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CJ Blower Fan Upgrade

Since I was installing a dual battery tray, I thought that it would be the perfect time to upgrade my heater's blower fan. This upgrade has been floating around the internet for quite some time and it seemed fairly straight forward. Anyone that has driven a Jeep CJ in the winter knows that the heater is weak at best. My heater's actual heat output increased when I swapped in a Chevy 350; however, the blower fan is the weak link.

The basic idea is to install a blower fan from a 1973 Chevy Blazer with a 350 and A/C in place of the stock Jeep fan. I went to my local parts store and purchased a Siemens fan (Part #PM105) and at first glance seemed to be nearly identical to the stock fan. The only obvious difference was that the new fan's housing diameter was nearly 1" larger than stock. The Chevy fan had an identical bolt pattern so I figured that this would be a simple swap. I began by drawing an appropriately sized circle on the firewall. To draw a nice circle, I used what was left from the cutoff wheel that I used on my Tomken front bumper installation as a template. I centered it by eye and, using a black marker, traced its outline. Since I had already installed a fiberglass body, trimming the hole was no problem. I simply used a Dremel with a metal carbide cutting bit and cut out the hole.

I next pulled the fan off then old motor and installed it on the next Blazer motor. When I tried to install it back into the housing, I discovered a problem. With the fan installed, the motor could not be fully seated into the housing with internally hitting the heater box. The motor mounting plate was actually 3/4" too far from the heater box ... there was no way that I could mount it with the fan attached. I pulled the motor out and compared the motors side by side. Not only was the Blazer motor housing have a larger diameter but, the shaft was longer and forced the fan to stick out. To solve the problem, I filed the motor shaft so that the fan could site closer to the motor housing. However, this forced my to add some washers to the end of the shaft (no problem).

This alone didn't solve the problem but it allowed my to use some stainless washers as a spacer. I filled in the gap using some silicone sealant and I was on my way. The motor that I used had a hole in side of the housing. To prevent water or dirt from entering the housing a purchased a plastic hole plug for 16 cents from the local hardware store that fit perfectly. I reinstalled the heater box into the Jeep and fired up the motor. WOW! The Blazer fan really kicks out some air! In fact, it puts out as much air on low as the Jeep jan did on high. If you're tired of being cold in the winter, this modification is for you!

UPDATE: Since doing the swap, I have discoverd that there are two different fans out there for the '73 Blazer. The fan listed below should have a shorter shaft on it ... the spacers I needed should not be necessary with this one:

Siemens Part #102E

Application Info:
1973 Chevy Blazer 4WD 350
No A/C
Standard Heating