1985 300D Compression Test Results - PeachParts Mercedes-Benz Forum

sv-tex · #1 09-03-2009, 02:13 PM

I am looking at a 1985 300D Turbo with about 160 k on the odometer. The car is in really good shape overall with a ton of maintenance records. Runs well, no smoke to speak of, but I had a compression test done some insight into the engine. Here are the numbers:

310
320
225 on the #3
340
260

The valves were not adjusted at the time of the test, but had been adjusted a couple thousand miles ago.

This difference is more than what I have read is recommended, but is their life in this engine? Would it be wise to walk away? Any advice?

oldsinner111 · #2 09-03-2009, 02:26 PM

Run.Must have been lady driven.

toomany MBZ · #3 09-03-2009, 02:26 PM

Do a leak down test on #3.

#4 09-03-2009, 02:28 PM

Here's the thing! Yes, the engine needs work. The questions back to you; how much oil does it use? Are you getting the car REALLY cheap? How will you be using the car? How well does it run? How easy does it start when COLD?

The first question will be the toughest to answer. Unless you drive the car for a few weeks, you will have to take the word of the seller who may not even know, and if he does will he tell you the truth?

sv-tex · #5 09-03-2009, 03:43 PM

The current owner says it burns about 1 quart between oil changes, changing the oil about every 5000 miles. The car seems to run well, smooth idle, but it's hard to really say based on a test drive.

sv-tex · #6 09-03-2009, 03:46 PM

I would be using the car on a regular basis, ideally even daily. The seller was asking $3000 before the compression test, but I'm sure will come down in price. Aside from the engine though, all windows and the sunroof work, antenna works, locks work, and on and on. The owner says that when it is cold (20-30) he uses the block heater and it cranks right up, but without the block heater it struggles. As far as really cold, no idea (we don't have real cold down here)

b2948kevin · #7 09-03-2009, 05:18 PM

You might try adding some Xado from Xadousa.com. I'm not affiliated, but their case studies are pretty compelling.

Good luck!

ImBroke · #8 09-03-2009, 06:58 PM

definitely a leakdown test is in order, I'd do 5 too. With only 160k, I'd suspect a broken odometer, or something. I would say I better compression at 285k, but since I'm not the original owner, I don't know if my engine has ever been changed.

Whiskeydan · #9 09-03-2009, 09:23 PM

If it runs well, buy it and devote attention to the things that might let you down... belts, hoses, timing chain, tires.

brownrice78 · #10 09-03-2009, 09:29 PM

The car will continue to run good. Probably burns more than 1 quart in 3000 miles and expect the car to struggle to start below 40 degrees.

kerry · #11 09-03-2009, 09:41 PM

3 and 5 are unacceptable. Was the test done cold or hot? I'd do a leakdown test on those cylinders and a wet test.

ImBroke · #12 09-03-2009, 10:32 PM

Cali has one cylinder with low compression, starts quickly and runs good. However, when it's cold, it has a bad shake from running on 4 cylinders. If it runs fine, I'd say buy it and drive it.

sv-tex · #13 09-03-2009, 10:50 PM

The test was done by an MB mechanic, so I would guess the test was done hot. He did not do a leakdown test or a wet test. The owner again said he has not had an issue with the car not wanting to start, and in cold weather it starts fine with the heater.

Oracle12345 · #14 09-03-2009, 10:51 PM

how much is the seller asking?

Whatever he asks drill him down at least a grand just because of the potential repair needed on the engine. Any good tech or smart mechanic would do a leak down and wet test with the reading on clyinder #3.

kerry · #15 09-03-2009, 11:09 PM

Engine shouldn't need a heater at 20 or 30 degrees. It should start the same as it does at 60 or 70 degrees. At least mine always have.