[no-blue-screen]

Okay,

This is rather complicated scenario, but I don't want to completely overhaul the cooling system as a fix....so here is what is going on:

1982 300D Turbo with 158k on the clock

Problem: The coolant temp is running up higher than it does normally. It hangs around the 3rd hash mark (inbetween the middle mark and the last mark which is labeled 120). It only does this with the A/C on and it only seems to happen at highway speeds.

I am thinking the fan clutch is bad, but I am not sure. I went on a 1 hour drive yesterday afternoon and ran the A/C on max the entire way and I noticed it would hover around that third hash mark and sometimes fall slightly below and then rise again and then fall again. It is my understanding that normal operating temp is 90C, and that operating above this could cause damage to the engine.

Here is what I have inpected so far:

1) The aux fan on the condenser is operating properly

2) The coolant level is normal and there are no coolant leaks.

3) There seems to be a slight wobble in the pulley that the fan clutch is attached to, but again there is no coolant leaking and no wierd sounds that would indicate a failing water pump.

What I am thinking is that the fan clutch is bad, and this is preventing the fan from spinning at full speed. I have the old 6-blade fan on this car and I have already purchased the newer 9-blade fan and a new behr fan clutch.

Given these symptoms and that it only happens with the A/C on and driving on the highway, what do you experts have to say?