Interior fan woes

[jbg]

Dieselers,

About 2 years ago I replaced the HVAC fan (heater / AC) in my 740 as the bearings seized up and would not spin. Now that we are experiencing sub 20 degree temperatures daily the fan has again seized. I pulled it from the car and noted that the windings on the motor are rusted, and the fan "breather" tube has a dusting of rust.

Naturally this has me wondering, where is the rust coming from? Condensation formation? A plugged drain in the cowl? I would like to figure this out and correct the problem before replacing another fan. Being unfamiliar with this section of the vehicle, where could water enter that fan housing? Are there any known problems with the 700-series cars regarding cowl drainage?

Any comments / ideas in general? Thanks,

[casioqv]

Try pulling the sheet metal piece behind the hood, and you'll probably find it full of debris which is causing the water to overflow into the fan. Clean it out and you should be fine!

[jbg]

Try pulling the sheet metal piece behind the hood, and you'll probably find it full of debris which is causing the water to overflow into the fan. Clean it out and you should be fine!

Casioqv,

Based on your advice I pulled the cowl cover and cleaned out the leaves and debris. I also removed the "fan collar": the plastic piece that is sealed to the intake for the fan. This piece has 20+ year old sealant bonding it to the cowl, of which some of it was cracked and chipping off. I removed the old sealant from the collar and the cowl, and used RTV in its place. With everything reassembled I hope to install a new fan and not another for a long time!

Thanks for your help, Jim

[casioqv]

RTV might work, but it's more of a gasket maker than a sealant. If you really want it to last I'd probably use 3M 4200 (moisture cured polyurethane) sealant, or Butyl tape. You have to clean off the silicone residue to get these to adhere, which can be difficult.