Glow Plug Relay - Ambient Temperature Sensor

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GregL

New Member
Joined
Dec 16, 2019
Messages
3
Location
Shrewsbury
Car
R Class 320 CDI
Hi,

First post... first Mercedes...

2008. R-Class. 320 CDI V6. Lovelly car, just wont start...

Symptoms:
1. Takes a long time to start.
2. No Glow Plug Light

Checked Already:
1. Volts at the Glow Plug Relay = 12V full time
2. Volts at Glow Plug = 10V then almost immediately 2V
3. Brand new Glow Plug Relay fitted = same 10V then almost immediately 2v

Conclusion:(and I am NO mechanic at all!) it looks like the Relay is being told that the engine is at a good temperature and that the glow plugs are not needed.

Question...(at last) Is there an thermostat that provides information to the relay? It would seem to me it would have to be an outside temperature sensor. But I have no idea.

Any help greatly appreciated... this forum has helped me get as far as I have, but I cannot find reference to the location/existence of an ambient sensor, if in fact there is one!

Cheers,

Greg
 
The CDI engine does not require the glow plugs to operate to start.
You say it won't start then say it takes a long time to start.. How does it start once it's been run up to operating temp i.e. engine is hot?
Usual recommendation is to get the car to a good MB independent and have the error codes read. Can save a lot of guessing and messing!
 
Hi,

The engine will turn over and over for about 6 seconds. Trying this two or three times will get the car started. Once running it is perfect and drives very well.

It is the lack of glow plug light that has started me down this path...

Another test I have done just was to switch the ignition off and on a LOT. This I would guess gives the glow plugs more 9V bursts. It started first time.



Cheers,

Greg
 
Last edited:
I'd be looking for possible air bubbles in the fuel lines. When was the fuel filter last changed?
 
No idea... I will change that when the manifold is off and I am testing the glow plugs...
 
It seems I have the same issue, how did you end up fixing your car?
 
Reading the OP post I would have said his battery was toast. OP not been on here for over 2,5 yearsp
 
You mean you have no glow plug light either? You have same OM642 engine that OP?
OM651, but same cold issue, and no codes at all, checked with an Autel scanner. I'm going to change the glow plug relay and update if it fixes the problem.
 

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