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#1
09-24-2004, 01:29 AM
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Oil pressure troubleshooting
The 1971 250 W114 is now running, with smooth idle and plenty of power.
The compression readings are 143 psi for one cylinder, and between 147 and 154 psi for the rest. Milleage appears to be 154,000. But the oil pressure gauge reads 12-13 psi at idle. and 17-18 psi when running. Besides the oil pump, can I diagnose anything else to see why it is so low?
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1970 280S M130 engine- good runner 1971 250 M130 engine- #2 rod bearing, gone 1971 280SE (blown engine,parts car) 1977 German 280S W116-only 33 years old Last edited by MunichTaxi; 09-24-2004 at 01:32 AM. Reason: spelling 
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#2
09-24-2004, 06:46 AM
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What d'you mean that oil pressure reads 18 lbs while running.... Does this mean when you drive the car that's all you get?? If so, then it sounds like debris making the guage needle stick.... maybe a cockroach died in there or something.
Idle at/near 13 lbs is not so bad and niether are compression readings above 135. In fact I'd call 143-154 excellent high compression especially if cylinders range closer together after checking valve clearances. In case you havent thought of this already, you can never completely believe compression readings without checking valve clearances first. On the oil pump, my finbody 190c with 170k+ miles had worn out oil pump gears. Symptoms included oil pressure eventually dropping to about 7-9 lbs at idle..... then it would climb to the top while under load with the engine cold.... then when the engine warmed up it would creep down to about 32 lbs while driving and idled at/near a pitiful 5 lbs - that's when I finally freaked out. It was a sloooow and gradual loss in oil pressure over a couple of years before somebody eventually told me to fix the damned oil pump because it was a common prob at/near 150k miles on the Haeckflossen 4 cyl models. It cost about $100 in parts for new oil pump back in 1980, plus the hassle of pulling the sump while working under the car, otherwise an easy job. And hell yes, oil pressure sky-rocketed after replacing the pump on that old 110 Benz.... possibly my favorite MB of all time.
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#3
09-24-2004, 10:08 AM
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I would first test the oil pressure with a different gauge. If that confirms the problem, I would pull the oil filter housing and check for any blockage, then pull the small pan off and be sure the pickup tube is clean. If everything looks OK in both those areas, I would replace the pump, suspecting either worn gears or a bad relief valve.
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Chuck Taylor Falls Church VA '66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe
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#4
09-24-2004, 07:24 PM
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The relief valve is in the oil filter housing.
Peter
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1972 220D ?? miles 1988 300E 200,012 1987 300D Turbo killed 9/25/07, 275,000 miles 1985 Volvo 740 GLE Turobodiesel 218,000 1972 280 SE 4.5 165, 000 - It runs!
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#5
09-24-2004, 07:38 PM
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According to Haynes, it is "screwed into the front face of the cylinder block. On some models, a second relief valve is located in the base of the oil pump." But since I have never seen one on the face of the block, so I assumed it is in the pump.
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Chuck Taylor Falls Church VA '66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe
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