Transmission temp gauge question

[cbear34]

I was wondering how many of you use a transmission temp gauge? And if you do, where does the sender pick up the transmission fluids temp? Do you need to drill in to the oil pan?
I am a mechanic so I have always believed in external transmission coolers. I installed a big Hayden cooler and was wondering if a trans temp gauge would be a good idea?
Thanks for any input!

 

[Silvertip]

Re: Transmission temp gauge question

Transmission temp gauges are a nice addition to a vehicle that is used for heavy towing. Yes -- they go into the oil pan. However, if the tranny fluid does get hot, what are you going to do about it? All you can do is pull over and let it cool which is very unlikely to happen if you have an external oil cooler. As you know, modern tranny's have lockup converters so once locked up, they build up far less heat than the older non-locking versions bercause there is no slippage in the converter. I know of a municipality that had tranny failures on the their Ford snow plow trucks until they installed gauges and instructed drivers to downshift if tranny temperature rose. That ended the failures. However, plowing snow in a city at under 30 mph is very different that towing at highway speeds. You can't downshift (except for mountain driving) lower than direct unless you want to be a rolling road block. And chances are if you had to do that there are other tranny problems. So you are aware, if you add an external cooler and live in a cold climate like Minnesota/Wisconsin, you should install a bypass type as transmissions can be "overcooled" which is bad also.

 

[cbear34]

Re: Transmission temp gauge question

Silvertip
Thanks for your thoughts. That's pretty much what I figured. I guess a gauge, like other gauges just let you know what is going on internally. All you would be able to do is to pull over if it is overheating. With the setup I have, I figure I should be fine.

 

[jeeperman]

Re: Transmission temp gauge question

But if you keep an eye on the temps you will be able to establish the normal temp. And if you notice the temps increasing, you can at least take measures to correct what is wrong.

Why have a temp gage for your engine coolant?
No gage means you run it until you start to hear or smell something wrong.
Which is usually too late to correct or fix anything.

 

[Silvertip]

Re: Transmission temp gauge question

Valid point Jeeper -- but like I said, what are you going to do about it other than pulling over and letting things cool down. It is highly unlikely that tranny temp will be a problem even under extreme conditions with the external cooler he was installing. You have an oil pressure gauge as well but if oil pressure began to fall, what are you gong to do about it. Low oil pressure is rarely due to a lack of oil or low oil level. It's due to an internal problem. Again, nothing you can do about it. With coolant temperature there is something you can do about it. Turn off accessories (like the A/C), turn on the heater fan and open the car windows. Or pull over and pull the plastic bag off the front of the car.

 

[bruceb58]

Re: Transmission temp gauge question

If your tran temp rises you can shift into a lower gear and slow down to help reduce the temperature. Also, since tran fluid life is directly dependent on the temperature, if you happen to reach an excessive temp while towing, you can at least know that it would be a good idea to flush the tranny fluid with new fluid at the next oppurtunity.

 

[Silvertip]

Re: Transmission temp gauge question

Shift to a lower gear? When? You are likely to have a tranny fluid temp rise during periods of torque converter unlock. If that has occured, the tranny has likely already come out of overdrive, or if you were towing in direct and it unlocked, you now have no choice. During converter lock up there is no slippage in the converter and hence fluid heating is not likely to occur. It's during the shifting and unlocked converter situations that fluid heat builds and builds it fast. Therefore at freeway speeds, all you have available to you is downshift to second which makes you a rolling road block, or pull off to let it cool which makes for an even worse situation. Install the cooler and enjoy the ride. Add the gauge if it gives you confidence, but it really is not necessary. Keep the converter locked up and you will not experience fluid temp overheat.

 

[bruceb58]

Re: Transmission temp gauge question

It's during the shifting and unlocked converter situations that fluid heat builds and builds it fast.

Exactly my point...in a lower gear, the torque converter has less slippage and therefore less heat build up because it is easier for it to be locked up.

 

[MercGuy]

Re: Transmission temp gauge question

I installed a transmission temp gage in my '95 Jeep Cherokee and found/find the following benefits:

1) My Jeep had the factory tow package with an external trans cooler, but after installing the temp gage I felt that the factory cooler was not big enough. I routinely hit temps of 230 degrees while towing.

2) I installed a after market cooler (tube & fin design) and determined that this cooler also was not doing the job.

3) I installed a different, larger cooler (similar to a stacked plate design) and this cooler kept my temps below 200 degrees most of the time.

4) Now when I am towing in difficult situations I can keep track of what's happening to the trans fluid temps, and take preventative action if necessary before any damage occurs.

All in all, I think the tranny temp gage is an essential part of a tow package.

-Steve

 

[Silvertip]

Re: Transmission temp gauge question

Bruce -- our discussion seems to be in non-parallel situations. One typically does not tow heavy trailers in OD so the tranny is already in 3rd/direct. If fluid temps are rising while in 3rd/direct, its because enough throttle has been applied that the converter has unlocked -- it has not performed a downshift. Prolonged operation in that gear is going to result in rapid heat rise. The next thing that happens is the ECM will force a downshift (if you don't) into second if the ECM senses low manifold vacuum (equates to a high throttle setting) and slowing road speed. Since there is also no lock up function in 1st and 2nd, you still have temperatures rising although at a slower rate and the converter is still unlocked. The problem here is that you are at freeway speed. If you now jump between 2nd and 3rd, temps rise even more because clutch and band slippage is adding to the heat. If the need arises to lower fluid temp and shifting down is one way to do it, you would shift to 2nd. In lower gears (1st and 2nd) there is no converter lockup and that's when there is maximum slippage in the converter and hence maximum heat build up. Converters lock up only in 3rd/direct or OD. If you were to lock the brakes at standstill and floor the gas pedal , a torque converter will actually balloon and distort from the pressure and heat. So my point is, if tranny fluid overtemp is happening at freeway speed with the tranny in third/direct, what gear would you suggest shifting down to? 2nd? That would very likely get you a ticket as you would be under the 45 MPH minimum speed limit on most freeways. With the converter locked up (3rd/direct and OD) there is no slippage in the converter hence no heat build up. If one needs to shift out of third/direct to let tranny fluid cool, there is a serious overload condition or the tranny is already toast. Obviously a problem can occur if one is navigating a very steep grade on a secondary road where speed is not an issue. Then downshifting not only makes sense, but it is probably mandatory to maintain any semblance of forward motion.

 

[bruceb58]

Re: Transmission temp gauge question

The situation I am speaking of is transmissiom temperature rise going over long grades. By shifting into second gear you are reducing the torque required at the output of the torque converter and the slippage whichcauses the heat build up will be reduced.

I have had transmission temperature guages on trucks that I have owned and have never seen temp rises that would cause concern towing on the flats.

 

[Silvertip]

Re: Transmission temp gauge question

In that scenario we agree. I guess we beat this thing to death so I'm outa here.

 

[jeeperman]

Re: Transmission temp gauge question

Fluid flowing thru the trans will create heat. Even in park at idle.
A converter in locked-up mode is no guarantee of further heat production.
All heat produced has to be radiated via the transmission surface area, coolers and radiator. If not, it cooks.

Adding an aftermarket cooler can be tricky.
Most all autos are cooled via a cooler inside the main radiator.
Adding an aftermarket cooler in the tranny lines before it enters the rad is pretty useless if you want the tranny temps to be cooler than the rad water.

Although I presume the vehicle builders have engineered the trans to operate ideally in the same temp range as the rad water.

So the question is what is the best tranny temp, hotter or cooler or the same as engine temps?

 

[bruceb58]

Re: Transmission temp gauge question

Best temp for transmission fluid is 175.