OM642 cold starting

snoman

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I have a Chrysler 300C CRD, fitted with the MB OM642 engine. The Owner's Manual states: "that in very cold weather it may be necessary to engage the starter motor for up to 30 seconds before the engine starts". Can anyone explain the reason for this as I have never experienced this situation with any other diesel car that I have driven? Usually, the engine will start after a couple of seconds cranking, but yesterday it took about 15 seconds. Admittedly, the car had been standing for several days in near zero temperatures, but my Audi diesel, in the same conditions, starts instantly.
 

mattkh

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Admittedly, the car had been standing for several days in near zero temperatures, but my Audi diesel, in the same conditions, starts instantly.

Perhaps the time taken to build up the fuel pressure as the car had been standing longer than normal.
 

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with the MB's with the same om642 engine , the idea is that when the glow plug light has gone out and you flick and release the key , the car will decide when it will fire into life . I'm guessing the warning is for extreme cold climates when the car goes about additional glow plug heating before attempting a start ?
 
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snoman

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Thanks for the replies, guys, however, I'm still puzzled. If fuel pressure and/or temperature is the problem, surely the ECU would be smart enough to recognise these conditions and keep the glowplug light on for longer until rapid starting could be achieved. Also, I wouldn't categorise "very cold" as hovering around zero. Does anyone know if this 30 second caveat exists in any MB manual; maybe it's just a Chrysler quirk? I've posed the query on a Chrysler forum and not had any comments.
 

Westheath

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I have a Chrysler 300C CRD, fitted with the MB OM642 engine. The Owner's Manual states: "that in very cold weather it may be necessary to engage the starter motor for up to 30 seconds before the engine starts". Can anyone explain the reason for this as I have never experienced this situation with any other diesel car that I have driven? Usually, the engine will start after a couple of seconds cranking, but yesterday it took about 15 seconds. Admittedly, the car had been standing for several days in near zero temperatures, but my Audi diesel, in the same conditions, starts instantly.

Some diesel Chrysler's use a fuel heater, perhaps in "very cold conditions" it takes some cranking for the fuel to heat up and get flowing again.

It must mean very cold conditions though.
 

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Sounds like a typical glow relay fault.
 

Westheath

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Hmm

I read the 1st post as a question from the manual rather than a fault.

GP relay is a common fault.
 

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Hmm

I read the 1st post as a question from the manual rather than a fault.

GP relay is a common fault.

Your right, it’s a question about a statement in a manual?
 

John Laidlaw

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Your right, it’s a question about a statement in a manual?
Wow, as bad as my (today) 7 year old son who questions everything even when it’s in black and white and irrefutable!
:p
 

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Why? Is every kids question. :D
 

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Wow, as bad as my (today) 7 year old son who questions everything even when it’s in black and white and irrefutable!
:p

Encourage the why's, having got a child who wanted a breakdown of everything including whats in toothpaste before he would clean his teeth (aaaaaarrrrghhhh) it is now bearing fruit.

Now I encourage dissent and argument as long as we part on good terms.

As to the original question the manual is written for a range of users in different countries some who do have very very cold weather and a car that takes a bit longer to start will have had chance to circulate some oil, something which I think is a good idea.

That approach from MB is to my mind a plus.
 

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Maybe its a clever ploy by Chrysler... Accept that the Glow Plug Relay will fail, tell the customer that "they all do that sir" via the manual, check and change the relay during each service (charging the customer as necessary) and everyone is happy :p
 

Wighty

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It can't be because of an expected parts failure 10 years down the line if it's in the manual , it must be a mechanism for protecting/starting the car in "extreme" cold weather .
 

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All the OEM's work to the lowest common denominator so like another member stated it is based on several days of very cold weather. I cannot see the glow plugs getting over their maximum glow temperature after 10 seconds, cranking does gradually increase the pressure in the combustion chamber, this increases atomisation of the fuel for it to ignite. The higher the mileage on some engines requires more cranking.
I have a twin diesel boat with 200 hp Ford traction engines and the one i reconditioned starts after 5 to 7 crankings, the other engine which has not been touched takes 20 to 25 seconds of cranking and smokes more for 5 minutes or so.
Cold weather causes "waxing" were the molecules of moistue inhibit diesel flow, this can be slight but when bad you have no flow.
Re-mapping of the ECU is also made possible due to the OEM's (original equipment manufacturer), leaning towards all extreme conditions and also the need for longevity of their product. Herbie.
 
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snoman

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Some interesting replies above. As nobody has confirmed whether or not the text in question can be found in any MB Manual, I can only assume that it applies to the Chrysler variant alone - but why? The cold fuel effect seems plausible, but I don't consider zero degrees to be "very cold", so maybe there are other factors involved. As far as I am aware, there is no fuel heater in the Chrysler engine.

As an aside, 99% of my cold starts are achieved within a couple or so seconds of cranking. Consequently, I sometimes release the key prematurely and before the engine fires. Subsequent attempts can then prove very difficult, but if I wait a few minutes all is well again. A quirk of the ECU maybe?
 

Wighty

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Just checked the manual ( om642) , there is no mention of extended start times in cold weather .
 
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snoman

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Thanks for checking; so it does appear to be a Chrysler peculiarity. Maybe they are just trying to cover every eventuality.
 

Wighty

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Thanks for checking; so it does appear to be a Chrysler peculiarity. Maybe they are just trying to cover every eventuality.
Isn't there a Chrysler 300 forum , those guys would definitely know .
 
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snoman

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I've posed the query on a Chrysler forum and not had any comments.
So I thought I would try here and with some success. I was interested in seeking MB community experiences as not all OM642 engines are alike.
 
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mattkh

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As an aside, 99% of my cold starts are achieved within a couple or so seconds of cranking. Consequently, I sometimes release the key prematurely and before the engine fires. Subsequent attempts can then prove very difficult, but if I wait a few minutes all is well again. A quirk of the ECU maybe?
How old is the battery?
 


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