93-97 Coolant Temperature Gauge Modification

[rhyary]

RavenTi,
First thanks for this thread and the latest pictures.
After temp gage was modded my temp gage during long uphills sits just bellow the red line.
There is a 1/16" of black between the red and the needle.
Can your setup show what temp it is?
Also what is consider normal hot, I have a good cooling system with many new parts and modified blue fan clutch. So I have got to assume that on a long climb this is "normal" hot.

Rami

 

[CycloSteve]

RavenTi,
First thanks for this thread and the latest pictures.
After temp gage was modded my temp gage during long uphills sits just bellow the red line.
There is a 1/16" of black between the red and the needle.
Can your setup show what temp it is?
Also what is consider normal hot, I have a good cooling system with many new parts and modified blue fan clutch. So I have got to assume that on a long climb this is "normal" hot.

Rami

Rami, your truck is asking you to shift out of 2nd!



Steve

 

[rhyary]

nah,
This uphill I am towing my motorcycle and the truck has a hard time in D. Although I give up speed, I just put it in 2nd and 3500 RPM and enjoy the scenery. What's the rush?

Besides, on that day I had two days of speed coming up, another reason not to rush.

 

[96r50]

nah,
This uphill I am towing my motorcycle and the truck has a hard time in D. Although I give up speed, I just put it in 2nd and 3500 RPM and enjoy the scenery. What's the rush?

Besides, on that day I had two days of speed coming up, another reason not to rush.

You know there is a gear between D and 2 right?

 

[rhyary]

Adam,
It is interesting you mentioned it. It drops from tallest gear to the half gear in the first 100 feet of 2 mile uphill. It then strains itself thru that gear (3rd?) not quite dropping to second and the RPM keep falling and the temp keep rising. I can kick it to second, but it won't stay in second. The only way to keep it "automatically" in second is to bury the gas paddle to the floor, but that gets me to 5000 RPM. So hence manual 2nd and 3500 rpm and everyone is happy.

BTW, I tried getting the O/D off, but on that hill the gear is actually taller than 3rd. If someone care to explain this to me will be great. Never quite understood the relationship between D (4th?) 3rd, and O/D.

 

[96r50]

The A343F is a 4 speed automatic with overdrive (O/D). What this means is that there are 4 gear ratios, and the last one (4th) is overdriven (the output shaft spins faster than the input shaft). 3rd gear is "direct drive" since it is a 1:1 ratio (input and output shaft speed is the same), while 1st and 2nd are underdrive (output shaft spins slower than the input shaft). The transmission also has a locking torque convertor which allows it to minimize the power loss that is present in automatic transmissions due to the fluid coupling. The torque convertor can only lockup in 4th gear (a.k.a. overdrive).

On the centre console your shifter has three forwards-drive positions: 1, 2, and D (3rd). You also have the O/D switch on the shifter handle, which is essentially just saving you from having a fourth shifter position. With the shifter in D and the O/D switch on (pushed in, no light on the dash) the transmission has free range of all 4 gears, and can lock the torque convertor when in 4th (O/D). With the O/D switch off (popped out, light on the dash) the transmission can only use gears 1,2, and D (3), and the torque convertor will not lock. With the shifter in 2nd, it is limited to 1st and 2nd, and with the shifter in 1st, it is limited to first gear only.

Gear Ratios (found online)
1st: 2.804:1
2nd: 1.531:1
3rd: 1:1
4th (O/D): 0.753:1

Hope that helps!

 

[rhyary]

Thanks Adam, but this does not explain what I feel. If I drive in D, no light in the dash board, and the transmission switch to 3rd, and then I push the O/D, theoretically nothing should change. I was in third, and pushing the O/D I just limited the transmission into third. Same thing if I kick it into second, and THEN I shift to second, there is not difference in the RPM.

But this is NOT what I observe, if I drive in D, and transmission shift to 3rd (1:1) and then I push the O/D, if feels like the gear got higher.

Speaking in ratios, the O/D top gear feels like a higher gear than if the transmission shifter down from D to 3rd without the O/D. This is what confusing to me because I thought the same as what you described above.

Rami

 

[96r50]

Thanks Adam, but this does not explain what I feel. If I drive in D, no light in the dash board, and the transmission switch to 3rd, and then I push the O/D, theoretically nothing should change. I was in third, and pushing the O/D I just limited the transmission into third. Same thing if I kick it into second, and THEN I shift to second, there is not difference in the RPM.

Yup, that makes sense

But this is NOT what I observe, if I drive in D, and transmission shift to 3rd (1:1) and then I push the O/D, if feels like the gear got higher.

Speaking in ratios, the O/D top gear feels like a higher gear than if the transmission shifter down from D to 3rd without the O/D. This is what confusing to me because I thought the same as what you described above.

Rami

Are you sure that first shift you are feeling is not the torque convertor unlocking (the rpms bump up a couple hundred)? If you're cruising along flat ground at highway speeds, you are in 4th gear and the TC is locked. As you start up the grade, the first thing the ECU is going to do is unlock the TC. If that's not enough power, it will then drop it into 3rd. That might be the extra "shift" you are feeling.

 

[rhyary]

Yes, the RPM jumps up about 200. So it is not dropping it down a gear?

Still there is this scenerio where going up hill, the T.C is unlocked, and I push the O/D and it feels like I went up 1/2 a gear. This is were it feels like I am better off with the O/D on, which does not make sense to me. How does the O/D off feels less power then with the O/D on.

Does 3rd 1:1 feel less powerful then 4th with the T.C. unlocked?

 

[96r50]

Yes, the RPM jumps up about 200. So it is not dropping it down a gear?

No, that's just the TC unlocking. You are still in 4th gear (O/D), but with the TC unlocked the engine can rev higher and produce more power to push you up the hill.

Still there is this scenerio where going up hill, the T.C is unlocked, and I push the O/D and it feels like I went up 1/2 a gear. This is were it feels like I am better off with the O/D on, which does not make sense to me. How does the O/D off feels less power then with the O/D on.

Does 3rd 1:1 feel less powerful then 4th with the T.C. unlocked?

I don't know the last time you had your seat-of-the-pants-meter calibrated, but numerically speaking 3rd gear is more powerful than 4th gear, assuming all other factors (speed, load etc) are the same. I can cruise up some hills in 4th, but to accelerate up them the transmission will kick down to 3rd for higher engine rpms and more power.

 

[RavenTai]

In my opinion (there are others) normal temperature is within the range of the thermostat, 190 maybe a few degrees more, when you are beyond this you have exceeded the capacity of the cooling system. It may Find a new ballance point as the radiator can remove more heat as the water temperature increases but in this mode evry increase in load is an increase in water temperature, the cooling system is not under control and you are on your way to an overheat

For reference when I moved I Masde several trips from Atlanta to Florida with an enclosed 8x20 trailer the heaviest was with my tools 11,000 lbs combined gross weight. The needle remained near the middle even on long hills except for when I got stuck in slow moving traffic, I need to mod my fan clutch.

 

[Tools R Us]

In my opinion (there are others) normal temperature is within the range of the thermostat, 190 maybe a few degrees more, when you are beyond this you have exceeded the capacity of the cooling system. It may Find a new ballance point as the radiator can remove more heat as the water temperature increases but in this mode evry increase in load is an increase in water temperature, the cooling system is not under control and you are on your way to an overheat
...

Kinda,,, maybe? Look at the design:

The thermostat is a bottom, intake, bypass design. When cool, it bypasses the radiator, only circulating coolant through the motor. A little warmer it mixes recirculated and from the radiator. With higher load/temp it draws all of the intake from the radiator, closing the bypass. It's job is to attempt to control the coolant intake temp in the 190F range.

The gauge sensor is in the top of the motor, coolant output. The number that it sees is thermostat/intake temp plus the heat gain from cooling the motor. It will always reflect motor load, so will vary with load, ambient temp, etc. Attempting to cool the motor to always run at thermostat temp, would waste a ton of energy and probably is not achievable in all load situations.

I was a service manager before most gauges were "deadened" and in the first hot summer weeks, we would have tons of calls. My rig is running hot, it has never run that high on the gauge,,, what did you do to cause it??? Took the boat to the lake last Sunday,,, well it was 115F and the boat weighs 5000lb,,, yes, but it has never run there on the gauge,,, maybe last summer,,, I don't remember it ever running there, need to do something about it,,, no problem, call the weather man a order cooler weather, unhitch the boat or I can spend a bunch of your $$$ with little chance of change...... Yep, I was one that was happy to see the "safe operating range" deadened!

 

[e9999]

RT,
the thermostat controls the average engine temperature by modifying the flow rate of coolant. That is certainly one way of doing it. And I suspect one of the main reason is to get the engine to heat up faster to reduce emissions (and provide heating in the winter).
But that is not the only way to "control" the temp. You can also do this statically by simply letting the engine shed the excess heat after the thermostat (read flow rate) is already fully open. Assuming steady-state conditions, the engine will settle to the temp it needs to be at to shed the waste (not going to the wheels) energy given the heat transfer out of the engine (which is a function of the engine temp). This can be higher than the thermostat closed to open range. And it does not necessarily mean a runaway condition resulting in overheating. I may settle happily at 215, say. The higher the engine temp is, the more energy it can dissipate for a given flow rate. This is fine engineering. It doesn't have to be a dynamic control type of approach to work. And it would save energy (power) if it means you don't design a higher flow rate in.

I think the engine is likely designed to handle higher temps than the 190 mentioned above and even well above 200F. Witness the shut-off temp for the A/C. Set at something like 220+ IIRC. That suggests to me that the designers are fine with any temps below that and probably even somewhat above since they are surely putting in a safety factor. Heck, if an engine was not designed to run above 212, they would not need a pressurized coolant system.
I'm anal about my engine but I'm not going to panic if it reaches 210 on a hill in the summer. I'll just keep an eye on things. Yes, may well be better if it's cooler rather than hotter from a longevity point of view, everything else the same, but I don't think 210 is way hotter than is safe.

(and, yes, I probably already wrote that someplace else... )

 

[cody c]

Sorry to sidetrack, but I just pulled apart a instrument panel from a 92, and the coolant gauge seems to be identical, as well, the gauge faces appear identical, so new white gauge faces from White Face Gauges - Custom Gauges - Your Auto Gauge Specialist should fit on a 91-92 if anyone is wondering. I may order a set but Im going to see if I can get a custom set with "4000" rpm max and "diesel fuel only" instead of "unleaded fuel only"
on the speedo.

 

[azTony]

Well apparently I have done something wrong. After the mod my gaugue acts as I would expect as it sits just above the half way mark but when it starts to get a little warmer it will move up to have the top of the needle just touching the red. According to the pictures posted this should be around 217. I bought the rig last year in October and replaced the radiator, hoses and thermostat with OEM parts and flushed it. I was planning on flushing again in a year since I have no PM records from the PO. After I did this mod it looked like I had a heat up problem so I changed the fluid in my fan clutch (thanks Tools!) and bypassed my rear heater and replaced the PHH and hoses at the top of the engine with Samco hoses and the tension clamps and flush it. Take it for a drive same thing.

With the needle that high the engine was hit with the hand held temperature gauges and the first time it was 192 and the highest reading was 198. That is not bad at all when we are in a Heat Wave warning in Arizona.

Obviously my gauge is off. Any ideas what would be wrong? You can see in post 377 the value resistors I used.

 

[RavenTai]

Hit the water outlet on the left side of the head with some flat black spraypaint and check with your ir again, I. Don't think the emisivity of aluminum could make that much of a diffrence but it is worth looking into.

If that checks out take the gauge back out and check the resistsnce of your connectiions they sould be leaa than one ohm.

 

[azTony]

Before I put the gauge in the cluster after the mod I measured the ohms and all my readings were in line. I measured resistance for each of the resistors "down stream" of the circuit and measured the joints. I came up with 50 and 100 Ohms and a dead short (less that an ohm) at each of the 4 solder joints.

With the posted pictures stating the needle at the bottom of the red is around 217 and it was measured at 192/198, do you really think black paint would correct a nearly 20 degree difference? I am just trying to understand it. I am tempted to use an after market gauge to get an accurate reading so I have a baseline measurement.

 

[BirfMark]

. I am tempted to use an after market gauge to get an accurate reading so I have a baseline measurement.

For $50, that's what I did. While it's a novel idea that the factory gauge works like it should after this mod, you're still left semi-guessing what the actual temp of the system is. With the gauge I installed, one glance down & I know exactly what's going on. FWIW, the temp at the gauge matches the IR temp of the aluminum outlet exactly.

https://forum.ih8mud.com/80-series-tech/403336-gauge-install.html

 

[Tools R Us]

... FWIW, the temp at the gauge matches the IR temp of the aluminum outlet exactly. ...

This agrees with my experance.

...
With the posted pictures stating the needle at the bottom of the red is around 217 and it was measured at 192/198, do you really think black paint would correct a nearly 20 degree difference? I am just trying to understand it. I am tempted to use an after market gauge to get an accurate reading so I have a baseline measurement.

...
With the needle that high the engine was hit with the hand held temperature gauges and the first time it was 192 and the highest reading was 198. That is not bad at all when we are in a Heat Wave warning in Arizona.

Obviously my gauge is off. Any ideas what would be wrong? You can see in post 377 the value resistors I used.

I wouldn't worry about it. Would take several IR readings and compare to gauge readings, reset in your mind to what that gauge reading means. If the readings are consistent, just do a mind calibration?

 

[Buckru]

In my opinion (there are others) normal temperature is within the range of the thermostat, 190 maybe a few degrees more, when you are beyond this you have exceeded the capacity of the cooling system. It may Find a new ballance point as the radiator can remove more heat as the water temperature increases but in this mode evry increase in load is an increase in water temperature, the cooling system is not under control and you are on your way to an overheat
.

After a tremendous amount of reading and searching and asking, there should be some additional info to factor into the normal operating temp of the rig. The new oem headgasket's #6 water jacket is shaped so as to restrict flow more than the original. The theory is it allows more heat sink away from the #6 to the coolant. This design difference raises normal water temps from 188-192 to 195-204 based on my readings. The cometic hg's #6 is more closely designed like the original oem gasket and should produce a little lower normal operating temp, but I can't confirm this.

It's well documented the effects of proper cooling system maintenence and the many things we can do help the system to perform better. But, if we keep using Toyota's published number for a stock 80 as a baseline after new HG's, armor, extra fuel tanks, bigger tires, etc., we could all be chasing ghosts. I am completely comfortable with my water temp at 207 on a Houston freeway running 70mph in 98* sunny weather with ac on high. I would have never been comfotable with those number had I not spent hours reading threads and pm's.

We need a definnative temp thread so people can compare like rigs to like rigs under similar scenarios. In my example above, if I posted I was running 207 and provided little else, it's just a number. It's context that gives it meaning. Even the above context would need to be expanded to be effective.

I hope this adds some value to this thread. I have had the RT temp guage mod for probably 90k miles and she's working like a charm. A very scary charm when she gets near the red, but a charm none the less.

Good Luck,

Buck