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

[Rick Dobbins]

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.

I'm a retired 30 year Master Mechanic for GM, so I don't do homework. Yes electric fans work fine on modern engines, but they're a marriage of aluminum, plastic, et. Conduct heat very well. And they're a smaller displacement. The BBC is a huge heat sink of cast iron. And I'm towing up a hill in the summer. Like I said, electric fans worked fine around town, but not when stressed to the thermal limit. Plus I didn't find any fans that exceeded 5000CFM. If you live in a flat state, don't tow, and it's cooler than SoCal, electric fans are great. I wished I didn't have to replace them.

 

[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.

To clear up what I'm talking about, here's a pic of a dual fan setup. Mine was just like this pic, and sat ON the radiator (PULLER FAN- couldn't go Pusher cuz the AC condenser was in front of the radiator). Now, see the solid area? THAT'S blocking air flow. With the metal fan, you have 100% flow across ALL the veins. Like I say, the BB is a huge heat sink. Towing in the heat up a hill maxes out your cooling capability, so if I can pick up 20D.s that's the difference between O/Hing or just "running hot". BTW, my first electric fan was a single unit that overheated the engine when the fan assembly broke in half and jammed the fan (unit since discontinued I've noticed). That's why I went to dual fans, which also failed when maxed out. I dropped $600 on electric fans. Spent $150 on metal and thermo clutch.
EXAMPLE:

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[Bextreme04]

I'm a retired 30 year Master Mechanic for GM, so I don't do homework. Yes electric fans work fine on modern engines, but they're a marriage of aluminum, plastic, et. Conduct heat very well. And they're a smaller displacement. The BBC is a huge heat sink of cast iron. And I'm towing up a hill in the summer. Like I said, electric fans worked fine around town, but not when stressed to the thermal limit. Plus I didn't find any fans that exceeded 5000CFM. If you live in a flat state, don't tow, and it's cooler than SoCal, electric fans are great. I wished I didn't have to replace them.

lol, so you are saying you don't know anything about electric fans and didn't do any research on them first either? The fans you posted are about the worst design for your application I can think of. They are for a race car that needs to keep the engine cool while sitting still. Why would you drop $600 on something like that? You can get a set of dual fans from a stock application like a newer ecoboost F-150 or 2006-up chevy that would flow better and not restrict your airflow through the radiator while driving for about $100-150 brand new or $30-45 from a yard.

I'm just going to re-iterate that fan type and CFM are the least important factors in cooling while the vehicle is moving at highway speeds. If you are loaded to the very limit and moving very slow, yeah the fans need to be able to pull a lot of air. But going 65mph up a grade should be shoving plenty of air through the radiator on its own. I think maybe your engine or cooling system is just right on edge of being able to keep up...

What radiator were you running? The factory C30 454 radiators are the biggest and best. The 350/400 w/auto trans and AC had the next biggest 4-core radiators. I'll probably be using the aluminum one from my donor 97 K2500 454 for my truck when I swap. It is the same area as the radiator in my 2011 K1500 Suburban with the 5.3/6L80E but double the thickness. I'm also planning on using dual electric fans(from a 2006-up chevy) controlled by the engine ECM.

Do you have a nice free flowing exhaust? Timing good? Not running too rich/lean? The rest of the cooling system in good shape? Thermostat, cap, pump?

You say that electric fans work well on the modern engines because they "conduct heat very well and have smaller displacements" but that is nonsense. Technically a brass/copper radiator is far more efficient in heat transfer than aluminum or plastic. The fin design on the aluminum radiators is more efficient and allows it to come close to matching the brass radiators in overall efficiency while being significantly lighter and cheaper to produce. The biggest advantage the modern engines have is efficiency and engine management. The ECM has full control of spark and fuel delivery for various engine load conditions and temperatures. The old carbureted engines don't. That inefficiency is expressed as extra heat that needs to get removed from the motor. You can help it by making the combustion process more efficient, but ultimately there is only so much you can do.

 

[bigcountry78]

It’s ALMOST like the engineering that went into building these trucks was the correct way to do things. They built the big blocks with towing and harsh conditions in mind and then built the cooling system to keep it cool. I’m in the camp that says just because a company claims to be reinventing the wheel bigger and better, it’s not always the case. Sometimes, probably most of the time, the OE setup is the best way to go. Yes, they engineer with costs in mind, but they also engineer everything to work together to do the job. Just my 2 cents, well maybe a bit less due to inflation.

 

[fast 99]

Try a Griffin radiator. They are expensive but work. No, the offshore cheap ones are just that, cheap. Just looked on their site the do make one for that application. I have 2 vehicles with them.

Other items like a shroud, proper fan pitch, fan location front to back, no obstructions or aftermarket round grilles. The OEM's use electric fans because they work. Actually, in most cases better than an engine driven fan.

 

[Bextreme04]

It’s ALMOST like the engineering that went into building these trucks was the correct way to do things. They built the big blocks with towing and harsh conditions in mind and then built the cooling system to keep it cool. I’m in the camp that says just because a company claims to be reinventing the wheel bigger and better, it’s not always the case. Sometimes, probably most of the time, the OE setup is the best way to go. Yes, they engineer with costs in mind, but they also engineer everything to work together to do the job. Just my 2 cents, well maybe a bit less due to inflation.

Well, OE on everything after 2006 is dual electric fans. I now have dual OE GM Electric fans mounted on an OE 1997 454/4L80e radiator and the ONLY time they even come on is if I've been sitting still idling for 5-10+ minutes. As soon as I start moving AT ALL they never come on. That includes towing a 6500lb trailer through coastal Oregon mountains. That's with AC on too.

 

[bigcountry78]

Well, OE on everything after 2006 is dual electric fans. I now have dual OE GM Electric fans mounted on an OE 1997 454/4L80e radiator and the ONLY time they even come on is if I've been sitting still idling for 5-10+ minutes. As soon as I start moving AT ALL they never come on. That includes towing a 6500lb trailer through coastal Oregon mountains. That's with AC on too.

That’s true that OE has gone to electric fans, but I’ll stick with my previous statement that they were engineered into the overall system to be as effective as possible. They built it all to work together. Now, take that new technology and adapt it into a 40 year old system that was designed with a different type of equipment in mind and you may or may not get the desired results. That’s what I was getting at.

 

[Bextreme04]

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[Bextreme04]

That’s true that OE has gone to electric fans, but I’ll stick with my previous statement that they were engineered into the overall system to be as effective as possible. They built it all to work together. Now, take that new technology and adapt it into a 40 year old system that was designed with a different type of equipment in mind and you may or may not get the desired results. That’s what I was getting at.

That was exactly my comment to the OP. He didn’t understand the new systems, did no research, and got piss poor results. I have mine jury rigged to work similar to OEM 2006+ for now. They will be controlled by the 0411 ECM when it gets swapped in with the fuel injected 454/4L80 in the next few weeks. Low speed comes on when AC engages and high speed comes on when the engine coolant temp gets over ~205. It pulls the engine temp from 205 down to 185 in about 15 seconds and shuts back off again.

 

[bucket]

That’s true that OE has gone to electric fans, but I’ll stick with my previous statement that they were engineered into the overall system to be as effective as possible. They built it all to work together. Now, take that new technology and adapt it into a 40 year old system that was designed with a different type of equipment in mind and you may or may not get the desired results. That’s what I was getting at.

Imho, factory electric fan setups are leaps and bounds engineered better than the aftermarket ones. So as long as the fans and shroud chosen are correctly sized for the radiator being used, then all the factory engineering will be applied.

Also worth noting, newer vehicles don't have electric fans because a bean counter wanted to save money. Newer vehicles have electric fans for power and efficiency.

And also, the smaller and lighter engine theory that someone mentioned earlier doesn't really apply. A 6.6 Duramax will tax a cooling system just like an old cast iron big block, if not more.

 

[Bextreme04]

Exactly. Back in the day they didn’t have reliable electrical components like they do now. That’s why we have so many grounding issues and power window/lock issues. From an engineering perspective, electric fans are WAY better than mechanical if you can properly control them. The mechanical fan sucks an average of 40 HP depending on the fan and clutch setup. The problem is that really the only time you need the fans to do anything is when the vehicle is going slower than ~30mph. Above that speed you have more air going through the radiator from it moving forward than the fans can actually move on their own. At that point the fans and shroud just need to get out of the way.

Modern motors do lots of things to control heat under high loads like pulling up a grade including pulling timing, richening up the AFR and absolute worst case… running the fans. If you can’t get the thing to stay cool at highways speeds up a grade, you most likely need to increase airflow(get restriction to airflow out of the way) or overall heat dissipation capacity(radiator size).

 

[Matt69olds]

It’s really hard to beat factory engineering. People think they beat up and abuse their trucks, you can bet your last dollar it’s nothing compared to the torture the OEM put their products to during research and development. These trucks didn’t overheat when new, properly maintained they won’t now. If they do, something has changed or been modified or damaged.

Aftermarket electric fans for the most part are junk. The rated CFM is overly optimistic. As someone mentioned, a good indication of capacity is current draw. An electric fan is not going to pull 5000 cfm of air with a current draw of 10 amps!! And if the cooling fan in question is the type that is just stuck on the core with zip strips, forget it!! The fan needs a well fitting shroud to ensure all the air the fan is pulling is actually coming from the other side of the radiator.

The best aftermarket fans are the ones that have shrouds designed to fit the radiator. The absolute best choice would be a OEM fan and radiator combination. As I mentioned, it’s hard to beat the factory design.

The OEM started to use electric fans due to emissions requirements. If they didn’t have to meet such extreme emissions, they would probably still be using mechanical fans. The advantage of electric fans is more precise control. The ORM have to meet demanding cold start emissions, anything that can be done to get the engine warmed up as fast as possible is worth the effort. Electric fans don’t do anything until the PCM commands them on. A thermal fan clutch still spins even disengaged, it still draws airflow thru the radiator, and slows engine warmup ever so slightly.

If the truck overheats driving at highway speed, the fan isn’t the problem. The best fan in the world won’t pull nearly as much air thru the radiator as driving down the highway will. If it heats up at speed, then there is a airflow problem, more specifically the air is going AROUND the radiator instead of thru it.

If you look at a unmolested car or truck, you will see tar paper style shrouds, rubber seals that fill the gaps between the radiator and core support, all designed to make sure all the air entering the grill goes thru the radiator and not around it. How much of that stuff has been damaged or thrown away over the last 50 years of use?

My 81 GMC with the swapped in 455 Olds runs about 190 in the summer. It has a cheap parts store replacement radiator, 7 blade fan from the Olds 98 the engine came from, factory shroud and replacement thermal fan clutch. The truck doesnt have A/C (yet, we far guys don’t like to sweat!!) but it all works pretty well.

As far as mechanical fans robbing power, I say ********. I base this statement on some testing I did a few years ago. I was at the dragsrip with some friends on a test and tune night when the typical bench racing started. I like my cars with the kinda stock looks, even though very little is factory. The aftermarket go fast stuff I have added is either hidden in plain sight, or just not obvious. One of my buddies commented on the factory fan wasting power, I argued that unless the clutch is engaged, the fan isn’t doing much. To test my theory, I made a couple passes with the car as I normally run it, just to establish a baseline. I then removed the fan and clutch, and made a couple more passes. The E.T. was basically the same, the mile per hour did go up ever so slightly. There is zero doubt in my mind thermal fan clutches consume a slight amount of power, but certainly not the 20hp people seem to think they do!! In my opinion, the .04-.05 loss in mph is well worth never having to stress over engine temp. The hottest I have ever seen the Olds get is about 205, this was in bumper to bumper traffic, in 90*heat, with the A/C on.

 

[SirRobyn0]

Imho, factory electric fan setups are leaps and bounds engineered better than the aftermarket ones. So as long as the fans and shroud chosen are correctly sized for the radiator being used, then all the factory engineering will be applied.

Also worth noting, newer vehicles don't have electric fans because a bean counter wanted to save money. Newer vehicles have electric fans for power and efficiency.

And also, the smaller and lighter engine theory that someone mentioned earlier doesn't really apply. A 6.6 Duramax will tax a cooling system just like an old cast iron big block, if not more.

I agree with this. A guy has to drop a darn good bit of money to even get a mediocre aftemarket setup. Look at the CFM air flow of a $200 aftermarket setup vs a factory 5 or 7 blade fan. IMO the only reason new vehicles have gone electric is fuel economy and possibly because they can be better controlled by the computer though Ford did use an electronically coupled mechanical fan at one time, the electronic coupler was controlled by the PCM and took the place of the thermoclutch connected using clockspring style contact set.

 

[AuroraGirl]

It’s really hard to beat factory engineering. People think they beat up and abuse their trucks, you can bet your last dollar it’s nothing compared to the torture the OEM put their products to during research and development. These trucks didn’t overheat when new, properly maintained they won’t now. If they do, something has changed or been modified or damaged.

Aftermarket electric fans for the most part are junk. The rated CFM is overly optimistic. As someone mentioned, a good indication of capacity is current draw. An electric fan is not going to pull 5000 cfm of air with a current draw of 10 amps!! And if the cooling fan in question is the type that is just stuck on the core with zip strips, forget it!! The fan needs a well fitting shroud to ensure all the air the fan is pulling is actually coming from the other side of the radiator.

The best aftermarket fans are the ones that have shrouds designed to fit the radiator. The absolute best choice would be a OEM fan and radiator combination. As I mentioned, it’s hard to beat the factory design.

The OEM started to use electric fans due to emissions requirements. If they didn’t have to meet such extreme emissions, they would probably still be using mechanical fans. The advantage of electric fans is more precise control. The ORM have to meet demanding cold start emissions, anything that can be done to get the engine warmed up as fast as possible is worth the effort. Electric fans don’t do anything until the PCM commands them on. A thermal fan clutch still spins even disengaged, it still draws airflow thru the radiator, and slows engine warmup ever so slightly.

If the truck overheats driving at highway speed, the fan isn’t the problem. The best fan in the world won’t pull nearly as much air thru the radiator as driving down the highway will. If it heats up at speed, then there is a airflow problem, more specifically the air is going AROUND the radiator instead of thru it.

If you look at a unmolested car or truck, you will see tar paper style shrouds, rubber seals that fill the gaps between the radiator and core support, all designed to make sure all the air entering the grill goes thru the radiator and not around it. How much of that stuff has been damaged or thrown away over the last 50 years of use?

My 81 GMC with the swapped in 455 Olds runs about 190 in the summer. It has a cheap parts store replacement radiator, 7 blade fan from the Olds 98 the engine came from, factory shroud and replacement thermal fan clutch. The truck doesnt have A/C (yet, we far guys don’t like to sweat!!) but it all works pretty well.

As far as mechanical fans robbing power, I say ********. I base this statement on some testing I did a few years ago. I was at the dragsrip with some friends on a test and tune night when the typical bench racing started. I like my cars with the kinda stock looks, even though very little is factory. The aftermarket go fast stuff I have added is either hidden in plain sight, or just not obvious. One of my buddies commented on the factory fan wasting power, I argued that unless the clutch is engaged, the fan isn’t doing much. To test my theory, I made a couple passes with the car as I normally run it, just to establish a baseline. I then removed the fan and clutch, and made a couple more passes. The E.T. was basically the same, the mile per hour did go up ever so slightly. There is zero doubt in my mind thermal fan clutches consume a slight amount of power, but certainly not the 20hp people seem to think they do!! In my opinion, the .04-.05 loss in mph is well worth never having to stress over engine temp. The hottest I have ever seen the Olds get is about 205, this was in bumper to bumper traffic, in 90*heat, with the A/C on.

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between these two pics you can see the rubber seal, goes on top of the rad/condenser to seal the area between them(The bottom is sealed by foam and the sides are well sealed too) you can also see the ground, a deflector dam would be there

Then the

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that paper/tar shield thing you said
With a hood seal setup that locks the engine bay from most air flow then through/around it(Also NVH improvement) the air that hits the front of the car is either going through the radiator or its going up away from the car nicely and none of that wasted **** on gaps or OPs poor use of fans

GM factory fan use often had multiple relays, the PCM and ECT having direct discreet control over the grounds on most/if not all, and one being fo the ECT to manually trigger if it got real hot.

my car is 3 relays, low on both, 1 on all, 2 on high. I think. AC of course would also want more airflow esp with newer refrigerants that arent as efficient /low pressure as r12. plus AC wanst all it should have been on some cars based on things like no heat shield/insulations, poor fans(facotry sucks), or degraded performance.

 

[AuroraGirl]

I agree with this. A guy has to drop a darn good bit of money to even get a mediocre aftemarket setup. Look at the CFM air flow of a $200 aftermarket setup vs a factory 5 or 7 blade fan. IMO the only reason new vehicles have gone electric is fuel economy and possibly because they can be better controlled by the computer though Ford did use an electronically coupled mechanical fan at one time, the electronic coupler was controlled by the PCM and took the place of the thermoclutch connected using clockspring style contact set.

so did GM