Stan's Customs

http://www.parts123.com/parts123/yb....Z5Z5Z50000050x

Has anyone one ever use one of these variable resistors to correct a inaccurate C1 temp gauge?

My gauges are all freshly reconditioned...but my temp gauge is reading high.

Thanks...Stan

cbernhardt

I used a potentiometer to adjust the gauge on my wife's 62. The resistance of the sender is not linear so the best you can do with a variable resistor is make it accurate at only one temperature - I chose 180°.

Charles

vettepoor

I've got one on my 57. Set it with my IR gun and now it reads quite accurately.

0Willcox Corvette

Cbernhardt is right.. It'll work at one point.. but won't be right anywhere else on the gauge. That can cause a problem if you overheat.


IMHO,

Willcox

59BlueSilver

Mine read about 200 deg. after trying three sensors. IR gauge read about 175, so added a 10 ohm resister. Read about 190, so removed the 10 & added a 15. Stays right on 180. I assume that the gauge will rise if I truly have an overheating condition sometime.

jim lockwood

Yes, it will rise but by only a small amount. IOW, the engine can be really, really hot and the gauge will tell you that it's only slightly above 180. You will be lulled into a false sense of security. That's the true risk of using a fixed resistor to "calibrate" a temperature gauge to the sender.

Jim

cardo0

Now adding resistance to your sender/sensor wire will "shift" the entire output plot. Hard to tell if that is what your gauge problem is. But Stan how can we be convinced your gauge is reading "high"? U really need to calibrate your sending unit to your dash gauge. This is easily done with extension wire used to put the sender/sensor into a hot plate pot of water and use a thermometer (mouth thermometer or whatever u have) to trend the temp and see if it matches your gauge.

If u have a mismatch in temp readings then u may need a replacement gauge or at least have yours re-calibrated. Corvette Instruments is still in business AFAIK. U could try that variable resistor and see if can correct the problem u have.

Most owners are having problems when changing to alum heads and the old 3/4" NPT sensor now wont fit in the 5/8" hole in the cyl head while the 5/8" sensors have a different resistance curve. The best fix i know of is just take your old (or replacement) 3/4" sensor to a shop that can turn it down to 5/8" NPT.

Hope this can help as im not really sure where your temp gauge problem is.

59BlueSilver

It looks to me like the same would be true using a variable resistor.

Frankie the Fink

This is funny because the SeaRay factory fix for the inaccurate temp gauge in my 2001 Bowrider boat was to install a resistor in the circuit...

Stan's Customs

I'm pretty sure either the sender or gauge is off...but to clarify.

My engine is a new just out of the crate ZZ4...and all my instruments are unused till now and were reconditioned/upgraded by a company in Florida a couple of years ago...the name of which eludes me, but well known and one MIke Coletta uses. I've forgotten the origin of the temp sender...as I have been gathering parts a long time....but it is a 3/4 " NPT thread.

The engine doesn't seem warm but the gauge fluctuates from 180-200. IR thermometer readings are under 180 considerably...( I also bought a new IR thermometer to double check the one I already had). The thermostat is a Mr.Gasket 180 degree (Robert Shaw type)

I have a new BeCool radiator like Corvette Correction uses...and a have a full time high flow Spal fan like Mike Coletta and others use.

For the initial start up...the timing was at 10 degrees with no vac advance...and the new SMI Quadrajet Carburetor adjusted perfectly with the lean drop beginning at 1 -1/4 turns out on both jets.

Sooo...the variable resistors are inaccurate except in one spot?? That's next to worthless isn't it...???


Thanks...Stan

jim lockwood

Any resistance in series with the sender and the gauge serves to limit how high the gauge will read (but NOT how hot the engine actually gets). So, yes, a variable resistor does the same thing.

C-1 Generation 2

On my 62 with a ZZ4 that came with a GM intake and correct sending unit for engine I only get a 120 reading at 180.

Stan's Customs

So do you just run it that way...and know that you have a heating issue if it gets higher like 140 or 150? (200 or 210)

Thanks...Stan

PS..off topic but do you know how much vacuum your ZZ4 pulls at idle (about).

Thanks...Stan

0Willcox Corvette

And it very well could be if the SeaRay boat used a linear gauge and sender or maybe they just needed a slight tweak.

All Chevy sending units and dash gauges are non-linear. On 1965 and new gauges I made a adjustable resistor which will allow the gauges to be adjusted. On the cars older than 1965 I don't have anything that will work because they didn't use the external resistor.

C-1 Generation 2

Yes. I did see it hit 180 one time when waiting in a long line to get into a car show but it still ran fine when a lot of cars quit on them. I did try to find a different sending unit but because of the size of the hole this is the only one for my intake.
I do actually have a vacuum boost gauge hooked up all the time and it reads around 17-18. I'm using GMs HEI that came with the engine without any vacuum hookup. I did put hardened a gear on my old HEI with tach drive but haven't ever used it. I'm running a QF 650 square bore with mechanical secondaries.

Stan's Customs

Thank you sir..

cardo0

Ya know each sensor manufacturer has a thermistor with a little different resistance curve. U can buy the assortment of sensors to try but u still need to know what the actual temp is and sorry but the IR gun aint close enough. U really need to dunk the sensor in a bath and hook up with extension wire to see what the gauge really reads.

Something else is your system voltage will affect the gauge reading so if that has changed enough the gauge will be off.

Stan's Customs

Agreed... not close enough but enough evidence to let me know something is amiss..

Good idea on the bath...but the pot of hot water it's in would have to be grounded as well.

Regarding voltage and grounding..I suppose a poor engine ground could be a factor on the temp gauge accuracy on one of these cars also...

Thanks...Stan

GTOguy

What Cardo0 says is exactly right. The resistor needs to be variable, and usually of the thermistor type, which drops resistance as it gets hotter. The right way to do it is to get the exact sending unit with the right curve. Had this issue with my old GTO's, and found that the generic temp sending units were not calibrated correctly. Installed Lectric Limited senders, and now have accurate temp gauges.

Stan's Customs

I guess the best way for me to accomplish that would be to order a sender from Lectric Limited for a 1961 Corvette...and see if my gauge is calibrated correctly (like original equipment) or close enough for the sender Lectric Limited has to read more accurately ?

Stan..