CHT sender

[Scooter311]

Happy Monday Doods, welcome back to work!
My old motor had a CHT sender that fit onto one of the spark plugs (looked like a washer), and my current 2.0 has the screw-in type, all neat and tidy - can I just connect the new sending unit to the existing wire, or is that a no-no? Is there a different gauge I need to use as well, if this is not the case?
I don't mind re-using the old one, as it worked just dandy, albeit a small pain in the arse when changing plugs - the new one looks so sano though.............
Jeff




Coffee and Easter candy at 8:30am YESSS!

[jamcleod]

sounds like you have a sender for a cylinder head temp gauge (ring around a spark plug) which is different than the CHT (screw in) for the fuel injection system. the "ring" sender is probably a thermocouple that generates voltage in proportion to temp (as temp increases, V also increases) but FI sensor (screw in) is a negative temp coefficient, that is, as temp increases, resistance decreases, so i'd say they are not compatable. DD?

[tat2dphreak]

you hit the nail on the head... not compatible... the screw in CHT basically had 2 readings: hot and cold... a thermocouple under the plug is used to measure a more specific temprature and is more accurate... under the plug is the only way to fly!

[Dave at Pelican Parts]

I wouldn't say that one is necessarily more correct than the other--but most of the response of the FI's sender (the screw-in one) is in the "engine is still warming up" range.

You gotta get a thermocouple ring sender to use with the CHT gauge.

N.B.--an FI sender can be used to run a stock oil temp gauge, as the oil temp sender is also an NTC Thermistor. Not sure what the range of readings will be, though. It could be comlpetely useless, or only sort-of useless....

--DD

[pbanders]

Both sensors types can be used to monitor head temp with a good degree of accuracy, assuming you have a guage/meter that reads the expected response. The VDO guage is designed for a thermocouple, so you want a thermocouple as a sensor.

[Scooter311]

Well then, thermocouple it is!
I'll hafta figure out a clean way to route the sensor wire through the tin, as the old setup had it poking through the spark plug hole, alongside the plug wire - not very purdy, and I never liked the idea of it rubbing against the 1.7 tin. There's a hole in the 2.0 tin close by, with a nice grommet, but I'll have to wrangle the end around under there while changing plugs. Anyone ever do this, or have a better idea how to route the wire?
Thanks for the responses everyone, and especially PP for all the help and patience with all of us!
Jeff

[tat2dphreak]

I'm going off jake's info... if you put the CHT sensor anywhere but under the plug, there can be up to a 200 degree difference... and 200 degrees is too much of a margin of error...

[pbanders]

The purposes of the two sensors are different, hence the location difference. The FI sensor's job is to determine the engine's general operating temperature, so that the correct degree of warm-up enrichment can be supplied. A more stable location is used. The VDO-gauge based sensor's purpose is to provide combustion chamber temperatures for performance tuning and warning for out-of-range conditions. This is best determined by placing the sensor on the relatively thin section of the plug hole.

[Dave at Pelican Parts]

Scooter, I take it that you're going carb'ed on the 2.0 motor? If not, you will need that temp sensor for the FI...

--DD

[Scooter311]

Ahh yes I neglected to mention I was a-carburettin'.
How do the carb guys route their CHT wire through the tin, any suggestions?
Cheerio

[Dave at Pelican Parts]

Usually through one of the spark plug holes.

--DD