R1234

Has anybody done this and if so, how did you do it?
I'm going to use a pot of boiling water. Hook 12 volts to the gauge (+) terminal, Ground the gauge (-) terminal to pot, hook temperature lead gauge terminal to sending unit and drop into a pot of boiling water. this should move needle to 212 degrees. Will this work?

73 LS-4

That seems like an awfull lot of work to do that, you could get a cooking thermometer and put it in the radiator and once the thermostat opens up it should read close to the gauge, it's not an exact thing but it should be fairly close.

:cheers:
Pat Kunz

R1234

That does sound like a easier way! I was just wanting to check out my gauge while it was out of the car. I don't know if my temp. gauge works or not.

73 LS-4

Let me try and think back to school here. The actual ground on the gauge should be for the light, then you should have another power wire going to it that will take 12v to power the gauge and then another hookup that goes to the sending unit. The gauge works by using a variable resistance to ground through your sending unit so the trick here is suspending the sending unit in the water without it touching the sides which would be hotter then the actual water temp and then you would have to run a ground wire from the threaded part of the sending unit (body of it) to a good ground. Then you could double check your gauge readings with a cooking thermometer throughout it's range rather then just at the boiling point. I hope this is the info you were looking for. In school the had a tool that has a variable resister to it that you can hook up to the gauge to see if the ohm readings you set match up to the temp readings on the gauge.

:cheers:
Pat Kunz

427V8

It sounds like your gauge is already out? if so what you said would work, but I'd also recommend keeping the sender off the bottom, it'll be a good degree or two hotter there :D
I'd also ground the sender, not the bucket...

The way you're doing it is actually the best way since you have YOUR sender hooked to YOUR gauge, youll get the system accuracy that way, not just one part.

BTW, I spent about 10 years in the research department of a company that makes precision temperature sensors. So I'm pretty confident :)

R1234

Thanks guys, I'm going to try the boiling water method and I'll let you know how it turns out.

MikeE.79

If it was my car I would take it to a garage where they have a lazer tester and have them shoot a beam at the radiator hose and get a instant reading of the temp. with the engine running and check the gauge against it! It would be alot less work! :yesnod:

Mike

427V8

Except for the fact that the temperature of the hose could be completely different than what the sender sees....

GTR1999

I checked mine by using a digital thermometer in the expansion tank and letting it idle until the 180* t stat opened and it seem to work pretty close-within a few degrees. The meter was calibrated where I work so i know it was dead on and the dash gauge was right on the little hash mark between 210 and cold.
Gary

Bill W

The infra red gun works just fine. Have them shoot various places such as the thermostat housing, radiator hoses, etc... When I had mine tested it the gun was right on the nose with the degree thermostat I had installed. The guage was reading 45 degrees high.

Garys '68

Infarred gun, I love mine and you can get it for under $100. They also make "wax" sticks that will melt a predetermined temp. You can buy a set at a marine supply store, they used to be used on OB motors before infarred testers.
Gary

R1234

I tried using the boiling water method to check for temp. gauge accuracy but, I must have a bad gauge. After hooking up the temp. gauge, the needle moves to a location below 100 degrees and does not move from there regardless of having the sending unit in boiling water or cold water. I can take the sending unit lead off and ground it and the needle will move to the oppisite side of gauge above 250 degrees. I was trying to get my gauge working correctly for the start up of my rebuilt motor which has not been started for a year. Guess I'll have to buy a new gauge. Any suggestions?

427V8

Sounds more like a bad sender to me.

If the gauge was bad grounding the sender wire would have no effect...

R1234

That's what I thought too. I bought a new unit this afternoon and get the same results. Maybe the new sending unit is bad too?

427V8

Do you have an Ohm meter?
You could measure the resistance of the sender to see it is changing?

But it just occurred to me, how do you have it hooked up?
Maybe you have it hooked up wrong???

BTW on those senders, lower resistance means a HIGHER temperature!
So when you gounded the wire and it went to high, thats a good sign ( unless you fried the sender! )

R1234

The (+) wire hooked to the (+) battery post and bottom terminal on gauge.
The (-) wire hooked to the (-) battery post, center terminal on gauge and threaded part of sending unit.
The sending unit wire hooked to mushroom pin and top terminal to gauge.
Using a Fry daddy for the boiling water, and using a cooking thermometer to check temperature.
I have the sending unit suspended over the boiling water with the threads submerged in the water.
Needle moves between the 100 and 210 mark when power supplied. Dropping the sending unit down into boiling water and letting sit for 30 minutes has no effect on needle movement. Ground the sending unit wire causes the needle to move toward the 250 mark. I going to bring home an ohm meter today and check sending unit.

Chuck Harmon

When I bought a new temp sending unit the guy behind the counter told me that they will read much higher than actuality. I had a second mechanical (not electric) temp gage from Summit hooked into the intake manifold. The Summit gage confirmed the thermostat ratings. With a 165 Thermostat, the gage read 165 at 70 mph on highway; with 185 thermostat 185 on the gage on highway. HOWEVER, the factory gage and new sending unit reads 45 degrees hotter. I was told to get a resistor from Radio shack and wire inline. I will be playing with this later, for now, I know that a scary 250 reading is only 205 degrees F.

Chuck

zwede

Strange. Mine seems to read accurately. I have the stock sending unit in the head, plus a sending unit in the intake for the EFI. I've always read that a sending unit in the intake manifold will read higher than the head, and this is the case with mine. The intake typically reads 10-15F higher than my gauge. Driving down the road the gauge will read 180F (with a 180 thermostat). EFI will read 190-195 from the intake.