excessive potassium in oil sample

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7 replies [Last post]
Former Member
fjbertrand's picture
Towanda, PA
Joined: October 13th, 2003


1993 300D
1991 350SDL
1985 300SD
1984 300DT
1983 280SL
1983 240D
1971 220D
1969 230
1968 280S

I have had my oil sampled in my 350sdl for over a year now, everything is in very
good shape (1991 101K at present)
except for potassium levels that are
elevated. Last 3 changes: 43, 30, 30 ppm

Glycol is negative. Can anyone out there
comment on this high potassium level??

The oil is a mix of 50-50 Mobil one and
Delovac (5w-50)

miles between change about 3100.

soot very low at .2, TBN at 8.5

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Adamson's picture
Corpus Christi, TX
Joined: June 26th, 1974


1951 220 SEDAN
1961 190Db

Check with George Murphy since he knows about oil analysis.

Grey Ghost's picture

motor oil?

sounds like you're talking about someone's blood workup!

Jim Grillot (not verified)
Jim Grillot's picture

The high levels of potassium could indicate a slight coolant leak. It also might be part of the additive package.

If you are using oil sampling, you need a baseline to work from. You get this baseline by sending a sample of new oil, right out of the bottle, to the lab.

Palangi's picture


You would expect to see elevated sodium as well as potassium if you had coolant getting into the oil. My 300D always shows potassium around 30 to 40, doesn't seem to be getting worse. Sodium is not elevated and no water or antifreeze detected. Blackstone (Labs) seems to think it could from be a fuel addative. They asked me to send in a fuel sample, but I haven't done it yet.

FYI, If you want to pursue this with some very knowledgable people, run it up the flagpole at . They have a specific forum header for diesel oil samples.

Jim Grillot (not verified)
Jim Grillot's picture

Back when I was involved in an oil sample program on my employer's diesel trucks, high sodium was almost always a precursor of a coolant leak. On a slowly-developing coolant leak,
sodium levels would begin to elevate before glycol went positive.

We also had a couple of trucks over the years with thermal leaks. They would leak with engine hot but not cold. You could run a cold pressure test for a day and the pressure wouldn't change. But oil samples were coming back positive for glycol.

If you are losing coolant and a cold pressure test doesn't show anything, run a test with the engine at operating temperature.

Also test the pressure cap. Most of the coolant loss complaints I have seen trace back to caps that won't hold pressure.

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