HI I'm new to the list.
Does anyone have a take on what's going on inside diesel motors during cold start? In other words what's the equivalent to a choke in a gas motor with a carburator?
I'm asking because our 82 240D will start when cold, and run well after warmup, but during the time it takes to warm up, it runs noisy and skips.
Not much smoke from tailpipe. What there is is gray.
Changed both fuel filters, air filter.
Took apart one injector, it was very clean.
Motor rebuild less than 20k miles ago.
Have heard it might be glow plugs - do they play a role after motor starts?

Thanks for any ideas.

Harvey

Harvey,

Your simple question opens up quite a large subject. There is no such thing as a choke on a diesel engine, there's not even a throttle. Diesels draw a complete gulp of air with every intake stroke. The power is controlled by the amount of fuel that is injected into the cylinder. The ignition heat comes from the air being compressed by about 21 times. Upon start up while a diesel is warming up they do not run very well. However, it should not run rough for very long, maybe a minute or two.

The late 123 diesels from '81 on had parallel glow plugs. They work quite well, but I seem to have to replace them every couple of years. Yes, the relay does keep them on for a short time after the engine starts, depending on the temperature sensed by the temperature sensor which is connected to the glow plug relay.

There also is a flat knob below the instrument cluster and just above the left side of the steering column. In cold weather, you can turn this to the left, pressing a little on the accelerator pedal makes it easier, this will speed the engine up a little while it warms up.

You may very well find that replacing the glow plugs will correct the rough idle upon start up.

Good luck,

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Larry Bible
'84 Euro 240D, 516K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in
Mercedes automobiles

The glow relay turns off the glow plugs on all engines before the 60x series. If you have any of the 61x series, it turns them off when you hit the starter. IF you have a 60x series, it will allow the glow cycle to complete before turning off the plugs.

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Benzmac:
Donnie Drummonds
1992 500E (very soon I hope
1981 280GE SWB
ASE CERTIFIED MASTER AUTO TECHNICIAN
SERVICE MANAGER FOR 14 BAY FACILITY
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