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Mercedes-Benz 560SEL mod 91,MB 560SEL mod 90
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500 Posts
Discussion Starter #1
Hello guys,
My brother in law is going to repair his car engine for W126 due to too much oil lose. For about 160km trip with a speed of 140- 160km/hr, it looses about one quarter of oil. He replaced the valve stem seals because he thought seals is the culprit but did not help. I suggested to do a cylinder compression test and see what his engine doing. When we did the compression test, we got these readings :mad: :

cylinder reading ... cylinder reading
.... 1 = 180 psi .......... 5 = 165 psi
.... 2 = 178 psi .......... 6 = 158 psi
.... 3 = 180 psi .......... 7 = 160 psi
.... 4 = 175 psi .......... 8 = 150 psi

As you can see from readings, there is quite big difference which indicates engine is very bad. What is the best way to fix his car? shall he do the total repair " overall " or to look for another used engine? I think both ways almost have the same cost price. your ideas are great help to me, thanks.
 

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1979 280SL, 1984 280SL
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5,654 Posts
Abdullah,

Not sure what the used parts versus rebuilt engine situation is in your part of the world. Here in the US, there is no doubt- finding a good used engine is the way to go. Here, it is much less expensive and also easier to find a good used engine, and simply replace the old one.

As far as compression relating to oil consumption, that may or may not be the problem. In any event though, if your brother in law has replaced all the valve seals and your oil loss is that high (1/4 oil volume over 160km?) then a replacement or rebuild is in order. Or he can just add oil.
 

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W124 400E, W126 500SE
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971 Posts
It's an old engine, this difference is not _that_ bad, I also don't know many people who can do a compression test properly (disconnecting injection etc.). Does it smoke visibly and constantly? My old 420SE ate lots of oil in high RPMs, but nearly no oil when cruising, the engine still lived the last I saw it (no work, 100kkms more on the clock, average oil consumption about 3 liters/10000km).

Also what do you mean by "one quarter of oil"?
 

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Mercedes-Benz 560SEL mod 91,MB 560SEL mod 90
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500 Posts
Discussion Starter #5
Was the compression test done hot with the throttle held open?
Engine was warm for about 15 minutes, disconnected battery, open throttle wide open, removed gasoline relay, removed all spark plugs and tested each cylinder by cranking engine till the gauge stops increasing pressure. The lose of oil that I mentioned only at high speed, during city driving there is a lose but little. I meant by one quarter, one forth of a gallon.
The amazing thing here is that all the weak cylinders are located on the driver side.
I forgot some thing very important that I should have done, I could put some oil on the pistons that are being suspected and redo the test to know if the piston rings are leaking or some thing else. I think, it is better to do the test again.
 

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1979 280SL, 1984 280SL
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5,654 Posts
So, he only burned one quart during a 160km high speed run, but doesn't use any the rest of the time? Just keep driving it, and check the oil.

If oil consumption were to get out of hand, here in the US I would be looking for a replacement engine. The cost of a used vs. rebuilding is just not worth it.
 

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Mercedes-Benz 560SEL mod 91,MB 560SEL mod 90
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500 Posts
Discussion Starter #8
Bad news guys, :mad:

I re-did the compression test and made sure that the piston rings are damaged also I saw through the spark plug hole some very tiny pieces of aluminum on the top of the piston heads. I will replace the engine by a used one rather than repairing it. By the way, this engine is with me for 7years now I have bought it as a used one from UAE before. I think 7years for a used one is quite enough. I will look for another one although engines for 560sel are very rare now.
 

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560 SEC
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100 Posts
Iv got a good running 560 engine I'm parting at the moment. It's the HV 10:1 CR version, I can send you a short block with pistons, crank, etc if it's any use to you? I'm taking the heads off today so will post pictures if interested.
 
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