Fan question

[03BlkZ]

Hello, my 70 C10 does not have a clutch on the fan. This seems odd to me and that it could be robbing power. The engine does run nice and cool even in 100 degree weather and in traffic but I just wonder if it would be more efficient to install a clutch. Could I just buy a nice aftermarket clutch to install and would it adapt to my current fan or would I need to buy a full assembly. My dad has owned the truck since new and he said it never had a clutch. Thoughts?

[jimijam00]

https://www.youtube.com/watch?v=ZXdLgaFXZzs

[Accelo]

Yes, they rob power. With a clutch it will still rob power, when it's hot out.
I would add it. The clutch addition may possibly quite the cab some?
The fan should be spaced so the center of the fan is at the outside edge of the shroud.

[72SB]

A clutch fan does relieve some load from the engine, especially at cruising speeds

If the new clutch fan is shorter overall than the current spacer, than a shorter spacer the thickness of the difference would be needed so the fan blades remain 1/2 in/out of fan shroud. Spacers are available at the typical sources, Summit, etc.

Hayden is a good brand for clutch fan, They typically come with a bushing that may be needed depending on size of tip of water pump flange. Confirm specs of fan opening and hole spacing when picking the fan clutch

Many went with a 7 blade fan also

[Stocker]

All good info above. Clutch fans seem to have usually been spec'd with factory A/C and / or high-performance engines due at least in part to their superior cooling capability.

My K20 is running a Hayden #2747 heavy-duty fan clutch with the factory 18", 7-blade fan and it stays at normal operating temps even when it's 100+ outside with A/C on.

[03BlkZ]

Originally Posted by jimijam00

https://www.youtube.com/watch?v=ZXdLgaFXZzs

So it looks like I need to look at other fan options. My truck is now a restored mostly original truck and I in no way built it to be an absolute hot rod but I don't want that kind of drag on my engine all the time. Thanks for the video.

[Stocker]

I just now watched the video -- very interesting results!

One more detail which I have posted before.... I once put an aluminum flex fan (temporarily) on my K20. That was the only time it ran hot. Went back to a clutch fan, no problems.

[72SB]

well even though my little 250 6 cyl with its fixed 4 blade and no shroud to speak of (just a small top piece to supposedly keep one's hands out of moving fan) a clutch fan alone using the same 4 blade would likely yield 10 hp gain, maybe more but can't compare to the V* dyno numbers of Engine Master test...which would be the cheapest way of gaining 10hp



otherwise for me even during these 100+ days it does not run any hotter than cooler days

[tim_mc]

I wound up using a Hayden 2705 & 6-blade Derale 17118 (18" rigid fan).

[xr4tic]

Originally Posted by tim_mc

I wound up using a Hayden 2705 & 6-blade Derale 17118 (18" rigid fan).

I did the exact same thing.

With a SBC in the forward position and a long water pump, it puts the fan fully into the stock shroud.

I know they say it should be half in, half out, but that doesn't seem very safe. I have no idea where the stock fan was located, but I don't have any cooling issues.

[Grumpy old man]

Originally Posted by xr4tic

I did the exact same thing.

With a SBC in the forward position and a long water pump, it puts the fan fully into the stock shroud.

I know they say it should be half in, half out, but that doesn't seem very safe. I have no idea where the stock fan was located, but I don't have any cooling issues.

Short water pump with 6 blade fan / Hayden 2705 and A/C shroud the non A/C shroud comes back a little further .

[OregonNed]

For my truck, I bought it with a flex fan (very noisy!) and went with suggestions here for a rigid fan and clutch - worked out great - stays cool even without a shroud., used the Hayden and Derale mentioned above..

[oldgold70c10]

Seems like most manual trans. trucks came from the factory with non-clutch fan, just the automatics had clutch fans.