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Old 04-11-2000, 03:13 AM
DieselGuy DieselGuy is offline
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Join Date: Feb 2000
Location: Santa Clarita, CA, USA
Posts: 133

I have a 1984 300SD. I was wondering what the 2 temperature sensors (thermistors)on the cylinder head are for. They are on the left side (injection pump side). I know the one towards the rear is for the temp guage on the dash. I have some questions regarding them and the sensor on the thermostat housing.

1) I want to know what the sensor towards the front of the cylinder head is for. It's not obvious to me what it operates. I thought it might be associated the glow plug timer, but the pre-glow light on the dash comes on for a consistent 3 sec. no matter what engine temp or with the plug on or off. The car starts easily by the way with only those 3 sec. What does this sensor control?

2)Does the auxiliary fan have a high coolant temp switch or is it solely operated by the a/c rec./drier switch?

3) The sensor on the thermostat housing is for the a/c cutout I assume. I observed with it disconnected, the climate control will not run. Does this sensor control anything else?

Any input would be much appreciated. I plan on modifying the cooling system wiring so that the aux. fan comes on with high coolant temp. I hope to put in a thermal switch on the t-stat housing. Thanks in advance


1984 300SD 268,000 miles
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