What is this in a 616 head? - PeachParts Mercedes-Benz Forum

JimmyL · #1 07-26-2007, 12:56 AM

The old seized engine from China has two "probes" in the head.

The "new" engine in China only has one.

I'm guessing it has something to do with the glow plug system, as it goes to the relay.

I know one usually checks temp during glowing (right?). What would the other be? Where is the temperature guage probe, btw?
Thanks.

#2 07-26-2007, 01:06 AM

I believe the early style used cylinder head temp to control how long to glow and the later used a sensor built into the GP relay.

The second should be for the temperature display in the instrument cluster.

JimmyL · #3 07-26-2007, 01:33 AM

Quote:

Originally Posted by ForcedInduction

I believe the early style used cylinder head temp to control how long to glow and the later used a sensor built into the GP relay.

So, the original GP relay is going to want a temp reading from a probe that isn't there. Should I swap back to the other harness provided I can find where I put the other relay from Scar? Seems like other wiring is different too, at the relay.....
Uffffff.....

Mustang_man298 · #4 07-26-2007, 11:58 AM

This one's an easy fix. Lance is right about their functions. I ran into this same thing when I put the 617 in my '80, my fist thought had been to take out one of those coolant plugs and replace it with the bushing and sensor from my old engine, only the plug was frozen in, yours will probably be too. I did try to glow it without the sensor, the GP's did work from what I remember, but they didn't work correctly.

Here's the fix:
First, did either of the car's have an EGR setup that used the plastic v-shaped vacuum switch on the t-stat housing? Use that housing, remove the switch, put a plug in the smaller hole if you have 2 holes. The sensor will now fit right into the housing, will not interfere with the t-stat, and since it's above the t-stat it will still read the temp in the head. Then you can either solder an extension to the existing wire for the sensor, or do what I did. I didn't want to cut up the wiring, so I went to the wrecker and found a newer model (I think 82 up has these) look at the GP relay, there will be a single round connector with a single wire on it. I don't know what it was for (it only apeared on the later models) you want the male half of that connector, and you also want one of the sensor connectors from the wrecker too. I then carefully popped the connectors open, and soldered in an extension wire, which now plugs to the factory wire and the sensor and looks clean and factory-ish. I even took some of the plastic sleeving fron a GP wire too to put on my new wire for the look (& protection). I then ran it along the upper A/C hose in front of the engine with a pair of zipties. My only dead giveaway that it was added was that I only had white zipties on hand, factory would've been black,lol. (you could even snag a couple of the factory reuseable ones while you're at the wrecker.

JimmyL · #5 07-26-2007, 09:28 PM

Chris, you are a stinkin' genius!! I do believe that I have a plug on the t-stat housing in that location. I'm headed outside to see if that sender will budge from the seized engine.
I'm optimistic for now......

Quote:

Originally Posted by Mustang_man298

This one's an easy fix. Lance is right about their functions. I ran into this same thing when I put the 617 in my '80, my fist thought had been to take out one of those coolant plugs and replace it with the bushing and sensor from my old engine, only the plug was frozen in, yours will probably be too. I did try to glow it without the sensor, the GP's did work from what I remember, but they didn't work correctly.

Here's the fix:
First, did either of the car's have an EGR setup that used the plastic v-shaped vacuum switch on the t-stat housing? Use that housing, remove the switch, put a plug in the smaller hole if you have 2 holes. The sensor will now fit right into the housing, will not interfere with the t-stat, and since it's above the t-stat it will still read the temp in the head. Then you can either solder an extension to the existing wire for the sensor, or do what I did. I didn't want to cut up the wiring, so I went to the wrecker and found a newer model (I think 82 up has these) look at the GP relay, there will be a single round connector with a single wire on it. I don't know what it was for (it only apeared on the later models) you want the male half of that connector, and you also want one of the sensor connectors from the wrecker too. I then carefully popped the connectors open, and soldered in an extension wire, which now plugs to the factory wire and the sensor and looks clean and factory-ish. I even took some of the plastic sleeving fron a GP wire too to put on my new wire for the look (& protection). I then ran it along the upper A/C hose in front of the engine with a pair of zipties. My only dead giveaway that it was added was that I only had white zipties on hand, factory would've been black,lol. (you could even snag a couple of the factory reuseable ones while you're at the wrecker.

Mustang_man298 · #6 07-27-2007, 12:11 AM

Quote:

Originally Posted by JimmyL

Chris, you are a stinkin' genius!! I do believe that I have a plug on the t-stat housing in that location. I'm headed outside to see if that sender will budge from the seized engine.
I'm optimistic for now......

Genius? Lol, thanks, I dunno about genius, but I'm pretty resourceful and I've been tinkering for a long time.

FYI, if you ever decide to go with a 5 cyl, all you need to do is add one pin and wire to the gp relay harness going to the block in the hole labeled "G5" on the connector. The relay, even on a 240D, is already set up internally to power up to 5 plugs

I had the harness with the 5 cyl I used, but the covering of it was crispy and my 240 one wasn't, so I pulled out the 5th wire from that one and slid it into my 240's harness, so its essentially still all factory wiring,lol.

mplafleur · #7 07-26-2007, 12:28 PM

Yep, it's a temp switch for the glow plug relay. I had one go out on my '75 300D.