The Stovebolt Site Forums The Shop Area Engine Shop Thermostatically controlled fan

Hi Bolters,
I have a six blade, 18-inch fan on my 3800. Trust me, it's necessary. It keeps the engine cool but it's noisy, it uses extra fuel and takes significant power to run. I've tried electric fans but the 16-inch pushers don't move enough air. At one point I had two, a 16-inch pusher and a 10-inch puller and it still overheated on a long, hot pull and cooked the diodes in the alternator. Think 7-mile Cabbage Hill east of Pendelton OR on a hundred degree evening, foot to the floor, lights on, flashers going, 35MPH.

So for now I live with the downsides of a big fan but I would like to devise a fan clutch such as is used on big trucks so that the fan runs only when needed. I researched viscous-drive fans and the only one I could come up with that might have worked was listed for Jaguar sixes and didn't swing a big enough fan. I thought of adapting an A/C compressor clutch but the water pump still needs to turn all the time. On bigger Ford trucks of the era, like an F8 I once had, the fan is driven separately from the water pump. That would have made it easy but GM? No.

I'd love to hear any ideas you all might have.

Sounds like you need to address your stock cooling system, clean out radiator, clean rust out of block, make sure t'stat is functional, can use 4# radiator cap, install overflow tank- Dodge has some vertical ones that fit old trucks well, make sure engine timing is correct. Back flush radiator with garden hose to get bugs and seeds out. Can use cab heater when necessary. Puller fans are more efficient.

Good luck.

Ed

I agree with Ed, you have some sort of cooling system problem that needs addressed. A bigger fan isn't going to fix the problem.
Another thing you might look at, since I see you're running a '55 engine, is the water pump relocation plate. It moves the pump up to the stock location for the original 216, which also centers the fan in the radiator. If you have already done this, or have the early '55 high water pump engine, then disregard.

x3...I agree, you have issues.

Mike B

If you overheat above 35 mph the problem isn't not enough air (although a pusher fan does block the radiator very efficiently).
The most efficient fan is the largest diameter that fits, turning at the lowest speed.

I think you guys missed the point. It doesn't overheat now. It's just that the mechanical fan is noisy and uses power and fuel full time and I want a de-clutching fan so it doesn't run all the time.

I know of no such "de-clutching fan". Go as suggested with an electric fan AND a good shroud that covers the whole radiator. Then put it on a thermo switch.
BTW, I understand a pusher and puller fan don't work well together. They say a vortex is created between the fans which kills air flow.

Your initial post is misleading. The way it is worded, it sounds as if you do have an overheating problem.
I do know of some electric fan clutches that will disengage the fan when not needed, but none that can be easily adapted to a older engine.

Have you considered a high quality flex fan? They are designed to flex at higher RPM, reducing blade angle and reducing drag on the engine, while providing maximum blade angle/higher volume at lower RPM.
Carl

I have used flexi-fans in the past and while they pull lots of air at low speed they don't pull enough at around 2800 which is where I pull the engine. Plus, I have to flatten the pitch to clear the harmonic balancer and the A/C compressor pully. One of those I bought on the road was a reverse pitch and was mis-boxed. I didn't notice it, which created quite an adventure until I got back to the FLAPS to exchange it.

You are seemingly talking in circles about whether you are, or are not having a cooling problem.

He's NOT having a cooling problem he's just looking for ideas on a different way of operating the cooling fan. That's how I read it anyway. Sometimes I think we read too much into some of these posts, me included. Sorry I don't have any thoughts on how to do it.

If you indeed need more airflow at 2800 RPM than what a flex fan provides, then will you be satisfied with the reduced airflow of a fan clutch at 2800 RPM?
Carl

Extra airflow is a Band-Aid fix for a radiator that's too small for the job.
Jerry

I don't need more airflow. I just need to be able to shut off the fan when it's not needed.

You need air flow from a fan at slow speeds, and also at "2800 RPM" (your words). So under what conditions do you not need the fan at full flow?

52Carl and all,

I appreciate your interest but I'm beginning to suspect that my situation is a bit unusual as I'm working the truck harder than maybe GM intended. It's set up as a long-haul highway truck with an overdrive. Please read on.

I don't need high airflow, let's say, at highway speeds on flat ground or rolling terrain. Or in winter -- most of the time.

I've run just an electric fan at times and found that it only goes on midway up a long grade or at city speeds (the fan switch goes on at 210F, off at 190). It's in summer on long grades when loaded that the electric isn't enough.

So here's an example -- Every December we leave Seattle loaded with the 11 ft. camper (3600 lbs.) and it's 35 deg. We're headed for LA. There's lots of flat, flat, ground for 300 or so miles till you get south of Eugene OR. Don't need a fan at all. Then you hit the mountains of southern Oregon. As long as it's cold you still don't need much of a fan. Then you hit the Siskyous (serious 7% climb for miles). Still no problem in winter. But then after hundreds of miles of flat through the California Central Valley, and you're pretty tired of listening to the fan, you Hit "THE GRAPEVINE" just north of the LA basin. It's rarely cold enough that you don't need some serious airflow. It was in the 70s last winter when we went over. One year I stopped at the RV park 50 miles north of the Grapevine and put on the mechanical fan I had brought with me. I can do it in half a hour but it's a hassle I can do without, especially when you want to be through LA before 2PM. This is not an unusual problem all over the mountainous West.

Makes sense now Tommy. Easiest fix for you would be sound deadening cab insulation, and maybe a radio.
I have always been skeptical of electric-only fans (without any mechanical fan). I understand that many newer vehicles are set up that way, but they are not Stovebolt engines. So I lean toward keeping the original style fan and live with the noise.
Carl

why not install a toggle switch then you can control when you need it

joker, not to speak for the OP, but he has a noisy mechanical fan now which is keeping everything cool right now. He has tried electric fans in the past and they didn't keep it cool under load during hot weather. He wants to add something to disconnect/slow down his mechanical fan to save gas mileage and make it quieter.
I think that's where we are at, anyway.
Carl

You can get a thermostatically controlled viscous fan, they spin along using a viscous drive ,when the air flow through the rad gets hotter a thermostatically controlled valve allows more viscous liquid into clutch drive and the fan drives faster. As the air flow cools down the valve opens and declutches the fan . Kind of works like a torque converter drive.it does this automatically no electric controls. I had this kind of fan in my ford pickup.

I have looked into the viscous-drive fan option but have not found one that will fit between the radiator and the fan pulley. Perhaps someone knows of a "low profile" unit that I could adapt. Lately, I'm at a disadvantage as my FLAPS closed up the store near me. They had old parts books that had things listed by dimension rather than strictly by application. Big loss to me.

I think that would be neat if you could find a viscous-driven fan that would fit. I was measuring my '40 with a 235 and looks like I could do 2 12" puller electric fans fit diagonally so the outer blades are in front of the water pump. Then could have them come on at different temps even. Lot of hassle though. But I agree the 5 and 6 blade fans do get noisy at higher rpm but they do cool nicely.

Dennis