Building a custom fan shroud to cool my 454

[jsudar]

First a little back story: I bought a 1995 K3500 four door long bed with a 454 and 4L80E. The previous owner had installed some LT1 Camaro dual electric cooling fans when the mechanical fan clutch went bad. Unfortunately, to get them to fit he trimmed the Camaro fan shroud down too far and it was basically flat against the radiator; the only place air could move through the radiator was through the fans or little around the edges where the shroud didn't cover. I figure I had lost at least 30% of the surface area of my radiator

It worked ok some of the time, if the weather was cool or I was on the freeway, but I had to run the heater full blast to make the drive up to Tibble Fork. The upper fan shroud for the mechanical fan got hacked up to make room for the electric fans and it proved to be quite difficult to find a replacement, so going back to the mechanical fan wasn't going to work. Plus, I had seen posts where guys claimed to get a 2-3 mpg improvement in fuel mileage after switching to electric fans. Since we're talking about 7000 pound truck with a big block, any help with fuel mileage would be welcomed.

An aftermarket drop-in cooling fan setup for this truck was just about $700, so that wasn't an option either.

I had a sheet of .120" aluminum from the hood of an old truggy laying around and it got me thinking. I took some measurements and realized the aluminum was large enough to cover the radiator. I already had the electric fans, so I figured I would take a shot at making my own.

The LT1 fans are twelve inch fans, but I made provisions on the shroud to fit some 14" Flex-a-lite fans if the Camaro fans don't cut it. I kind of like using factory fans because they seem to hold up pretty well.

I attached a couple pictures of the fans before (as they were installed against the radiator) and after I trimmed them to fit my new shroud and a couple of the shroud getting laid out. I will get it bent up tomorrow.

There is a long standing adage in my family that says: Don't stand behind the saw! I was cutting my aluminum to size using my table saw and the blade caught the piece being trimmed off. It sent it across the garage and stuck it through a 7/16" sheet of OSB (see the first two pix). It probably would have gone further through if it hadn't bent. That's why you don't stand behind the saw.

 

[STAG]

Here is a nifty thread on this.

http://www.offroadfabnet.com/forums/showthread.php?t=10186

 

[jeep-N-montero]

If that doesn't work out and you do decide to go back to a factory shroud let someone up this way know, I see mid 90's GM trucks with the 454 quite often in the salvage yards. Make sure your alternator is up to the task of the extra amp draw, I looked into swapping in dual electric fans on my 95 diesel but just the alternator upgrade alone would have taken 3-4 years to break even on the mpg gains with as little as I drive the truck.

 

[jsudar]

So I got the shroud all bent up and the corners welded. I have to give a shout out to Creer Sheet Metal Works in Provo. They did some darn fine work and got it finished very quickly. I will definitely use them again if the need arises.
I worked at the Ford dealer for a number of years and I did a lot of pre-delivery inspections on new vehicles. For some reason, I saved all the rubber door bumpers that came on the trailing edges of the front doors which prevented damage during shipping. These little bumpers fit perfectly on the edge of the shroud to prevent it from sawing a hole in my radiator should the two decide to move independently. I guess being a pack-rat pays off. With the bumpers, the shroud fit so perfectly on the radiator it literally "snapped" into place. I couldn't be happier with the fit.

I fabbed up some steel brackets to hold the whole thing in place. They have speed holes to make sure it looks fast.

I had to mount the fans to the radiator side of the shroud to give me a little extra clearance. It only gave me an additional 5/16", but that made all the difference. It's pretty tight. I have to remove the AC compressor and the idler pulley to get it in there.

I am running a temp switch in the port next the the bypass hose on the water pump. It will kick the fans on at 200° and off at 185° with a 180° thermostat. I hope there isn't too much fudge factor on the temperatures at which these things actually happen. I don't want the thermostat to close every time my fans cycle. I felt like a 160° stat was too cold for winter around here.

 

[morty]

looking good,:thumbs:

I've used creer too, those boys know how to work with metal

 

[dodgezilla]

Yes looking good. Nice write up. Good to see the old truck getting some much needed love from someone with skills.

 

[jsudar]

Now I have a couple questions:
Would it be a good idea to hole saw a couple large holes in the back of the shroud to allow more air to pass through when the fans are not running, i.e. freeway driving? Or would that make the shroud less effective when the fans are on? I'm just thinking that there are 680 square inches of radiator area vs. ~225 square inches of holes in the shroud. It looks like the $700 Perma-Cool shrouds made for this truck have extra holes in them.

This truck is equipped with an auxiliary electric fan on the condenser that runs only with the AC. Should I still wire the main cooling fans into the AC circuit? Running three electric fans at once seems like it might be a good way to fry an alternator. Right now, the main cooling fans only cycle with engine temp and a manual switch.

Anyone's thoughts would be appreciated.

 

[jsudar]

The thermostat I pulled out of it was a 195° unit. I think that was part of my problem. I drilled a couple 3/32" holes in the new 180° unit, just to help bleed the air off and keep things flowing. It will warm up a little slower, but I will live with it. It's not like they're huge holes.

Just driving around the neighborhood and sitting at idle, it seems to like to sit at one tick mark past the center of the temp gauge. I guess that's around 215°. I'd like it to be a little cooler, but the fans are cycling so I think it may be a function of the temp switch as opposed to the fans ability to cool the motor. If I turn them on manually, they will pull the temp down lower. So far so good. I need to drive up a big hill pulling something heavy now.

 

[I Lean]

I wouldn't cut holes in the shroud. I have seen factory setups with them, but they always have a little door to "seal" it off when the fans run. That seems like too much work to have it work properly, so I'd just skip it.