Resistors Correct Temp Gauge Readings

[Vermont Rock]

Had my 70 Road Runner gauge assembly rebuilt, restored & calibrated by a professional company. Gauges were still not accurate. Gauge restorer blamed the sending units; sender suppliers blamed the gauge restorer. Sound sadly familiar ? The fuel gauge still refuses to read above 1/2, but I'm still working on that with no success. Installed a set of aftermarket oil pressure, voltmeter & water temp gauges that are accurate. ( water temp confirmed with a laser thermometer ) But the factory water temp gauge read about 220-230 F. compared with the accurate readings of 170-180 F. No real problem except that watching that needle so close to the maximum drove me crazy.
Bought 5 different resisters: 5,10,15,22 & 32 ohms. Installed a 15 ohm between the sending unit & pickup wire and the dash gauge read about 160. Replaced it with a 10 ohm & the gauge now reads accurately & the same as the aftermarket. ( 170-180 ) Your gauge may be different, but there is help for us. Try different ratings to get the gauge to read accurately.
Resisters were: 1/4 watt & available for about $2.49 for a package of 20 on eBay.
Hope this helps bring a little mental peace for some of you.
Tim

 

[69f6bee]

Had my 70 Road Runner gauge assembly rebuilt, restored & calibrated by a professional company. Gauges were still not accurate. Gauge restorer blamed the sending units; sender suppliers blamed the gauge restorer. Sound sadly familiar ? The fuel gauge still refuses to read above 1/2, but I'm still working on that with no success. Installed a set of aftermarket oil pressure, voltmeter & water temp gauges that are accurate. ( water temp confirmed with a laser thermometer ) But the factory water temp gauge read about 220-230 F. compared with the accurate readings of 170-180 F. No real problem except that watching that needle so close to the maximum drove me crazy.
Bought 5 different resisters: 5,10,15,22 & 32 ohms. Installed a 15 ohm between the sending unit & pickup wire and the dash gauge read about 160. Replaced it with a 10 ohm & the gauge now reads accurately & the same as the aftermarket. ( 170-180 ) Your gauge may be different, but there is help for us. Try different ratings to get the gauge to read accurately.
Resisters were: 1/4 watt & available for about $2.49 for a package of 20 on eBay.
Hope this helps bring a little mental peace for some of you.
Tim

Great information!! I'm having the same problem with my 69 Super Bee. I did what you did by sending my gauges to a professional restoration company and I'm getting the same results. I will get some of the resistors that you mention and see if that corrects the situation.

 

[Vermont Rock]

I bought different ohm ratings to make sure I could correctly calibrate the gauge to the actual engine temp. The resisters usually are made with about 2" leads at both ends. I tested them by just wrapping one end around the sender stud & securing the other end in the cap that attaches to the stud. (use a small machine screw to hold it in ), then ran the engine. Once the correct ohm rating was determined, I soldered the resister into the wire & used heat-shrink to protect it. Looks factory with the braided covering.

 

[wagonman]

Will this work for the fuel gauge as well? When empty I can get 10 gallons only on a 19 gallon tank.

 

[Vermont Rock]

I'm not real good at electronics, but I understand that the resisters reduce the signal and, therefor, will cause a temp gauge that reads high to read lower. I've had several conversations with gauge restorers & companies that sell sending units, and there is no solution to the fuel gauge problem. I did find out that the sending unit & gauge must be matched for ohms. That is, a sending unit that is calibrated 10-85 ohms in its full range, must use a similar gauge. Year One's technical person told me they have the same problem when building new cars. The unit works perfectly outside the car, but is not accurate when installed in the tank. And, they have confirmed that the sending unit is not hitting anything inside the tank. I just bought a Classic Instruments fuel gauge & hope it solves my problem. I'll write about it.
BUT... why hasn't a supplier seriously addressed this fuel gauge problem ? All they seem to do is blame someone else's product, but there is never a solution. Here's a good business opportunity that would help all of us.

 

[wagonman]

I'm not real good at electronics, but I understand that the resisters reduce the signal and, therefor, will cause a temp gauge that reads high to read lower. I've had several conversations with gauge restorers & companies that sell sending units, and there is no solution to the fuel gauge problem. I did find out that the sending unit & gauge must be matched for ohms. That is, a sending unit that is calibrated 10-85 ohms in its full range, must use a similar gauge. Year One's technical person told me they have the same problem when building new cars. The unit works perfectly outside the car, but is not accurate when installed in the tank. And, they have confirmed that the sending unit is not hitting anything inside the tank. I just bought a Classic Instruments fuel gauge & hope it solves my problem. I'll write about it.
BUT... why hasn't a supplier seriously addressed this fuel gauge problem ? All they seem to do is blame someone else's product, but there is never a solution. Here's a good business opportunity that would help all of us.

Yeah Rock I hear Ya. I had a post on the fuel gauge issue and one of the members talked about a module added to the circuit. Not what I want to add. I guess I will just keep track and fill it up when on E. LOL