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1990 SEC
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It would help if you could fill us in on some more details, such as:
- Mileage on car and engine
- What was the compression
- Which cylinders are affected (MB numbers them as 1,2,3, & 4 on the passenger cylinder bank, and 5,6,7 and 8 on the driver's side on their V8's)
- What is the general condition of the car (interior, exterior, transmission, etc.)

Low compression are either headgasket or the heads. Could be quite expensive, and if the rest of the car is questionable the repairs might not be worth it to you.
 

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Discussion Starter #3
hey thanks for the info the car has 113000 miles and the cylinders that have low compression are 7 and 8 they are at 90 and the rest are at 120 and the condition of the car is good
 

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1989 560 SEL BLACK ON BLACK
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Cosmo 2 Sounds Like The Piston Rings Are Stuck On Those 2 Cylinders Their Are Several Additives For This
 

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E320
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that's not all that low for the age of our cars. do you have an oil consumption problem? any smoke from the exhaust? white or blue?

unless your dead set on fixing it, just switch to synthetic and use 20-50.
 

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Discussion Starter #6
no it doesn't use any oil, no smoke eather, the exhaust does puff out the tale pipe like it's missing. should I use some additive? if I switch to 20-50 should that fix my proplem? and what kind of oil should i use
 

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a Lucas additive may help a little, but you either have a worn cylinder/piston ring, bad valve seal, head gasket leak.. the are a number of things that can go wrong. did you use a standard threaded hose that goes into the spark plug hole with a pressure guage on the end? did you do a leak down test? that will determine wether or not it's a *problem*. if anything, synthetic 20-50 and an additive will at least reduce further wear on the cylinder walls/rings.
 

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Discussion Starter #9
yes to your 1st question, and no i didn't do a leak down test. how do you do a leak down test?
 

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I have a 560 with 111K, low compresion in 7 & 8, shudder at idle, but seemed to run OK otherwise.

Turned out to be head gasket.

Good luck!
 

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i want you to do something else. retest your compression on the two low cylinders but this time, pour a bit of fresh motor oil in the spark plug hole first. this will help eliminate some variables so we can narrow it down to the exact problem. get back to me with your results. :thumbsup:
 

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1990 SEC
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Seriously though......

How can 90 and 120 not be low? :confused:

Our engines in good nick should hold 150 - 160 psi.

.......or are you refering to a different scale here?
 

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"500"sel, 560sec
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so 7 & 8 are now at 130? with the leak down procedure? this would indicate that the rings are indeed letting pressure out. Theres no real fix apart from a tear down.
 

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^^^ what lander said.

just deal with it for now. switch to synthetic 20-50 motor oil and if you want, use an additive. when you have the money in the future, just have a rebuild done. new seals, gaskets, piston rings, and all the internal wear items. when your ready, be sure to do plenty of research, and find someone experienced with these cars.
 

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that's a tough one. i wouldn't spend anything less that $3,000 for a rebuild. and it would have to be at an indy mercedes speacialist.
 
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