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Marty
Marty, Mercedes Technician
Category: Mercedes
Satisfied Customers: 53153
Experience:  Bosch Certified Master Tech. Over 35 years experience.
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Mercedes-Benz 300 sel I have a 1988 Mercedes 300 sel with

Customer Question

I have a 1988 Mercedes 300 sel with a 3.0 inline 6 cylinder. The transmission fluid smells burnt, and had a gradual loss of power. No slippage, no visible leaks, shifts like it should, if it cools off seems to run okay with no loss of power for 100 plus miles. What would you suggest?
Submitted: 5 years ago.
Category: Mercedes
Expert:  Marty replied 5 years ago.

eurotec :

Hi, are you saying that the transmission starts to slip after 100 miles?

Customer:

no, it doesn't slip at all.

eurotec :

ok so what happens exactly?

Customer:

after the 100 miles or so you smell the trans fluid getting hot like a rubber burning smell then it starts to slow the car down, if put in neutral it still idles, but will almost not move u

eurotec :

Are you sure it's a transmission problem? It sounds like the brakes may be locking up.

eurotec :

If it were a transmission the motor would race but the car would not move in drive.

eurotec :

When you press the accelerator

eurotec :

The smell would go along with the brakes locking

Customer:

the loss of power only

Customer:

the loss of power only occurs when going a steady 60 plus down the road

eurotec :

Does the car eventually slow to a stop?

Customer:

yes it I didnt stop it would

eurotec :

Ok, when you place the car in neutral will the car roll freely?

Customer:

yes

eurotec :

Ok, and this is when you are having the problem correct?

Customer:

i lose power on the freeway and the car starts slow down and pressing the accelerator makes no difference, so i have to pull over, i can shift from neutral back into drive and back and forth and the trans engages, but there is only enough power to move it back or forth and thats it.

eurotec :

It makes a difference if the motor races when you press the accelerator. If you put the car in drive and press the accelerator and the engine rpms increase but the car makes no attempt to move that sounds like the transmission is slipping. If however the car somewhat squats or lunges when trying to accelerate it would sound more like the brakes are locked up. If the car is able to be rolled easily in neutral when this problem is occurring then it would not be a brake problem.

Customer:

when the rpms increase in drive the car will move forward or in reverse, when in neutral it can be moved back and forth by pushing, so if not brakes does this sound like a trans problem?

eurotec :

Possibly. But I get the feeling that maybe the motor is losing power due to loss of fuel pressure.

eurotec :

When you are having trouble are you able to place the car in park and race the motor?

Customer:

yes

eurotec :

If that is the case I would say the transmission is at fault but the symptom is unusual. I would start with a fluid and filter change.

Customer:

what about a transmission flush to remove all the old fluid?

eurotec :

A flush is nice but for this symptom I would want a new filter installed. The torque convert on your car has a drain. The shop should also drain the torque converter. Doing it that way is as good as flushing. They can also check for debris in the pan that may indicate an internal failure.

Customer:

so, what about fuel pressure, what are those symptoms, if the motor is raced would it be sluggish getting to higher rpms above 3500 rpms?

Customer:

could fuel injector cleaner help?

eurotec :

If the motor was struggling for lack of fuel pressure the car would act the same way that you are describing. What does not make sense as far as transmission slippage goes is that when you are having trouble and you try to accelerate in drive the motor should race easily even in drive.

Customer:

in drive though it doesn't it is sluggish and the temperature gauge shows that the engine is getting hotter, but no where near overheating, oil pressure is great, so i guess i should do the trans filter and fluid, and try some injection cleaner and so what happens?

eurotec :

And perhaps even replace the fuel filter

Customer:

thanks for your advice, i will try those things and see what happens

eurotec :

You're quite welcome. One other thought I had is that your car has two fuel pumps.

eurotec :

It's possible that one of the pumps is failing.

eurotec :

If that happens the car could act the way yours is acting.

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