Here's an interesting comment by Stu Ritter, current technical editor of the MBCCA's "The STAR" periodical, and former MB shop-owner (35+ years experience), on overheating M119's and modifying the viscous-fan cut-in, as well as possible problems with the resistor-trick, and a lower temp. thermostat.

JimF, Guido, comments?

:-) neil
1988 360TE AMG
1993 500E
===========
> Thanks Stu! I was just getting ready to install a *new* radiator
> (mine's original 10-years old), and replace the viscous fan with a SPAL
> puller-fan at 2780 CFM, on an adjustable thermostat as well.

The problem is the viscous coupling. I've done a lot of work here
to get my car to run cool. Now, with 95 degrees in Denver and full tilt
A/C running, I'm staying under 90C. Actually, it only goes up to 90 when
I'm idling for awhile at a stop. It stays at thermostat most of the time
now.
I was seeing 115-120 under these conditions. I found that the viscous
coupling wasn't working as it should. I went through three of them, and
guess what, they all worked the same way. I discussed this with the
chief
MBUSA engineer. He said that is the way they are supposed to work.
The fan clutch wouldn't engage until the strip saw 107C which really
meant
110C air going through which meant the radiator saw 115-120C. If you
listen carefully to the fan you will see how quickly it cuts out. It
only locks
on when you get up around 120-125C which is really bad. This little mod
takes care of the problem and counters the factories pathetic
engineering.

I took the viscous off the engine. You can carefully remove the
bimetallic
strip which has the pin attached. Drill a small hole (say 4mm) and
thread
it (say 4mm). Get a little 4mm bolt with two nuts. There isn't enough
thread on that thin strip to trust the threading. Screw the bolt in and
double
nut it, one on each side of the strip. Bow the bimetallic strip around
1mm.
This will give you full tilt fan engagement right up to the high speed
disconnect
around 3,200 rpm. You won't believe the amount of fan noise. It's noisy
but the engine runs cool as a cucumber. For winter, I reach down with a
4mm wrench, loosen the nuts, back out the bolt the 1mm and have a normal
(ha ha ha) viscous coupling during the winter when I don't need the fan
howling all the time.

> Also, the resistor trick
> (http://pages.prodigy.net/jforgione/MB_CTS.html) hasn't helped enough. I
> can really feel the "retard" and loss of power when the engine gets hot.

There are problems with the resistor trick that took me a long time to
figure out. Don't do it. That temp switch provides a temp signal to far
to
many things to trick it the way I did. It shouldn't be done. Once you
study
the wiring diagrams, you'll see what I mean.

> BTW- Satish had mentioned some 70-C thermostat, but I can't find one.

DON'T EVER, under any conditions use a thermostat that is rated lower
than
the factory spec. There is no quicker way to wear out an engine
than to run it cool. It is better to run it at 120C than at 70C. At 70C,
the
engine
still thinks it's in the final part of the warm up cycle. Wanna talk
about
wearing
something out. Excess fuel will wear it out so fast it will make your
head spin.

You will also be running the cat with too much fuel for too long. No
good.
Disastrous
idea.

Stu


Date: Fri, 28 Jun 2002 10:24:45 -0600
From: Stu Ritter
Subject: Re: [MB] Viscous fan fix for hot M119s (Was: 124 aux fans on
all thetime)

> Stu,
> As someone who has never removed a viscous fan clutch, how hard is it?
> Also, for switching back to "normal" operation in winter, do you have to
> remove the clutch?
>
> Steve Wengel

The manual says to remove the radiator. We have been able to sneak
it out without taking out the radiator. Just take off the shroud.

Switching back does not require removing it again. Don't put the 4mm
bolt at the center of the strip but rather out toward the end. Just
figure
that you have to lift it about 1mm to get full tilt fan action. I have
done
it twice now and it takes a minute or two on a cool engine. When I go
to set the 1mm clearance, I use a screwdriver and pry the strip up
and use the screw as a set screw, rather than trying to use the threads
to set the clearance. Works like a champ.

I just came back from the shop. I had to deliver something. It's about
88-90 in Denver right now and with A/C on, it was staying at thermostat
temp. One needle width above the 80C mark. Just right.

Doing research for my book, I found that the temp sensor that I had
jumpered provided a signal to the LH-SFI injection unit that determined
mixture. My car has been running better since I removed it. I didn't
think to go past my nose when researching the resistor affect on the
switch and changing the value seen. That signal is looked at by both
the LH control module and the EZL/AKR ignition module.

Stu