Transmission Tmp gauge - should I ? where?

> My point is since it's a liquid to liquid heat exchanger, if the Dexron is much above 260F it would be boiling the coolant in contact with the
> heat exchanger

That's a really good point.

--
Dave & Ellen Silva

1972 Revcon Olds 455, toro drive train. All Stock
 
There 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 Lebetski
Woodstock, IL
77 Eleganza II
 
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&tbm=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
 
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 <

> 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&tbm=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
>
 
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 <

> 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 <

>
> > 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&tbm=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
>
 
> There 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 - '73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan
OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Twixt A2 and Detroit
 
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
 
> 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.

As I want to know how much trouble I will be in and how soon is why that is exactly where I monitor both the engine lubricating oil and the
transmission fluid temperature. Those cooler should be sized to never let the associated fluid return over temperature.

Matt
--
Matt & Mary Colie - '73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan
OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Twixt A2 and Detroit
 
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
 
> 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.

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
 
> Here 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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