I purchased a 1962 Unimog with and OM636 Mercedes diesel with 11,000km on the clock. Due to time constraints I was not able to check out the truck before purchase. I should know better. The truck has sat for about two years in a closed garage. It is bear to start and probably has some bad glow plugs. It smokes like hell on start but cleans up after 30 seconds. The engine has little power and a mechanic that looked at it said it appeared to have low compression but he did not do a compression test. Could it be possible that the valves are hanging up after sitting so long? What should I look at other than doing a compression test. Thanks. Ed
Unimog Mercedes Diesel Engine Problems
- Thread starter allfoden
- Start date
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The smoke on start up is most likely glow plug issues like you stated complicated by low compression.
First check your valve clearances if they are manually adjustable. If they are hydraulic lifters then maybe some of them are stuck which means disassembly. Striking the tops of the valve keepers with a rubber mallet or a piece of wood while at TDC will show whether they are free. They should snap back closed instantly.
The low compression could be due to coked rings which depending on previous service, oil changes, type of oil, seems to be even more evident when the engines sit for long periods. It seems that the rings just weld themselves to the lands in gum and crud. I am not sure about successful decoking with additives. Some swear by them but if it is bad.....I had a VW 1.6 that did this after a longer period of storage. The only real cure was to pull the pistons, peel out the rings, decoke the ring lands chemically and by skraping. There was left a hard carbon in the lands that would not be moved except by careful skraping. Then fitting new rings in lightly deglazed cylinders restored the engine to better power and reducing oil consumption to normal.
Why would this autoprogram edit the correct spelling of skraping with a "c" to show as a foul word????????
First check your valve clearances if they are manually adjustable. If they are hydraulic lifters then maybe some of them are stuck which means disassembly. Striking the tops of the valve keepers with a rubber mallet or a piece of wood while at TDC will show whether they are free. They should snap back closed instantly.
The low compression could be due to coked rings which depending on previous service, oil changes, type of oil, seems to be even more evident when the engines sit for long periods. It seems that the rings just weld themselves to the lands in gum and crud. I am not sure about successful decoking with additives. Some swear by them but if it is bad.....I had a VW 1.6 that did this after a longer period of storage. The only real cure was to pull the pistons, peel out the rings, decoke the ring lands chemically and by skraping. There was left a hard carbon in the lands that would not be moved except by careful skraping. Then fitting new rings in lightly deglazed cylinders restored the engine to better power and reducing oil consumption to normal.
Why would this autoprogram edit the correct spelling of skraping with a "c" to show as a foul word????????
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Marvel...
I agree that the symptoms may be due to stuck rings... this seems to be a common problem in vehicles that have set unused for some time. IIRC some have used Marvel Mystery Oil to free up the rings - go to the MB diesel forum for expert advice on MB diesel engines including Unimog. I've read some threads there about stuck rings - good luck, here is the forum:
PeachParts Mercedes ShopForum - Powered by vBulletin
Search on Marvel Mystery Oil - you'll get lots of hits
James
(mercfan)
I agree that the symptoms may be due to stuck rings... this seems to be a common problem in vehicles that have set unused for some time. IIRC some have used Marvel Mystery Oil to free up the rings - go to the MB diesel forum for expert advice on MB diesel engines including Unimog. I've read some threads there about stuck rings - good luck, here is the forum:
PeachParts Mercedes ShopForum - Powered by vBulletin
Search on Marvel Mystery Oil - you'll get lots of hits
James
(mercfan)
I have wondered this for a while too, thought it was some american swear word until now lol
rchalmers3
I speak Toyota
I recommend driving it a few weeks to see if the engine loosens up and corrects itself. I have driven diesels that have sat for a while and a few times I have noticed that fresh fuel and 3 hours on the interstate do wonders for restoring power.
On coked up engines there is a low cost remedy available: water ingestion. If you carefully add small amounts of water to the intake of the motor while running at medium revs, you can clean off piston tops and restore smooth idling. This is not for the feint of heart but works wonders.
Rick
I tried this on my mother's 95' Nissan Maxima that doesn't get used enough, her car started surging on take offs, and felt low on power when up to speed. By recomendation from a mechanic she went to, he said the valves could be a little on the sticky side, and to add an oil additive to clean it up. I put a can of Engine Tune Up from Wynn's, and fuel additive in the tank. It seems to have worked, the engine runs smooth and power is back. Has the oil been changed, and are you using fresh diesel? Maybe add 2 cans to your engine oil, and a bottle of Standyne in your fuel tank. Worth a try.
Try SEAFOAM you can get it at NAPA, put some in your tank and drive the s*** out of it.
