I had always had compression in all cylinders at 300 or more psi. The last time I tested was 2 years ago. I checked yesterday (when putting in copper seals in injection valves on IP). I had adjusted valve clearances a month ago and rechecked/adjusted them yesterday (a couple were a little tight). I then ran the car up to running temp., then checked compression. Here are results:

1. 290 psi
2. 310
3. 320
4. 328
5. 265

I will re-adjust valves on #1 and #5 wide..probably .2+ mm (in), .5+ (ex), run for 1,000 miles, re-adjust clearance and re-check compression. The 290 is not bad, but the 265 I assume is not good....probably cause of rough idle?? Any
thoughts??

Happy Thanksgiving to all of you and your families!

Thanks,

Mark

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1984 300TD Wagon, 407,800 mi (current daily driver)
1985 300DT Sedan, 330,000 mi (gone to that great autobahn in the sky)

What you would like to see is all cylinders within 10%. The good news is that the lowest is still 265 making this a drivable engine. I expect that the variation does indeed have some effect on your idle. Unless there is some other negative indication, I would not consider this engine in need of an overhaul unless you are just very, very particular.

The other data I would be interested in is the volume of oil consumption.

Good luck,

Larry, thanks for the feedback...I wasnt sure how far out was way out. The car drives very well and Im not inclined to do an overhaul. Instead I will play around with the valve clearances....I have had very good luck on this car after opening up valve clearances a little to find compression come up from 285 to 315. This car has had frequent oil changes all its life, and doesnt drink oil ...so any compression problems I have always attributed to valves, although Ive never done a leak down test.

Regarding oil consumption, I generally do not add oil between oil changes...once I ran synthetic oil for 10,000 miles before a change, and only added a half quart in this time. Now i just run regular Rotella 15w40 (in winter Rotella 10w40 synth blend) and change every 3,000 and dont need to add oil between oil changes.

Out of curiosity, how exactly is a leakdown test done....if you pressurize the cylinder, what is to stop leakage via valves?? Or does a leak down test pressurize crank case, and you watch for leakage up past rings into combustion chamber????

Thanks again Larry

__________________
1984 300TD Wagon, 407,800 mi (current daily driver)
1985 300DT Sedan, 330,000 mi (gone to that great autobahn in the sky)

In the leakdown test, you pressurize the cylinder and measure the percentage of pressure lost. If you apply 100PSI regulated and only read 90 when you apply it to the cylinder, you have a 10% loss. Typically you don't do a leakdown test unless you have a really bad compression test. The leakdown pressure can be heard where it's leaking. If it's the rings, you will here it through the valve cover, if it's the valves, you will here it through the intake or exhaust manifold. Thus the leakdown test allows you to determine if compression is lost past rings or valves.

Have a great day,