Hi People-
I live in CT and have noticed that sinse the weather has started to get a little cooler at night that it is difficult to start the car in the AM. I'm wondering if it might be that the heater plug(s) need to be replaced. Any help would be appreciated.
Thanks

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Ed
1985 300D w/ 196,000 miles

Well, it's that time of year again, when the cold start questions start rolling in.

The best thing to do is simply put a voltmeter on one of the glow plugs to see if it is getting 12 volts or so when you first turn on the key. If it is, replace all five glow plugs, if it is not, start by removing the plastic cover from the rectangular glow plug relay on the drivers side wheel well. There is a bar fuse in there that should be checked for 12 volts on both sides under the same conditions. If there is not 12 volts on both sides replace the bar fuse.

Good luck,

On an 85 you should be able to check the resistance of each glow plug at the glow plug relay with a digital volt/ohmmeter. The Haynes manual explains how to do it. You could have one or more bad glow plugs.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

If you want to check the resistance, you don't have to do it at the plug, you can simply pull the rectangular connector at the glow plug relay and check them one by one from there.

That said, IMHO this is a waste of time. I have checked them numerous times, found them to measure good electrically, but after replacing them, the car starts perfectly.

If you are getting voltage to them and the car is not starting well when cold, just replace them. You will be glad you did.

Been there, done that.

Good luck,

Hi drawde:
I just fixed same problem. Car would start but with a lot of shakes, telling me 1 0r more glow plug is the problem.

Resistance at relay connector showed all fine. SO THIS TEST COULD BE DECEIVING.

Did not want to remove each plug as that would be too much.

So used a little trick I learned from a local car mechanic from my father's small town in India.

When the engine is cold, turn the ign- switch all the way but dont crank. Let the glow plug warm up sign in dash board go off. Then quickly feel area around each glow plug for warmth. It will be warm and not hot so you really will have to feel it good.

If the area around a glow plug is not as warm as others ( or not warm at all) that the bad plug. Turn off the key let the block cool off for 15-20 minutes and repeat the test. I have always found the bad plug doing this with near perfect accuracy.
Mind you at times I have had friends with more than one bad GP and this method still worked.

Hope you give it a shot and let us know what happens.

MVK

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One penny saved is three penny earned.

1985 300D Turbo 179,000miles

I'd check your valve adjustment if you haven't done it in the last 15K miles. Tight valves....hard start. Cold makes it more apparent.

__________________
The Golden Rule

1984 300SD (bought new, sold it in 1988, bought it back 13 yrs. later)

Hello People-
Well I finally got around to MB starting problem this weekend. I followed Larry B's advise and checked the voltage at the plugs. All showed positive. I went out and bought the plugs and put them in. It was a bit of a job. The fuel injection tubing is in the way and thus only allows a quarter to half turn on the wrench. It called for a little patience (not always found in men). Anyway, it worked perfectly. The car starts better than it has in a long time. I appreciate all the input and help. Thank you.
Ed

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Ed
1985 300D w/ 196,000 miles

Between Bosch and Beru glow plugs, other than around $2.00

JCD