, butcept in auxiliary configuration as a helper - which I got some uv on my truck...............
 
gmctd said:
Good input - been doing that trick since the viscous clutches began showing up back in the '60's - I'm firmly not a believer in electric primary fans, butcept in auxiliary configuration as a helper - which I got some uv on my truck...............
Click to expand...

How much do you usually pull out?
 
Different oem's spec different bimetal and strip width and length so it depends on the clutch - fortunately, AC Delco designs have plenty of extra length so I tuned as required, which was usually for a really big engine in a really small chassis with little real estate for a radiator to match - that was B4 I got into turbo-charged Diesels which need big fans with big radiators in big chassis' - start with halfway, see whatcha got to keep ECT within your desired range

Back then, the slots were peened or crimped or epoxied, somewhat more difficult - took finesse and a slow hand
 
i need this too....just got back from draggin' my Gator(Gator and trailer about 3800#) 800 miles this weekend with the burb and cleaned rad and cond. put in brand new A/C delco 195f T-stat before i left....temp was just below 210f with a/c on....runnin' 75mph never heard the fan kick in!!!

pic's please!!!
 
Me too, family full, lots of gear, big climbs, AC cranked, and temps higher than I liked. I would hear the fan kicking on, but it was too late at that point.

I had to back outta the power, turn off the AC, and coast over the tops of the hills.
 
The fan is for low air speeds

Guys, I'm hearing too many talk about fan clutches to help the cooling at 60-75 mph. At freeway speeds your fan clutch shouldn't need to be doing squat. If you're having cooling problems at that speed you're not transfering heat well enough. Throw in some Red Line Water Wetter, bleed the air out of the top hose, clean the rats nest from between the rads, or something. My Kennedy clutch kicks in (KICKS in) when I'm going slow; that is with little or no air speed. Once I get some air speed I can feel and hear it unload. On the freeway it's freewheeling even with my trailer on and the ECT (scangauge) stays in the 190s. It was in the 90s here on Saturday and I never saw over 200* with the trailer on.

Mike
 
My Kennedy clutch kicks in (KICKS in) when I'm going slow; that is with little or no air speed. Once I get some air speed I can feel and hear it unload.
Click to expand...

High speed is no problem, but at city driving it hardly ever (15-20%) disengages.
 
Tookie said:
Ditto - if all you ran was interstate, you wouldn't need a fan at all
Click to expand...

Unless you have a 9' x 3' square piece of Steel hangin in front of the radiator with a nice arch designed to re-direct whatever comes in contact to it away from the truck. Including, but not limited to, SNOW, AIR, RAIN, WATER, PEOPLE, FORDS, CAT's DOG's and everything else that is not bigger than me.

As mentioned above, on highway ONLY My temps also climb up to 210ish and I have to back out of the momentum and RPM's to allow my fan to engage. Brand new OEM replacement from Dealer. If I don't back outta it, when will it engage? Not sure, won't find out.

BUT, If i can tweak this spring a little bit to have it kick on at 200ish or 205 or even 209 I'll be happy.



Back on track. How does this coil inside work? Does it snap instant engage, or the hotter it is, the more engagement?
 
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