1991 500sl - PeachParts Mercedes-Benz Forum

Sid The Kid · #1 12-09-2003, 06:58 PM

Hi....recently I made my parents trade in their 1999 BMW for a 1991 500SL. They were reluctant to pay 18K CDN more after the trade in for an older car but I assured them it was a better car. However I feel guilty now because I made them trade a perfectly working car for a less perfectly working car. I'm hoping with your help I can fix these problems before they inconvience my parents.
Problem 1 - The water pump leaks and every morning when the car is driven the belts squeel due to coolant dripping on the belts over night. The temperature will rise to 100 and then drop below close to 80 from time to time. Is it crucial that the water pump be replaced ASAP? Is there a procedure I can follow to make the work easier. Any tips or problems to watch out for?
Problem 2 - the transmission will sometimes vibrate when changing from 2nd gear. Usually when going up hills. This vibration can be felt on the steering wheel aswell. Its a 4 speed automatic. Also, when driving the car aggressively the gears will thunk on the first downshift upon de-accelerating.
Major Problem 3 - The engine oil was never changed in this car between 1992 and 1996. The mileage put on this car between this interval was 30K. Then from 1996 and 1998 The oil wasnt changed again and 26K was put on the car. After this engine oil was changed at 12K intervals until we bought it. The car now has 112K on it. The car was switched to synthetic oil at 108K just before we bought the car. Is this a major problem like I think it is?
I hope someone can help me so I can these problems fixed for my parents. Thanks for reading my long, and probably boring, post.

engatwork · #2 12-09-2003, 07:03 PM

Change the water pump. Change the tranny fluid/filter (don't forget the torque converter) and I would not worry about the synthetic oil in the crankcase. I would be concerned about, what it sounds to be, the lack of a proper maintenance program prior to ya'll getting the car. Sounds like it was not maintained the way it should have been, in my opinion.

Sid The Kid · #3 12-09-2003, 07:11 PM

Wow that was fast. Thanks engatwork. I am the most worried about the maintenance performed on this car. Is this engine going to be able to surrvive long after this sort of neglection. It doesnt seem to have any major leaks, just some sweating around the gaskets. It takes off smooth but has a constant ticking or chattering sound coming from the passenger side. Sounds like my 91M5 everytime its in need of a valve adjustment. Is this sound normal for the Mercedes aswell? I have noticed that the oil pressure reads at 1 when the car is idling at a traffic light but it does rise to 3 as soon as I take off. My friends Mercedes with twice the mileage sits at 2 when idling at a light.

engatwork · #4 12-09-2003, 07:20 PM

Does your friend drive a diesel? Oil pressure sounds right for a gasser.

Other than changing the fluids/filters I would drive it and not worry too much about it except for trying to get it back on somewhat of a scheduled maintenance program. The lower ends on these cars are pretty robust and can take some neglect. It just shows up by going "only" 180k versus 300k miles. Keep an eye on oil usage. If it uses alot then it may need new valve stem seals but other than that you are probably ok. Also, watch the temp gauge. They are unlike any other car because it can move around over a pretty wide range without causing any consternation. If, during normal operation, it goes much over the 100dC mark (and stays up there) then you need to service the cooling system. It will and should creep up over 100 when if you start it back up after having run it hard and then shut it down. Change the coolant when you do the water pump.

Sid The Kid · #5 12-09-2003, 07:37 PM

Thank you again engatwork. My friend has a 1991 400E. I think the pressure is okay in our car, he was just bugging me about it because his sits at 2. Thanks for the feedback, I dont feel that concerned about the prior lack of maintenance now. I will change the oil every 12K from now on with synthetic oil.

placo1 · #6 12-09-2003, 08:05 PM

Sid,

Just a thought, if the oil changes were neglected I'd imagine all other fluids throughout the car were neglected. Spend the $$ and have all fluids changed and then use a regular schedule to change fluids.

That ticking noise can be caused by the oil check valve, also the cause for the low oil pressure. Do a search and you should find plent of info. Oil pressure in these engines also varies significantly with various oil viscosities. Look in the manual for recommended oil viscosities vs outside temperature.

Good luck.