Stupid Question about engine noise on hot days
 

OK, I have a dumb question and I apologize for having to ask it, but I have been away from this forum for a long time and my knowledge is rusty.

I notice my engine sounds louder on hot days. Like there is a big fan attached to it. Is this because the radiator fan clutch is engaging and the fan is spinning at or near the same speed as the driveshaft?

Also, I had a weird thought. About two years ago I removed the the fan to do some repair I cannot recall. Is it possible to put the fan on backwards? Should the fan be blowing air at the radiator or sucking it away?

I am not sure which way mine is blowing, and since it is cooling properly I don't really care, but just a couple of dumb questions for the forum on a nice, hot, Monday in Virginia. :)

If the fan is engaging, it would be turning at, or nearly at, the speed of the water pump and pulley. Yes, it would make a louder noise than if it is disengaged.

I doubt you could put the fan on backwards. The converse side faces forward (and the convex side toward the engine). A fan running backwards will still move air in the same direction, but not as efficiently.

Cheers,
Wes

You WOULD have cooling issues if you could conceiveably, install the fan backwards...

The fan blade pitch and direction would be reversed, so instead of scooping the hot air and drawing it away from the radiator, you would be drawing the radiated heat from the engine and blowing it into the radiator!

Then your aux fans would be running all the time trying to keep things under control...whether or not the outside temps were hot or cold!

Wes, G-Benz, thanks for the scoop. I figured it was that.

My aux fan is off, and when standing by the car with the hood up, the radiator fan appears to be blowing back over the engine, so it seems all is in order.

For the experts--Does the 260E have an actual fan clutch, or does it have a visco drive like my 560SL of the same year?

if the fan was installed backwards, it will still be drawing air in the correct direction, as the "screw" direction will still be correct.

It will just not be optimized for that task, because of the reversed curvature of the blades.

Your engine has a viscous fan clutch that tightens based on the temperature of the air exiting the radiator. In hot weather stop and go driving this occurs when the engine temp hits about 100C, and when the engine revs up you will hear fan roar.

If the engine temp reaches about 105C the electric pusher fan(s) will engage at high speed and make a "whirring/roaring" noise that you will probably hear, even at idle speed.

Duke