I grew up in the generation of plastic fantastic vehicles like the NBS 2nd Generation Chevy Tahoe. Despite their low quality interiors, they hold a certain nostalgia so I took on the project to restore a 2001 Z71 Chevy Tahoe, one of my dream trucks as a kid. I’ve had somewhat of an attachment to keeping the original mechanical clutch fan. However, after my about millionth tank of gas I’m growing less attached and have the impression mechanical fans may improve my MPGs by a touch. Thus I’m taking on the project to upgrade my coolant fans from mechanical to electric. If you’re looking to do the same you’ve come to the right place!
First my build philosophy
My goal with the truck build was to improve on factory reliability, efficiency, and power. To maintain as purely mechanical and or simple of solutions as I could find. Specifically none of the displacement on demand, variable valve timing, or active fuel management stuff newer vehicles have which can be prone to failure.
I’d intended to keep a mechanical clutch. I love the simplicity of the design. They are also designed to reduce drag on the motor by decoupling the fan from the shaft on the water pump. This is accomplished through a fluid clutch where as temperature increases a fluid presses against a clutch transferring toque to the fan. It’s quite elegant and I love that part about mechanical fans.
Unfortunately though, it’s hard to beat the efficiency and performance of mechanical fans. After several years of low gas mileage (12 to 13 MPG), I’ve set out to upgrade the fans.
Severe Duty Fan Clutch
A couple years back I discovered my factory original fan clutch was no good. With around 250,000 miles on the truck it was certainly overdue for a new clutch. If you are going to keep your mechanical fans you may like to consider a severe duty fan clutch. This engages the fan more often.
I’d also took a large hit in gas mileage. Went from 14 to 15 MPG city and 17 or better highway to 12 to 13 MPG across the board. Now, part of that was due to issues in fuel system another part to plugged cats. However, moving to a severe duty fan clutch certainly didn’t help gas mileage.
I’d thought about reverting to a standard duty clutch. They’re not expensive. It maybe worth doing just to test. However, I’d rather spend the dollars at this point to upgrade to electric which surprisingly doesn’t seem that expensive.
Electric Water Pump
I think this would be too far to take my build but is worth mentioning. Years ago I installed a Meziere electric water pump on my 1994 Z28 Camaro. It was worth every cent. However, they were substantially less expensive. I was able to install the pump on the factory housing. I haven’t seen anything like that for the 3rd Gen small block Chevy though.
This would be a good upgrade if you were say highway only. I go off road. I can tolerate even fix a leaky pump or snapped belt on the trail but not a shorted or broken electric pump. I’d need a backup system if I had an electric setup to swap on.
That aside, electric pumps are AWESOME. You can keep the pump running for a couple minutes after vehicle shuts down. They also free up some decent horsepower. If you have a tow vehicle or mainly drive highway it maybe worth looking into. However, the cheaper DIY kits they used to sell are no longer sold so they pumps are big money now.
Best electric fans for GMT800
Fans purchased at junkyard from a GMT900 6.2L Escalade (2007 to 2014)
The newer, next generation GMT900 truck fans are superior to the GMT800 electric fans. Specifically the ones from the “Enhanced Cooling Package”. Otherwise, I believe most of the GMT900 Cadillac Escalades with 6.2L have 9 blade fans and 700 watt motors. I am told any other GMT900 fan assembly will directly bolt to the GMT800 radiator as they’re similar if not the same.
Fans purchased at junkyard from a Cadillac with NorthStar engine
I went down a side path after visiting the junkyard. There I was told fans from a Cadillac NorthStar engine are a close fit and cool well. I bought a set for $40 then did a test fit when I got home. The entire fan assembly was both narrower and shorter than the radiator core. Would have been very tricky to mount reliably.
There are two alternator options on the GMT800 both of which are too small to run the 700 watt fans. You’ll need to upgrade your alternator or purchase the fans with 400 watt motors. I already have a high output alternator from Tucson Alternator so this isn’t a concern of mine.
Here’s the 700 watt part numbers for the fan motors themselves if you want to upgrade and or rebuild a fan assembly:
- 700 watt right motor 15-81697
- 700 watt left motor 15-81696
Electrical Connections
Here’s where the wizardry starts to come into play. The P59 PCM from 3rd gen Small Block Chevy supports electric fans. However, you’ll need to pin the unpopulated fan control line. You’ll also need to wire up relay and fuse.
Some of the GMT800 trucks switched to electric fans in 2005. The harness from those trucks can be used to wire up these fans. I’m told it’s safest to run a factory junction block so is what I’m going to do despite I’d really like an aftermarket junction block to keep the upgrades I’m doing separate from factory wiring.
Charge provides an idea of wire capacity for 12v electric system in vehicles. Different strand count and even temperature can impact these ratings.
I’m a bit confused by the 700 watt rating on the fans though. The fuse blocks for these fans are populated with 40 amp fuse per fan. However, 700 watts at 14 volts is 50 amps. Not sure how they arrived at the 700 watt rating.
The factory harnesses leave LITTLE headroom (excess capacity for increased power). It maybe prudent to upgrade wiring to the fans themselves with a higher gauge wire. I have 12 gauge GLX in my garage but may even go to 10 gauge wiring. The factory harness is likely 14 gauge if not 16 gauge.
Tuning
There’s a small possibility your PCM is programmed to turn on the fans regardless of having them or not but I’d not plan on that.
I have access to tuning software to turn on the control signal for the electric fans. You’ll need to get in touch with somebody who can do this and or figure out how to do it yourself. It’s not hard but plan on spending another $400 give or take if you plan to do this with off the shelf tools by yourself.
Open Source Tuning
Otherwise, there’s another route. You can try open source tuning software such as TunerPro and a bidirectional scan tool such as OBDx. I’ve yet to experiment with these but it would likely handle setting the temperature for your fans to turn on at.
Thermostat control
Lastly, you can install a thermostat sensor on the radiator. I’m not a huge fan of this. However, have seen some kits come with a sensor that inserts into the radiator core to turn the fans off and on.
Project is in progress
I use this website to save and share my notes. If you have questions feel free to contact me. I’m still in the process of completing this project. I plan to update this post as things progress.
