As your problem is still that the fan is not cutting in when it should, could I suggest that you go back and check the fuses again; the bullet fuses fitted to these cars are a known problem area and although on visual inspection they look ok the only way to be sure is to remove the fuse and clean the end contacts ,also the contacts on the fuse holder . I have known people with problems pull out the fuse and it fall apart although it looked intact.
Best of luck, Geo.

Okay, so I yanked out the thermostat and replaced it. Changed the aux fan switch and the fan kicked on at 100c and the temp went down. However, when I was on the freeway with the a/c on high pedal to the medal at 107F outside the temp climbed all the way to 110 and only changed when I turned around, turned the a/c off and coasted back. Some of that might be caused by improper fuel air mixture, but I also found out that there was a mixture of three different brands and color of antifreeze in the car, actually mostly water. But that's because I didn't pull the block drain plugs (BE VERY VERY CAREFUL WITH THOSE THE SOCKET EXTENSION DOESEN'T REACH AS THERE IS A OIL LINE IN THE WAY AND THERE IS A STEEL DRAIN PLUG IN AN ALUMINUM BLOCK, BE CAREFUL). So now I drained the antifreeze and put the 50/50 mixture in. So will see what happens.

The aux fan helps cool at low speeds and idle. Good job getting it working.

I would say at this point that you need to investigate your radiator.

__________________
Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe

put in the correct antifreeze, but it did not seem to make any difference, however after the car hit 105 I kept going, but pushed harder and never pushed beyond 107....... another thing that was odd, I thought I would shift it into third gear which put the car at ~4000 rpms and I thought that would cool it (especially going down hill) it did not make a difference...... as soon as I put it back in d (4th gear) the temp went down to about 90....... So it seems like the higher rpms the faster it gets heated up. On the way back which is mostly downhill the car stayed at 90c. Forgot to mention it did not matter whether the a/c was off or on.

I hoping it's the fuel air mixture or the fact that i advanced the timing to 8deg, but it's probably the radiator or a pulley on the motor which binding up and causes extra load (when the car starts up in the morning a pulley is making a noise) so may be it's that. It's going in Wed to have the fuel air ratio adjusted to the specified mark.

Try Water Wetter(sp) by Redline. In my 450SL, it kept the temp at 175deg/f even with a/c on. Of course the recored radiator didn't hurt either.

The pulley noise is probably a weak bearing in the a/c idler pulley. They cost around $30.00.

The aux. fan must work in order for the car to not overheat with the a/c on.

Try reading radiator temps with a infrared thermometer, it's possible the core is partially blocked causing it to overheat in high load conditions.
Just my .02 .