I have some sort of a leak. Today's a very rainy day, and I noticed a white foamy substance on the driveway. Does this PROVE that it's an oil leak, or are there other fluids in the car that could react with water to form the white foam?

Thanks.

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14 E250 Bluetec "Sinclair", Palladium Silver on Black, 153k miles
06 E320 CDI "Rutherford", Black on Tan, 171k mi, Stage 1 tune, tuned TCU
91 300D "Otis", Smoke Silver, 142k mi, wastegate conversion

19 Honda CR-V EX 61k mi
Fourteen other MB's owned and sold
1961 Very Tolerant Wife

Windshield washer fluid will foam, oil will not. Trans fluid will repel rain water, the water will go around trans fluid. Power steering fluid same thing. So ck your washer fluid tank and hoses.

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81 300CD (sold) 1972 280 SEL 4.5 (sold) 1966 250 S 4 spd (sold) 1974 450 SL (sold) 86 BMW 325ES (sold), 1973 280C (sold) 1988 300 SE.

But it's an oily white sludge, of the same consistency that you'll see under an oil cap. That's why I was thinking it might be oil. Wiper fluid wouldn't be oily, would it?

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14 E250 Bluetec "Sinclair", Palladium Silver on Black, 153k miles
06 E320 CDI "Rutherford", Black on Tan, 171k mi, Stage 1 tune, tuned TCU
91 300D "Otis", Smoke Silver, 142k mi, wastegate conversion

19 Honda CR-V EX 61k mi
Fourteen other MB's owned and sold
1961 Very Tolerant Wife

washer fluid was an educated guess. If washer soap is in it then yes, it would feel oily.

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81 300CD (sold) 1972 280 SEL 4.5 (sold) 1966 250 S 4 spd (sold) 1974 450 SL (sold) 86 BMW 325ES (sold), 1973 280C (sold) 1988 300 SE.

It sounds like coolant mixing with oil, somehow, and how is it being expelled and from where? Headgasket failing and the substance described, being expelled under pressure from the coolant recovery system? Have you checked or added oil and coolant to your car lately? How much?

Have an expert take a look as it may require pressurization of the cooling system and or more. Don't let it go. Good Luck.

I had a coolant flush several weeks ago.

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14 E250 Bluetec "Sinclair", Palladium Silver on Black, 153k miles
06 E320 CDI "Rutherford", Black on Tan, 171k mi, Stage 1 tune, tuned TCU
91 300D "Otis", Smoke Silver, 142k mi, wastegate conversion

19 Honda CR-V EX 61k mi
Fourteen other MB's owned and sold
1961 Very Tolerant Wife

I'm with pastmaster. Looks like coolant mixed with oil. Check you oil and coolant levels and apperance. If those are mixed, It could be a cracked head, a head gasket, the oil cooler....

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Juan
1995 E320 Sedan
2008 Ford Escape
RC Helicopter

YES it is most likely an oil leek (motor) it need not be very severe,an oil leek will spread like water soaking into paper,the least amount of dew will cause it to foam though it is not foaming it more closely resembles milk the thick milky looking gunk you might find on the oil stick if you had an internal water leek