Looked at an 85TD today on a dealer's lot. It is a trade-in. 120k on the clock. The previous owner says the odometer quite working a number of years ago. Body is fine, no rust, a few missing trim pieces in the interior. It started right up even when the diesel ignorant salesman did not wait for the glow plugs to energize.
My question concerns the engine. I took the oil fill cap off at idle and there was virtually NO blowby. Just the slightest whiff of smoke. Much less than on my 77 300d with just 55k. I'm inclined to take this as an indication that despite the unknown mileage, the engine is healthy. How reliable an indication of engine health is blowby?
By the way, they want $3400 for it.--it needs a winshield and a good cleaning.

Not a real indication but no blowby is better than alot. If it is an oil burner it will likely have blowby too.

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Mark
82 300SD 110k
91 Caprice SS
92 Jetta TD
97 Cadillac Concours(300hp)
84 Celebrity 4.3L diesel

Kerry Edwards,

Blow by is a good corroborative indication of a specific set of problems if they exist or are indicated by other symptoms. There is a range of blow by "volume" that is normal and acceptable, especially with a Diesel and its high compression ratio. But it is only a very crude indicator of when things are bad, partly because the visual response to blow by is a poor quantification of the actual blow by. On a cold engine, with relatively little of the oil at an elevated temperature, you may get an artificially low blow by "reading" too as there may be less oil near a vapor state, and the oil on the cylinder wall is likely still remaining a liquid with relatively high viscosity (especially with turbos as they have the little oil spray nozzles aimed at the underside of the pistons).

With the engine hot, at idle, you will see a more "accurate" reading, which is still mostly emotional or qualitative, not quantitative. I usually feel if there is enough volume to make getting the cap back on a little more trouble than just doing it with the engine off, you have a significant amount of blow by. And you probably burn oil. With less than that, I would look elsewhere for high oil consumption or some other problem diagnostic. Before I bought a car I would have a compression test done by a dealer or other reliable mechanic with nothing to lose or gain in the transaction as that attribute is very well understood and readily measured with accuracy.

The car sounds pretty nice, so, good luck, Jim

__________________
Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)

That quick start with out using the glow plugs is a very good indication of good compression. If it had bad compression, it wouldn't start without sufficient warm up of the glow plugs.

Go for it.

P E H