[W126 Coupe] Cold Start Valve & Engine Temp Sensor Question

[Sharan Bains]

On the M103 engine, there is a thermo-time switch, located at the rear side, 
top of the block.

Green, with two green pins attached. 22mm socket wrench required to 
remove....make sure coolant system is de-pressurised if removing on a hot 
engine.

I am fairly sure that is what regulates opening and time of opening of the 
cold start valve on the M103. From memory, it's only 3degC or below that the 
cold start valve opens for more than a few seconds. At temps above 3degC, 
it's about 1.5 seconds and below zero, it can be upto 12 seconds.

talbir



>From: "Dick Spellman" <spell.yy at verizon.net>
>Reply-To: Mercedes Coupes Mailing Lists <mbcoupes at mbcoupes.com>
>To: <mbcoupes at mbcoupes.com>
>Subject: [W126 Coupe] Cold Start Valve & Engine Temp Sensor Question
>Date: Wed, 26 Oct 2005 19:19:30 -0400
>
>My SEC is soon to be tucked away for the winter.  Which brings me to an 
>interesting situation on one of the 126 chassis 300SE (1990).  I have the 
>engine at operating temp, I have the cold start valve set-up with fuel line 
>and electrics in a clear glass jar.  I crank the engine and see the valve 
>spewing fuel and remember now the engine is at operating temp (80 C or so). 
>  The cold start valve does not leak at all with fuel line pressure and a 
>30 minute visual check.
>
>Is there a timer circuit in line somewhere that shuts this valve off after 
>say 10 or 15 seconds or is it solely dependent on the engine temp sensor 
>going 'open' at a prescribed temp???  What is the prescribed temp as the CD 
>instructions are ambiguous?  If there is a timer, what component manages 
>it?  What would a constant cold star valve operation do to gas mileage and 
>possibly dilution of oil?  This engine runs smooth and does not demonstrate 
>any issues other than a 2 time use of ignition switch to start when hot.
>
>I'd appreciate anyone who can shed light on this subject.
>
>Many thanks,
>
>Dick
>
>BTW: the engine temp sensor I have tested I am assuming is 'no good' and is 
>a 4 pin unit at the back of the intake manifold with readings of closed 
>(NC) on the diagonal pins when engine is both hot and cold.  I tested this 
>identical sender unit on my parts car (which still runs) and found that at 
>some point these diagonal pins do go 'open'.
>


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