C2 Temp.sending units.

[Richard S.]

I used my digital ohm meter to measure the resistance of the water temperature sending units currently installed in my 66 and 67 BB Corvettes. I expected around 700 ohms at room temperature. With the ignition in the "ON" position the 66 unit reads 005. and the 67 reads 369 or 274 depending on which lead I use to ground. Can someone help me to understand what may be happening here. Thanks.

[Clem Z.]

Re: C2 Temp.sending units.

only use very little sealer around the sender and never use teflon tape as it is a insulator. if the sender get all covered over with stuff in the water jacket it will read wrong and this is a big problem with these late model computer controled engines the temp sender reads wrong and the computer sets the the fuel and timing incorrectly making for a bad running engine

[Clem Z.]

PS

unless you have a expensive digital meter do not trust it. the $30/50 are waste of money. buy a fluke or a keithley in the $100+ range

[Jack H.]

Re: C2 Temp.sending units.

First, room temp resistance is NOT a reliable way to assess temp sender functionality.... The thermal transfer function of the temp sender (resistance vs. temperature) is given in the article I wrote for the Rocky Mtn Chapter Newsletter (Sept/Oct edition; posted on our website, NCRSRMC.ORG and available for download via Adobe Reader for free).

Second, why in the world would you attempt to measure resistance with the temp sender in-circuit and power applied?????? If you really want to know the resistance, disconnect the temp gauge sender wire and probe across the button head center post and brass case. Better yet, do this with the engine hot, at a temperature you've measured externally and compare to the transfer function given in my article.

Last, the expectation you'll see 700 ohms at room temp is somebody's old wife's tale. If you model the original transfer function using a damped exponential curve and extrapolate the upper/lower 'accept' asymptotes back to room temp, you'll get a wide & sloppy range of acceptable values with the mean/average falling closer to 600 ohms.

But, in the end, it's not an individual ohm reading you want from the sender. It's the SLOPE of the transfer function that's important with the UPPER asymptote (indication of engine entering overheat/danger zone) coming in around 40 ohms....

[Richard S.]

Re: C2 Temp.sending units.

I guess my meter must be junk because with no power applied both senders read 001 ohms. So if I go to Autozone and buy two TU 5 senders what ohm resistance should I measure for? Thanks.

[Mike McKown]

UH HUH,

And out of the 100% that read this, how many do you think will have any idea what you just said? Including me.

[Ed Jennings]

Re: C2 Temp.sending units.

Rick, not to contridict what anyone has posted, if you get a TU5, most will read close to 700 ohms at room temp, and most folks have found that if the sender reads close to this value they will give fairly accurate readings with C1/C2 gauges.

[Gary Cederman]

[Mike McKown]

Good answer!

I'm just glad to see Rick got his question answered. I thought your clarification of resistance of the sender vs. relative room temperature was excellent!

Mike

[Richard S.]

Re: C2 Temp.sending units.

Ed, thanks very much to you and the others kind enough to reply and for the help. It is very much appreciated.
Rick.

[Dennis C.]

Re: Good answer!

Thank you Gary C...

[Mike M.]

Re: Good answer!

agreee with the dipstick, excellent answer gary c. lets have fun with this hobby we call NCRS, not undergoe the trauma of Physics 301, we endured 40 years ago. simplicity makes a better teacher that an einstein.