CHT monitoring

[lmcchesney]

I will be adding a CHT in cabin monitoring and was wondering about the sensor to use. The typical one I have seen/heard about is the copper thermocoupler in a ring fashion to be placed under the #3 spark plug. Our Type IV's have a CHT as temp sensor #2 which is read by the ECU with measurment of resistance. Is it possible to tap onto the #2 temp sensor CHT to drive a CHT in cabin gauge? My initial thinking is that tapping a gauge into the #2 sensor would alter the resistance of the circuit and thus disrupt the ECU monitoring. Do others think this is correct?
As an alternative, when using a spark plug sensor, what is the wiring circuit to the VDO CHT gauge?
L. McC

[Jake Raby]

The thermocouple MUSt go under the sparkplug- Period.

I tested 12 different loctaions on the same engine last July and saw over 180 degrees difference between the stock CHT position and the spark plug. The stock CHT was alkways colers and would never go over 220 degrees even when the head was 400!

[Dave at Pelican Parts]

If you realize that it will read low and it will react very slowly, you can use the CHT location. But you'll have to guess at what the temperatures mean, as the experience base is all for the spark plug location.

--DD

[Jason Porter]

Go under the plug man. If you're gonna end up guessing because it's in the wrong place, you may as well have a "psychic" give it a reading too. After all, the kit is only like $59.95~ if I'm not mistaken.

[Alfred1]

Does Pelican sell this type of spark-plug temp sensor? If not, does anyone have a link to a retailer that does sell them?

[Jason Porter]

I'll supply the information needed to purchase this from Pelican tomorrow.

[Dave at Pelican Parts]

Third item down here:
http://www.pelicanparts.com/catalog/shopcart/9144/POR_9144_electr_pg2.htm#item9

That's the gauge and sender setup, complete. If you're just talking about the sender, you'll have to wait for Jason to get back to you.

--DD

[Alfred1]

Thanks. I guess I'll replace the oil temp gauge in the console with the cylinder head temp gauge.

[jamcleod]

what you need is the oil temp gauge in the left dash gauge (where the emergency brake flashing red light is on most) and the CHT in the console.

[lmcchesney]

Jason, Dave,
What is the connection between the CHT sender and the CHT gauge. I have been told that the connector is a thermocoupler and should not be cut or a connector added. I have a VDO CHT gauge. The Ring Sender would be mounted beneath the spark plug for Cylinder #3. What is used to connect the gauge and sender that does not alter the thermocoupling reading?
L. McC

[Dave at Pelican Parts]

The sender is a thermocouple. The kit comes with the sender, the gauge, and the wires that go in between. VDO supplies all of it as a kit; presumably they have it all set up to work correctly.

--DD

[Jake Raby]

I have both shortened and lengthened the wiresleading to the instrument and never seen a variance in readings when doing so.. In a VW bus 8 feet of wire needs to be added and I did so with no ill effects at all.

[lmcchesney]

Thanks guys,
I assume the lengthing wire should be of 12-14 gauge with minimal resistance. Thus, not changing the resistance/temp equation of the sender/gauge.
Jake, how is Dad doing?
L. McC

[jamcleod]

there is a wire harness that connects the thermocouple sender to the gauge. it is stated that the length should not be altered but as Jake says, he did and no ill effects. one thing to consider is the sender has a connection "device" that mates to the wire harness that would not be available if you did your own harness. i got the harness for about $16 including shipping so i just went that way.

[synthesis]

Originally posted by Jake Raby
I have both shortened and lengthened the wiresleading to the instrument and never seen a variance in readings when doing so.. In a VW bus 8 feet of wire needs to be added and I did so with no ill effects at all.

Just ordered dual EGT and CHT with senders. Book said any length up to 10' was OK without having to recalibrate.

dr