2nd Coolant Resevoir?
 

What is the purpose of the second coolant resevoir behind the passenger wheel well? 1987 300TD

SLS resevoir?

You are probably referring to the reservoir for windshield washer fluid. It would spray on the BACK glass in this case. Is the liquid blue by chance? Not that this is a 100% dependable clue - but blue is very common for WW fluid.

Ken300D

No to both. This resevoir is located behind the front passenger wheel behind a panel. Right next to the Vacuum resevoir.

The SLS is behind the driver's headlight, the rear washer bottle is in the rear just under the antenna.

yup. the reservoir in the rear passenger wheel well, (under the jack / first aid kit) is for the rear wiper pump.
John

hmm, on my TD's I have no resevoir near the antenna. it's on the passenger's side. perhaps somebody added something?
John

i would imagine he is reffering to the overflow tank behind the front passenger wheel are just infront of the passenger door area behind the plastic inner fender liner. it is an actual over flow tank, the main one is the reservoir and this one collects any expansion fluid.

That's how it is on my car.

Chris

If you have the metal one, you are lucky. If you have the plastic one....check it for cracks.

i would imagine he is reffering to the overflow tank behind the front passenger wheel are just infront of the passenger door area behind the plastic inner fender liner. it is an actual over flow tank, the main one is the reservoir and this one collects any expansion fluid.
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Yes, That's the one. What is its purpose. Does coolant stay in there to be sucked back up to the upper tank? Or does it have another, or no function?

Coolant overflow tank behind right front wheel
 

Does coolant stay in there to be sucked back up to the upper tank?

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Yes, that is correct. The overflow tank is attached to the drain line at the pressure cap that is visible on the passenger inner front fender.

Not necessarily peculiar to Mercedes. Fords of the fifties, for example, had a similar configuration, a separate tank from the radiator that had the fill opening and pressure cap.

Overflow tanks are outside of the pressure boundary, and the feed line is sunk low into the overflow tank so that as the system cools and depressurizes, the expelled fluid is then drawn back inside the pressure boundary.

Jim

Which is why you just keep losing coolant with a blown head gasket or cracked head? Because the system never depressurizes?

Not quite....
 

The overflow reservoir eventually fills up and when it does, you will get water loss out the overflow overflow, so to speak.....

When the system pressurizes from a head gasket leak, it experiences higher pressure over a longer period of time than would be the case for a normal system. Hence the potential for more water to blow out, as well as a reduced likelhood of the water returning as you surmised.

Once the water is allowed to boil, and with a head problem this can easily be a localized phenomenum within the engine, steam is created and steam occupies a much greater space than water, encouraging greater amounts of water to escape into the overflow.

There's only so much water that can be sucked back into the partial vacuum of a cooled cooling system, and if you've generated steam, the loss will always exceed the return.

Jim

Thanks.

It helps to have an understanding of how stuff works.I can guess all day long but usually that course of action will lead me astray of reality.

Thanks again,

Joe

The tank inside the the passenger fender is a vacuum reservoir. There is no overflow reservoir for the expansion tank, it vents to the atmosphere.