My 1985 MB 300 SD will crank but wont start
Thread Starter
Newbie
Joined: Aug 2024
Posts: 1
Likes: 0
Mercedes Benz 1985 300SD
My 1985 MB 300 SD will crank but wont start
So a little info to get you up to speed. I bought this Mercedes from a fellow co worker about a month ago, I needed a car and I've always liked older models compared to the newer ones, the interior looked great and it ran , I was excited to own something so cool and have it for around 5000$ as my first car. I know nothing of cars at all. I work in a complicated electrical field so I figured wrapping my head around these old diesel systems would be a tight learning curve but doable if I put my mind too it. The car was running, and thats all I needed for now. It was a bit slow to acceleration but would get me up to 80 mph on roads I was allowed to go that fast on. Glow plug sound would go every time and it would start without a hitch every time. Up until last week, It would crank for a minute and not start. I would recycle the glow plugs and try again, nothing. One more time and it would go, puff of white smoke would come out the muffler and Id let her run for a few minutes and than head out to work. For about a week this was a my morning routine. Once I was at work, and would get let out for lunch, it would start just fine, and on the way home it would start fine. Than the next morning it would repeat. Until this weekend where I went to start it on Saturday and there it goes, cranking but not starting. Tried a few more times, and this time nothing. It'll crank but just wont start. I'm still in the process of moving so funds are a bit tight and Im without tools for now. I looked up a few things, I haven't tried the glow plugs for volts and ohms yet, but I did unscrew the manual primer to give it a few primes just to see if the fuel filter wasn't getting any fuel, to my dismay when I unscrewed the primer and as I pushed in on it a decent amount of diesel came out. I left it at that. I had the guy I bought it from swing by and look at it, we connected batteries cause the battery is dying now due to trying to get it started, with a bit of charge, it still wouldn't start, just cranking. I bought a repair kit for the lift pump and the replacement for the primer, that after a few days of letting sit is leaking now. Just hoping for a few bits of advice, cause Id like to learn this and do it myself before having to save a bit of cash and turning it over to a mechanic.
MBWorld Fanatic!
Joined: Jun 2021
Posts: 1,928
Likes: 523
From: New Hampsha
'17 GLS450, '14 GLK250, Grandpa's Roadster
If air is leaking into the fuel system when it's shut down that could be causing your problem, otherwise it sounds like your glow plugs are bad. I'm not sure which glow system you have, but some of the early ones fail completely; when one plug fails it prevents the others from working. These systems can be upgraded, should that be the case.
White smoke on start is unburned fuel, so that supports the glow plug theory.
One test you can try is to plug in the block heater and see if it starts after about two hours of heating.
White smoke on start is unburned fuel, so that supports the glow plug theory.
One test you can try is to plug in the block heater and see if it starts after about two hours of heating.
Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
