300D > 190D glow relay swap? - PeachParts Mercedes-Benz Forum

300GD · #1 02-07-2009, 06:36 PM

My new-to-me 190D came with a flakey glow plug relay. Sometimes I'd get a pre-glow indicator light, sometimes not, and in any case, the light would usually come on shortly after the engine was started and would remain on for about 30 seconds. Installing a new set of glow plugs had no effect on this.

Today I removed the original relay and swapped in a spare W123 glow relay I had on hand. I realize they're different parts, but it seems to work fine. Now, I get a pre-glow light every time, and never get it back on after the engine is started. Testing under the hood with my meter confirmed that the glow plugs are getting pre-glow voltage, and nothing after the engine is cranked.

The W201 relay had an extra input line, labeled T (temp sender?) But having one less pin on the W123 relay isn't a problem, at least as far as fitting the connector is concerned.

This was a free fix so I'm pretty happy about it as of now. Anybody object? I can't think of anything that I might be damaging by doing this, but I'm no expert. Thanks.

aaa · #2 02-07-2009, 06:41 PM

This might explain the "temp sender" line:
Interchangeability of glow plug relays

babymog · #3 02-07-2009, 10:06 PM

The 190D turbo has "afterglow" where the glow-plugs will remain on after starting if the engine is cold. You have eliminated that feature.

Bio300TDTdriver · #4 02-07-2009, 10:23 PM

Quote:

Originally Posted by babymog

The 190D turbo has "afterglow" where the glow-plugs will remain on after starting if the engine is cold. You have eliminated that feature.

The 190D had afterglow in '87? Why didn't the 300D have it in '87?

babymog · #5 02-07-2009, 10:33 PM

I'm not sure on that one either. AFAIK, the 602 has always had it, where the 603 didn't until '90 (3.5L). I felt I was going backward in technology when I sold my 190D turbo and bought the 300D.

Bio300TDTdriver · #6 02-07-2009, 10:39 PM

Quote:

Originally Posted by babymog

I'm not sure on that one either. AFAIK, the 602 has always had it, where the 603 didn't until '90 (3.5L). I felt I was going backward in technology when I sold my 190D turbo and bought the 300D.

I know the 602 got it in 1990. Maybe all MB diesels got it that year. What did your 190 have that your 300 didn't?

300GD · #7 02-08-2009, 04:58 AM

Quote:

Originally Posted by babymog

The 190D turbo has "afterglow" where the glow-plugs will remain on after starting if the engine is cold. You have eliminated that feature.

Ah...I've seen references here to the 190DT having the afterglow feature. And the response as seen in this thread is typical - a lot of people have the impression that this feature didn't appear until the 300D got this engine in 1990. But I think this settles it. The OM602 turbo had the afterglow feature from the beginning ('87).

If that's all I'm giving up, I have no problem with that. Living in the South, I can easily make do without it, and from what I've read, my glow plugs should last longer this way. Which is a bonus, because that job wasn't something I'd care to do very often on this car.

Maybe the only thing wrong with my original relay was that it often failed to turn on the dash light during pre-glow. In any case, I think I'll just stick with the W123 relay.

babymog · #8 02-08-2009, 12:00 PM

Quote:

Originally Posted by Bio300TDTdriver

I know the 602 got it in 1990. Maybe all MB diesels got it that year. What did your 190 have that your 300 didn't?

My '87 190D had afterglow, I thought that you caught that. It was original, covered in the 1987 operator's manual.

Bio300TDTdriver · #9 02-08-2009, 12:05 PM

Quote:

Originally Posted by babymog

My '87 190D had afterglow, I thought that you caught that. It was original, covered in the 1987 operator's manual.

Yes, I think it sunk in. What else did that car have the your 300D didn't?

Jeremy5848 · #10 02-08-2009, 12:15 PM

Mercedes tended to "experiment" by putting changes on only one model or series at a time. Thus, the cars that would evolve into C-class got the afterglow feature first. It's hard to compare glow relay part numbers because of the different number of cylinders.