# Transmission temp gauge



## IA Farmer (Nov 7, 2004)

I am putting a transmission cooler on my truck this week and was also wanting to put a transmission temp gauge in the cab, I was wondering if anyone know how to install a temp gauge any help would be great. Thanks


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## 440trk (Nov 27, 2003)

I've got mine run "in line" directly off of the trans pump. Plumbing it "in-line" will give you the most accurate fluid temp. Basically, find the trans cooler line that is taking the hot fluid from the trans...install a temp sending unit in the line, as close to the transmission as possible. Trans temps from this location can safely run up to 230º-250º. From what I've found, trans fluids start breaking down somewhere between 280º and 300º (temperature at the pump).

You can also install the temp sending unit in the trans pan, which also works pretty well, but it only monitors the ambient temp of the fluid, and not the "in-use" temp. The problem I have with this setup, is that by the time the guage hits 250º...you've probably already done damage and overheated the fliud. If using the "in pan" sending unit, you will have no way of knowing what the "safe" temp limit is, possibly until it's too late. The "in pan" method is good for monitoring what the trans is doing...but it's response time to temperature spikes is non existant.

Hope this helps.


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## Tarkus (Nov 19, 2004)

440trk said:


> I've got mine run "in line" directly off of the trans pump. Plumbing it "in-line" will give you the most accurate fluid temp. Basically, find the trans cooler line that is taking the hot fluid from the trans...install a temp sending unit in the line, as close to the transmission as possible. Trans temps from this location can safely run up to 230º-250º. From what I've found, trans fluids start breaking down somewhere between 280º and 300º (temperature at the pump).
> 
> You can also install the temp sending unit in the trans pan, which also works pretty well, but it only monitors the ambient temp of the fluid, and not the "in-use" temp. The problem I have with this setup, is that by the time the guage hits 250º...you've probably already done damage and overheated the fliud. If using the "in pan" sending unit, you will have no way of knowing what the "safe" temp limit is, possibly until it's too late. The "in pan" method is good for monitoring what the trans is doing...but it's response time to temperature spikes is non existant.
> 
> Hope this helps.


You are way to generous with your tranny temps. You should never really exceed 230 or so ever under a heavy load if you want tranny to last a long time. Tranny fluid oxidises quicker that hotter it gets and above 230 degress it starts happening faster, Around 280 or so the fluid is "trashed" in very short order and 300 and above can be almost certain death, even if it is delayed some. Also then there is the cumlative effect of excess heat on tranny seals which hardens them and shortens their lifes. I my opinion, if you ever get above 230 for a period on time on a long pull it is time to let things cool a bit if you want maximum life. I few minutes up there will not hurt but you do not want to be above 250 even for a few minutes. Heat is your trannies number one enemy not the load you place on it.


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## crashz (Jan 12, 2004)

I installed a tranny temp guage on the output line from the tranny on my F150. With my additional cooler, I never see temps above 180, even when towing in traffic in the summer. I wish I had installed it before adding my aux. cooler, so that I could have a baseline temp. Very worthy yet time consuming upgrade. I notice a lot of the newer 3/4 tons and up have a factory tranny guage.


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## Tarkus (Nov 19, 2004)

"Ideal" tranny temp is between 180 and 200. You want to watch that you do not overcool it in the winter though as you want it to get to at least 160 or so to evaporte the condesation that can build up during colder months sometimes in fluid.


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## aces (Nov 15, 2004)

FWIW... My trans guy recommended i install the temp senser in the return line from the cooler back to the trans. This will NOT show the hottest temps but will show me if the cooler is working. If you put it in the line TO the cooler you will get the hottest temps as the fluid exits the TC. I want to know if the coolers are working - if they fail so will your trans!

He also told me to look for temps similar to the engine oil temp. For my Dodge diesel that is around 190.

BTW i got my guages here: http://www.genosgarage.com/


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## Tarkus (Nov 19, 2004)

aces said:


> FWIW... My trans guy recommended i install the temp senser in the return line from the cooler back to the trans. This will NOT show the hottest temps but will show me if the cooler is working. If you put it in the line TO the cooler you will get the hottest temps as the fluid exits the TC. I want to know if the coolers are working - if they fail so will your trans!
> 
> He also told me to look for temps similar to the engine oil temp. For my Dodge diesel that is around 190.
> 
> BTW i got my guages here: http://www.genosgarage.com/


Not a good idea to put gauge in return line as really does not matter what return temps are as it can be okay and still have very hot tranny temps. Read it in the pan or the outlet to cooler but not in the return line if it is the only gauge. Now two gauges would be kinda cool and you could monitor tranny oil temps before and after cooling. Also you a pretty safe below 220 outlet oil temp and about 180 to 200 is ideal


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## 440trk (Nov 27, 2003)

Tarkus said:


> You are way to generous with your tranny temps. You should never really exceed 230 or so ever under a heavy load if you want tranny to last a long time. Tranny fluid oxidises quicker that hotter it gets and above 230 degress it starts happening faster, Around 280 or so the fluid is "trashed" in very short order and 300 and above can be almost certain death, even if it is delayed some. Also then there is the cumlative effect of excess heat on tranny seals which hardens them and shortens their lifes. I my opinion, if you ever get above 230 for a period on time on a long pull it is time to let things cool a bit if you want maximum life. I few minutes up there will not hurt but you do not want to be above 250 even for a few minutes. Heat is your trannies number one enemy not the load you place on it.


Thanks for the clarification on fluid temp breakdown. All I had ever heard was that it breaksdown around 300º. 
Personally, I've never seen more than 210º in my setup, and my sending unit is _ MAYBE _ 3" from the trans outlet. 210º only comes around in the summer time when sitting in traffic, or travelling for hours on the turnpike at 75+ mph.  I want to build a heat shield for my sending unit as well, as it's located fairly close to my exhaust pipe on the drivers side, and I think that effects my temp reading just a bit (it can only make it show higher than it actually is though).

Wintertime plowing, in 4 LO keeps my trans temps around 150º-165º.


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## Bldrs83 (Nov 26, 2004)

I installed a B&M transmission temperature guage on my '01 F-350. Their directions say to install the sending unit in the return line from the cooler. I originally had the guage on my '97 K-2500 and it usually ran about 160*. The F-350 runs a little cooler than that.


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## streetsurfin' (Jan 22, 2004)

I'm installing the B&M guage also, but I think I'll put it in the line leaving the trans as Tarkus says. I know as long as my engine temps dont get too hot that the return temp will be ok, as it goes through the trans cooler and radiator. I'd like to know what B&M's reasoning is for using the return line. Maybe because they also sell the coolers and want you to know how well they are working?


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## jimsmowin (Jul 28, 2000)

i have b&m on most of mine the directions call for the install on return line


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## Tarkus (Nov 19, 2004)

streetsurfin' said:


> Maybe because they also sell the coolers and want you to know how well they are working?


Maybe but it is the temp before cooling that will cook tranny, not temp of oil going into tranny. On your engine you measure water temp leaving block, not entering it, (same deal with tranny). Also, you route oil through radiator cooler first then thru aux cooler then back to tranny.


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## lance49726 (Oct 28, 2004)

My trans temperature gauge sending unit is mounted in line from trans to cooler and covered the sending unit with high temperature RTV sealant for a more accurate reading.And you want to keep the trans temp under 260 any thing over that will cut you transmission life in half.


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## Tarkus (Nov 19, 2004)

lance49726 said:


> My trans temperature gauge sending unit is mounted in line from trans to cooler and covered the sending unit with high temperature RTV sealant for a more accurate reading.And you want to keep the trans temp under 260 any thing over that will cut you transmission life in half.


260 is way too hot!! You want to keep under 230 max if you plan on keep tranny for a while. At 300 tranny is dead or close to it and temps above 230 are not olny hard on oil but seals in tranny too and repeated overheating can harden them and greatlly shorten their life.


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## lance49726 (Oct 28, 2004)

lance49726 said:


> My trans temperature gauge sending unit is mounted in line from trans to cooler and covered the sending unit with high temperature RTV sealant for a more accurate reading.And you want to keep the trans temp under 260 any thing over that will cut you transmission life in half.


My mistake i meant to say 200 at least that is what i try to do. I have even installed 2 electric fans in front of the radiator i can turn on or off. But of course the lower you keep the temp the better. It doesn't take long for the automatic transmission fluid (ATF) to heat up once the vehicle is in motion. Normal driving will raise fluid temperatures to 175 degrees F., which is the usual temperature range at which most fluids are designed to operate. If fluid temperatures can be held to 175 degrees F., ATF will last almost indefinitely -- say up to 100,000 miles. But if the fluid temperature goes much higher, the life of the fluid begins to plummet. The problem is even normal driving can push fluid temperatures well beyond safe limits. And once that happens, the trouble begins. 
At elevated operating temperatures, ATF oxidizes, turns brown and takes on a smell like burnt toast. As heat destroys the fluid's lubricating qualities and friction characteristics, varnish begins to form on internal parts (such as the valve body) which interferes with the operation of the transmission. If the temperature gets above 250 degrees F., rubber seals begin to harden, which leads to leaks and pressure losses. At higher temperatures the transmission begins to slip, which only aggravates overheating even more. Eventually the clutches burn out and the transmission calls it quits. 
As a rule of thumb, every 20 degree increase in operating temperature above 175 degrees F. cuts the life of the fluid in half! 
At 195 degrees F., for instance, fluid life is reduced to 50,000 miles. At 220 degrees, which is commonly encountered in many transmissions, the fluid is only good for about 25,000 miles. At 240 degrees F., the fluid won't go much over 10,000 miles. Add another 20 degrees, and life expectancy drops to 5,000 miles. Go to 295 or 300 degrees F., and 1,000 to 1,500 miles is about all you'll get before the transmission burns up. 
If you think this is propaganda put forth by the suppliers of ATF to sell more fluid, think again. According to the Automatic Transmission Rebuilders Association, 90% of ALL transmission failures are caused by overheating. And most of these can be blamed on worn out fluid that should have been replaced. 
On most vehicles, the automatic transmission fluid is cooled by a small heat exchanger inside the bottom or end tank of the radiator. Hot ATF from the transmission circulates through a short loop of pipe and is thus "cooled." Cooling is a relative term here, however, because the radiator itself may be running at anywhere from 180 to 220 degrees F.! 
Tests have shown that the typical original equipment oil cooler is marginal at best. ATF that enters the radiator cooler at 300 degrees F. leaves at 240 to 270 degrees F., which is only a 10 to 20% drop in temperature, and is nowhere good enough for extended fluid life. 
In some cases, transmission overheating can even lead to engine coolant overheating! That's why there's a good demand for auxiliary add-on transmission coolers.


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## Tarkus (Nov 19, 2004)

Nice post but if fluid is leaving tranny at 300 degrees, you have bigger problems than how much the cooler is cooling it. Also even if you keep it cool, you should still change it as it does become contaminated with time too.


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## dieselfreak (Nov 22, 2004)

*what tempature dose your trany run when your plowing moderate*

what temperature dose your trany run at when your plowing at moderate snowfall. and dose your truck come with pods for temp gages or no (for Diesel only)


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## Bldrs83 (Nov 26, 2004)

Kind of off the subject but might raise some eyebrows. I drive a front-discharge concrete truck with an Allison automatic transmission. Their transmission temperatures run 260-320 degrees all day long usually staying right around 280 degrees. The warning lights don't come on until about 330 degrees. What's more impressive than that is the oil only gets changed once a year and even after 20,000+ hours of service, failure is almost existent (MAYBE 1 a year out of 90+ trucks).


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## Bad Luck (Sep 30, 2004)

The temp is going read differently for different makes and models of trucks, especially if you're running a trans cooler other than stock, period. You best bet is to place it on the outlet line going to the cooler, this way you see MAX temp that the fuild is leaving your trans. If it get hotter as you drive, your cooler isn't doing what it should. 

RAM_ON97 - Check out the January issue of Peterson's 4 wheel drive, they did a pod install with a trans and other guages on your very truck. 

Good luck man.


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## plowman350 (Jul 19, 2004)

*No temp on the guage!*

I have an 03 F350 with the snowplow prep package from the factory. They have a trans temp guage already on the instrument panel right above the oil temp. Now, the problem is that it only shows a range.....meaning just like the oil guage there's no temps listed.....you can only see if its running high or low, but no numbers.... Does anyone know what the range of temps is on this guage so I can at least eyeball what I might be at?

Also, my only complaint about the instrument panel on this truck is that since they put a trans temp guage, they eliminated the voltmeter......which has been an important tool in the past....When your alternator is dying, it'd be nice to have a voltmeter to "guess" how much time is left on the battery.

We spent a long night once in negative temps with high winds and a dying alternator on our salt truck. the batteries lasted 2 hrs, and we'd have to go back to the shop and switch them every 2 hrs....until the parts store opened. IT really sucked plowing in those temps with the lights and heater off in the truck....had to leave windows open to see.....miserable night.


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## Bad Luck (Sep 30, 2004)

Is your truck a diesel? You should set yourself up with a tri-guage pillar mount set up. Add a voltometer, EGT temp, and boost guage.


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## derekbroerse (Mar 6, 2004)

I think this was posted on here once before:


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## Tarkus (Nov 19, 2004)

Nice chart but I think it is a little off because I have learned from experiance that as long as you keep at or below 200 or so and do not abuse it to bad it should last well over 100k miles and I have gottem close to 200K out of a few before I sold the vehicals.


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## derekbroerse (Mar 6, 2004)

Hey, I didn't make it. I think it came from the ATRA originally.. I'm sure its only a rule-of-thumb...


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## Tarkus (Nov 19, 2004)

derekbroerse said:


> Hey, I didn't make it. I think it came from the ATRA originally.. I'm sure its only a rule-of-thumb...


Oh I do not think you did nor was my comment aimed at you. Sorry if you think it was.


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## derekbroerse (Mar 6, 2004)

lol it takes more than that to upset me, don't worry. I will admit to enjoying a good arguement though.....  

Shame on me  tehehehehe


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## Tarkus (Nov 19, 2004)

derekbroerse said:


> lol it takes more than that to upset me, don't worry. I will admit to enjoying a good arguement though.....
> 
> Shame on me  tehehehehe


So do I but I like to call them "debates"


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## danno (Sep 16, 2004)

I had the B&M tranny gauge installed on my truck a couple of days ago, and it sounds right, installing after the tranny. But I went with B&Ms suggestion and did the return line. Too late. Anyway, my needle only "touches" the first white square when driving. Moves a 1/8 inch. I`m guessing its saying 100 degrees? Can this be accurate ? Outside temps have been 30s -40. I also have a cooler.


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## Tarkus (Nov 19, 2004)

danno said:


> I had the B&M tranny gauge installed on my truck a couple of days ago, and it sounds right, installing after the tranny. But I went with B&Ms suggestion and did the return line. Too late. Anyway, my needle only "touches" the first white square when driving. Moves a 1/8 inch. I`m guessing its saying 100 degrees? Can this be accurate ? Outside temps have been 30s -40. I also have a cooler.


Gauge in wrong place and on little value in return line (though one in both lines would be kinda cool) You need to know actual temp of oil in tranny and outbound line or pan is the place to read it.


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## Makndust (Feb 6, 2004)

I think it depends upon what tranny you run as to what the temp will run at. I just had my TH400 rebuilt in my 87 Chevy. I had them beef it up with an Allison Torque converter, a shift kit, and an extra set of clutch packs. They also installed a temp guage in the pan. I agree with you guys, I wish that they would have put it inline from the pump. I panicked when it ran right up to 240 and stayed there until it was not under load. When I called the tranny guy, he said that that specific tranny wouldn't be aproblem at that temp and to worry if it got up to 280 to 300 and wouldn't cool off when taken off load. I'm sure the tranny can handle the heat but my question is can the ATF fluid? I doubt it. I believe a guage is great, but sometimes they make you panic possibley prematurely. Do you guys know of any fluids that will handle extreme heat better than others?
My 03 chevy has a temp guage in it. Sometimes when I am running it hard in the summer it will run up to 220 - 240 but that is about it.


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## danno (Sep 16, 2004)

TARKUS, I know you`re right, and I think I`m going to buy another sending unit and install the fitting after the tranny. At least I`ll have 2 T-fittings next to each other. Or, I might just buy another gauge package and have the before and after reading you mentioned.


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## Tarkus (Nov 19, 2004)

danno said:


> TARKUS, I know you`re right, and I think I`m going to buy another sending unit and install the fitting after the tranny. At least I`ll have 2 T-fittings next to each other. Or, I might just buy another gauge package and have the before and after reading you mentioned.


Before and after would be kinda neat to have if you have the room for the gauges anyway


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## osbo68 (Dec 1, 2004)

As a rule of thumb any temps. under 240F are safe. 270F is the max you should let it get. After that you start to slip the clutchs. If your trans. just happens to get that high change your fluid ASAP. Fluid is cheap. Rebuilds are not. 
Remember when plowing to let the trk idle for approx 10min. before shutting it down. It will let your fluids cool off.


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## osbo68 (Dec 1, 2004)

By the way Tarkus I like youir train of thought on runnig 2 guages. Not necc. but would be nice to have.


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## Tarkus (Nov 19, 2004)

osbo68 said:


> As a rule of thumb any temps. under 240F are safe. 270F is the max you should let it get. After that you start to slip the clutchs. If your trans. just happens to get that high change your fluid ASAP. Fluid is cheap. Rebuilds are not.
> Remember when plowing to let the trk idle for approx 10min. before shutting it down. It will let your fluids cool off.


240 is too hot in my book. I would ay 220 or so tops and 200 or less is best because it is not just clucth life, it is seal life too and it is shortened a lot if temps get to or above 220 or so for long periods of time. The hotter it gets, the shorter the possible seal life. At 280 to 300 and above you are on borrowed time.


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## osbo68 (Dec 1, 2004)

I agree with running in the 200-220 range. Lower is always better. But not always possible. We change our trans. fluids twice a your. In the fall and again in the spring.


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## danno (Sep 16, 2004)

Do you think it should be OK to use the same B&M gauge, even if they say to install on the return line ?


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## Tarkus (Nov 19, 2004)

danno said:


> Do you think it should be OK to use the same B&M gauge, even if they say to install on the return line ?


Yes no problem as long as it will read up to 250 or so (if it gets that high or higher you need to shut down anyways)


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## Tarkus (Nov 19, 2004)

osbo68 said:


> I agree with running in the 200-220 range. Lower is always better. But not always possible. We change our trans. fluids twice a your. In the fall and again in the spring.


Wise advise but if you cook oil, you have also baked the seals some too. You need to keep temps below 220 anyway possible for maximum life.


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## danno (Sep 16, 2004)

TARKUS, you da man ! :salute:


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