79 240d, oe style series glow plugs, car starts fine. I noticed recently that with the motor running the zig-zag wire coils between the plugs are getting hot, glowing red after a 30 minute drive.

I don't know what those coils do but don't expect they should be powered during running and certainly not glowing red hot. Malfunctioning controller?

Something is stuck on for sure. The glow plugs should not be energized once the engine is started.

__________________
Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

sounds like you have a stuck on relay. pull the fuse, then take apart the relay... (under the steering column) then open it up, and see if the contacts are fused.

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

Those heavy wire coils are the resistors to lower the voltage each glow plug in series sees. Never check one of those glow plug types out of the engine with twelve volts. They only see something like 1.2-1.4 volts each in service. Forget the actual number but it very low.

A kind of strange design as that system generates a lot of heat in those resistor wires.Where it really is needed is by the glow plugs. Wasted energy.

Reminds me that I should get a spare used controller. The 1977 300 d we have still uses this system. Since the car is used only in the warmer part of the year. It does not need the improved parallel system upgrade.

Although you should carry at least a test light and a short piece of heavy wire with two clips in the trunk. When you own one of these series systems. If one glow plug fails they all will not function. Some of these older diesels will not start without the glow circuit working even in decent weather.

With the two piece repair kit you can easily locate what glow plug has burnt out and just jump it. With the wire and clips. Also the system strip fuse is cheap and they can eventually just age out with cycling.

I think the controllers are expensive new. Well at least for what they are. It is the silver box held in place with one screw above the brake pedal cluster. The one in our 77 300d failed years ago. In that case the internal relay would not close up. Used ones where really cheap back then as well and easily available.

OK, I am trying to locate the preheat relay. Haynes manual simply says some cars its located on front left fender but doesnt say anything about my car (79 240d). Others mention that its under the left dash near the brake pedal or steering column. I have three silver boxes under there;

1. just behind the dash, right up next to the left of steering column, about the size of a pack of cigarettes.
2. Far forward, almost touching the firewall, a little farther left of box 1, size 1.5x4x5.5, ten pin plug.
3. far left side next to e-brake, about 1.5x2x2.

Can anyone provide a little more detail as to which box is the preheat controller?

If you have series plugs, I believe it's located under the dash. It should look something like this:

Had an ignition key that was cut slightly different than the original, the ignition lock cylinder did not return fully to the run position causing a similar problem. Found it after the starter wouldn't disengage.

The problem though is much more likely a sticking relay as stated in previous posts.

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"Rudeness is a weak man's imitation of strength" - Eric Hoffer

If you have a chance... change to the pencil type glow plugs
if yours go out.. they all go out...like old fashioned Christmas tree lights.... LOL
the pencil types can go out one at a time and not cause you big problems all at once.

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1980 240d ,

chain elongation, cam marks reference:
http://www.peachparts.com/shopforum/diesel-discussion/10414-help-i-need-check-stretch.html

http://www.peachparts.com/shopforum/diesel-discussion/305365-9-degrees-chain-stretch.html

evap fin cleaning:

http://www.peachparts.com/shopforum/diesel-discussion/156207-photo-step-step-post-showing-w123-evaporator-removal-1983-240d-1982-300td.html?highlight=evaporator

A/C thread

http://www.peachparts.com/shopforum/diesel-discussion/297462-c-recommendations-mb-vehicles.html

Aslo check your temp. sensors if the one closest to the front of the car is lose or disconnected. The glow plugs will stay on.