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Old 08-17-2011, 04:09 PM
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Join Date: Aug 2011
Posts: 108
Thermostat housing cover ?

I need some help identifying what is missing. I bought my 72 250 (W114)about a month ago. It's had a M130 (single overhead cam straight six) with a blown head gasket. I tore into the valve job without taking any before pictures. I went to put the thermostat housing back in and there is a hole in the top of the housing cover that something obviously screws into, but I don't know what and nothing in my pile of parts seams to fit. Any ideas?

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Old 08-18-2011, 12:24 AM
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Join Date: Jan 2007
Location: Santa Barbara, CA
Posts: 179
That is for is a thermal switch

I believe it should have some effect on the vacuum solenoid switches on the passenger side that control vacuum advance & possibly vacuum retard at the distributor.

You would have to study thee emissions control diagram for you specific year/model in the service manual data as there were a number of variations in the early to mid 70's.

The temp switch will certainly be available but is probably >$50.

Car will run without it, but advance/retard will be affected. There are plugs available with this thread. It is not tapered and a sealing washer is required.

It is likely that you could find one of the temp switches in the junkyard. Just get one off a W114 or W115. There may be a couple of different temp variations, but I would think that would not be a huge issue. My recollection is that the switch becomes a short circuit above the switching temp. You can check for functionality with an Ohmmeter & a pan of hot -> boiling water.

Hope this helps.
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Old 08-18-2011, 07:18 AM
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Join Date: Jan 2006
Location: Tucson, AZ
Posts: 4,551
It's probably the "over heat" fan sensor. It activates the auxiliary cooling fan above 100 degrees C.
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Old 08-18-2011, 11:57 AM
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Join Date: Aug 2011
Posts: 108
Thanks for the responses.

Thermal switch. Ahh, It is probably still attached to the wire and shoved into the corner of the engine bay. Now at least I know what to look for.

I reinstalled the head, intake and exhaust manifolds, and the carbs last night. Accessories/brackets, fan and radiator tonight. With any luck she will be running this weekend. I bought her not running, so I am anxious to see if the valve job was the only (major) problem.

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