[Cube Dweller]

Another data point on operating temps- assuming my ISSPRO gauge is accurate, temps on my '97 were around 185-188 in Sacramento. About 90-95 today. This was varied driving, some at 65 on flat highway, idling at stoplights, driving around town, A/C on.

Truck has 82K miles, coolant is 50-50 green, new oem fan clutch, new oem tstat, no noticible sediment in radiator or cooling system.

[Darwood]

I'm going to post one of the equations I've been using since Rich requested it in another thread. I'd like to post all of what I have but I have 20 pages of calulations and I'm just to lazy to post it all at this time.

Pretty much everything is based of thevenin equivalents for a wheatstone bridge.

To figure out R2 with the following given:

voltage across L1 = VL1
a resistor value for D1 = RD1
a resistor value for R1 = RR1
thevenin equivalent for L2 and L3 = L2||L3 = RL2L3
input voltage = VI
thevenin equivalent voltage for L2 and L3 = input voltage * L3/L2+L3 = VL2L3
current = VL1/L1 = I
voltage across RL2L3 = RL2L3 * I = VRL2L3
voltage across RD1 = RD1 * I = VRD1
a resistor value for R1 = R1

I use:

R2=-R1*(VRL2L3 + VRD1 + VL1 - VL2L3)/(R1*I+VRL2L3 + VRD1 + VL1 - VL2L3 + VI)

And now some interesting values for R2 I calculated based off of Raven's pictures of tempurature and voltage across L1.

161 degrees R2 = 110.092 ohms
200 degrees R2 = 50.6317 ohms
208 degrees R2 = 44.0578 ohms
218 degrees R2 = 36.8199 ohms
224 degrees R2 = 33.0365 ohms
236 degrees R2 = 29.2056 ohms

I'll post the results I calculated playing with R1 = 150 and 180 with RD1 = 100 later

[semlin]

darwood what exactly does that all mean?

[Darwood]

Originally Posted by semlin

darwood what exactly does that all mean?

Good question. Say I want to know what R2's value is for a given voltage across L1. I would use that equation. The reason I would do this is the voltage across L1 directly correlates to the position of the needle on the gauge. If I know where I want the needle to be (i.e. I know what I want the voltage across L1 to be), I can calculate what temperature the sender is sensing at that needle height given a certain resistor value for the diode replacement and R1 (the centering resistor).

I would use this equation to test out different resistor values for the diode replacement.

For reference as to what L1 and R1 mean here is Raven's diagram for reference.

[semlin]

um cool. so... how about just a resister to position for dummies chart?

[Darwood]

Originally Posted by semlin

um cool. so... how about just a resister to position for dummies chart?

that's something I need to work on.

[MoGas]

Has anyone checked to see if the temperature is the same where the factory sender is versus where CDan and others have put the aftermarket sensor/sender?

[RavenTai]

someone, maybe Lxtreme? has both an aux gauge and the mod, IIRC he stated they follow each other.

makes sense that they would they read water temperature a few inches apart, the stock gauge reads right before the water leaves the head, AM gauge right after it leaves the head.

I could see there being a slight variation during warm up as the water outlet (where an AM gauge picks up at) does not have much flow until the thermostat opens, but as far as I know no one has reported such.

[cpg]

Originally Posted by RavenTai

someone, maybe Lxtreme? has both an aux gauge and the mod, IIRC he stated they follow each other.

makes sense that they would they read water temperature a few inches apart, the stock gauge reads right before the water leaves the head, AM gauge right after it leaves the head.

I could see there being a slight variation during warm up as the water outlet (where an AM gauge picks up at) does not have much flow until the thermostat opens, but as far as I know no one has reported such.

I have a scan gauge and ravens mod on the stock gauge. They follow each other very well. The modded stock gauge works great.

[MoGas]

Originally Posted by cpg

I have a scan gauge and ravens mod on the stock gauge. They follow each other very well. The modded stock gauge works great.

But they both read from the same point right?

[cpg]

I think so but not sure there is 2 temp sensors in that area I tink 1 is ac shut off but not sure.

[RavenTai]

The gauge sender, ECU sender & AC shutoff are all together on the left side of the head near the water outlet where an after market sender would be located.


MoGas what exactly are you trying to figure out ?

[MoGas]

Originally Posted by RavenTai

MoGas what exactly are you trying to figure out ?

What the offset would be by reading the engine temp at the boss versus where the factory sender is.

BTW,
I decided to check the accuracy of a gauge that I just got.
Auto gage # 2313 by Auto Meter 2 1/16" 100-280F mechanical gauge.

Test equipment is a Hart Scientific model 9122 dry well.

The results were less than desired:

Test equipment setting/Gauge indication

65.5C (150F)/ 150F
82.2C (180F)/ 180F
93.3C (200F)/ 198F
110.0C(230F)/ 225F
121.1C(250F)/ 245F

At work this would fail. We would calibrate to +/- 2.8 F (.01% of full scale) on something of this range. I could have lived with it being off at the low end and more accurate between 200-230, but not with it off by 5* in the middle of the scale.


I guess I'll take this one back and spring for the Auto Meter Sport Comp and try again.


Dave

[MoGas]

OTOH, I just checked the calibration on the oil pressure gauge, and it was much more accurate.

I used a Ametek Mod Cal II on a Auto gage model 2312 4-100 psi mechanical oil pressure gauge.

Pressure indicated on gauge / mod cal indication

20psi / 21.66psi

50psi / 51.23psi

80psi / 81.34psi

This would be out by our standards of +/- 0.25 psi on a 0-100 psi gauge but for this application, I'll go with it.


Dave

[semlin]

let us know how the oil pressure gauge calibrates against the stock gauge. that would be interesting to know.

[MoGas]

Originally Posted by semlin

let us know how the oil pressure gauge calibrates against the stock gauge. that would be interesting to know.

I could do it, but the factory indicator isn't graduated in psi. I could just put different pressures in the ModCal and take pics of where the needle goes. would that work for you? Id rather do it that way instead of comparing it to a gauge that is an average 1.4psi low.

Dave

[RavenTai]

Originally Posted by MoGas

What the offset would be by reading the engine temp at the boss versus where the factory sender is.

BTW,
I decided to check the accuracy of a gauge that I just got.
Auto gage # 2313 by Auto Meter 2 1/16" 100-280F mechanical gauge.

Test equipment is a Hart Scientific model 9122 dry well.

The results were less than desired:

Test equipment setting/Gauge indication

65.5C (150F)/ 150F
82.2C (180F)/ 180F
93.3C (200F)/ 198F
110.0C(230F)/ 225F
121.1C(250F)/ 245F

At work this would fail. We would calibrate to +/- 2.8 F (.01% of full scale) on something of this range. I could have lived with it being off at the low end and more accurate between 200-230, but not with it off by 5* in the middle of the scale.


I guess I'll take this one back and spring for the Auto Meter Sport Comp and try again.


Dave

5 degrees is more than I would like but this is about what you can expect from a consumer type product,


one other thing is how tight was the metal to metal contact between the insert and sender?

if there was any air gap heat loss through the top of the sender and thermal resistance of the air could keep the sender at a lower temp than the tester, more than would be were it immersed in good thermally conductive coolant.

[semlin]

Originally Posted by MoGas

I could do it, but the factory indicator isn't graduated in psi. I could just put different pressures in the ModCal and take pics of where the needle goes. would that work for you? Id rather do it that way instead of comparing it to a gauge that is an average 1.4psi low.

Dave

better still. it would be good to know what psi there is below and above the two ideal hash marks. i think all trucks will run below at idle when they are hot and my truck will sometimes run above that when cold, especially climbing on the highway cold.

[MoGas]

Originally Posted by RavenTai

5 degrees is more than I would like but this is about what you can expect from a consumer type product,


one other thing is how tight was the metal to metal contact between the insert and sender?

if there was any air gap heat loss through the top of the sender and thermal resistance of the air could keep the sender at a lower temp than the tester, more than would be were it immersed in good thermally conductive coolant.

I'm going to double check it on the stove with water and a calibrated thermometer. (after my wife goes to work tomorrow)

Dave

[RavenTai]

water will only get you to 212f or so (210 at my altitude)

http://www.biggreenegg.com/boilingPoint.htm


50/50 coolant will get you to 223F (pan can never be used for food again)

I used ATF for the mod, it smokes pretty good at temps over 250, I did it in the garage on a hot plate



I am also interested in what the oil pressure gauge reads, Instigator came up with some 100 PSI for the high range of oil pressure with a mechanical gauge,

[MoGas]

I double checked the calibration of the temp gauge using a Fry Daddy and cooking oil and a calibrated thermometer as a standard with the same results. I returned that gauge and sprang for the Auto Meter Pro Comp electric water temp gauge. I rigged it up with a car battery and did the hot oil testing and it was dead on.

Installed it to the boss that others have used and I get 185-195 *F as normal around town driving with the air on and an ambient temp of ~80*F. The factory gauge goes to the middle at ~140*F and doesn't move at least until after 195*F

Another question: when splicing the instrument lamp to the lighting circuit, do I splice the green wire or the white with green runner?


Dave

[turbocruiser]

Originally Posted by RavenTai

someone, maybe Lxtreme? has both an aux gauge and the mod, IIRC he stated they follow each other.

makes sense that they would they read water temperature a few inches apart, the stock gauge reads right before the water leaves the head, AM gauge right after it leaves the head.

I could see there being a slight variation during warm up as the water outlet (where an AM gauge picks up at) does not have much flow until the thermostat opens, but as far as I know no one has reported such.

Wow, missed this thread for a while. Not sure if LX stated this but I did, I have a very accurate Greddy Gauge and it is within zero to one degrees difference from stock temp sensor as read through the auto enginuity software (in other words not eyeballing the stock gauge but reading the raw data from the stock sensor). The two are exactly aligned ... with the exception of warmup like RT wrote and the reason for this is whatever conduction of heat within the head causes the stock temp sensor to read temps while at the same time the after market one (located right after the aluminum neck tube off of the head) wont read temps until the thermostat opens and allows flow. It is really a pretty cool phenomenon really; you can start the rig, see the stock gauge go up slowly and then all of asudden the aftermarket gauge responds with the tstat opens and allows flow. Anyways, HTH.

[MoGas]

Originally Posted by turbocruiser

Wow, missed this thread for a while. Not sure if LX stated this but I did, I have a very accurate Greddy Gauge and it is within zero to one degrees difference from stock temp sensor as read through the auto enginuity software (in other words not eyeballing the stock gauge but reading the raw data from the stock sensor). The two are exactly aligned ... with the exception of warmup like RT wrote and the reason for this is whatever conduction of heat within the head causes the stock temp sensor to read temps while at the same time the after market one (located right after the aluminum neck tube off of the head) wont read temps until the thermostat opens and allows flow. It is really a pretty cool phenomenon really; you can start the rig, see the stock gauge go up slowly and then all of asudden the aftermarket gauge responds with the tstat opens and allows flow. Anyways, HTH.

And your sender is tapped into the boss?

[RavenTai]

Originally Posted by MoGas

Another question: when splicing the instrument lamp to the lighting circuit, do I splice the green wire or the white with green runner?


Dave

to get a light that both dims with the rest of the instruments and turns on and off with the lights you need the light hooked to both.

the green is straight battery + that turns on with the parking lights,
the white with green stripe is a variable resistance ground through the rheostat for dimming.

if your gauge light grounds directly to the housing you will not have a dimming function on that light.

[RavenTai]

Turbo Cruiser Thanks for the info.

[MoGas]

My light is grounded independant of the instrument.

So black from light to white/green stripe and red to green should make the light operational and dimmed along with the rest of the lights?

Dave

[turbocruiser]

Originally Posted by MoGas

And your sender is tapped into the boss?

No, like I wrote, right after the aluminum neck tube off of the head. Its prolly 8 to 10 inches after the path the stock sensor. This explains both the accuracy and alignment once flow starts and it also explains the delay in reading of temps at startup before flow starts.

[RavenTai]

Originally Posted by MoGas

My light is grounded independant of the instrument.

So black from light to white/green stripe and red to green should make the light operational and dimmed along with the rest of the lights?

Dave

yes that is it.

[sandcruiser]

While looking at various cooling things, and reading this thread (thanks for the work, everyone) it occurred to me that the Water Temp Cut Switch could work for a dummy light as well. It kills the A/C at 226* (108C). Haven't looked at the circuit yet, but the FSM says that the switch turns "ON" at 226 and "OFF" at 217. I'm assuming that to mean it is a normally open switch that closes at temp to complete ground... thus tripping a kill relay in the A/C compressor.

Now, I'm not sure if this would screw up the A/C, but seems that a really simple approach would be to rig an LED and/or buzzer into the guage area somewhere that takes 12v from IGN ----- LED ---- Cutoff S/W ---- Ground

Might have to throw a diode onto the existing A/C wire to prevent the current from the LED from going anywhere. Not sure about that part.

I'm thinking that I'd also like to rig up a relay to turn on my Aux Cooling fan such that no matter what (even if the motor is off) the Aux Fan blows when the temp exceeds 226. But I still want the Aux fan to turn itself on whenever the compressor is active.

Guess I need to learn some more about electronics!

Originally Posted by RavenTai

R2, Desire yes, but have not put much thought towards it except the removed zener might be possibly be used as a trigger, problem is the source is pure analog and a light and/or buzzer is an on/off thing, need to bridge that gap without messing with gauge readings (IE drawing much current from the gauge circuit, witch means needs sense and amplification) . Probably could be done with only a few components but need to put some effort towards it. Time is short right now.


If you are trying to wait for a light and or buzzer you probably would be better off to do this mod for now and possibly adding to it later, the light and or buzzer (basically a power out to power whatever alarm you want) should be an add on no effecting the base mod.


Rick that defiantly covers instructions for the mod but is not very electrard friendly.

[RavenTai]

on my 96

The temp switch connector has two pins

pin 1 green with yellow stripe leads to a normally closed relay that interrupts the AC clutch power when the overheat switch activates.
pin 2 white with black stripe is a ground,

If you connected the ground end of your alarm to pin 1 it would see
nothing when ac is off
battery + when the ac is on
and ground when the switch hits 226.

only remaining question is how much current overhead the switch has, an LED should be no problem, a large buzzer or incandescent light might, ifyou wanted to run something with any meaningful current draw a realy could be used to take the load off the switch ( with is how it is used stock)