617 engine will start without glow plugs ??? - PeachParts Mercedes-Benz Forum

soothappens · #1 09-29-2010, 10:39 PM

My wife's 81 300SD has been giving her problems starting in the morning.
When I say problems I mean 2 to 4 revolutions and it fires up. It usually starts like a Gasser firing when you fully engage the key.

Hardly a problem When you compare it to my worn out 240D.

I checked the glow plugs and figured I would find one bad...... To my surprise I found three dead. Only 4 and 5 are functioning yet the car still starts.

My question is if all were to fail would these engines still start ? temps are in the 50's in the mornings so I guess that helps .

According to my 240D this shouldn't be possible. One goes out on it and it stays home.

jonbobshinigin · #2 09-29-2010, 10:56 PM

I bought a 1981 300D which sat for 4-5 years at previous owners without being run. It ran fine until a belt broke and then he just let it rot. I was just messing around and being excited about it turning over one day when it fired up! The glow plug relay was dead at the time and I imagine it had several bad glow plugs anyhow. Granted this was mid summer, but it still started.

#3 09-29-2010, 10:56 PM

Depends on several factors; temperature, compression, valve adjustment, starter/battery condition, injector condition, fuel cetane, etc.

bobodaclown · #4 09-29-2010, 11:10 PM

Quote:

Originally Posted by Craig

Depends on several factors; temperature, compression, valve adjustment, starter/battery condition, injector condition, fuel cetane, etc.

Agree!

pawoSD · #5 09-29-2010, 11:17 PM

A high compression well adjusted 617 can start completely without plugs down to probably 40-50F pretty easily. My brother's 300D is insane, you can disable the glow relay and it will start cold at 50 degrees with less then 7 seconds of cranking. Mine is not so friendly, it takes about 10-12 seconds with a moderately warm motor (run within the past 4-5 hours) to start without them, but with plugs it will start all the way down to below 0F reliably. Weird.

moon161 · #6 09-29-2010, 11:37 PM

Can be done, skinny pedal on the floor and crank it. I gather you should give the starter and battery a break after a minute if you haven't started. Lost a glow plug or 2 a couple 2 winters ago (-11 F), had to use a hair dryer to heat the torpedo heater till it started, used the torpedo heater to get the engine cozy. Had to idle the car at work periodically to keep it in the cozy zone till the air temp got above 15F.

Stretch · #7 09-30-2010, 02:51 AM

Quote:

Originally Posted by moon161

...Lost a glow plug or 2 a couple 2 winters ago (-11 F), had to use a hair dryer to heat the torpedo heater till it started, used the torpedo heater to get the engine cozy. Had to idle the car at work periodically to keep it in the cozy zone till the air temp got above 15F.

Nightmare!

layback40 · #8 09-30-2010, 04:26 AM

These diesels will sometimes start without GP's, but at the end of the day its better to have your GP's all good & save your starter.

Cr from Texas · #9 09-30-2010, 02:02 PM

I've never replaced or even tested my glow plugs. It always starts!!!

soothappens · #10 09-30-2010, 10:21 PM

Quote:

Originally Posted by layback40

These diesels will sometimes start without GP's, but at the end of the day its better to have your GP's all good & save your starter.

Its a good feeling knowing they will start but after changing out the 3 bad ones and listening to it start I have to agree on better to have them all working. Fired right up and purred !!!

Moon all I can say is that's true dedication .......... I would have given up at the hair dryer part.

Going down Craig's check list I think all is well. Now I feel confident going into our harsh 30* winters.

#11 09-30-2010, 10:28 PM

Quote:

Originally Posted by soothappens

Going down Craig's check list I think all is well. Now I feel confident going into our harsh 30* winters.

If the engine's in reasonable condition and everything is maintained, 30F should be a piece of cake. Starting at 0F requires everything to be closer to perfect (especially the battery).

pawoSD · #12 09-30-2010, 11:27 PM

Valve adjustment precision really begins to play a roll in the sub 30F range, another reason on-time adjustments are necessary

compress ignite · #13 10-01-2010, 12:19 AM

CR,

Now you've got his ear...

compu_85 · #14 10-01-2010, 12:36 AM

I've never tried starting mine without the plugs, I should sometime just to see what it does.

I have started my VW IDI in the cold without glow plugs. When it gets down to 20*F it took about 25 sec of cranking, and before it fired it shot little round balls of soot out of the exhaust. There was snow on the ground and the little sootballs slid on top of it in the wind.

-J

Squiggle Dog · #15 10-01-2010, 05:30 PM

My 1980 300SD was having trouble starting right away in 40 degree weather. One morning it got into the 30s and wouldn't start at all. I tested the glow plugs and NONE of them were working. I replaced them with some used plugs and BAM, it fired right up!