1989 Mercedes whines over 40 MPH

I have a 1989 Mercedes 300F, automatic transmission, with 175,000 miles (give or take). It runs great, starts well, we have no problem driving it 30 miles back and forth on back roads up to 60 mph. The problem seems to be when driving 40 miles at 75 mph. At that point, it will start to run rough, and then will not go over 40 mph without whining. The first time this happened, I had a leak in the transmission fixed and fluid put in. The second time, I had the fluid and filter changed, a new alternator, and a complete tune up. For a month after that we drove it for miles but not on the highway, with no problem. I thought I would chance it on a longer trip, got 40 miles down the highway at 75 mph when suddenly it started acting up and had to call a tow truck. When the tow truck arrived, we did not see any fluid under the car. It’s been sitting in the driveway and now there are fluid leaks (appears to be oil). So, does it sound like something in the transmission, or maybe a bad alternator?

Unless the alternator is siezing up, it sounds more like a transmission problem. What is the transmission fluid level?

When you can only do 40 MPH…how is the enigne running? Do you not have enough power to go beyond 40 mph? It could be your engine or trans but I dont think I have enough info here.

WHen it is whining we might be talking about internal clutch slippage in the tranny or a Torque converter issue…or both? Do us a favor and pull your trans dipstick…look at the color of the fluid…it should be nice bright RED…also SMELL the fluid…does it smell burnt and have a more Brownish color, if so that is clutch slippage and needs a rebuild of the tranny to remedy…

WHere is TRANSMAN when you need him? He would be more likely to know methinks.


I would tend to agree with Texases, particularlly since you know you’ve had tranny problems in the past and have dealt with them by refilling the fluid.

Don’t be fooled by the “no puddles”. Automatic transmissions are hydraulically operated. That means basically that when they’re operating the fluids are under pressures and conditions (turbulance in the torque converter for example) that don’t exist when the car isn’t operating. It would not be unreasonable for a fluid leak while operating to disappear when parked. And, depending on where the leak was, I’d be reluctant to put too much stock in having gotten the leak previously fixed. Leaks in systems like trannys often have underlying causes.

By the way, have you checked the tranny fluid level since you got towed?

Having said all that, there are countless opportunities for a 22 year old engine to develop a whine. Without seeing the car, it’s tough to speculate.

Thanks so much! I’ll check the levels again and re-visit this thread.
Once the car starts to do this, it doesn’t have enough power to go over 40. When I try to bring it up to 60, it starts to whine and then starts to slow down. When I back off the gas and bring it back to 40 it rides ok. The first time it happened I drove it at 40 for a while, this last time I pulled right over. I will check the fluid level, but since I just had it changed I don’t know if it will smell burned. I had them change the fluid because I was concerned it may have been over-filled, causing this to happen when the fluid got hot.

Step one figure out where the leaking oil is coming from and why. Sounds like neither, find the source of the leak, thinking bad PCV.

A bad PCV would’nt/could’nt do this at all…a seizing alternator would be accompanied by clouds of burning rubber smoke and would stink to high heaven…I would think she would tell us about the burning rubber smell first and formost…dont you think? I think the jury is still out…

I just thought that it could possibly be a fuel pump not being able to keep up with flow? Or a clogged Air or fuel filter perhaps?

“It’s been sitting in the driveway and now there are fluid leaks (appears to be oil).”

I agree with Honda re: the PCV valve.

A PCV valve has no relationship to the tranny which is where I suspect the problem originates. A PCV valve is only a “check valve” (a one-way valve) between the convoluted “cavity system” that is the crankcase, the space under the valvecover, and the return paths (drains) through which the oil runs back to the pan after having lubricated the camshaft and its corrosponding components. The air in these cavities can contain volatile fumes from blowby, and the sole function of the PCV valve is to protect the engine aginst possible combustion from a backfire as the the fumes drawn into the engine’s intake and burned.

A stuck PCV valve will cause leakage of the oil simply because it is the only way for the aforementioned spaces to vent. If they cannot, the same blowby can pressurize the crankcase to the point of pushing oil past tired rubber seals, generally those that seal the ends of the crankshaft where it exits the block.

But a PCV valve cannot affect the transmission.

What’s a Mercedes 300 “F” ? Is this a deisel?

It’s probably a 300E. I don’t think these have a PCV valve. They have a breather hose though.

I little oil leaking and dripping is probably normal, nothing to do with the “problem.”

I’d bet on an old fuel pump not able to keep up with the demand.

When was the last time the rear differential gear oil was serviced? That rear diff can make a whining noise.