71VetteLover

After the recent discussion about electric engine cooling fans and after watching the Engine Master's video on mechanical fans and how much horsepower they consume at a high rpm I decided to spend $250 and see if I could squeeze a 17" Derale fan into my '71's big block fan shroud. First of all I had to remove my water pump and idler pulley so I would have enough room to work. The 17" Derale is about 2-9/16" thick and I had to cut 13/16" off the front of it (except for the bottom 10") and bevel the top mounting lugs so they wouldn't hit the 1/2" radius inside the top of my shroud. Then I glued 1-1/4" diameter 3/8" foam rubber pipe insulation (from True Value) to act as a seal and to support the weight of the fan after installing it. I had to cut the bottom two mounting lugs off so it would fit into the shroud and clear the lower cross member (no picture). I drilled and tapped the top mounting lugs for 1/4" NC bolts. After stuffing it into my shroud 1/4" deep I drilled two 1/4" holes in the top of my shroud to fasten the fan. Then I RTV'd a short 2" X 4" onto the bottom of the shroud to act as a stop to prevent the fan from moving foreword. I mounted my two Derale relays next to my left hood latch and got their power from a 6-fuse BUSS fuse block that I had installed several years ago.

I drove it about 10 miles this afternoon and immediately noticed the lack of the ROAR of the 7-blade clutch fan and I noticed the fan never came on until a couple of minutes after I got back home and shut my engine off so it didn't consume any horsepower while I was driving it. I will drive it 60 miles tomorrow morning to run some errands in the valley so I'll get a better understanding of how it'll work when I'm running 50 to 55 mph for an extended period of time. Right now I'm only using a single 210 ON/195 OFF fan control switch but tomorrow I'll add a 200 ON/185 OFF switch and see if it'll turn on at the lower temperature. I may have to go to a cooler 180 degree thermostat to get the most out of this fan. And I'm wondering if I will realize any noticeable increase in my fuel mileage now that I'm not spinning that heavy 9 pound 7-blade clutch fan.

So yes, you CAN install a 17" Derale into a OEM fan shroud.

Frankenvette

My compliments to your work an ingenuity. I installed an electric fan about 16 years ago but did not even attempt to use the stock shroud. Great job!

bazza77

well that doesn't look too bad at all, interesting to see how it goes on a longer trip but really cant see why it wouldn't work .

only thing I can see that might cause a problem is the power cable running close to a drive belt , but you probably already fixed that

71VetteLover

The picture is very deceiving as the wires are actually 3" above the belt. Here's another picture taken from just above my idler pulley and another taken from just above the front corner of my left valve cover. I'm wondering if my fuel mileage will increase enough to notice. The first thing I noticed was the lack of the familiar ROAR of the 7-blade clutch fan when I fast idle it.

71VetteLover

The OEM 7-blade clutch fan weighs a whopping 9 pounds so I would think the lack of it would help my fuel mileage on long trips. The only negative thing about it is I would be in a world of hurt if my alternator ever quit on me. Because of that I carry a good set of tools and all of the parts needed to repair my alternator including the stock 61 amp stator.

cv67

may not come on at hwy spds curious to see what it does in stop and go traffic. you wire in a small LED indicator light to let you know when its on

keep the results coming .

71VetteLover

I took it to the valley this morning and my fan didn't turn on and on the way back I took a shorter but steeper 8% grade and it hit about 212 degrees and it still hadn't turned on. And by the time I got home it was running 230 degrees and my fan STILL hadn't turned on. I shut my engine off, popped my hood, turned the key back on, and after about 10 seconds it FINALLY turned on so maybe the fan control switch is bad or there is a bad connection in one of the two relays. It turned on at 212 degrees yesterday afternoon so I'm wondering why the 28 degree discrepancy today.

And when it finally turned on I don't know if it was running on its low speed or on its high speed. It puked out about a pint of coolant but I had my reservoir grossly overfilled so that was my fault. I'll find out more tomorrow after I get the lower temperature 200 ON/185 OFF fan control switch installed.

71VetteLover

Yeah, I'm going to add two LED lights to tell me when it's on and whether it's on its low speed or its high speed. I would think Radio Shack would stock them. For the fan to run on its high speed it has to already be running on its low speed so two LED's would tell me what's happening.

I just tested the 210 degree ON fan control switch in a pan of boiling water and it tested good and I tested both of the relays and they tested good too so I can't imagine why it didn't turn on today, My ignition switch is almost new so I doubt that could be the problem.

71VetteLover

I just finished re-wiring my two relays to make absolutely sure they have power to them. I ran a 10 gauge wire from my BUSS fuse block to feed them and I ran a new 16 gauge wire to feed the electromagnets in the relays. The 30 amp circuit breaker I'm using is about 50 years old so maybe I need to replace it. I think my local True Value stocks them so I'll pick one up tomorrow.

silver74vette

How accurate is your temp gauge? Are the sensors far apart? Both of the switches being 3% off in different directions or being in different coolant streams can give you these kinds of issues.

I really like the way you did this, looks clean under the hood and you should get a nice even pull across the radiator.

71VetteLover

I just don't know why it failed to turn on even at 230 degrees. It had turned on at the correct 210 degrees the day before AND when I tested the switch in a pan of boiling water yesterday afternoon so it appears it had a bad connection somewhere.

At this moment I'm only using one fan control switch; the 210 ON/195 OFF and if my other 200 ON/185 OFF switch ever arrives I'll install that one too. I ordered it from a vendor 250 miles from me on Saturday of last week and it still hasn't gotten here.

silver74vette

I had an issue once where I used too much Teflon tape on the threads and did not get a good ground signal. Maybe something to check?

I hear your pain on shipping, especially when you are ready to install something. Thanks for posting, unique idea and install.

71VetteLover

It worked the day before but not yesterday. I had used a popular pipe sealer with Teflon so it shouldn't have any problem grounding. It's just the Teflon tape that CAN cause problems. About an hour ago I took it to the True Value in a neighboring town and on the way back I turned my A/C on to force it to build more heat. When I pulled it into my garage the fan kicked on at exactly 210 degrees and within two minutes my gauge was showing 175 degrees. It felt like it was blowing just as much air at idle in DRIVE as my 7-blade clutch fan produced so it may work okay after all.

71VetteLover

I took my fan assembly back out this morning so I could fasten the pulley onto the water pump's flange with grade 8 bolts and shorten the shaft about 1/4" to gain more clearance from the fan's motor. But to my utter disbelief I noticed all of the ends of the studs had made contact with the motor even though they were about 1/4" to 5/16" away. Which would mean my engine is shifting foreword that much or my radiator is shifting backwards that much or a little of both. It's also possible the frame is twisting enough for them to make contact when I drive in and out of my lumpy bumpy property. I also had a 10" section at the bottom of my fan assembly that didn't have any foam rubber sealing so I glued some on. Also I noticed the foam rubber had scooted toward the rear when I installed the fan so I squished RTV between the foam rubber and the housing to hold it in place better. So far I am very satisfied with the outcome and I hope it will perform just as well next August when the temperatures can exceed 110 degrees.

71VetteLover

After installing bolts instead of studs and nuts and after cutting about 3/8" off the water pump's shaft the front of the pulley now has almost 3/4" of clearance to the rear of the motor. I can't imagine my motor mounts ever flexing that much. I am really impressed over how much air this Derale blows because it feels like it's just as much as my OEM 7-blade clutch fan produced at idle. Now hopefully it'll do the job next August when the temperatures here in Modesto reach 110+ degrees.

71VetteLover

My lower temperature 200 ON/185 OFF fan control switch will finally arrive in today's mail after waiting 10 days for it to travel 250 miles. And my 180 degree Robert Shaw thermostats will arrive today too so I can finally finish this job. It's supposed to hit 87 degrees on Wednesday so it'll give me the chance to test my fan in stop-and-go city traffic with my A/C on.

71VetteLover

Crap, I burned up another hood release wire so I had to go to the auto parts store to buy another 5 foot choke cable. My two new fan control switches FINALLY arrived this morning only to discover they're both wrong. One turns on at 170 degrees and the other at 180 degrees and I had ordered two 200 degree switches. And when I went to my rural mailbox this morning my fan failed to turn on again and the temperature went clear to 240 degrees. I turned the key off and back on three times and the fan finally started running so either my fan control switch isn't grounding or the relay isn't energizing when the switch grounds.

As far as the burned hood release wire goes my circuit breaker had to be moved foreword about 1" so the upper hood latch wouldn't touch it (again) and burn the release wire up (again).

71VetteLover

These Derale fans come with very confusing wiring instructions as they can be interpreted in more than one way. It appears they intended for the fan to run on its low speed all the time and THEN go to its high speed when the temperature was high enough to ground the fan control switch.

But I wanted my fan to remain OFF until it was needed so I installed two relays; one for the low speed and one for the high speed and each has its own fan control switch. But the instructions say the high speed can't be run unless the low speed is already running and that's where the problem was. The relays MUST be energized in order; the low speed relay first then the high speed relay.

I have it working perfectly NOW but it took some deep thinking to get it all sorted out. I just need the correct low speed fan control switch and that could take several more days. But in the meantime it works and seems to do a good job of cooling my engine.

71VetteLover

My new 200 ON/185 OFF fan control switches finally arrived this morning and I just finished testing one to see if it's accurate. It is so now I can complete the installation. So far my 17" Derale fan is doing very well as I tested it on an 89 degree afternoon with my A/C on and it did the job. The only issue I have is my alternator won't charge enough at an idle in DRIVE to keep up with it but I can deal with that.

Rather than wiring it like Derale recommended (always on the low speed but switching to its high speed when the temperature got hotter) I wired it so it would remain OFF until it was needed which will dramatically increase the life of the fan motor. Its low speed will turn on when the temperature hits 200 degrees then go to its highest speed when the temperature hits 210 degrees. Which means it'll never run during the cold winter months unless I have to idle it in city traffic for an extended period of time.

71VetteLover

My new 94 amp 12-SI Delco Remy alternator will arrive via UPS tomorrow morning so I'll quickly find out if it'll handle the 24 amp load of my 17" Derale fan and my A/C on high at idle speeds in DRIVE. According to the Delco Remy performance specifications it'll produce a whopping 50 amps at only 1000 engine rpm so I am pretty certain it'll do the job. But if I feel this venture isn't producing reasonably good results I'll just re-install my 7-blade clutch fan and call it another lesson learned the hard way.