Radiator cooling fan quandary

Over the weekend I replaced the original cooling fans with two 10" 1760 cfm fans. Everything went as smoothly and they work as expected (changed them to pusher rather than puller). With the old fans I never had an overheating problem as the temp would seldom get above 195 even on 110 degree days ins So Cal. The reason I made the change was to try and get more air flow through the AC evaporator when in traffic. The AC is stock and works great (40 or less degrees) while on the road but is marginal (55 to 60 degrees) around town on very hot days so I figured the problem was not enough air flow through the evaporator via the fan(s).

After completing the fan swap we went to lunch at a local restaurant. Outside temp was 107. I noticed the engine temp was hotter than normal, about 205, and the AC was 55. On the way home in fairly heavy traffic the engine temp got to about 215, hotter than I've ever seen it with both fans working, and the AC temp was 60 but would rise to 65 when idling in traffic.

So my question is . Has any one actually seen the temps decrease with fan "upgrade" as I am not?

My theory is that on my installation the fan shroud is virtually against the ac evaporator and therefore cuts down on the surface area the fans blow through where as the stock fans are a ways from the evaporator and distribute the air flow over a much larger area.

Does anyone know the CFM rating of the stock fans?

I'm considering cutting the van "cage" and "shroud" off so the configuration is more like stock. Image Unavailable, Please Login

I am looking for suggestions as at this point I will probably put the original fans back in.

Thanks

Barry

 

yeah
That's what I think. I just wonder about all the threads with guys doing this with no problems of note. Something else I hadn't considered is the center section of the fan. It also blocks the rad.
Think I'll clean up the original fans and reinstall. Oh Well yet another think where I don't know as much as I think I do.

Thanks
Barry

 

Steve
Yep I reversed the fans per instructions to make them a pushers then checked air flow direction and they are indeed pushing. I, just for grins, reversed polarity on one fan and it did indeed rotate the opposite direction and "pull". I checked all switch configurations, AC only turns on left fan, coolant switch on rad turns on both. I didn't check the blade curvature vs rotation to insure the instructions were correct. I'll do that. Like I said I never had an overheating problem with the stock fans just trying to get more air pushed through the AC evaporator for around town. On the hottest days and I mean really hot (112) it never gets to 200 with the stock fans while it got to 215 yesterday on a 107 degree day.

I reviewed all the threads I could find on this "upgrade" and they all look pretty much like my installation. I seem to remember a thread where a mod was made to the electrics so both fans turned on when the AC is on. I might try that with the stock fans.

Waymar
It doesn't run hot with the original rad and stock fans even though its a 78 and sat for 20 years. The cooling system has been trouble free with the exception of the water pump and expansion tank cap (rad cap) which I replaced. I attribute the lack of rust and corrosion to always running good antifreeze and a overflow tank which always keeps the expansion tank full hence no air so no rust. I had to pull the rear head a while ago to replace the valves (don't ask) and it came right off with little grief which seems to be unusual.

Thorn
Yep fans pushing and blades orientated the correct way. Feels like lots of air flow between rad and spare tire enclosure when I checked with hood up. At this point I am beginning to think the fan assemblies just block to much of the surface of the evaporator and there for radiator. When you look at it there is only about a 10 " diameter by 4 " fan area. I think if I could move the fans forward away from the evaporator they would work better. I may cut the plastic fan cage and shroud off so its more like stock and see what happens.

Thanks All
Barry


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Doug

 

Doug
Sorry about blowing last post. I am actually using the original fan mounting rings. When the picture was taken I hadn't mounted the left fan yet. And you are correct the fans would work better as pullers as it leaves the front of the evaporator with no blockage except the horn but I can't see where there is room for puller fans without substantial modifications (I'm trying not to modify anything that would make it difficult to return to total stock). I do, at this point, think the part of the problem is that the outside ring which is used as the primary mounting fixture for normal installations is virtually flush against the evaporator thereby cutting down the area the fans blow through. The outside ring also increases efficiency by suppressing tip vortices and providing a smooth entry for better air flow which probably isn't doing me any good.

So I just measured the stock 4 blade fans and the diameter of the fan is 11 1/2" as compared to 10 for the new ones. The stock blades are much wider and appear to have more pitch. All else being equal I would think the stock fans would flow more air than the new ones. It doesn't appear there is room to mount larger fans and still use the original mounting rings while keeping the outside fan ring intact as it adds about 1" to the overall diameter. The overall diameter of the 10" fan is a little over 11" so not much room. I really which I had some idea what the CFM of the original fans are.

One of the things people have commented on is how many amps the stock fans pull. I wonder if the heavy amp draw converts to more air flow?

Anyway as I see it my only two practical options are to 1. remove the cage and ring from these fans or 2. reinstall the originals and I'm leaning towards just reinstalling the originals and do the electrical hack that turns both fans on when the AC is on.

 

Kcabpilot
This fan is designed to be a pusher or puller. To change from puller (default) to pusher the blade assembly can be removed and turned upside down. Then all that's necessary is to insure the rotation is correct using polarity. The blades are cupped, however, they don't appear to have as much pitch (angle) as the original. In my original post I asked to hear (kinda) from someone who had actually done this "upgrade" and got acceptable results in verrrrry hot conditions around town. My 308 is great on the open road no matter the .outside temp. It runs about 185 to 190 degrees engine temp (not enough to turn the fans on) and if on the AC puts out 40 degree or less air with AC fan on high and all vents open. If I turn it the fan to low the temp drops to about 35 degrees (less air velocity over ac condenser lets air get colder) but is for all intents and purposes useless in hot weather due to low fan volume.

 

Thorn
I bought some generic fans on ebay rated at 1760 cfm. Yes I found you thread very helpful. I used 1" home depot angle brackets and of all things deck drains for the hub which are almost the same diameter as the originals. All the stock foam seals are in place for the hood to radiator and hood to spare tire compartment. Mine is a 78 carb car without the extra vent on the hood.

If I may ask how much space between the fan outside ring and the ac evaporator? My fans are flush against the evaporator.

Thanks
Barry

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Doug
Yep. As I only use the center portion of the fan for mounting I could clip the guards / cage and remove the entire thing including the ring leaving only the hub similar to the stock configuration. I may try that.

Anyone know the gap between the stock fans and the AC evaporator? I could reinstall mine and measure it but someone probably already knows.

Barry

 

Thorn
Sorry I thought the condenser was inside the car. Anyway the fans are flush with the condenser. Never been much of an AC pro. Just replace and recharge.

Does it get really hot where you live? If so how much difference did you see in engine temp and interior AC air temp? We have been experiencing 100 + degrees for what seems like forever.

 

Thorn
Thanks. I was just wondering. I have all the equipment to vacuum / recharge the AC. I'm going to check it in the morning.

 

Yeah, the extreme heat in So Cal's San Fernando valley is really tough. Had the car out for lunch a couple of days ago. Sat in the sun with the windows cracked for 2 hours. Was 125 degrees inside when we got in. Makes it very tough on 40 + year old AC which is anemic anyway by today's standards. I think the tops only been off once all summer.