Hard Cold Starting
 

My '80 300D just doesn't seem to like the block cooling below 100*F . It acts like the glow plugs aren't working and just cranks and belches smoke until it finally (sometimes) catches and runs. Once it's running,even just for a minute, if I shut it off it'll start again as it always used to and run fine . Filters are clean , gp's work , valves adjusted and a diesel purge done , cranking speed seems normal . Next on my list is to upgrade my gp's to new afterglow style c/w new relay , and following Thomaspin's manual I'm going to clean my injectors.

Make sure the contacts on the glow relay are clean and intact.

Replaced the glow plugs and glow relay on the '85 and she now starts easier than my '97...

I've seen so many posts where people said they worked and they didn't. You can do the ohm test, replace only failed ones, yada yada yada, and still not be able to start well.

Since LarryBible isn't here, I'll repeat the advice that he's given here probably dozens of times. Replace them all.

Kyle:

My experience with a low compression diesel engine is that altitude affected starting ability more than temperature.

For example, as long as the glow plug system was working properly, one low compression engine I had would start just fine at 3000 feet elevation with temperatures ranging from 30 to 90 degrees (f). Taking that same engine to 8000 feet resulted in extremely hard starting at temperatures of 25 to 80 degrees (f).
At the higher elevation I resorted to putting an electric heater under the oil pan, in addition to the block heater. Battery was in good shape. Starter too. It appeared to me that the air molecules were just too far apart at 8000 feet and the low compression that would start OK at 3000 feet wouldn't cut it at the higher elevation. Once I got it started, it would run just fine at either elevation.

I don't know your elevation, but I concur that you need to verify that your GP system and battery are doing their job.

Cheers,
Wes

Where did LarryBible go?

He's got a new job as a service writer at a Chrysler dealership. So he can't spend his breaks helping us out here on Mercedesshop. He's around, just not nearly as much.

Thanks for the responses guys, Rick I know what you're referring to as far as replacing all the gp's. The relay compares the current between gp1 and the others and if they aren't drawing similar loads then the relay will signal through the dash lite. The imbalance can also affect all the gp's operation.My dash lite has never worked so if that is the problem I'm left in the dark , so to speak. I picked up the new relay today c/w new gp's though I need to adapt my plugs to connect it. Tonight I'll change out my gp's and see if it does help. I suppose I need to think of them like spark plugs ( replace all at the same time) rather than light bulbs.
Wes , I'm at sea level here so altitude isn't an issue for me , I'll check the specific gravity of each cell in the battery tonight as well. I'll let you know how it goes tomorrow , I won't plug in the block heater .

This is probably not your problem, but I will point it out anyway.The cranking speed of the heavy duty starter designed for the turbos is a lot higher than the old non-turbo starter. My wife's 77 300d with 50k (original starter) has been slow to start in temperatures below about 20 degrees. The starter would need to continue to be engaged when a few cylinders started,until they all fired up. I realized this was probably the problem when I bought the 85td. The difference in starting rpm's was startling. I replaced the starter in the 77 with the heavy duty one a few weeks ago. The difference is clearly obvious. It starts much more quickly. Today it was about 20 degrees and it fired right up without hesitation. I would no longer consider putting the standard model starter in any 616 or 617.

Rick- Ok I'm ready to chant Larry's mantra with you - REPLACE ALL THE GLOW PLUGS , REPLACE ALL THE GLOW PLUGS , REPLACE ALL THE GLOW PLUGS!
After replacing the gp's I tested the old ones ( I tested them in the car 2 weeks ago) , 4 were dead !?! and one was fine (0.4 ohms). The turtle started after a full cycle (about 40 seconds) and ran much smoother than before ( no wonder :rolleyes: ). The relay was still frigged up so yesterday I found the connectors to adapt the new Bosch afterglow relay . Wow what a difference ! The glow lite comes on and turned off in 5 seconds , the turtle started immediately and ran smooth :) . So I'm assuming my compression must be pretty good still if it would start on 1 gp after cranking for 10 seconds.
Kerry- the upgraded starter is a smart fix and I did replace my starter a few months ago with a turbo model. The battery cells checked out as good to very good. A good battery and starter (as well as the connections between them) is a must for any diesel.

Replace all the GP?

But Larry thinks GP can be bought for $3 each.

Try getting them for that.

If you GP test OK on the resistance test and you think they still might be bad, remove them and connect them individually across the battery. If they glow red hot in a few seconds, thay are OK and replacing them will do nothing except make you about $60
poorer.

P E H

PEH- what you're saying does make sense, if a light burned out in your house would you change all the light bulbs in the house...NO!But.... I think Larry's point is that as they age gp's will run at lower and lower currents so by replacing a single gp in the system the balance is upset within the relay's 'diagnostic' circuit eventually leading to the problem I had with my car. The relay would put 11.75 volts to each gp but the gp wasn't receiving enough current (amps). I don't have a ammeter that will read above 10 amps so I could never test it . Am I on the right track here or am I just jumping to conclusions ?

Kyle,

I=ER or current = voltage * amperes.

So if the resistance reads about 1/2 ohm on all the GP, the current will be about the same. If any GP has a noticeable higher resistance, I might only replace that one after I did the visual test by removing it and connecting it to the battery and observing hot it got and comparing it to a new GP.

Hard starting is a more of a condition of low compression in the engine than old GP not getting hot enough. However, replacing the original GP with a set of the newer Bosch GP and relay may help get a low compression engine started when cold.

P E H