Mark VIII fan install + 100 amp alt.

[gezn2]

Since I put my '76 K10 on the road I've had problems with the salvaged clutch-fan I wound up installing, after some research I found it was going to run me about $80 for an exact replacement. At this point I started researching junkyard electric fan setups, I figured that if I had to spend money I might as well go for the slightly more gas-saving alternative.
I asked for input here in the 'engine & drivetrain' forum and wound up with a member hooking me up with a Mark VIII, the current Gold Standard of junkyard e-fans, and a controller for a price I couldn't pass up.
Thanks Gerardo!
The fan arrived at the end of last week, I was going to need a bigger alt., the 37 amp unit I scrounged up to get the truck running wasn't going to cut it, the Low speed on a Mark VIII pulls 20+ amps and High pulls 40 amps. No joy on any high-output 10 or 12SI alternators from the local scrapper, but he *did* have an early '70s school bus back in a corner with the 100 amp 'big case' SI and I figured it was worth trying for $20. The stock lower mount works fine, you can stack washers on the mounting bolt or build a spacer, either way if you've got the front face in the stock location the pulley will line up. The issue with the 'big case' SI alternators is that our stock upper bracket will not fit anymore, I stumbled on a 'workaround', with a tiny bit of file-work on the pivot end and some washers a Ford #C8AE-10145-A alternator adjusting arm drops into place and works perfectly!

The Mark VIII fan is the unit used on '93 to '98 models, they all move roughly the same CFM but they did play around with fan speeds and blade pitches trying to quiet them down so there are three different part numbers.
The stock unit measures 22"x18.5"x6.25" but you can trim close to 1" off the front lip of the shroud if needed for clearance, mine had already been trimmed so I had to use some 'ingenuity' to seal it up.
The shroud was *just* tall enough that I could mount it flat against the stock radiator supports and have a roughly 1/2 inch gap between the sides of the shroud and the fins on my 3-row radiator.
Mounting was pretty straightforward, on the bottom I used some heavy 'L' brackets from a farm-sale 'goody box', I believe they are overhead door track hardware, and I fabricated some straps out of sheet metal to hold the top in place, a few coarse threaded screws hold the whole thing in place quite solidly.


I centered the fan on my radiator mostly because it 'looked right', if there had been clearance issues with the water pump there was *plenty* of room to offset it.
The fan came with a Hayden adjustable controller, it's certainly enough to control the fan low-speed only like it's wired right now, I've got something homebrewed and a bit heavier in mind for the High speed later.
After a bit of thought I elected to put the temp sensor on the outlet side of the radiator, my thinking is that way the fan won't run when the radiator is getting enough air-flow on the road, lots of Euro stuff does it this way with the temp-sensor in the outlet tank on the rad. or in the return hose to the water pump.
I finished this Saturday night, it worked well enough running around Sunday but it was quite clear that there was a lot of lost air flow through the gaps I'd left.
Today I scrounged up some tin J-channel, cut it to size for the open gaps at the shroud sides, applied some sticky-foam, and screwed it into place.

With some RTV silicone applied to remaining holes and duct tape covering the clearance notch in the bottom rad. support my fan runtime has been cut by half!
After replacing the dead fan-clutch it's like driving a different truck, it only gets better from here

[Pyrotechnic]

Good way to use utilize some junkyard parts! You can get a rebuilt 12Si for around $70 provided you give them a junk alternator. I gave them a 10Si with a stripped bolt hole....they didn't know the difference.

[BLE 'BURBAN]

Dude all you need is a 94 amp small case alternator that way you're not trying to rig up something out of spare parts that may or maynot work/stay together in the long run.
Here's NAPA's part number and a pic of it for you......
NAPA 94 AMP ALTERNATOR
PART # 13-4352

[gezn2]

Originally Posted by BLE 'BURBAN

Dude all you need is a 94 amp small case alternator that way you're not trying to rig up something out of spare parts that may or maynot work/stay together in the long run.

If I hadn't 'struck gold' at the scrappers I would've kept on driving into town and hit NAPA
Making a $20 oddball *work* appeals to my inner cheap-a$$
Hi-po alternators don't last long in the wild, but the big truck units sit around, nobody wants them because 'they don't fit'.....
I *was* pleasantly surprised at how *perfect* the geometry worked out on that Ford arm so I thought I'd throw it out there for the benefit of my fellow scroungers