Home » Public Forums » GMCnet » Transmission Tmp gauge - should I ? where?
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| Re: Transmission Tmp gauge - should I ? where? [message #351518 is a reply to message #351517] |
Wed, 22 January 2020 11:53   |
Deb
Messages: 349
Registered: October 2016
Location: Logan Lake, BC
Karma: 2
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Still lurking & enjoying this thread. On my first trip I was returning across the Kootenay Pass here in BC & had trans temps climb to about 230 - 250 during the climb (long climb, about 10% grade, & nowhere to pull over if you need to, until you get to the top). Made me VERY nervous! Engine was good - running between 185-195 as the fan clutch kicked on and off (I very quickly learned to appreciate the roar of the fan clutch!) When I got home, I asked the question here about when to worry about tranny temps, and got all of the above info. Short periods of time at the higher temps are OK, (like long climbs) but consistent high temps will kill the fluid quickly. Most of the time, my 403 w/ 3.42 FD barely gets above the low end of the gauge (150) until it starts getting warm out, and/or I'm climbing a grade. Then, it runs happily at ~ 170. So I was able to breathe easy for my subsequent trips through mountains. The sensor is in the pan.
My GMC is the first vehicle I have owned that HAD a TT gauge of any sort. Now that I am passing along the old girl (and getting into a trailer and a tow vehicle - sorry for the herecy  ), I am going to get a TT gauge installed in my TV. I just don't think I would feel ever comfortable without one in these conditions. GMC Spoiled, and informed! Thanks folks.
Deb McWade
Logan Lake, BC, CAN
GMC Alumnus
It's Bigger on the Inside!
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| Re: Transmission Tmp gauge - should I ? where? [message #351519 is a reply to message #351514] |
Wed, 22 January 2020 14:16 |
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Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
Karma: 7
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JohnL455 wrote on Wed, 22 January 2020 09:58There are Dexron life vs temp charts on line. It's a sliding somewhat log scale where it is fine, then quickly degrades as temp exceeds threshold points. When it hits 305F it's pretty much done with zero time constant. The problem is measured average temp vs peak temps that SOME of the molecules are exceeding in key critical hot spot areas of the trans. Those oxidized molecules are then diluted into the fluid capacity. Eventually the fluid becomes overall darker. Hotter areas might be found in the converter, leaving the pump or sandwiched between friction materials during shifts.
John is quite correct here, and it is true for all the dino lubricants not just transmission fluid but also for engine oil. That 305°F number has no time constant. When a molecule of the oil gets hot, it comes apart and is no longer oil. The basic lubricity and film strength are both gone. While I really don't know automatic transmissions that well, I can tell you that the hottest place in any regular engine is the underside of the piston crown. Many heavy duty engine actually have nozzles that squirt lube oil there just to cool the piston. So, when you see a collected lube oil temperature of over 250°F, that is a good time to start worrying.
Matt - the refugee from DynoLand
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
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| Re: Transmission Tmp gauge - should I ? where? [message #351523 is a reply to message #351517] |
Wed, 22 January 2020 16:02 |
Glenn
Messages: 92
Registered: February 2004
Location: Northwestern Ontario
Karma: 2
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You do not want to monitor the temp at the output to the cooler. The temp will blow your mind. I tried this and temps were way too high. Talked to Manny and he told me that is why I do not monitor it there.
HTH.........
Glenn
76 Glensbroke
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| Re: Transmission Tmp gauge - should I ? where? [message #351528 is a reply to message #351524] |
Wed, 22 January 2020 18:24 |
Glenn
Messages: 92
Registered: February 2004
Location: Northwestern Ontario
Karma: 2
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Well Matt put in an appropriately sized cooler and let it flow. The only temp important in my mind is the temp in the pan as that is what the trans uses. I have way too many other things to worry about while driving than the temp coming out of the trans.
HTH.........
Glenn
76 Glensbroke
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| Re: Transmission Tmp gauge - should I ? where? [message #351543 is a reply to message #351523] |
Thu, 23 January 2020 13:00 |
tmsnyder
Messages: 151
Registered: January 2014
Karma: -9
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Glenn wrote on Wed, 22 January 2020 16:02You do not want to monitor the temp at the output to the cooler. The temp will blow your mind. I tried this and temps were way too high. Talked to Manny and he told me that is why I do not monitor it there.
I did this once also, makes for a very nervous driver indeed b/c those temperatures can start to look pretty high and meanwhile you have no idea what temperature the internals of the transmission or the bulk of the fluid is seeing. After about 5000 miles with it I realized that I should have put it in the pan. That's the temperature that actually matters. Then I sold that motorhome to buy a GMC.
Todd Snyder, Buffalo NY
1976 Eleganza II
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| Re: Transmission Tmp gauge - should I ? where? [message #351544 is a reply to message #351462] |
Thu, 23 January 2020 13:51 |
Larry
Messages: 2875
Registered: January 2004
Location: Menomonie, WI
Karma: 10
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Larry wrote on Mon, 20 January 2020 12:21Here is how I added a temp prob to my trans pan. Study the pan and valve body carefully before you drill the hole. Things that you stick inside the pan through a hole you created have to clear everything. I've had this set-up on my trans pan for 13 yrs. No leaks, no problems. JWID
Look at this pic and the next two in the album.
http://www.gmcmhphotos.com/photos/transmission-install/p3851.html
Forgot to mention, doing this to a stock pan also gives you a drain. Just unscrew the temp probe and drain most of the fluid. Works for me. I have been reluctant to use the Ragusa pan because of some reports in this forum of the aluminum "seeping" trans fluid. In addition, the stock pan runs right up against the trans filter, so if the filter should for what ever reason drop, the pan will hold it in place. The Ragusa is an inch deeper and if the filter drops, it could potentially drop out of the receiver allowing the trans to suck air. Just what I think might happen. IMO, the original steel pan is more than adequate for the task at hand. JWIT other opinions vary.
Larry 
78 Royale w/500 Caddy
Menomonie, WI.
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| Re: [GMCnet] Transmission Tmp gauge - should I ? where? [message #351683 is a reply to message #351441] |
Mon, 20 January 2020 08:18 |
jimk
Messages: 6734
Registered: July 2006
Location: Belmont, CA
Karma: 9
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Trans temp is important.
There are two ways people monitor the temp.
The one that makes sense to me is to monitor the temp of the fluid that
will enter the system, as that is considered to be important.
The other to monitor the temp of fluid leaving the trans.
This is rather a good indicator of load that is put into the trans and how
hard the convertor is working.
Hot fluid is cooled at the radiator and brought back into the pan.
Also what is important is to change the fluid frequently, as the
additives in the fluid gets exhausted from heat and when one changes the
fluid, your lucky to change about 1/3 of the total.
This topic of where to measure the temp can be very controversial.
On Mon, Jan 20, 2020 at 5:11 AM Russell Keith via Gmclist <
gmclist@list.gmcnet.org> wrote:
> Dave,
>
> Yes, a transmission temperature gauge is a good idea to monitor tranny
> temps and hopefully avoid burning up a transmission. Many GMCer's have
> installed tranny temp gauges. My tranny temp is monitored in the pan
> (ragusa). Others have installed a Tee in the cooling lines and monitor the
> temp
> there. I had to replace my gauge this past summer. Here is a link to my
> pics.
>
>
> http://www.gmcmhphotos.com/photos/g7225-new-transmission-temperature-gauge.html
>
> Safe Travels,
> Russell
> --
> Russell Keith,
> 1978 E2 "Harry" 403 (still carbureted), Danny Dunn Tranny, Thorley, Stock
> Brakes w/Remote Vacuum Brake Booster, Quad Bags, Dakota Digital Dash, 6.5 kW
> Onan, Dunedin, Florida
>
> _______________________________________________
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--
Jim Kanomata
Applied/GMC, Newark,CA
jimk@appliedairfilters.com
http://www.appliedgmcrvparts.com
1-800-752-7502
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Jim Kanomata
Applied/GMC
jimk@appliedairfilters.com
www.appliedgmc.com
1-800-752-7502
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| Re: [GMCnet] Transmission Tmp gauge - should I ? where? [message #351691 is a reply to message #351450] |
Mon, 20 January 2020 10:39 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Yes, the digi panel makes a lot of sense. Flashing lights have a way of
getting one's attention, right now. I do not have one, but it might be a
worthwhile expenditure. I am a gage guy myself, I have a tachometer and
vacuum gage up high, above the dash, tucked into the v where the drivers
side of the dash pad meets the curve of the windshield. I also have a
Ragusa transmission pan with an analog temp sensor in it, as well as a
sensor in the final drive cover. That one is a real eye opener for sure. I
have 3:70 final drive ratio, and was curious how hot that sucker got. Well,
now I know, and it gives me cause to worry. Before I installed the gage, i
was fat, dumb, and happy in my ignorance. But, i am a eyes down the road
kinda guy. So, the digi panel makes sense.
Jim Hupy
Salem, Oregon
On Mon, Jan 20, 2020, 8:21 AM dave silva via Gmclist <
gmclist@list.gmcnet.org> wrote:
> Thanks, that's impressive.
>
> For now I am really digging the fact that all my original Stewart Warner
> gauges work. And they make a matching trans temp gauge that will fit right
> in. I'll probably relocate vacuum or amps off the main instrument
> cluster.
>
> I'm not a luddite though. I like technology. I may look at a high temp
> alarm for the trans.
> --
> Dave & Ellen Silva
>
> 1972 Revcon Olds 455, toro drive train. All Stock
>
>
>
> _______________________________________________
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| Re: [GMCnet] Transmission Tmp gauge - should I ? where? [message #351697 is a reply to message #351469] |
Mon, 20 January 2020 16:43 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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The ideal place to measure temps is where the oil comes from the torque
converter. That is going to be the hottest place you can easily get to to
install a sensor. My oil temp sensor, fitted into my Ragusa finned aluminum
pan rarely registers over 160° farenheit. So it never sees converter oil.
That goes to the cooler before it returns to the pan, so if you are having
a bunch of slippage and overheating, you will never see it on a gage. Guess
you could have more gages, in and out, etc. Somewhere there is a chart that
tells you the temps that various fluids can tolerate. If memory serves me
correctly, the synthetic transmission fluids can tolerate the most heat.
That is what I use in my Manny Tranny, along with fairly frequent oil
changes. Fluid is cheaper than transmission parts, by a whole bunch.
Jim Hupy
Salem, Oregon
On Mon, Jan 20, 2020, 2:11 PM dave silva via Gmclist <
gmclist@list.gmcnet.org> wrote:
> I'm not sure i want it at the pan. On my tow vehicles i always put it on
> the return line from the trans cooler. The idea being that you measire how
> well you are removing heat.
>
> Does heat in the pan tell the story?
> --
> Dave & Ellen Silva
>
> 1972 Revcon Olds 455, toro drive train. All Stock
>
>
>
> _______________________________________________
> GMCnet mailing list
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| Re: [GMCnet] Transmission Tmp gauge - should I ? where? [message #351701 is a reply to message #351469] |
Tue, 21 January 2020 07:00 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Dave,
I've monitored the temperature in the pan, and those to and from the
cooler. But I consider the pan the important one because it averages all
the others. That conclusion of mine is supplemented by the Chevrolet P-30
Chassis Owners' Manual (available at bdub.net). That formerly free, no
longer available, manual has an extensive section on transmission cooling,
including comments on heat sources and system upgrades. I highly recommend
it to everyone. Their temperature guidance, including a table of ATF
mileage life vs temperature is based on PAN temperature.
Ken H.
On Mon, Jan 20, 2020 at 5:11 PM dave silva via Gmclist <
gmclist@list.gmcnet.org> wrote:
> I'm not sure i want it at the pan. On my tow vehicles i always put it on
> the return line from the trans cooler. The idea being that you measire how
> well you are removing heat.
>
> Does heat in the pan tell the story?
> --
> Dave & Ellen Silva
>
> 1972 Revcon Olds 455, toro drive train. All Stock
>
>
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: [GMCnet] Transmission Tmp gauge - should I ? where? [message #351705 is a reply to message #351491] |
Tue, 21 January 2020 10:19 |
Emery Stora
Messages: 959
Registered: January 2011
Karma: 4
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You actually don’t need another gauge. Just a switch. You can have a sensor going in and another going out and just switch the two sensors to the one gauge with a switch.
Emery Stora
> On Jan 21, 2020, at 9:14 AM, dave silva via Gmclist wrote:
>
> JohnL455 wrote on Tue, 21 January 2020 08:32
>> I simply use coolant temp as a guide to trans temp.
>
> I'm thinking if the coolant is entering the radiator at, say, 210F, and it's returning to the engine at 190F then you might not know if the trans temp
> is climbing. Or, you won't know it until it goes past the point where the radiator can remove the heat.
>
> For the price of another gauge, maybe i'd want to see the temp going in and going out? Probably overkill but i see transmission failure as the most
> disruptive thing that can happen.
>
> - can't see it coming
>
> - can't get parts quickly
>
> - can't work on it myself
> --
> Dave & Ellen Silva
>
> 1972 Revcon Olds 455, toro drive train. All Stock
>
>
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
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| Re: [GMCnet] Transmission Tmp gauge - should I ? where? [message #351716 is a reply to message #351516] |
Wed, 22 January 2020 11:05 |
powwerjon
Messages: 849
Registered: March 2013
Karma: -2
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Senior Member |
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I am with John and Russell on the transmission temps. Mine tpicall run at
about 165F which is near the bottom of the temp gauge range. I had a
torque converter failure that damage the transmission too. My gauge in the
pan when to over 300F+. IMHPO if your transmission temperature is anywhere
over 210F+ for extended periods then you need to look into the possible
causes, granted if your climbing any grade it will increase with the
extended load and you should downshift to S to get the motor speed up and
not lug the engine or transmission. When I had the 77 coach with the 403
and 3.55 gears I could climb most any grade and not have the speed fall of
much below 50 mph.
Regards,
J.R. Wright
GMC Great Laker
GMCGL Tech Editor
GMC Eastern States
GMCMHI
TZE Zone Restorations
78 Buskirk Custom 29.5' Stretch
75 Avion (Under going Frame up Restoration)
On Wed, Jan 22, 2020 at 8:48 AM Russell Keith via Gmclist <
gmclist@list.gmcnet.org> wrote:
> The THM 375/400/475/425 Troubleshooting Guide by GM states a normal
> operating temperature of 170F.
> http://www.bdub.net/manuals/THM_425_Trouble_Shooting.pdf
>
> Other transmission related websites say an "Ideal" operating temperature
> is 175F.
> https://aljetsautomotive.com/transmission-fluid-flush-tips
>
> https://mechanicbase.com/transmission/normal-operating-temperature-for-an-automatic-transmission/
>
> If you look at the many transmission fluid temperature charts online,
> you'll see that transmission life and transmission fluid life are greatly
> reduced at temperatures sustained over 200F.
>
>
> https://www.google.com/search?q=transmission+fluid+temperature+chart&sxsrf=ACYBGNQaUEqnina7kD2Cbe07foDyUHe9DQ:1579706774434&source=lnms&tb m=isch&sa=X&ved=2ahUKEwiFq46pwpfnAhWvmuAKHZZZDy0Q_AUoAnoECAsQBA&biw=2133&bih=1076
>
> My transmission temp gauge usually stays between 150F and 180F; while my
> coolant temperature gauge hovers around 190F (190 thermostat). I do not have
> an auxiliary cooler.
>
> The consensus is definitely "cooler is better" for transmission life. If
> you can't keep it under 200F, then other measures should be taken to reduce
> the temp, such as an auxiliary trans fluid cooler, or reduce the load, and
> change the fluid more often.
>
>
>
> --
> Russell Keith,
> 1978 E2 "Harry" 403 (still carbureted), Danny Dunn Tranny, Thorley, Stock
> Brakes w/Remote Vacuum Brake Booster, Quad Bags, Dakota Digital Dash, 6.5 kW
> Onan, Dunedin, Florida
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
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| Re: [GMCnet] Transmission Tmp gauge - should I ? where? [message #351717 is a reply to message #351716] |
Wed, 22 January 2020 11:34 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Senior Member |
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Any time you are below the lock-up rpm of the torque converter, you will
have some heating of the fluid. The greater the torque load you have at
that time, (steep grades, trailer towing, etc) the more heating you will
have. That is why you manually downshift on steep grades. Keeping the
torque converter turning fast enough to "lock it up" prevents excessive
slippage, and reduces the torque load. Try to keep your transmission pan
fluid temperature below 200° farenheit, lower than that is better if you
can. In spite of what you have always believed, RPM's below the red line
when climbing hills are far better for both engine and transmissions than
staying in high gear and lugging the engine.
What is lugging? Anytime you can add more throttle when pulling hard
and not gain rpm's, you are lugging the engine.
Jim Hupy
Salem, Oregon
On Wed, Jan 22, 2020, 9:06 AM John Wright via Gmclist <
gmclist@list.gmcnet.org> wrote:
> I am with John and Russell on the transmission temps. Mine tpicall run at
> about 165F which is near the bottom of the temp gauge range. I had a
> torque converter failure that damage the transmission too. My gauge in the
> pan when to over 300F+. IMHPO if your transmission temperature is anywhere
> over 210F+ for extended periods then you need to look into the possible
> causes, granted if your climbing any grade it will increase with the
> extended load and you should downshift to S to get the motor speed up and
> not lug the engine or transmission. When I had the 77 coach with the 403
> and 3.55 gears I could climb most any grade and not have the speed fall of
> much below 50 mph.
>
> Regards,
>
> J.R. Wright
> GMC Great Laker
> GMCGL Tech Editor
> GMC Eastern States
> GMCMHI
> TZE Zone Restorations
> 78 Buskirk Custom 29.5' Stretch
> 75 Avion (Under going Frame up Restoration)
>
>
>
> On Wed, Jan 22, 2020 at 8:48 AM Russell Keith via Gmclist gmclist@list.gmcnet.org> wrote:
>
>> The THM 375/400/475/425 Troubleshooting Guide by GM states a normal
>> operating temperature of 170F.
>> http://www.bdub.net/manuals/THM_425_Trouble_Shooting.pdf
>>
>> Other transmission related websites say an "Ideal" operating temperature
>> is 175F.
>> https://aljetsautomotive.com/transmission-fluid-flush-tips
>>
>>
> https://mechanicbase.com/transmission/normal-operating-temperature-for-an-automatic-transmission/
>>
>> If you look at the many transmission fluid temperature charts online,
>> you'll see that transmission life and transmission fluid life are greatly
>> reduced at temperatures sustained over 200F.
>>
>>
>>
> https://www.google.com/search?q=transmission+fluid+temperature+chart&sxsrf=ACYBGNQaUEqnina7kD2Cbe07foDyUHe9DQ:1579706774434&source=lnms&tb m=isch&sa=X&ved=2ahUKEwiFq46pwpfnAhWvmuAKHZZZDy0Q_AUoAnoECAsQBA&biw=2133&bih=1076
>>
>> My transmission temp gauge usually stays between 150F and 180F; while my
>> coolant temperature gauge hovers around 190F (190 thermostat). I do not
> have
>> an auxiliary cooler.
>>
>> The consensus is definitely "cooler is better" for transmission life. If
>> you can't keep it under 200F, then other measures should be taken to
> reduce
>> the temp, such as an auxiliary trans fluid cooler, or reduce the load,
> and
>> change the fluid more often.
>>
>>
>>
>> --
>> Russell Keith,
>> 1978 E2 "Harry" 403 (still carbureted), Danny Dunn Tranny, Thorley, Stock
>> Brakes w/Remote Vacuum Brake Booster, Quad Bags, Dakota Digital Dash,
> 6.5 kW
>> Onan, Dunedin, Florida
>>
>> _______________________________________________
>> GMCnet mailing list
>> Unsubscribe or Change List Options:
>> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
_______________________________________________
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