Big Block Cooling w/Electric Fans: DON'T DO IT

[Rick Dobbins]

MY STORY: Took out the 350 SBC 4/sp in my '77 GMC C25 and rebuilt a 454 BBC/TH400 from a '74 identical donor truck headed for the boneyard and put it in. I installed "The Best" Dual Fan/Dual Relay set up cuz I also installed the Vintage Air System (which I love). Ran like a raped ape, and couldn't wait to make a trip from SoCal to Utah to ride the Piute Trail System with my Buddies.

PROBLEM: I never made it up the Halloran Grade outside Baker.

For those of you who have driven to Vegas from SoCal, you know this is a brutal grade for trucks. Add 100+ D. temps, and you're going to really test your gear. The thing about electric fans is: your engine will get to fan switch temp no matter what the ambient temp is, cuz the fans won't come on until you reach the thermo switch that grounds the fan relay and activates the fans. That was fine driving around town, or tooling down the hiway when it's 75d. and flat.

Not hauling a camper and towing a 10' trailer with a Rzr on it, which I did. Now, I thought long and hard why my 5000CFM fans didn't perform, and came up with the answer: THE FAN SHROUD BLOCKS 30% OF MY RADIATOR!!!

The elec fans mount to a shroud, and if you look at one you'll see how the air ONLY goes thru the holes for the blades! That leaves the radiator BLOCKED for the portion covered by the shroud! Pissed me off.

FIX: Old technology my friend! What came on the truck in 1977: big fat 7-blade METAL fan w/thermo clutch.

ANOTHER PROBLEM: You cannot buy that fan anywhere! Even Dorman is sold out! So I went on eBay and bought a 7 blade off a '72 454 Chevelle, and put a new clutch on. Thankfully I kept the old shroud, but not the fan. But I'm sure the SBC fan was 6 blade anyway.

THE AFTERMATH: New/old fan blows like a $10 hooker, and my temps ALWAYS run cooler cuz air is going past the rad fins ALL THE TIME. I haven't gone up Halloran yet, but there are a couple hills here on the 15 that are steep, and I've run up them with NO PROBLEM! Temp climbs yes, but never gets close to the red like the old setup did.

Hope this helps anyone tempted to put electric fans on. BTW, ya I know there are elect fans now with no shroud, but I'm done with them. They pulled 40 amps on mine, which always taxed that old alternator technology. I put the hottest alt I could find on, and when the fans are on, voltage drops below 13.3 volts and it won't 'excite' my isolator to send voltage to my camper, and I always wondered why I'd arrive at the campground with a low camper battery. Go figure. Now, all the juice can go to the batteries when I'm cruising in the daytime.

 

[mcarlo86]

Interesting post. I have been contemplating a different radiator and electric fans for my '78 P30 motorhome with a 454 to see if I can get it to cool better. Maybe I will just get the radiator rodded out or re-cored and keep the original fan/clutch setup.

 

[Turbo4whl]

This is very much like what I did years ago, in my '82 when I replaced the 305 with a '71 402 BB. Used the original SB radiator but needed to remove the shroud to clear the BB accessories. Replaced that with a 6 cylinder top fan guard/radiator bracket.

I used the original '71 thermal 7 blade fan with a different spacer to locate the fan the correct distance from the radiator. Never had any overheating problems, even pulling my trailer.

 

[Frankenchevy]

I always figured if I went with e-fans I’d make a shroud to replicate the factory one that stands off the back surface of the rad, fits tight around the edge, but with cutouts for dual fans rather than a large one in the center for the clutch fan. The nice thing about aftermarket efi is being able to trigger one or both fans whenever you want.

Three questions for you:

1. what make and model of fans did you get?

2. what amp and brand alternator?

3. did you notice the engine revved more readily with the e fan setup?

 

[SirRobyn0]

MY STORY: Took out the 350 SBC 4/sp in my '77 GMC C25 and rebuilt a 454 BBC/TH400 from a '74 identical donor truck headed for the boneyard and put it in. I installed "The Best" Dual Fan/Dual Relay set up cuz I also installed the Vintage Air System (which I love). Ran like a raped ape, and couldn't wait to make a trip from SoCal to Utah to ride the Piute Trail System with my Buddies.

PROBLEM: I never made it up the Halloran Grade outside Baker.

For those of you who have driven to Vegas from SoCal, you know this is a brutal grade for trucks. Add 100+ D. temps, and you're going to really test your gear. The thing about electric fans is: your engine will get to fan switch temp no matter what the ambient temp is, cuz the fans won't come on until you reach the thermo switch that grounds the fan relay and activates the fans. That was fine driving around town, or tooling down the hiway when it's 75d. and flat.

Not hauling a camper and towing a 10' trailer with a Rzr on it, which I did. Now, I thought long and hard why my 5000CFM fans didn't perform, and came up with the answer: THE FAN SHROUD BLOCKS 30% OF MY RADIATOR!!!

The elec fans mount to a shroud, and if you look at one you'll see how the air ONLY goes thru the holes for the blades! That leaves the radiator BLOCKED for the portion covered by the shroud! Pissed me off.

FIX: Old technology my friend! What came on the truck in 1977: big fat 7-blade METAL fan w/thermo clutch.

ANOTHER PROBLEM: You cannot buy that fan anywhere! Even Dorman is sold out! So I went on eBay and bought a 7 blade off a '72 454 Chevelle, and put a new clutch on. Thankfully I kept the old shroud, but not the fan. But I'm sure the SBC fan was 6 blade anyway.

THE AFTERMATH: New/old fan blows like a $10 hooker, and my temps ALWAYS run cooler cuz air is going past the rad fins ALL THE TIME. I haven't gone up Halloran yet, but there are a couple hills here on the 15 that are steep, and I've run up them with NO PROBLEM! Temp climbs yes, but never gets close to the red like the old setup did.

Hope this helps anyone tempted to put electric fans on. BTW, ya I know there are elect fans now with no shroud, but I'm done with them. They pulled 40 amps on mine, which always taxed that old alternator technology. I put the hottest alt I could find on, and when the fans are on, voltage drops below 13.3 volts and it won't 'excite' my isolator to send voltage to my camper, and I always wondered why I'd arrive at the campground with a low camper battery. Go figure. Now, all the juice can go to the batteries when I'm cruising in the daytime.

This is not the first time I've heard stories similar to this one. The only concern I'd have with the Chevelle fan is if it has the pitch on the blade as the truck fan, which it may very well, but it's something to keep in mind. Another thing that I think sucks about electric fans is most of them draw so much your putting quite a strain on the older lower out put alternators, so folks end up grading the alternator, and then if your going to do that they go with a serp belt to drive the thing. A person can spend a lot of money doing electric fans.

"blows like a $10 hooker", sounds like something I'd say, so I got to say at that price point the hooker must be a street walker or a lot lizard at a truck stop lol.

 

[Shorty81]

When the big block first went in I had a 3 core radiator and clutch fan. The clutch was a little worn. So I extended the fan deeper into the shroud and went with direct drive fan. Ran cucumber cool. Then one day under some rpms one of the blades fractured and took out the radiator and tried to exit through the hood. ARRGH.....nasty!!

 

[shiftpro]

Don't rely on the listed CFM a fan pulls... better to look at the amps they draw. And SPAL imo is the only way to go as far as fan manufacturer.

 

[bucket]

So really, the problem seems to be with the particular shroud design, rather than the electric fans themselves.

 

[Vbb199]

Interesting.

While I've put no load on my 502 ci yet, I'm just running a 4 core rad, no shroud, and just a 5 blade flex fan, and she runs at 208° with an oil cooler
(Temps dropped from 220 to 208 with cooler)

Was wanting to move to electric fans and see if I could bring the temp down to 190.

 

[Poppy 87]

Interesting.

While I've put no load on my 502 ci yet, I'm just running a 4 core rad, no shroud, and just a 5 blade flex fan, and she runs at 208° with an oil cooler
(Temps dropped from 220 to 208 with cooler)

Was wanting to move to electric fans and see if I could bring the temp down to 190.

Just adding the shroud should get the result you are looking for

 

[SquareRoot]

MY STORY: Took out the 350 SBC 4/sp in my '77 GMC C25 and rebuilt a 454 BBC/TH400 from a '74 identical donor truck headed for the boneyard and put it in. I installed "The Best" Dual Fan/Dual Relay set up cuz I also installed the Vintage Air System (which I love). Ran like a raped ape, and couldn't wait to make a trip from SoCal to Utah to ride the Piute Trail System with my Buddies.

PROBLEM: I never made it up the Halloran Grade outside Baker.

For those of you who have driven to Vegas from SoCal, you know this is a brutal grade for trucks. Add 100+ D. temps, and you're going to really test your gear. The thing about electric fans is: your engine will get to fan switch temp no matter what the ambient temp is, cuz the fans won't come on until you reach the thermo switch that grounds the fan relay and activates the fans. That was fine driving around town, or tooling down the hiway when it's 75d. and flat.

Not hauling a camper and towing a 10' trailer with a Rzr on it, which I did. Now, I thought long and hard why my 5000CFM fans didn't perform, and came up with the answer: THE FAN SHROUD BLOCKS 30% OF MY RADIATOR!!!

The elec fans mount to a shroud, and if you look at one you'll see how the air ONLY goes thru the holes for the blades! That leaves the radiator BLOCKED for the portion covered by the shroud! Pissed me off.

FIX: Old technology my friend! What came on the truck in 1977: big fat 7-blade METAL fan w/thermo clutch.

ANOTHER PROBLEM: You cannot buy that fan anywhere! Even Dorman is sold out! So I went on eBay and bought a 7 blade off a '72 454 Chevelle, and put a new clutch on. Thankfully I kept the old shroud, but not the fan. But I'm sure the SBC fan was 6 blade anyway.

THE AFTERMATH: New/old fan blows like a $10 hooker, and my temps ALWAYS run cooler cuz air is going past the rad fins ALL THE TIME. I haven't gone up Halloran yet, but there are a couple hills here on the 15 that are steep, and I've run up them with NO PROBLEM! Temp climbs yes, but never gets close to the red like the old setup did.

Hope this helps anyone tempted to put electric fans on. BTW, ya I know there are elect fans now with no shroud, but I'm done with them. They pulled 40 amps on mine, which always taxed that old alternator technology. I put the hottest alt I could find on, and when the fans are on, voltage drops below 13.3 volts and it won't 'excite' my isolator to send voltage to my camper, and I always wondered why I'd arrive at the campground with a low camper battery. Go figure. Now, all the juice can go to the batteries when I'm cruising in the daytime.

Obviously you did NOT install the "best" electric fans as you claim.

Do the fans say SPAL on them? You get what you pay for. Of course, anyone can put SPAL fans on a cheesy homemade shroud and peddle it on fleabay.

You just didn't do your homework. Setup properly, electric fans perform as well as mechanical all day long. That's why 99% of new vehicles use them.

 

[Vbb199]

Just adding the shroud should get the result you are looking for

Find me a bbc shroud and I will

 

[SquareRoot]

Interesting.

While I've put no load on my 502 ci yet, I'm just running a 4 core rad, no shroud, and just a 5 blade flex fan, and she runs at 208° with an oil cooler
(Temps dropped from 220 to 208 with cooler)

Was wanting to move to electric fans and see if I could bring the temp down to 190.

Flex fans should be outlawed. Have you not watched that episode on Engine Masters?

 

[Vbb199]

Flex fans should be outlawed. Have you not watched that episode on Engine Masters?

No sir, I have not followed along with the latest TV series of self proclaimed engineer Masters haha

Ask anyone, they've built the world

 

[Vbb199]

BUT I will say, I wanna get rid if the flex fan, and totally skip that gimmicky clutch fan ****, and run electric fans.