Sorry - how are you measuring temps? Forgot if you have an aux temp gauge.
Fuel Gauge & Temperature Gauge Calibration (1 Viewer)
- Thread starter Spook50
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- calibration fuel fuel gauge gauge
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- Thread starter
- #42
Using my non contact thermometer on the thermostat outlet side of the housing.
I wish a had a more "guaranteed" way to verify engine temp, but this is really the best I've got without an auxiliary gauge.
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- #43
Just got back from topping off my tank. This leaves me less leeway than I thought I would have for adjusting the gauge regulator. If I dial it all the way back to a reasonable level on the temperature gauge, my fuel gauge will read far too low. What I'm going to try first is adjusting the gauges back so that the fuel gauge needle sits on the topmost line with a full tank. At that point I'll see what my temp gauge shows and go on from there.
If it looks okay overall, I'll see how it behaves on my upcoming trip and then check indications and resistance at two and fifteen gallon quantities.
Here's a driver's eye view of how both gauges sit as of this afternoon's top-off and the engine holding a steady 185º (after adjusting my fan controller up a bit, based on how I've been measuring it). A "straight on" view of how the fuel gauge sits can be seen on post #35 of this thread.
If it looks okay overall, I'll see how it behaves on my upcoming trip and then check indications and resistance at two and fifteen gallon quantities.
Here's a driver's eye view of how both gauges sit as of this afternoon's top-off and the engine holding a steady 185º (after adjusting my fan controller up a bit, based on how I've been measuring it). A "straight on" view of how the fuel gauge sits can be seen on post #35 of this thread.
I replaced my FJ60 temperature gauge with a good quality used FJ62 temperature gauge.
Then I got a brand new Toyota temperature sensor and calibrated it with two data loggers (Ohms + resistance).
After logging the sensor, I knew exactly at what ohm the sensor would read at any given temperature.
I then got a precision potentiometer and dialed in each ohm value for a given temperature — then connected it up to the temperature gauge, and Blammo! My gauge dial was easy to calibrate.
See my attached picture array for the needle position on my 62 temperature gauge at various temperatures.
Really…. The only needle position that’s important is where it is at 239°F. Mine is right before it hits the red zone.
Then I got a brand new Toyota temperature sensor and calibrated it with two data loggers (Ohms + resistance).
After logging the sensor, I knew exactly at what ohm the sensor would read at any given temperature.
I then got a precision potentiometer and dialed in each ohm value for a given temperature — then connected it up to the temperature gauge, and Blammo! My gauge dial was easy to calibrate.
See my attached picture array for the needle position on my 62 temperature gauge at various temperatures.
Really…. The only needle position that’s important is where it is at 239°F. Mine is right before it hits the red zone.
Not intending to hijack Spook’s thread -
For calibration purposes, I partially submerged a new Toyota temperature sensor in a small pot of olive oil and slowly heated it. The vapors from heating coolant are toxic so I used olive oil instead.
Water can only be heated to 212°F.
I recorded the temperature and resistance as the oil slowly heated up. Then I knew what resistance the sensor put out at a given temperature.
Then with my precision potentiometer I purchased from Mouser electronics, I could dial in a given resistance with the pot and hook it up to the temperature gauge in the car.
Example:
I now knew that 220°F was 38.4 ohms after calibrating the sensor. I dialed in 38.4 ohms on the potentiometer, hooked it up to the gauge, waited a while, then took a picture of the needle position.
Remember that the thermostat rating is the temperature that the thermostat BEGINS to open. The engine (at least my engine) ran a bit hotter than 190°F.
My readings were the sensor only. Other places in the engine would have different temperatures.
Also FJ60 2F engine has the sensor at the rear of the engine while FJ62 has it in the very front in the thermostat housing. So that’s going to read a bit differently.
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- Thread starter
- #48
No man this is great! This gives me a great idea for how with your method, I or anyone else can differentiate adjustments between the fuel gauge and the temp gauge. Messing around with it this afternoon, I couldn't really find a "happy medium" for a comfortable placement of the two gauges. So I had pondered the thought of throwing a resistor in line with the temp sender wire, though using an adjustable potentiometer like you did is a far better solution IMO. And you even did the legwork with finding the resistance to temperature values already!
—Splicing in a Resistor
If a resistor is spliced in-line with the temperature gauge to drop the needle to a more desirable location at normal temps, its best to test the gauge function at high temperatures if it is the only gauge in the cab. Otherwise its kind of worthless.
Probably the most important mark on the dial (after operating temp) is where the 239°F is, and you want the needle to be in a position that alarms you if that event ever happens.
The easiest way to test the gauge needle position for 239°F is to wire in a 27 ohm resistor then add your resistor of choice inline with the gauge sender wire to ground. 27 ohms (actually 26.4 ohms +1.7, -2.21 ohms) is the Toyota 239°F calibration point for the sender. Take a look at the needle on the dial at that virtual temperature with your extra resistor added in and see if you're happy where the needle is sitting at that dangerous virtual temperature.
I think it’s important that the gauge needle is right next to or in the red zone on the dial when the temp is 239°.
If a resistor is spliced in-line with the temperature gauge to drop the needle to a more desirable location at normal temps, its best to test the gauge function at high temperatures if it is the only gauge in the cab. Otherwise its kind of worthless.
Probably the most important mark on the dial (after operating temp) is where the 239°F is, and you want the needle to be in a position that alarms you if that event ever happens.
The easiest way to test the gauge needle position for 239°F is to wire in a 27 ohm resistor then add your resistor of choice inline with the gauge sender wire to ground. 27 ohms (actually 26.4 ohms +1.7, -2.21 ohms) is the Toyota 239°F calibration point for the sender. Take a look at the needle on the dial at that virtual temperature with your extra resistor added in and see if you're happy where the needle is sitting at that dangerous virtual temperature.
I think it’s important that the gauge needle is right next to or in the red zone on the dial when the temp is 239°.
So, tested in a pot on the stove with a thermometer in the water? Nice.
If anyone’s buying resistors for this, I would suggest Vishay/Dale mil-spec resistors. You can get them in 1% or 0.1% tolerance, which is pretty good for a metal film resistor.
@OSS @Spook50 Any idea on the wattage requirements going on here? I guess if the wattage is higher you might want flame proof metal oxide, which won’t have as good of tolerance. Choices choices.
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- #52
V/D are definitely the best to go with if it's going to go behind the dash or near the engine. I'll put my ammeter on the sender wire today and see how much current goes through it. At ~7.2VDC I don't expect more than one amp, so as an initial guess, probably about 6-8 watts total; increasing as temperature rises and resistance decreases of course.
@OSS as part of your work in dialing in your temp gauge, did you end up permanently splicing in a permanent resistor or pot into the sender lead? In the pictures you first posted, I can see that my temp gauge reads considerably higher at 185º. If I were to dial back my solid state regulator far enough for the temperature gauge to indicate on par with what you show, my fuel gauge would indicate FAR lower than it should.
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I replaced my FJ60 temperature gauge with a newer used FJ62 gauge. It plugs right in. I lost confidence in my original FJ60 gauge.
The FJ62 gauge needle position was higher when driving normally than my original old gauge needle ever was. My guess is because the FJ62 gauge accounts for the sensor located in the cooler thermostat housing.
On the FJ60 2F, the temp sender is screwed into the top of the cylinder head all the way to the rear of the engine — where the coolant is the hottest.
So my needle position with the FJ62 gauge in a 2F likely doesn’t equate to the position on a FJ62.
Also…. Coolant temperature varies widely depending on engine location. Probably by a lot. So I don’t think it’s possible to dial in a “perfect” temperature. It all depends on where it’s measured.
I know on the 2F, the sensor is reading temperature approximately 10° hotter than the radiator inlet temperature.
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- Thread starter
- #54
Ah so your research was just to see where exactly your 62 gauge would indicate given certain readings?
If that's the case, it does still give me a good baseline for what temperature my new OEM sender indicates based on its resistance that I can use to dial in my temp gauge while keeping my fuel gauge at a reasonable level.
Great discussion. I just wanted to say that @OSS 's readings on post #44 are super close to what my factory temp gauge shows in relation to my auxiliary Autometer. Nowhere near as precise as his, for sure, but perhaps a worthwhile second point of reference. Before I installed the Autometer sending unit, I tested in a pot of boiling water and used 2 thermometers as reference, all were within 2 degrees of each other so that's probably close enough for this purpose. @Spook50 apologies for hijacking your fuel sender thread twice now.
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- #56
No worries. With the fuel and temp gauges sharing the same circuit as far as their positive lead, each will affect the other so it's good info to have altogether in one thread. I'll be playing around with it a little more this afternoon to gather some more info and ultimately I hope I can figure something out that'll allow both fuel and temperature gauges to function with at least a baseline degree of accuracy.
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- Thread starter
- #57
With the sunlight outside I couldn't get a good picture of my gauge, but based on the resistance of the temp sender after running my engine hard in the driveway to check & service my AC, my engine was right at 210º (multimeter showed 43Ω). I'm going to scale down the temp for my fan controller just a hair, but that aside, my temp gauge sat right between the 225º and 230º indications on the pic sheet that @OSS posted. This is at the lowest voltage output that I'm comfortable setting my gauge regulator to, due to fuel indication reading way too low if I go any farther. Based on that, I think starting with 11.5Ω of extra resistance in the sender lead will be a good jump-off point.
Since I now have an idea how I'll differentiate the two gauge indications, I'll focus exclusively on calibrating my regulator to the fuel gauge alone, then based on that I'll see where my temp gauge sits at certain temperatures and find an appropriate resistance to use based on that.
This also tells me that using my non contact thermometer is NOT a good way to get an accurate indication of coolant temperature.
Edit: running the sender lead through my multimeter showed that the maximum current through it is only 106mA at 6.9VDC. About 730mW, so a full watt resistor would definitely be a wise choice given the surrounding heat, whether installed behind the cluster or in the engine bay.
Since I now have an idea how I'll differentiate the two gauge indications, I'll focus exclusively on calibrating my regulator to the fuel gauge alone, then based on that I'll see where my temp gauge sits at certain temperatures and find an appropriate resistance to use based on that.
This also tells me that using my non contact thermometer is NOT a good way to get an accurate indication of coolant temperature.
Edit: running the sender lead through my multimeter showed that the maximum current through it is only 106mA at 6.9VDC. About 730mW, so a full watt resistor would definitely be a wise choice given the surrounding heat, whether installed behind the cluster or in the engine bay.
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Yeah I think the crucial needle position on the fuel gauge is when there’s 5 gallons in the tank and the needle can clearly show that (compared to empty).
Anything above 1/2 full is interesting but not all that important.
Anything above 1/2 full is interesting but not all that important.
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- #59
Precisely. When I first ended this thread I had set the regulator to have the fuel gauge show 1/2 tank with 13.5 gallons in it. IIRC that would leave you with 3.8 gallons by the time the needle would be at the bottom line. I'll have to remember to verify when I dive back in to this after my trip.
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- #60
Oof, I definitely need to figure out a good way to add a resistor (or combination of) to the temperature gauge circuit so that I can have a realistic indication there when the fuel gauge is set correctly. Granted it was 102° outside, but driving up a long incline this afternoon with the AC on, my temperature gauge sat just barely into the red; a hair above @OSS's 239° mark. Realistically I guesstimate I was riding between 230° and 235°, which honestly is too warm for my liking, especially with brand new coolant (but that's for a different thread)
I also noticed that 11.5Ω resistors with a 1W or higher rating are ridiculously difficult to come by. The ones listed as available on DigiKey and Mouser all show an eight or more week lead time. I still have some digging to do, but it might result in having to just bite the bullet and order some.
To work on getting a more broad average of how high my gauge is indicating, I let the engine heat soak when I got back home tonight until the resistance at the sender stabilized at 43.3Ω (210º) then quickly plugged my temp gauge wire back in to it. The needle settled at almost exactly @OSS's 230º indication, giving me an approximation of 10Ω difference between my actual indication and reading on par with @OSS (you're probably getting tired of the constant mentions, huh? I'll just refer to it as "calibrated indications" and spare you the multiple alerts). 10Ω are readily available from Vishay/Dale in wirewound style, 3W power capacity (more than adequate) through DigiKey. Looks like I found my first step of the rest of this research!
I also noticed that 11.5Ω resistors with a 1W or higher rating are ridiculously difficult to come by. The ones listed as available on DigiKey and Mouser all show an eight or more week lead time. I still have some digging to do, but it might result in having to just bite the bullet and order some.
To work on getting a more broad average of how high my gauge is indicating, I let the engine heat soak when I got back home tonight until the resistance at the sender stabilized at 43.3Ω (210º) then quickly plugged my temp gauge wire back in to it. The needle settled at almost exactly @OSS's 230º indication, giving me an approximation of 10Ω difference between my actual indication and reading on par with @OSS (you're probably getting tired of the constant mentions, huh?
I'll just refer to it as "calibrated indications" and spare you the multiple alerts). 10Ω are readily available from Vishay/Dale in wirewound style, 3W power capacity (more than adequate) through DigiKey. Looks like I found my first step of the rest of this research!
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