'80 300D preglow relay temp sensor? - PeachParts Mercedes-Benz Forum

Kyle Blackmore · #1 10-24-2003, 12:40 AM

I've been having a cold start problem since August , now that it's getting a little cooler sometimes it takes 10 seconds to start. Since I bought the car 3 yrs ago, the glow light has never come on. I've adjusted the valves, resoldered the relay, checked gp resistance (0.6 ohms),voltage (11.7 volts), the relay clicks off after 45 seconds or so.Everything is normal except no glow light .On the CD it shows a temp sensor on the schematic and I have the lead on the gp engine harness but the sensor isn't there.The manual says that the temp sensor is no longer installed but I think it's referring to '81 models.The glow system changed in '80 from the filament gp's to the pencil gp's and then in '81, the relay changed again to include a self-contained temp sensor. This is what the schematics show and what I'm wondering is if the lack of temp sensor would cause a no light condition, and what is the part number of the sensor ? I've noted on the pic where I assume the sensor should be installed , thats where the lead reaches to.

wgreen · #2 10-24-2003, 09:09 AM

i think you are right about the temp. sensor. i noticed on my 79 it has the sensor you are explaining and is not on my 81.
you may just have a bulb burnt out in the cluster.
i can look at the sensor for the 79 and get you the numbers off of it..

make sure that you can remove the plug that is there now,it was NOT easy to remove the one for my block heater..

Kyle Blackmore · #3 10-25-2003, 12:09 AM

Thanks Bill , I have checked the light as per the test in the manual and it does work , the wiring is correct , all functions work except no glow light . The fact that the plug looks original makes me wonder if it ever had the temp sensor installed at the factory . I've finally located a used relay for it so I'll try that first and see if it gives me a glow light . I'm wondering if somehow I'm not getting enough current flowing to the glow plugs, the manual says 14 amps and my DMM will only read to 10 . Tomorrow I'll try bench testing a spare gp I have and see if it glows red hot in the time specified. If this isn't the problem I'll have to start at square one and do a compression and leakdown test to ensure I haven't suddenly developed a bad cylinder.It starts as it always has once it's warmed up or if it's plugged in.

Kyle Blackmore · #4 10-25-2003, 12:16 PM

ttt

wgreen · #5 10-25-2003, 01:02 PM

kyle, here is the number off of the sensor , 005 540324.

also i thought of a way to check if the gp's work.
check the voltage at the battery first, let's say it is 12.5 volts.
than pull all but one wire off of the gp's, so only one gp is connected, now while the volt meter is on the battery try to cycle the gp,s , if it is drawing current you should see a voltage change (lower) at the battery, lets say it reads 11.5, that should indicate a working gp, now check all the other gp;s the same way.....

Kyle Blackmore · #6 10-25-2003, 01:53 PM

Hi Bill , yes that would work , but it would be easier to unplug the gp engine harness and use a jumper to each gp in turn. That way I don't have to remove each wire at the gp's

.I'll check that part number but it seems to be missing a digit , is it a Bosch number ?