Hello, new to this board but hope someone can help. I purchased an 84 300 sd off of ebay that was in a front end collision. It sat for about a year and was headed to the bone yard but I got it cheap and replaced the front clip - including welding in a front inner fender. I am officially addicted to the Mercedes diesels and am impressed how this car drives considering what she's been through. I live on the great lakes and now that it's cooler at night, I'm having a horrible time getting the engine running in the morning, block heater plugged in or not. Once I get running after ALOT of cranking, it'll start fine the rest of the day, under any conditions. Every morning is a chore, though, and as it gets colder will really become an issue. Any suggestions? Thanks in advance.

Check your glow plugs.

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1979 240d 216k (W123) Daily Driver
Volvo 245DL 210k

1979 300D FOR SALE
2002 Tahoe 91k FOR SALE

1980 300sd 177k (W116) Sold
1980 300sd Parts (W116) Junked
1979 240D 121k (W123) Sold
1982 300TDT 298K (W123) (Sold)

Welcome to the forum.

The very first thing to check when a diesel won't start is the glow plugs.

Odds are that you've got one, or more than one, burned out plug. Or, the fuse inside the relay is burned and none of the plugs are working.

So:

1) Put a 12V test light or meter on each of the glow plugs after you turn the key to the #2 position. You've only got 30 seconds for this test until the relay cuts out, so move quickly.

If you have voltage at the plugs for 30 seconds, the relay is fine.

If you don't, then the fuse or the relay is NG.


2) If you have voltage at the plugs, then it's time to check for resistance in the plugs. You'll need a good meter that can measure resistance down to 1 ohm........not always available.

When you buy or borrow such a meter, pull the plug on the side of the relay (on the driver's fenderwell) and there will be five sockets inside. Connect one probe of the meter to each of the five sockets, in sequence, while the other probe is connected to ground.

Read the resistance values.

Anything over 1.5 ohms is NG.

Any open circuit is definitely NG.

Change the glow plugs that fail this test.

Use either Bosch or Beru plugs. They are available from the forum sponsor by pressing "buy parts" at the top of the page.

Good luck.

Do a compression check. A marginal engine will start fine in warm weather, but as soon as it gets cold

I'd make sure your block heater is working. That may be the quickest fix. You should be able to hear it working when you plug it in. There's a good chance that the cord is worn through and shorting out since it's right up against the engine and exhaust, mine was when I bought my car. The cord is fairly easy to unplug and fix or replace from underneath the car.