I'm new to owning or working with diesels and Mercedes. I have a 1979 300d. The car will start fine if the temps of 50+ degrees. When it gets colder the engine seems to have a hard time cranking fast enough to get it to start. The only way I've been able to successfully start the car is by hooking up jumper cables from my Suburban and keeping it revved up to around 2k rpm while trying to start the Mercedes.

I have checked the glow plugs. They are new but I checked them still with an ohm meter. They all measured at or just over 1.0. The battery has been checked by two different parts shops (Napa and Autozone) and cycled through 3 different charges just to make sure it was fully charged. Had a mechanic walk through the whole system just to see if anything was obviously wrong. He checked the wiring and said that it all checked out fine.

At this point the mechanic is suggesting swapping out the starter. He doesn't have any specific test to suggest that it is bad. And I'm not sure how to test a starter. I'm looking for any advice on what else I might try to narrow down the issue. I'd love to be able to test a certain part and say for sure that it is bad/good before I just go paying for exploratory repairs.

Battery selection / Charging System / jump starting / cold weather battery issues

Glow plugs link thread

Starter health is important to your diesel.

Cold weather starting links


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1985 300SD
1983 300D
1984 190D
2003 Volvo V70
2002 Honda Civic

https://www.boldegoist.com/

Have the valves been adjusted lately?

You can check your starter by its RPM sound.
My research indicates that a starter must spin min150 rpm for good starts. Here's link to my thread on starter sound files.

Starter cranking RPM sound files

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Some parts stores have the capability to test a starter. Where I live, Autozone can do it.

FIRST thing I'd do is verify the ground strap is on the block.
then, I'd loosen the ground cable from the battery to the body of the car, clean the cable, the bolt, the body mount, and then get a 40" or longer ground strap, and put it under the stock one, and connect the other side to the intake manifold somewhere. then drain the motor oil, and put in fresh synthetic oil. 5 W 40 rotella seems to be the lowest priced oil.
next, I'd pull all the glow plugs, as they are supposed to be around .6 ohms, not "just over 1.0" and replace them with a fresh set of BOSCH glow plugs.

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
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My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

Can you please elaborate on your exact starting procedure that you utilize in the cold weather?

Can you please advise on the brand and type of motor oil that you use in the engine?

Could you also indicate whether you have loop plugs or pencil plugs?

__________________
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

I wouldn't bother pulling the glow plugs since they are new. 1 ohm vs 0.6 ohms is your meter that is not accurate, not bad glow plugs.

Pulling the starter is a big job so I would suggest doing the easy stuff first. Since you verified the battery is good and fully charged and your starter seems to be spinning slow, check and clean the battery terminals and grounds and the wiring to the starter. Do a voltage drop test at the starter terminals, that will tell if you have wiring problems. If your starter sounds slow compared to the 164 rpm sound file, you have a problem. I've found out the hard way (over 2 winters) that sufficient starter rpm is required for good starts.

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

I wish it were mandatory that everyone include a general geographic location their header.

If the OP is in the northeast, and seeing the same temps I am seeing right now, if he has conventional motor oil in the crankcase he isn't going to get the car started without:

- a fully charged battery of the correct spec
- functional glowplugs and relay (which he apparently has)
- a starter turning fast enough
- correctly adjusted valves
- at least two glow cycles (waiting for the relay to click off each time)
- preferably a block heater

Given that the car starts to exhibit symptoms at 50 F, I am waiting to hear about the valve adjustment as a start point.

__________________


Mac
2002 e320 4matic estate│1985 300d│1980 300td
Previous: 1979 & 1982 & 1983 300sd │ 1982 240d

“Let's take a drive into the middle of nowhere with a packet of Marlboro lights and talk about our lives.” ― Joseph Heller, Catch-22

If I were going to use my 77 300d in the cold. I might consider getting a geared starter if I felt the old one was tired. There appear to be advantages to the series glow plug changeover as well. Massive energy loss on the series connecting resistance wires is eliminated just for starters. A total waste in my opinion. Where the block heater can be employed is a good ideal as well. For sure things are wrong if below fifty degrees it wil not start.

I know that my engine still has excellant compression though is a given. Also with mercedes experiences with diesel engines on the russian front during the second world war. I would have thought the cold starting of their diesels would have gotten engineered solutions long before the 123 series of cars came along.

Some of their earlier gas engines I owned were abnormally good at starting in really cold temperatures. This I did atribute to their experiences in Russia.

A good tdi diesel engine will start in the cold when gas engines are not even that interested. If and I am not holding my breath we ever see current japanese car diesels in north america. I really think cold starting wil not be an issue.

You can use a tachometer to accuratly find whatever revolutions per minute you car is cranking at. I have a cheapie that you put a reflective strip on and read it for example. Very accurate.

To answer a few questions:

-The valves have not been adjusted lately as far as I know.
-I live in Utah. Temp yesterday was around 20 degrees F when I as trying to start.
-The sound file for the starter is helpful. My starter does not crank that fast when it is having problems. After I hook up jumper cables from my Suburban and keep it running at around 2k RPM I can eventually get the starter to crank faster which in turn leads to the car starting.
-Starting procedure is as follows: Cycle glow plugs twice. Try to start. If it fails, hook up a portable jump start booster. Cycle glow plugs twice then try to start. If that fails hook up to Suburban with jumper cables. Cycle glow plugs twice. Try to start. Usually have to repeat the Suburban step 4 or 5 times. Seems like it will crank faster if I wait for about 5 mins after hooking up to Suburban.
-Not sure which type of motor oil is in the car. Sounds like time for a change to make sure I have the right stuff in there.
-I have pencil plugs.

-What I'll try out next: Get the oil changes and make sure I'm using the oil suggested here in the forum. Also will make sure the batter terminals are cleaned and wiring to starter is good.

Anyone have a link to a good video about how to do a voltage drop test on a starter?

Thanks for all the advice!

Okay that bit is pretty funny right there

Move it to south Florida .......I got room in the drive way

__________________
81 Mercedes 300SD 289k.......SOLD
82 Mercedes 300CD 252k......slow ride

82 mercedes 300 SD...mi Unknown
83 Mercedes 300D ????ksniff..gone too
84 Mercedes 300D 148k........SOLD
85 Mercedes 300TD 386k and holding some one elses project

I see no mention of checking 12 volts to the glowplugs.

__________________
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