87 300d t viscous fan
 

My 87 300d t has always run on the hot side, however living in the desert, that may be expected. On hills, the temp rises to 105 C at which point I would back off the throttle but the temp would no doubt go higher continuing at 70mph. The aux fan works as it should. The viscous fan seemed to be working in that it was very uncoupled cold and rotated a couple revs when hot when the eng is shut off. But my goal was to lock up the fan at all speeds because of our extreme heat.

While overhauling the A/C, I added 2 tubes of Toyota's 6000 CST fluid to the viscous fan. I should note that popping the bimetallic strip off and again back on is made a lot easier by applying a heat gun to develop a normal curve then simply wiggling it out to avoid bending the strip excessively. The fluid was applied using a syringe with the needle cut off. Some loss of fluid will occur and I would estimate that I lost about 20%. It helps to periodically heat the fan.

After the mod, the fan when given a good flick, will now rotate about 40 Deg. (about one blade) whether hot or cold. It seems to be at max lockup. The engine may run somewhat cooler. Before the fan mod, the eng temp would continue going higher when idling with the A/C on but now stays at about 85C. I have yet to get it out on the hills. We have extreme heat right now and I am not sure it would be a fair test.

As coincidence would have it I was thinking of this very topic today.

I was wondering exactly how much play should be in the fan hot and cold. Which makes me wonder more if your baseline is correct.

Danny

I wonder if the loss or viscous fluid might also play a reole in the failure mechanisms of the OM603 engines? I spoke with someone at Potomac German Auto Parts today and they said they see a lot of late model diesels (91- 95) fail with overheated heads. Even with the new castings. I am not referring to the bent rod problem here, just overheating. I recall someone saying their fan was freewheeling, warm or cold.
I have always felt my fan periodically, whenever I am checking oil level or have the hood open, to see if it feels "normal." To me normal means some friction. I know what a bad clutch feels like on the 617 engines. BTDT.

Another thing that has possible involvement is that new fans are plastic and the thermo clutch is different, it was designed to engage at 105 C. The reason was for lower emissions. I think the earlier metal fans used with the '87 make more sense to keep, any upgrades to install the later version fan/clutch assy will only raise engine operating temp.
Anything that helps keep these engines cool is worth pursuing, esp with the cost of a new thermo clutch, adding fluid makes a lot of sense, so I am going to buy a glycol measuring gauge to try optimizing the water to antifreeze percentage level about 35 - 40%.

That is the problem. Without some sort of test appratus, and factory procedure, it's just guessing to determine what is "normal". I am not convinced that observing the fan when shutting off the engine really tells us anything. It may give some gross test of performance (freewheeling ) but whether the fan turns 1 rev or 2 revs at shutoff and being able to actually see what it is doing, and what it really means - that is the difficulty.