difficult to start on cooler days - PeachParts Mercedes-Benz Forum

tomparsi · #1 10-09-2002, 01:29 PM

Back again with the same problem. I have a tough time starting my 1983 300CD on cooler days. after the golw plug indicator goes out, I try to crank it and I get no response. After the intial start, I don't have any problem with it the rest of the day.
I got some feed back on this site to replace the glow plugs. I did that yesterday and I still have the same problem. I make sure the tank is full at all times. The battery is new. I use mobile one delvac synthetic oil. Any sugestions as to what's causing the problem?

1983 300 CD
195k

#2 10-09-2002, 02:19 PM

I would have to agree with Bill, don't crank when the light goes out, wait a few seconds. I always wait 10-20 seconds for the light to go out and it starts right up. Sometimes I forget to wait, and it won't start right up.

kerry · #3 10-09-2002, 02:35 PM

I wait 40 seconds after the light goes out on my 77 300d and it starts on the first compression stroke. If I try immediately after the light goes out it cranks for 5 or 6 seconds before it starts.
On the other hand, with my 85 300td it starts much better if I try immediately after the light goes out. I assume that difference is accounted for by the different kind of glow plugs in each vehicle (seriel versus parallel).

diesel don · #4 10-09-2002, 03:19 PM

The glo plug relay (black box on driver's fender wall near the front) has a 30 cent metal fuse in it. Mine was bent but still in tact when a veteran pointed out that it won't work very well bent. You might look at that.

In addition, the glo relay can have some loose contacts. Try tapping the black box on the side next time it happens to see if it stirs anything back to life. On my '84, this happens several times per winter. Just bought another one from a junkyard but haven't installed it yet.

Don

kerry · #5 10-09-2002, 03:20 PM

If it's not cranking at all, I would first look at all electrical connections and make sure they are tight and clean.

Stevo · #6 10-09-2002, 04:07 PM

Are you guys using the new pencel type plugs? It made a BIG differance on my '79". It fires right up now..

I bought the kit for my daughters 240d but havent quite figured out the wiring yet,

not my strong point. The cost was not that much more than a set of plugs.

tomparsi · #7 10-09-2002, 05:24 PM

If it's an electrical problem, then how come it just does this only when initially starting it and then no problems the rest of the day?

JimSmith · #8 10-09-2002, 06:15 PM

tomparsi,

The behaviour of batteries and starters, as well as a few hundred pounds of metal/water/oil over a 24 hour period with a few hours of operating time, sunlight, etc. can be a little confusing.

First, the battery is a chemical energy storage device that prefers to be warmer than colder, and under cold conditions can show indications of internal damage that just don't get over the threshold of your noticing them when the battery is warm. In addition, oil has a tendency to be more viscous when it is cold, adding friction and pumping loads to the process of starting compared to when the system is warm. And, a Diesel as you know uses the heat of compression to ignite the fuel, with an assist from the glow plugs. With low compression, or slow starting engine rpm even new glow plugs won't help you get one started. Tight valves, by the way, can lead to low compression symptoms as the valves stay open too long and part of the compression stroke is lost. If they get too tight and there is zero clearance, it is feasible the entire compression stroke is lost.

So, all this sums up to much greater strain on the battery as the normal starting load tends to go up (oil, etc), longer glow times draining the battery before the starter is engaged, and you likely get a slightly slower engine speed that decreases as the starter runs longer. A slower engine speed means somewhat lower compression (more time for the leaks to leak) and more of the heat of the available compression gets sucked into the engine block, resulting in the air temperature at the moment of injection being significantly lower than when the block is warm. Leading to longer cranking times which damages the starter motor over time. Which shows up as slower cranking speed all year round, but is most significant when the temperatures fall.

Once the engine is warmed up (I like the term "heat soaked")after running for some time, it takes time, depending on how low the ambient temperature is, for the block, the water and the oil to get below a critical value that causes the symptoms (weak battery, starter, possibly even valves out of adjustment) to show as a car that is hard to start cold. This time can be short, if the outside temps are below zero, or they can seem like most of the day, if the outside temps are just below the critical value where all these individually minor effects add up to your car not starting.

So, I would check the valve clearances and set them on the loose side, then try a new battery and possibly a new starter. If you elect to try a new starter, try FastLane, and get the one listed as HD for the later 300D models. They are interchangeable and the HD one has some extra capacity. Good luck, Jim

#9 10-09-2002, 06:28 PM

Couple of years ago I bought some AC glow plugs at NAPA for my 81 SD. The car would not start at all after about a week. (It was January then) Finally pulled them and ran 12v to them and NONE of them would heat.
Always buy OEM. Especially with electrical parts.