W123 glow plugs - PeachParts Mercedes-Benz Forum

Guest987 · #1 07-22-2019, 11:57 AM

I was in a hurry a few days ago & didn't wait on the glow plugs, but it started right up. Well, I noticed after that it is still starting up without the glow plugs warming up. Can you help on what might be the issue? The light in the dash for them is still operating correctly. It comes on with the ignition key & goes off like it always did.

Diseasel300 · #2 07-22-2019, 12:30 PM

And the problem is? If it's warm outside and your engine is healthy with good compression, glow plugs aren't needed to start.

BWhitmore · #3 07-22-2019, 12:33 PM

That is correct. If I am driving my 300D on a warm day and making several stops and starts, after the initial glow time in the morning, I have no need for glow time the rest of the day.

Maximan1 · #4 07-22-2019, 01:03 PM

X3. Previous owner hid the issue of improperly wired glow plugs on my '79 240D by getting it started and warmed up well before I got there to check it out. I drove around the rest of the day with no working glow plugs, unbeknownst to me. Next morning the issue became apparent, when the now completely cold engine did not want to start in.

I wired the glow plugs correctly and didn't have any more issues. Glow plugs aren't really needed on a warm engine/in a warm climate.

Guest987 · #5 07-22-2019, 01:15 PM

The issue is even on overnight cold. It will start right up now with out warming up the glow plugs!

Diseasel300 · #6 07-22-2019, 01:48 PM

Quote:

Originally Posted by Guest987

The issue is even on overnight cold. It will start right up now with out warming up the glow plugs!

That's not an issue, it's a sign of health. Your engine has good compression and no air in the fuel system.

Guest987 · #7 07-22-2019, 02:37 PM

Thanks for all the help. I just thought something might be grounded out, and maybe burn up the relays and glow plugs or something.

barry12345 · #8 07-23-2019, 07:39 AM

Quote:

Originally Posted by Guest987

The issue is even on overnight cold. It will start right up now with out warming up the glow plugs!

Just a sign of a good healthy engine that still has good compression..Usually.

I should ad because it is important. With or without glow plugs quick starts are a good sign the fuel system is not back draining either. A lot of winter and summer start problems are the fuel had back drained so the engine has to crank some to get the fuel back up and under pressure to feed the injectors. Before it will consider starting.

t walgamuth · #9 07-22-2019, 01:23 PM

Are you thinking it is a problem because the gp might be working all the time?

JHZR2 · #10 07-22-2019, 01:41 PM

Unless the gps are staying in too much (which would kill your battery), this is all good.

t walgamuth · #11 07-22-2019, 03:33 PM

Keep an eye on it. If the gp relay gets hot and hums it can be stuck.

Diseasel300 · #12 07-22-2019, 03:51 PM

Quote:

Originally Posted by t walgamuth

Keep an eye on it. If the gp relay gets hot and hums it can be stuck.

A dead battery would be a quicker sign of problems. Stuck on GP's will kill it quick.

t walgamuth · #13 07-23-2019, 07:36 AM

Quote:

Originally Posted by Diseasel300

A dead battery would be a quicker sign of problems. Stuck on GP's will kill it quick.

True. It has been about 24 years since it happened to me so some details are fuzzy.

Diesel911 · #14 07-22-2019, 08:31 PM

Quote:

Originally Posted by Guest987

I was in a hurry a few days ago & didn't wait on the glow plugs, but it started right up. Well, I noticed after that it is still starting up without the glow plugs warming up. Can you help on what might be the issue? The light in the dash for them is still operating correctly. It comes on with the ignition key & goes off like it always did.

When you are cranking your Engine your Glow Plugs are on because there is a wire that connected it to the starting circuit and goes to the Glow Plug relay.
I don't know if the Temp Sensor would prevent that or not if the temp was high enough.

If you don't believe me have someone connect a volt meter to a Glow Plug while you crank.

Maximan1 · #15 07-22-2019, 10:43 PM

Quote:

Originally Posted by Diesel911

When you are cranking your Engine your Glow Plugs are on because there is a wire that connected it to the starting circuit and goes to the Glow Plug relay.
I don't know if the Temp Sensor would prevent that or not if the temp was high enough.

If you don't believe me have someone connect a volt meter to a Glow Plug while you crank.

My glow plug relay did not have an input for the temp sensor(s). The one I am using is from a 1983 federal 300D. Not sure if I missed something when wiring it up.