300gd and 300d - Mercedes-Benz Forum

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post #1 of 2 (permalink) Old 04-09-2012, 07:03 AM Thread Starter
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300gd and 300d


I own a 1979 300sd that is my daily driver (Love it!). I recently came across a 1981 300gd that has been sitting for 10 years. I bought the car in non running condition, figuring that it was a mercedes diesel and it would have to run with the proper mechanical tweaking. First off, the injection pump was stuck and it had 10 year old diesel fuel in it. I added octane booster and lucas fuel treatment to the tank and rebuilt the pump. The car fired up and ran, but only on 4 cylinders. I checked the non firing cylender for compression and it was 150. The next one was 150 as well the following one was 250. I had to rig a snap on compression tester with a bunch of different fittinggs to get one that was close to the glow plug thread. Not sure if I loosing pressure through the fittings or not. I foud another engine complete for $350 on craigslist and bought it. It too shows low compression and the owner says that it has been sitting for 9 months but came from a running car as he proceed to show me a picture of a wrecked 1985 300sd. What gives? Any suggestions on wher to get the exact fitting for the compression test on the glow plug hole.
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post #2 of 2 (permalink) Old 04-09-2012, 10:15 AM
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The glow plug fitting for the tester is pretty standard as lot of German makers are using the same glow plugs. Is your tester lacking proper fitting?
Diesels should compress well above 200 psi, so you really need to check the lower cylinders.
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