Mercedes: knocking noise, blown head gasket, independent mechanic

Question
QUESTION: I just bought a 1988 300 sel mercedes, and noticed that when i first start driving, I noticed a knocking sound... I checked all the fluids. Also there is 350,000 miles on it

ANSWER: Sarah,
From where is the knocking coming. From the engine, transmission, or drive train? Does it appear at start up and go away, or is it related to the vehicle in motion?
Rob

---------- FOLLOW-UP ----------

QUESTION: it starts in beginning and goes away and now its sucking up coolant like crazy

ANSWER: Sarah,
I suggest that you have a crack in the block, or a blown head gasket. Also, you have a milky look to the oil. Do not operate the engine, as you have water in the oil and severe engine damage will occur.
I would contact an independent Mercedes mechanic and have the car checked out.
A complete engine rebuild is probably going to be requires. The cost will probably exceed the value of the car.
Good Luck
Rob


---------- FOLLOW-UP ----------

QUESTION: well, i was advised it could be the water pump.... i didnt say there was water in the oil or it looked milky yet... it was having issues sgifting yesterday and thats when i stopped driving it, but it didnt shut off due to over heating which is when i was told a blown head gasket or whatever occurs... i just bought the car for 2500 so i dont want to just flush that down the toilet, how much would it cost to repair it, as i dont know what other option id have other than flushing 2500 down the drain?

Answer
Sarah
If the transmission is not shifting, it could be because the fluid overheated when the engine overheated because the transmission fluid cooler runs inside the radiator. A vehicle with 350,000+ miles is at the end of its useful life, even for a Mercedes.
If this is a V8 you are probably looking at $1,000 to replace the head gaskets depending on where you live and it could be more, if there is not crack in the head or block. You would just need to find an independent mechanic and get an estimate.
If it were me I would probably part out the vehicle.
I have a 1986 420 SEL with about 180,000 on it. I am trying to get $2500 for it with no takers. It is  in really good shape, but from experience it is quite expensive to purchase used parts and out of site for Dealer parts.
The cost to benefit ratio is too out of line.
Sorry to bring bad news. Personally, I would never own a Mercedes again.
Good Luck
Rob