I'm stumped.

Noticed a while ago that the temp gauge was reading to the far right "high" mark. Sometimes just below, sometimes past the high, but not all the way to "high-high" mark. Radiator never did blow steam out, so it wasn't boiling. Been running half and half antifreeze and water.

Decided to see if the thermostat was working, seemed to be opening because the radiator would overflow with the cap off right when thermostat opened. Ok, but decided to take out the thermostat anyhow to clean it up, and proceeded to snap off the bolt. Two days later and a helicoil I was able to reinstall the thermostat. Was working fine, btw (opened up just fine at 180 degrees on the stove top).

Took the radiator and had it rodded out. Guy said half the tubes were blocked. Reinstalled everything and made no difference in the dash gauge reading. However, it no longer overflows when the thermostat opens. So at least that. Ran it around without the thermostat for a day, and it seemed to solve the "problem", as now the gauge read exactly where I would have expected it, right in the middle, just past straight up, say 12:10. So maybe it was the stat, right? So I got a new thermostat, but to no avail. Still reading to the high mark.

Finally decided to put the meat thermometer into the radiator once the thermostat opens (I don't have an infrared meter). Reading right at 180 degrees (or right at poultry. Apparently poultry likes 180 degrees too). But the dash gauge is still at the high mark.

So then I'm thinking electrical rather than flow. I've got an extra instrument panel, so I swapped out the temp gauge, but no change. Still reading to the high mark with the other temp gauge. Last bet was the temp sending unit. Swapped that out today, but again no change. All the other gauges appear to be working fine, fuel level is accurate, the ammeter is accurate. I changed the voltage regulator a couple of months ago (the ammeter was jumping around crazily, and the new VR solved that. Also, the lights would dim and the heater would slow when idling, and the new VR now keeps everything steady regardless of engine speed). So now I am stuck, not sure what to do next. I feel comfortable that I'm not overheating, or doing any damage, because the meat thermometer is reading 180 just like it should.

Last note is I had a wiring harness fire a couple of years ago. I put in a new alternator, engine bay harness, and had to replace the ammeter and the ammeter wires under the dash. A couple of other wires were melted, but not too damaged. I was able to separate all of them under the dash and just wrapped them with tape.

So any ideas?

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63 Dart GT Convertible

Since the meat thermo reads right, and the change in the guages and sensors made no difference, and the engine is cooler with no 'stat, I would check for too high a voltage going into the temp guage and sensor circuit.

1st, I would first get a voltmeter and measure both the battery voltage and then the alternator output voltage with the engine reasonably warm and at fast idle. This just confirms that the system voltage is right. Should eb 13.7 to 14.3 volts in this operating condition.

If OK, then, with the meter, look at the voltage at the end of the temp sensor wire with it disconnected. It ought to cycle from 0 to battery voltage rather rapidly; may be hard to see this with a digital VM. This is the output of the instrument voltage limiter in the dash and should average 5V at it switches battery voltage on and off (slightly more off than on).

I checked the voltage this morning. With the engine warmed up, the battery was reading just under 15 volts. The same at the alternator. I have an analog multimeter (AW Sperry, HSP10).

At the temp sending wire, disconnected from the temp sender, it jumps from about 1 to 5, middle at 3. Perhaps the voltage is too low, and thus the resistance in the temp sender is reading too high?

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63 Dart GT Convertible

Mmmmm, I suspect your meter is not fast enough. If the average voltage was low, the temp guage would read low.

I would be more suspicious of the system voltage. The battery voltage being almost 15 V is a bit high. But, I don't know how accurate your meter is...that one is kinda on the cheap side (no offense!). Can you borrow another meter to double check? These cars have issues with resistance building up in the old wiring and the voltage regulator sees too low a voltage due to drops in the wiring, and commnad the alternator to put out more to compensate.

Put you meter on a low scale and measure from teh battery to the +12v feed to the voltage regulator, It should be well under a volt.

Do you have access to any power supplies? You could put a 5V supply to the guage circuit and see how the guage reads. Or, if someone could post the info on the temp sender resistances (I can't find it right off), you could substitute a resistor of the right value and see if the guage reads right.

Hey here you go; the Search function does work!
http://www.slantsix.org/forum/viewtopic ... nce#174295

One thing to keep in mind is that the sender calibration changed after '63. It's different in '64. Which is a little (or a lot) strange because the gauges themselves, fuel and temp, are the same for '63 and '64 Darts. And the instrument voltage regulator is built into the gauge in those cars, so it's not a different regulator. Not a different fuel gauge sender, either...just a different engine temp sender. The early ('60-'63) senders have 13.5 - 15.5 Ω resistance at 220°F. The '64-up senders have 15 - 19 Ω resistance at 220°F.

Your temp gauge is reading too high under all conditions, so I think your temp sender's resistance is too low. With no thermostat the needle should be left of centre, closer to "C". Perhaps a '64-up sender will make the system behave properly for you.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Very interesting. When I had the wire fire, I replaced my original cluster with my spare (from a 64!). Dan, you're saying nothing else is different other than sender resistance, but how could that be, otherwise there would be a different gauge reading? But regardless, I've got nothing to lose by trading my 63 sender for a 64. Actually, just checked on NAPA online, and the 64 is $10 cheaper than the 63. I'll report back tomorrow.

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63 Dart GT Convertible

Almost sounds like the guages just read high too often and they 'fixed' that with a higher sender resistance.....

No, the pre-'64 gauges do not routinely read too high; when everything's working correctly they read correctly. Some '60 Dodges left the factory with temp gauges reading high; the TSB called for a resistor to be put into the sender wire to drop the readings down.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

That's a very good question that's made me scratch my head a lot over the years. The P/Ns are the same for the temp and fuel gauges in the '63 and '64 FPCs. The '63 setup works correctly. The '64 setup works correctly. But if you mix components...the gauge reads too high or too low depending on which way the mix is.
It's a little less than simple. You'll need a 1/4" NPT male to 1/8" NPT female reducer bushing like this one to put the smaller '64 sender in the larger '63 hole. And the '63 sender uses a flat disc slide-on terminal arrangement, while the '64 sender has a post-type arrangement that needs a different terminal on the sender wire. See here (both parts of the advice). Make sure the reducer bushing you buy is metal, is not anodised, and do not use thread sealant or you'll block the electric ground path.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

This is what NAPA online calls up for a '64: looks the same as the '63, but it is a different part number. Perhaps the picture doesn't match the actual product?

http://m.napaonline.com/Tablet/parts/Pa ... 0372672180

(If the link doesn't work, the part number is ECHTS6707)

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63 Dart GT Convertible

I see it too -- Don't think they're giving you the right part; that doesn't look like the right number to me, either. Get a Standard # TS-17 or see if NAPA will cross that number.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

I chekced on the Standard Brands online catalog and they call for a TS-18 for the '64 Dart with /6 that has the button-top terminal. The TS-17 has a threaded top terminal for a ring terminal. I am assuming they are the same but with a different terminal style, but there are no-online specs to check the resistance to make sure of that.

The '62 calls for a TS-52, again with the button-top terminal.

Nope.
It's for the push-on terminal I linked above.
Guessing/assuming often leads one astray.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

So, inquiring minds want to know..... what is the TS-18? Just a different terminal v.s the TS-17? Again, I can't locate specs to see if they are the same electrically. (And if one actually looks at the Standard eCatalog, the TS-18 is what they list for '64 Dodge dart 225/6.) Actual electrical info would be useful.

I'm not real interested in repeating info a third time or debating catalogue errors.

Echlin TS6178 for '64 up if you're shopping at NAPA rather than somewhere that stocks Standard.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.