1970 250C Oil Pump Problems - Mercedes-Benz Forum

 
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post #1 of 8 (permalink) Old 09-12-2006, 06:51 PM Thread Starter
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1970 250C Oil Pump Problems

I recently lost oil pressure in my 250C and was wondering, before I really start tearing into the engine, what is the best way to get to the oil pump? that is what I am guessing the problem is since there are no external leaks or drop in oil level.

Will the engine need to be pulled and if so, will I be able to access the pump from the bottom after removing the oil pan? Dont know a whole lot, never had a Mercedes engine apart before.

Any help here would be great, I am getting very anxious to get the Benz back on the road where it belongs!
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post #2 of 8 (permalink) Old 09-13-2006, 11:06 AM
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Checking to make sure it is not an indication problem, i.e.: indicator gage or plumbing to the gage, a blocked filter or stuck open, oil pressure relief valve is a good place to start, rather than tearing into the engine to find a working pump. Failure of the pump is highly unlikely, less an oil pump drive chain is broken or similar. I'm not familiar with your car's engine, but this is a general approach to diagnostics. Do the easy things first. That said, there's little that is easy to do on a MB.

Good luck!
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post #3 of 8 (permalink) Old 09-13-2006, 06:39 PM Thread Starter
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I did not find anything to indicate a guage problem. a plumbing problem would probably mean oil somewhere where it was not supposed to be (ground). Also considering the fact that the needle on the guage dropped from normal operation to zero i think it might be something more serious.

I just hope that I had it shut down in time that I did not score any cylinder walls or wreck anything else, there wasn't a burnt smell from the valve cover, so i am really hoping i didn't burn it up.

Any help here from anyone that has dealt with the oil pump would be great.

nortonfan, you mentioned a drive chain for the oil pump, I was under the impression that this was a gear driven pump. anyone have some clarification here? the engine code is 130.923 (2.8L)
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post #4 of 8 (permalink) Old 09-13-2006, 08:06 PM
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First, a plumbing problem would NOT necessarily indicate an oil leak, as the plumbing may be blocked and not ruptured. As could the gauge. Again, I'm no expert on your car/engine. I hope you have a workshop manual of some kind to assist you along this path. The last thing you want to do is pull the pan to get to the oil pump, and this is what I am trying to point out. If, in the end, it points to a defective pump, then you can decide how to proceed. Of great value would be to have a schematic diagram of the engine's lubricating system and a complete understanding of the pressure relief circuit.

I've just looked up your pump on the Autohaus AZ webpage and it apears the pump has a tang/dog which is driven by a slot on the end of the distributor (my guess), and not a chain or gear. You would need to confirm this by removing the distributor, expose the distributor driver slot and see if the tang is not broken on the pump. If you opt to pull the distributor, remember to rotate the engine to TDC on number one cylinder. This is important! Place a witness mark were the distributor rotor points to the distributor body. This will allow you to replace the distributor in the correct position during reassembly.

Please post your findings and keep us apprised.
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post #5 of 8 (permalink) Old 09-13-2006, 08:52 PM Thread Starter
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Manual-wise I have a haynes manual that seems to be decent. And your thoughts make sense about not having to do more than is neccessary, when I have time I will check where it is driven off of the distributor. I leave for work tomorrow, and working in the oil field we work four days on four days off, so it will be a few days before I can do anything, but if anybody else has any pertinent information, i would appreciate it.

and thanks nortonfan, I appreciate you taking the time to help me out - this seems like a good community to become a part of... Wish me luck
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post #6 of 8 (permalink) Old 09-24-2006, 12:10 PM
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If your engine still runs, the oil pump is fine, because the oil pump drives the fuel pump through an intermediate shaft on the M130 engines as well as the M127s and M129s and M115s. If the drive tang at the top of the pump were broken off, the fuel pump quits working. In years past I got many chuckles from guys whos cars quit running and after a shade tree diagnoses it was discovered that the fuel pump had quit. After finding out how much a replacement pump cost, these geniuses thought they were cutting a fat hog in the aas by installing a $15 electric pump from Napa. They would fire up the car and be all smug and not paying attention to the oil gauge. Then they would get all freaked out by the screaching and knocking noise. Too late. Spun bearings.

One of the two oil pressure reliefs could be causing the problem, but I'll bet it's that aftermarket oil filter you installed.
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post #7 of 8 (permalink) Old 09-24-2006, 03:24 PM
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Quote:
Originally Posted by autozen
...the screaching and knocking noise. Too late. Spun bearings.

One of the two oil pressure reliefs could be causing the problem, but I'll bet it's that aftermarket oil filter you installed.
See the post about the Diesel with the napa oil filter....don't waste money with non genuine oil filters.It's seriosly false economy when you consider the price of a genuine filter compared to the damage done to an engine by fitting the wrong part.
Test your oil pressure the mercedes way,fit a test guage to the blocks out let fitting and see what it reads with the engine cranking and No sparkplugs in place.It must register Some pressure. Even a high milegae engine will show a good reading at cranking speed.
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post #8 of 8 (permalink) Old 09-27-2006, 09:28 AM
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Originally Posted by mercmad6.3
See the post about the Diesel with the napa oil filter....don't waste money with non genuine oil filters.It's seriosly false economy when you consider the price of a genuine filter compared to the damage done to an engine by fitting the wrong part.
Test your oil pressure the mercedes way,fit a test guage to the blocks out let fitting and see what it reads with the engine cranking and No sparkplugs in place.It must register Some pressure. Even a high milegae engine will show a good reading at cranking speed.
I agree that connecting a gauge to the block is an absolute test, but in my opinion not really necessary on an MB of this vintage. The car comes with a gauge in the dash that is the same as one in your test set up. I can't ever recall an MB gauge that has oil going to the dash failing with the exception of the W123s, and that was only a problem with oil leaking out of the dash. The gauge still functioned. Many years ago I bought an 87 560SEL. That was about the bginning of electric gauges with sending units. I had heart failure when I looked down at the gauge while driving once and it read zero. I stopped immediately. It was a gauge malfunction.
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