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Posted by: lmcchesney Jul 15 2006, 12:23 PM

I have a ring cylinder head sensor, the ring type that fits under the spark plug.
I have a VDO cylinder head temp gauge.
Two questions:
Does the ring fit between the spark plug washer and the cylinder head or bewteen the washer and the spark plug, providing the best seal for the spark plug?
What is the wiring of the sensor to gauge?
I have two 16ga. wires running from the engine bay, through the central tunnel up to the dashboard. My understanding is that the temp sensor acts as a resitor which varies with the temp. Thus you provide a positive flow through the gauge, to the sensor which grounds out on the engine block. How wrong am I?
Thanks,
Larry

Posted by: Dave_Darling Jul 15 2006, 01:18 PM

The ring-type sender either replaces the plug washer or goes between it and the head. You just slip the sender over the plug.

That sender (unlike the CHT sender for the EFI) is a thermocouple, so it creates a small voltage difference between the two wires when heat is applied to the sender.

Your gauge should have come with wires for the sender. The instructions say not to cut the wires (I'm not sure why).

--DD

Posted by: type47 Jul 15 2006, 01:26 PM

i got the wires for the set up at Lockwood Aviation (? along time ago but ran about $13 if i recall) i think you don't trim the wires as it affects the voltage signal to the gauge. "like" the voltage drop on a 100' extention cord.

Posted by: hcdmueller Jul 15 2006, 01:38 PM

You can't cut the wires because they are made from the same two metals as the thermocouple sensor. Obviously you can't mix and match the wires that are suppoesed to be different metals. If you accidentaly cut one wire, the only way to splice them back together is to weld them. I can't remember the exact reasons behind the splicing. Metalurgy class was a long time ago.

Posted by: lmcchesney Jul 15 2006, 01:51 PM

OK. The sensor is a thermocopuler which generates a voltage potential between the connecting wires. Then the gauge reads the voltage potential in direct/inverse proportion to the voltage/temp.
I remember that you can not cut the wires on the sensor, in order to have the gauge within the cabin, you need to extend the wires. Dependent on the length/resistance of the connecting wires/distance I guess you need to calibrate the gauge for the in cabin location. Is that correct? If so, how ?
Larry

Posted by: JPB Jul 15 2006, 02:06 PM

The reason for the thermocouple wire lenght is because it has been caliberated for an exact read/lenght condition. If you cut the wire(s), it will still work but the reading will not be as accurate for the temp range it is being used for. Size if thermocouple wire and lenght all play a factor in it's application.

Posted by: lmcchesney Jul 15 2006, 04:10 PM

Sooooo, what is the calibrated/standard length of the wires to connect to the gauge?
I understand that this system is used in aircraft where the engine is just in front of your feet. I guess I can use simular wires, connect to gauge and place the sensor in boiling water and see what the reading is.
Suggestions?
Larry

Posted by: lmcchesney Jul 15 2006, 08:40 PM

Well, we checked the calibration by placing the sensor in boiling water connected to the gauge and read just above 200F. Wired it up and with the engine warmed up about 250F. Looks like it worked .
Thanks everyone.