So, when I purchased my dart with a 225, initially, it always overheated on the freeway. It would spike from 180 to 210 for about 15 minutes, then drive right up to 280 if I didn't stop, and once stopped - it would instantly cool down. I had the head cleaned, and did a valve job and resurface on it, since when I bought it, one of the exhaust seats was out, and it was only banging on 5 cylinders.

I have since replaced all (yes all, hoses included) of the cooling system. I had the stock radiator replacement, and everything else stock replacement and nothing made it better. I played with probably 10 different brand new thermostats too, 180 and 190 ones. I have a 190 in it right now. I also shot high pressure water through the jacket when the water pump and rad were off, and none of it helped. The old radiator was about 50% cold at any operating temp, so it was clogged good.

I replaced the radiator with an aluminum, 2 core large radiator (it fills the entire rad opening) and now the overheating no longer occurs. However, my numerical gauge lists the temperature as 210 and it is constant after warm up. In town it will sometimes go down to 190, but fluctuates to 210, but on the freeway, it is 210, and stays there, and never goes above. I used the same gauge when it was overheating as well.

My issue is, I have a temp gun, and the gun claims the area around the temperature sender in the top of the head, closest to the outlet hose - is 195. I know the iron will make the surface temperature a little cooler (I've been told - not sure).

So... here's my question:

1: Is it more likely my gauge is bad, or poorly printed, and my thermostat is functioning correctly, and the surface temp is close if not exact to the thermostat rating.

Or 2:
Somehow I have bought a 190 degree thermo that is actually activated at 210

Or 3:
The thermostat is functioning properly and for some reason my car is operating above it and this is completely normal? (I don't know what's normal, since it was broken when I bought it)

or 4: I have no idea.

If it's an aftermarket guage it may not be calibrated to the resistance range of the temp sender (very similar to the issue the the gas tank sending unit has with the aftermarket sender and the stock gauge...or vice/versa)...

You may need to check the documents for the range with an ohm meter(if not a cheap chinese unit), and check the sender and see what discrepancies are there....

-D.Idiot

Can you run a mechanical guage? I really am a pusher of mechanical guages....oil pressure , and water temp.I still run the factory sweep guage in my wifes car.
My 2 cents anyhow.I know that thermostats can be bad from the start.
I also dont know if I read that you flushed the block when you changed radiators? I know the heater core can hold a lot of debris, so check that also.

_________________
Wife's: 64 Valiant
My: 70 Road Runner, 67 Barracuda, AND the 62 Valiant drag car!!

I did flush it. The heater core was replaced as well. I tried to buy a mechanical gauge as I thought that would be better, but all the adapters for it only made the sending part bigger, rather than small enough to actually fit the slant, so I returned it.

The gauge now is an electric Sunpro. I want to say it was about $20 and included its own sender. I had used the old sender before it. Both sender units say the same thing. The surface temp is really close to 190 though. I know thermostats can be bad, but I don't know if my luck is that bad that 3 in a row are bad.

IS there a way I could drop the resistance in-line so that it would calibrate 20 degrees less? I.E> would it be possible to increase the resistance to drop the temp with a resister, and if so, what is the correlation between resistance and degrees? Or would that be manufacturer specific?

There will be difference between the housing and the coolant temperature inside. How much? Depends, can be calculated with a lot of data, probably not but a few degrees.

You might want to check the calibration of your temp gun, and that the area you are pointing it at is the area the sensors are measuring. The lasers have nothing to do with temperature measurement itself. They're just for aiming, and are often way off.

Check with boiling distilled water, looking for a temperature to match the pressure/altitude corrected boiling point calculated HERE. I also like to check with an icewater slurry, to verify the lower end of the scale.

Make certain that any surface you are trying to get a measurement from has high emissivity. In other words, make sure it isn't very reflective to infrared. Put a square of good electrical tape on it, or spray some foot powder on it. Even plain, non-metallic paint is OK. That should get you close to 0.95 emissivity, where a lot of the heat guns are set.

_________________
"When you find a big kettle of crazy, it's best not to stir it." - Pointy-haired Boss

1964 Valiant V200, 225/Pushbutton 904
BBD, CAI, HEI, LBP, AC, AM/FM/USB, EIEIO

Presumably, when you say "once stopped", you mean stopped rolling but engine idling. Does the temperature still drop to near 190°F at idle after being on the freeway?
You can verify the thermostat temperature by putting a cooking thermometer in the radiator's neck (let it warm up with the cap off). Once you see flow from the engine in the rad, that would be the temperature that the thermostat starts to open. According to Stant's thermostat FAQ:

• The thermostat starts to open at the rated temperature, plus or minus 2 degrees (F).
• The thermostat is usually fully opened at 15 - 20 degrees (F) above the opening temperature.

You should have more than enough cooling capacity in your radiator and your thermostat should not need to be fully open (ie, 20°F above its rated temperature) on the highway, especially in mid-March.
An infra-red temperature gun does not measure temperature directly as slantvaliant correctly explains. The most accurate way to measure water temperature is with a thermometer in the water. You can use an accurate thermometer to calibrate your in-car temperature gauge - just don't tell your wife that you're borrowing her meat thermometer. Put cardboard in front the rad to raise the water temperature at idle.

Is it possible that your fan is installed backwards?

_________________
1965 Plymouth Barracuda,
225 engine, Quadrajet, HEI, Dutra Duals, 904 Torqueflite, 2.76:1 axle, Addco front bar
Rods & Relics - Fort Erie, ON / Collector Car Tech

Yes, that's exactly what I mean. I would either pull over to the shoulder and stop at idle, or slow down off an offramp. Both yielded the same results which were the car cooling down to 180-190, and the results were almost instant. After a lot of thought and trial and error, I thought the alternator was to blame, as somehow it charging made the temperature higher on the gauge. I thought this because if the idle was low enough, and you hit the blinker, the gauge would tick with the blinker. Back and forth at the same beat. It would go left to 180 and click right to 210. Back and forth, back and forth. I could never determine if that was the issue.

I completely agree. I figured with a larger surface area, it would be cooler, which is odd. With the new radiator, the temperature is consistant on the freeway at 210. Before it would idle and drive around in town a 180-190, then spike to 210, then go way past that if I let it, which I did not on purpose. Now in town, it's 210, on the freeway, it's 210, going 65 it's 210, going 80 - it's 210. It fluctuates above and below but negligibly. The car does warmup to that temp so I know the gauge is not "stuck"
I guess it's possible. I have a 7 blade stock (not stock on this car) fan. The rounded side of the fan points to the radiator, and it blows air on the motor. I had a plastic fan the original owner had on there before installed the same way, so I guess it's possible it was wrong both times, but I always assumed the fans installed only one way. The old plastic one had a flat part, and a part that sank back towards the fan spacer. I'll get a picture of it if I can. Luckily I take pictures of everything, so here's both fans. The plastic one shredded apart after time. I think it was a $10 ebay fan,and the o.o. chucked the 4 blade that was on there.

In the pic, both fans are pointing towards us. The top is facing the radiator, as installed on the car. They were both installed this way- Is that backwards?


I always assumed the palm part of it pointed towards the engine.

Standing in front of the car and looking at the engine, the fan spins clockwise. The trailing edges of the fan must be angled towards the engine for it to pull air through the rad. From your description and photo, it looks like the fan is mounted correctly.

It seemed to me from your description that there wasn't enough air flow through the rad at highway speeds, which would make sense if your fan mounted backwards and opposing the natural air flow from vehicle motion.

I think you may be onto something with your suspicion about your alternator. If your voltage regulator is working properly, your voltage should remain fairly constant at all times. However, at idle, stock alternators sometimes have insufficient output at idle so your voltage could be affecting the operation of your aftermarket 12V temperature gauge. I see in your My 68 Dart (build?) The Huntress topic that you've added an aftermarket stereo with an amplifier and subwoofer. Can you hook up a voltmeter and see how much your voltage fluctuates as you drive?. Does the temperature gauge read differently when the stereo is completely turned off (ie, fuse pulled)?

With the engine idling in your driveway, can you measure the water temperature inside the radiator neck with an accurate thermometer? How well does it correlate with your temperature gauge?

_________________
1965 Plymouth Barracuda,
225 engine, Quadrajet, HEI, Dutra Duals, 904 Torqueflite, 2.76:1 axle, Addco front bar
Rods & Relics - Fort Erie, ON / Collector Car Tech

I have to go get a meat thermometer. As it turns out, I don't have one, but will check.

I don't have a voltmeter on it now, but I'll run a cheap one and see what it says. My charge indicator on the dash will show the alternator charging a lot when the radio is loud. With it completely off and the subwoofer off, the gauge stays consistant with no draw, but temp gauge stays the same. This is a newer alternator I would think because its a two belt wheel and my car was only supposed to have one wheel - so likely a replacement.

When the music is loud and there's a lot of draw you can literally watch the gauge jump to charge when the bass hits.

Like I said earlier it was broken when I got it and the original owner was chasing down the issue, and removed a lot of the original equipment and tossed it, like the shroud, original fan, etc. I'm at a point where I don't have to stare at the temp when I drive, and its consistent, but still hot. I have a cheap fluke and contend to check the sender with it and the battery.

Then I'll get to the thermometer shortly here, or borrow from a neighbor and not tell them my intentions with it.

I also neglected to mention, there's a 180degree thermo in it, with 3 very small holes drilled in it. That was a suggestion from my dad. I put it in when I replaced the radiator, I know there's some theory behind it keeping air from getting trapped in there, but if anything I'd think that would make it run too cold... not hot?.

The meat thermometer is handy to have - you can even use it for cooking. The digital thermometer with the remote sensor is useful when roasting meats in the oven.

Seeing as you have an oversized rad and your temperatures appear to be fairly constant, my guess is that your cooling system is probably working properly. This was confirmed by your laser temperature guage reading 190°F surface temperature when you were using the 190° thermostat. Since it's reading 210° consistently in March with a 180°F thermostat and an oversized rad, I think the gauge is not calibrated correctly. An electric temperature gauge depends on a constant voltage supply and you ammeter's performance suggests otherwise.

You should be seeing around 14V at the battery (13.8V-14.2V, see Testing battery and charging system) with no load (all lights & accessories off) and the engine idling at 1000-1200 RPM. Dan would like to see 13.3V 13-8V (see Charging problem?). I'm not sure what happens to a temperature gauge's accuracy when it's getting more than 14V. I'm fairly certain that the temperature will appear to drop off as the voltage falls below 12V though. There are members more knowledgeable than me about electrical systems though.

In Mopar electrical systems, power from the alternator's B-terminal goes to the ammeter and then to the fuse block before connecting to the battery. The original alternator for your car would probably not be have enough output (nominal 37, 46, or 60 amp rating according to alternatorparts.com) for your stereo at idle and the ammeter likely reads ±40A at full scale (see old Real Time Engineering Gauge FAQ). You can check the output of your alternator with all of the accessories on with a DC Clamp Meter (like the Klein Tools CL2000).

The small holes in the thermostat won't hurt and will help to purge air from the system. Some thermostats (like the Stant SuperStat) already have this feature built-in. Living in California, I don't think that you ever have to worry about your engine being too cold.

_________________
1965 Plymouth Barracuda,
225 engine, Quadrajet, HEI, Dutra Duals, 904 Torqueflite, 2.76:1 axle, Addco front bar
Rods & Relics - Fort Erie, ON / Collector Car Tech

A lot of helpful info there. Using my tester, the battery sits around 12v with no charge and the car off. With the car on, and no headlights, stereo or any other draw, it reads 14.2 - with longer leads and driving I was able to see a fluctuation between 13.9 and 14.2 but that was mostly I think due to the cheap tester.

I'm sad to see having the digital heat sensor is not as cool as I thought it would be. I knew there was something up with it. I figured it would be as simple as pointing the laser and getting a number. I always thought the laser refraction had something to do with it, but I guess that was way off.

Tomorrow afternoon I'll have enough time to hit the store and get a thermometer. I am curious to see if the gauge is just not calibrated. The stock gauge was of no help decided what temperature things were, so I guess even uncalibrated it's better.

An infrared thermometer is still quite useful and can be accurate. It just helps to understand how it works and its limitations.
http://en.wikipedia.org/wiki/Infrared_thermometer
http://en.wikipedia.org/wiki/Thermal_radiation

From the photos in your other topic, it looks like you are still using the original mechanical regulator and single field alternator. I would expect some voltage fluctuation from a mechanical regulator. The alternator was a huge improvement over generators when they were introduced in the 1960 Valiant. Many members here have upgraded to a Nippondenso (Denso) alternator because of its better output at idle.
http://www.allpar.com/eek/alternators.html
http://www.slantsix.org/forum/viewtopic.php?t=49094

The original single and dual field alternators were able to supply enough current for the limited electrical loads at idle for the cars of the 1960s and 70s but they proved a bit inadequate for later cars equipped with rear window defrosters and more powerful stereos. The reason that your temperature drops to 180°F from 210° when you stop may be because your voltage at idle drops off.

I use the original temperature gauge in my instrument panel because, even though there are no numbers on it, the lines correspond to useful temperatures like 180° and 195°.

_________________
1965 Plymouth Barracuda,
225 engine, Quadrajet, HEI, Dutra Duals, 904 Torqueflite, 2.76:1 axle, Addco front bar
Rods & Relics - Fort Erie, ON / Collector Car Tech

I would hook up the stock temp, but it no longer works at all. It starts at cold, gradually moves up then goes back down to the left over and over.

I got a thermometer and put it in the rad. The car had just stopped after a freeway drive, i puked the pressure into the overflow bottle and opened the cap with a towel. The coolant was moving in the radiator so I'm fairly certain the thermostat was open. The car was idling when i did the test. The gauge inside was at the point where it operated pretty much 100% of the time.

Here's what I saw:



About 160-165 maybe? And I think the movement in the radiator may be due to the holes in the thermostat - I don't know if it's "open" yet. It probably would open when the interior gauge hit 210, at which point the temperature stays the same consistantly.



And probably 190-200,

So I'd assume if the thermometer said 180, the interior gauge would likely show 210. That's just a theory.

So is it safe to assume the temp is around 180 when the gauge is 210?

Where is the sending unit for the interior gauge located?

I would get a third gauge and see which gauge was more accurate.