Has anybody used a resister to fine tune your temperature guage? My Y-Block has a 180* thermostate installed in place of the stock 160* unit and the result is that the temp guage reads at about 90 percent hot. This bothers me because people (wife) think that the engine is running too hot. My plan is to intall a resister between the temp sender and the guage to reduce the reading. I'm just curious about the amount of ohms reduction necessary. 20? 40? Any help would be appreciated to help me avoid buying a whole assortment of resisters. Jag

 

A resistor won't really work well. The gauges don't work on pure voltage. The temp sender sends pulses more or less frequently based on temperature. Are you running 12v with a CVR?

You can (at least on BonusBuilts) adjust the temp gauge thru a little window on the back of the gauge. It is covered by a little circle of paper or tape. It's like an old watch adjustment, a toothed wheel you turn a little to fine-tune the reading.

 

I'm still 6-volt +ground on the 55 Fairlane. I've had the guage out a few years ago and don't recall seeing anything like a cover or hole in the back. That would be nice if there would have been one.

I thought that the sender just provided a ground that increased conductivity as the water temp rose.

 

Unless cars are completely different, they work like the attached. A new sender may be the easy fix, they do get old and drift off calibration. (the diagram shows the dual-sender arrangement for a flat V8, ignore the sender with two posts)

 

I know on my 48 the temp gauge is somewhat counter intuitive from what you might think. If the gauge goes to hot with the switch turned off then inserting a resistor in series would actually make it read hotter. If this is the case you could try putting a resistor in parallel with the sending unit and tweak it down a little bit.

 

You're right, less voltage = higher reading

 

I've never known any engine to have 160F thermostats as OE from the factory. Are you sure about that?

 

Keep in mind that is the temp the stats open, not the temp they maintain. I believe 160 was common well into the '60's.

 

Yea, the 160* is the stock temp. I run the 180* because I believe that the engine runs better.

The sender has already been replaced last year in the attempt of getting it to read right. There was no effect for my $50 I also exchanged the gauge about that time with another used unit that I had. Again, no effect noticed.

My 55 car guage is normally all the way to the hot side when the key is off. When you start the car it stays on hot for about 2 minutes and then slowly progresses all the way to the cold side and eventually returns to the 90 percent hot reading.

So do you think the addition of a resister will actually make it read even hotter? I'll check the spare guage again for any adjustment hole on the back. Jag

 

A resistor added in series with the wire to the sender will make it read hotter. However a resistor added in parallel (between the wire and ground) should make it read cooler.

jb

 

Have you checked the temp at the thermostat housing with an infrared? Your engine may be running too hot! With 160's in my flatty I consistently get 190 - 195 at the housings.

 

Ross, that is a good question. I have checked at the side of the engine and the heads, but not the therms housing. I will try that and compare the two engines' temps. Jag

 

Alright, tonight's the night. I have acquired some 10 and 22 ohm resisters. I will settle this once and for all. One 10 ohm? Two 10 ohms in series? Or, in parallel? Two 22 ohms? A little experimentation is good for the soul! Jag

 

Guestimating that the resistor will effectively see 6 V, or 12 V at 50% duty cycle, a 10 Ohm resistor will dissapate an average of 3.6 Watts. To prevent catastrophic resistor failure, one usually designs in a 2/1 safety factor. In other words, that 10 Ohm resistor should be rated at 8 to 10 Watts.
If it were mine, I'd calculate worst case (12 V continuous) or, actually, I'd pull the gauge and adjust the star mechanism. My 2c

 

I'd use a potentiometer. Since it will be in parallel, I can't even guess what the current will be, but you can measure the resistance of the heating element in the gauge to get an upper limit on pot value. It can't be real high current because the supply wire at 6v is an 18 ga.