Modified 90 Degree Auxiliary Fan Sensor

Thread view:

Enable EMail Alerts

Start New Thread

Thread rating:

Todd Brown - 02 Jun 2006 15:05 GMT

I recently saw a modified auxiliary fan sensor that was activated at
90 degrees, rather than the usual 100. Seems like a good idea, though
I imagine one pays for lower engine temps with more aux fan wear.
Still, the tradeoff seems well worth it.

Has anybody used one of these? Or is there any other downside to using
one of these devices that I haven't considered?

Thanks in advance

Reply to this Message

Tiger - 02 Jun 2006 15:55 GMT

Engine temp will be cooler but it will not be below the operating
temperature. The only sensor I know that runs at 100 or 105 degree is the
backup temp sensor in case the primary sensor for aux fan failed or the
engine fan clutch is failing.

So it seems like a good idea, it was telling you that you have problem in
the first place. So fix this problem first.

Reply to this Message

Todd Brown - 02 Jun 2006 18:21 GMT

>Engine temp will be cooler but it will not be below the operating
>temperature.

Thanks for the response, Tiger, but I'm not really sure what you mean.
The people that have been using this claimed that the engine temp was
5-10 degrees lower when they used the modified sensor, which seems
reasonable if the aux fan came on at a lower temp?

>The only sensor I know that runs at 100 or 105 degree is the
>backup temp sensor in case the primary sensor for aux fan failed or the
>engine fan clutch is failing.

Correct me if I'm wrong, but I was under the impression that the temp
sensor on the thermostat activated the aux fan circuit at 100 degrees
on my 81 380sl and other 107's?

Here's a variation of the them, called the Cool Harness, for other
models.

http://pages.prodigy.net/jforgione/MB_S500.html

>So it seems like a good idea, it was telling you that you have problem in
>the first place. So fix this problem first.

Actually, my aux fan went kaput, but I was thinking of trying a
modified, too.

Reply to this Message

Tiger - 02 Jun 2006 20:28 GMT

>>Engine temp will be cooler but it will not be below the operating
>>temperature.
[quoted text clipped - 3 lines]
> 5-10 degrees lower when they used the modified sensor, which seems
> reasonable if the aux fan came on at a lower temp?

What I meant is that the thermostat will ultimately dictate the lowest
operating temperature... if the thermostat is rated at 85 degree... that
will be the lowest temperature you can achieve before themostat will start
closing to increase temperature.

>>The only sensor I know that runs at 100 or 105 degree is the
>>backup temp sensor in case the primary sensor for aux fan failed or the
[quoted text clipped - 3 lines]
> sensor on the thermostat activated the aux fan circuit at 100 degrees
> on my 81 380sl and other 107's?

I had 380SE so there is no difference in engine. There is one or two
sensors... single pole connection with red coloring on it... these control
the aux fan. There is one I think double or triple prongs... this is for AC
aux fan trigger and overheating protection to turn fan on at 100 degree.

These sensors have date of manufacture stamped on the wrench hex side... if
it is more than 7 years old... change them all.

The black single prong on the thermostat housing is for engine temp
display... this rarely go bad.

Our temp gauge in the instrument cluster do go bad... showing increased
operating temp when in reality... it is not. I would use infrared
thermometer at the thermostat housing to check the accuracy of the temp
gauge.

> Here's a variation of the them, called the Cool Harness, for other
> models.
[quoted text clipped - 6 lines]
> Actually, my aux fan went kaput, but I was thinking of trying a
> modified, too.

Other thing you can do to lower temp is keep your radiator clean... blow
with air or wash with water... from inside the engine compartment toward the
front of car to backflush any bugs or dirt stuck in radiator cooling fins.

Reply to this Message

Wan-ning Tan - 03 Jun 2006 05:27 GMT

Agree. The thermostat determines the engine temp. The fan mainly cools
the radiator at lower vehicle speed. Unless the car is in stop-and-go
traffic much of the time, activating the fan at lower temp really does
not make much difference.

On the other side, the engine is designed to be operating at certain
temp. Lower it may not keep the best performance/efficiency or even the
emission.

>>>Engine temp will be cooler but it will not be below the operating
>>>temperature.
[quoted text clipped - 47 lines]
> with air or wash with water... from inside the engine compartment toward the
> front of car to backflush any bugs or dirt stuck in radiator cooling fins.

Reply to this Message

trader4@optonline.net - 05 Jun 2006 15:49 GMT

> Agree. The thermostat determines the engine temp. The fan mainly cools
> the radiator at lower vehicle speed. Unless the car is in stop-and-go
[quoted text clipped - 4 lines]
> temp. Lower it may not keep the best performance/efficiency or even the
> emission.

One would also think by now if there was an advantage to the lower
temp, the manufacturers would have done it a long time ago. After all,
the cost of a 90 or 100 deg switch is the same.

Still, I wonder if it would make any noticeable difference in the A/C
which has a switch to turn the fan on if the AC condenser gets hot
enough. That fan seems to only go on at a relatively high temp of
like 100 too.

Reply to this Message