If your old Mbz cools just fine, then feel free to ignore the following:
See this link for a demo of a variable proportional controlled electric fan.
http://youtu.be/i6go2VTr5bY
Here is what the fan looks like - the silver colored rectangle with barcode is a dc variable speed controller:
Close-up of the controller:
Link to
DipTrace and here are the
files and instructions.
Look at the evidence: the 80's era Mbz viscous fan hubs fail almost universally. Failure mode takes place in the form of the widely observed inability of the viscous coupler to "engage" at elevated radiator air discharge temperatures. Lots of "fixes" have been implemented over the years by committed die-hards.
My own situation produced a legacy of frustrated attempts to produce better cooling. Since I live in Albuquerque, have performed power upgrades on the engine, and need my A/C system to work well, I have been motivated to find a solution that really works.
My first attempt involved replacing my fan with a bigger solid mount aluminum fan from an 80's vintage 380 SEL v8 sedan. That fan produced excellent cooling, but literally sapped so much horsepower, that I had trouble accelerating uphill. I then tried injecting silicone oil into my oem viscous coupler, but got no results. I then tried modifying another viscous coupler from a later 450 sel to incorporate a temperature sensitive bimetallic element that would engage/disengage the fan at a certain temperature, but found that I could not adjust it properly and easily. I then tried injecting another newish oem viscous coupler with a much thicker silicone oil - which worked, but essentially locked up the coupling mechanism, which worked OK, but sapped more hp than was needed for cooling.
At this point, I have replaced the radiator with a new racing crossflow unit, installed a Mbz temperature sensor on the cool side of the radiator, will be replacing my fan & coupler with the electric unit referenced above, and finally upgrading my alternator.
I have already done all the basics such as a citrus flush, using a vacuum airlift to fill the system with fluid, etc...