450SL Noise Stumps Tech
 

my '79 450SL is making a noise that is best described as "wind howl" from under the hood, it appears. It's like you hear when you are in an enclosed room and you can hear the howl of the wind outside. Now, the interesting thing is this noise is present until around 3100 RPMS at which time it subsides. We even ran the car in second gear and the pattern repeats. It sounds as if it is from the engine compartment.

clues:
We recently rebuild the transmission, replaced the cruise control controller, removed an aftermarket security system.

Any guesses on what it is? As soon as I hear back from my tech I'll post the "answer". The winner gets a one year free subscription to MercedesShop.com :D

Fan clutch maybe?

A friend of mine had a 1967 GTO with a small block Chevy with dual quads on a Wieand Cross Ram intake manifold which made a noise as described. One of the carb mounting nuts were loose and the carb gasket was making a noise almost like a kazoo at a certain range of RPMs. Maybe an intake leak or gasket vibration somewhere?

Thanks for the inputs... just one note to Steve: I really appreciate your sound advice on many of your posts. I especially appreciate your insights on timing chains in that the chain is many times not the problem but the tensioner... when the tensioner creates slack, then the rails get pounded, etc,, etc,,, I followed this advice when getting my chain examined just last week. We did replace the tensioner and everything else looked fine.

back to the subject... I should be hearing something this morning from the tech. The sound tracks along with the engine speed up to 3100 rpm's at which time it shuts off much like the sound when a car is revved in second and shifts to third. However, the car is running in third the whole time.:confused:

JDub... interesting idea. I also had the fuel injector seats and seals replaced... could be a clue...

One thing you must note about my timing chain recommendations. I am a firm believer that the rails do all the damage. I believe that periodically the chain tentioner will bleed down no matter how new. The real preventive maintenance is to replace the rails before they turn brittle. This happens with age and mileage. I would do just the rails every 75k or 5 years. They are cheap around $3 a piece (three of them). They do require a piece of labor as everything must be removed from the front of each head (alt, P/S).

Damn.... you're good
 

We have a winner!! No surprise it's Steve... Just got word.. it is the fan clutch... As it was explained to me, the clutch had gotten stiff and would not shut off until the engine speed was high enough to disengage it. I'm impressed:D

In the archives are some nice explanations of how the fan clutch works and why. My question is does the fan clutch pull enough power to materially impact the MPG and engine performance, especially in my case where it was always engaged?