"Can you hear a roar when the fan cuts in at around 90dec water temp"

I dont quite understand....The engine fan is always on....As i understand, it never stops. The electric fans on the otherhand do kick in at around 95 degrees. But they dont make a difference, the temperature pretty much stays the same and if I continue to stay in gear and crawl in traffic the temperature rises and rises. I havnt taken the risk of seeing what happens if it keeps rising, because I have already dealt with the coolant boiling over out of the expansion tank.

I had read on another forum that the engine fan spins at different speeds depending on engine RPM. And the "fan clutch" apparently controls whether the fan spins correctly, according to the engine rpms.

Also today while I was in some slow traffic the temp rised to about 100 degrees, then as I pulled over to a parking lot, I reved the engine to about 3500 rpms slowly, this drastically brought the temp down within a second or two. In front of my eyes I could see the needle drop to about 85 degrees.

__________________
190e 2.6 1990. 300,000 KM
C230 K 2000, 130,000 KM

The viscous fan clutch keys off radiator exit air temperature. At low radiator exit air temperature the fan clutch is "loose" and the clutch will slip when the engine is revved, so the fan won't rotate at more than about 1000 revs. At about 100C coolant temperature in mild to hot weather the radiator exit air is hot enough to "tighten" the clutch and the fan will spin up to higher revs with the engine, and you should be able to hear "fan roar" above about 2000.

You need to understand that the engine driven fan speed keys off radiator air temperature due to the viscous clutch' reaction to radiator exit air temperature. It will never turn faster than engine speed, but unless the radiator air exit temperature is high enough to tighten the clutch it will usually turn slower than engine speed.

You can also check under the hood. At 80-90C coolant temperature rev it up to 2000 and feel the air flow - probably not much. Let it idle until the temp hits 100 C then rev it up and you should feel much higher air flow and hear more fan noise.

Another test is to spin the fan with your finger when the engine is off and cold or cool. It should turn with little resistance. Try the test again when the engine is at 100C or better. Shut the engine down and turn the fan with your fingers. It should offer much more resistance.

It looks like you performed the "flow test" and your results indicate that the fan is probably operating properly.

In hot weather stop and go driving it is normal for the coolant temperature to stabilize in the range of 100-105C. Once you get up to speed, such as freeway driving the temperature will usually drop to 90 in hot weather and 80 in cool to cold weather.

Duke