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Re: What happens to Transmission Fluid When It Gets Hot? [Re: Fitz98] #5171650 07/26/19 07:44 PM
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atikovi Offline
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My 2008 Silverado 3500HD is usually around 150 when warmed up during the summer and has never gone over 180 when towing. In the winter it may stay under 130. Probably why it's gone over 200K so far.

Re: What happens to Transmission Fluid When It Gets Hot? [Re: Fitz98] #5171662 07/26/19 07:56 PM
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69GTX Offline
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You could measure the fluid either hot or cold on the dip stick with the engine operating. The cold operation will be lower on the stick.

You can also measure your fluid level dead cold with the engine off. On my vehicle it's much higher up on the dip stick - well above the "normal" range. I have it marked on the word "Cross" of "cross hatched area." And it's always at that same point with the engine off and cold. So that's a quick way to check level when you don't want to go through the time of a full heat up and cycling the gears.

I've done it all 3 ways and have a pretty good feel when it's dead on. Same transmission type (AX4N) on 3 different vehicles for past 18 yrs.

Last edited by 69GTX; 07/26/19 07:57 PM.

----------------

2001 Lincoln Cont 4.6L DOHC/ 50K mi / QS HM 5w30 / FUG XG2
1999 Camaro SS M6 /19K /Mobil 1 0w40 /Fram UG /GM MTL-ATF
1969 Ply GTX/RRs
Re: What happens to Transmission Fluid When It Gets Hot? [Re: Kawiguy454] #5171690 07/26/19 08:41 PM
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Originally Posted by Kawiguy454
Silverado 1500 has a 180 degree trans thermostat that bypasses the cooler. Idea is to get the temp up to operating more quickly probably for .1 mpg fuel savings. some people mod the thermostat Open all the time. The known problems of the 8 speed TC seem to be resolved by new fluid flush. This to me indicates the heat is causing some breakdown to occur. the 2500 and 3500 do not have the trans t-stat.

My 2017 3500 HD has a trans thermostat.

Re: What happens to Transmission Fluid When It Gets Hot? [Re: MolaKule] #5171776 07/26/19 11:08 PM
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RoyFJ Offline
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Originally Posted by MolaKule
In transmission parlance we use two temperature definitions and one is "flash" temperature and the other is "Bulk" oil temperature in the sump.

A flash temperature is one that occurs for a very short time at clutch surfaces and can hit 500F, but this temperature only lasts for milliseconds because of continual cooling.

The bulk oil temp in the sump is essentially the average temperature of the "mix" of fluids coming in from the clutch packs, bearings, Torque Converter, and the heat exchanger (cooler).

When the ATF becomes degraded from being in the sump too long, or due to extreme heat cycling (insufficient temperature control), the fluid oxidizes, the dynamic coefficients of friction change, and the fluid may start leaving varnish deposits on the clutch faces. Hence, my recommendation for ATF OCI's of ~ 30-35k.

Now remember, cooling of the clutch plates and discs is accomplished only when oil flows into and out of the clutch material and faces. The clutch disks are faced with a porous material of a cellulose composite. That porous material allows oil to flow into it during disengagement, and squeezes some oil out during engagement.

Once varnish deposits are allowed to form a "glaze," no cooling oil can flow into or out of the porous material and it and the oil degrades even faster because of the (flash) higher temperature spikes.

Quote
Oil flow is supplied to the clearance between the clutch discs and clutch plates through radial pathways on the hub for cooling and lubrication purposes.

During a clutch engagement, a piston compresses the plates. The oil between the plates is squeezed out of the interface and permeates into and or out of the pores in the friction material. Engagement is completed when no speed differential exists between clutch discs and clutch plates.


Internal Heat Generation in ATs





Thats why the AISIN brochure even for their synthetic ATW+ is recommending full flush at 20000 rather than the usual lifetime.

Re: What happens to Transmission Fluid When It Gets Hot? [Re: Fitz98] #5171792 07/26/19 11:33 PM
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automobilexyz Offline
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Due To Low Transmission Fluid, it Becomes hot, Hot Transmission Fluid Not acceptable, It causes fails the transmission gearbox, Vehicle Speed Becoms Slower, Abnormal Noise Comes trough the Transmission Gerar Box.


Hi
I am Rakibul Hasan , And I am Automobile Engineer.
Re: What happens to Transmission Fluid When It Gets Hot? [Re: automobilexyz] #5171855 07/27/19 06:08 AM
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kschachn Offline
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Okay thanks.


1994 BMW 530i, 252K
1996 Honda Accord, 288K
1999 Toyota Sienna, 434K
2000 Toyota ECHO, 284K
Re: What happens to Transmission Fluid When It Gets Hot? [Re: MolaKule] #5173862 07/29/19 01:31 PM
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bullwinkle Offline
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Originally Posted by MolaKule
In transmission parlance we use two temperature definitions and one is "flash" temperature and the other is "Bulk" oil temperature in the sump.

A flash temperature is one that occurs for a very short time at clutch surfaces and can hit 500F, but this temperature only lasts for milliseconds because of continual cooling.

The bulk oil temp in the sump is essentially the average temperature of the "mix" of fluids coming in from the clutch packs, bearings, Torque Converter, and the heat exchanger (cooler).

When the ATF becomes degraded from being in the sump too long, or due to extreme heat cycling (insufficient temperature control), the fluid oxidizes, the dynamic coefficients of friction change, and the fluid may start leaving varnish deposits on the clutch faces. Hence, my recommendation for ATF OCI's of ~ 30-35k.

Now remember, cooling of the clutch plates and discs is accomplished only when oil flows into and out of the clutch material and faces. The clutch disks are faced with a porous material of a cellulose composite. That porous material allows oil to flow into it during disengagement, and squeezes some oil out during engagement.

Once varnish deposits are allowed to form a "glaze," no cooling oil can flow into or out of the porous material and it and the oil degrades even faster because of the higher (flash) temperature spikes.

Quote
Oil flow is supplied to the clearance between the clutch discs and clutch plates through radial pathways on the hub for cooling and lubrication purposes.

During a clutch engagement, a piston compresses the plates. The oil between the plates is squeezed out of the interface and permeates into and or out of the pores in the friction material. Engagement is completed when no speed differential exists between clutch discs and clutch plates.


Internal Heat Generation in ATs


Entertaining presentation, Mola-so you’re basically saying there’s no such thing as “too big” when it comes to transmission coolers & sump pans, and even in arctic temps-cooler ATF is ALWAYS better?


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Re: What happens to Transmission Fluid When It Gets Hot? [Re: bullwinkle] #5174041 07/29/19 04:06 PM
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MolaKule Offline
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Originally Posted by bullwinkle


Entertaining presentation, Mola-so you’re basically saying there’s no such thing as “too big” when it comes to transmission coolers & sump pans, and even in arctic temps-cooler ATF is ALWAYS better?
[/quote]

No, I never said that nor was I inferring that.


Quote
When the ATF becomes degraded from being in the sump too long, or due to extreme heat cycling (insufficient temperature control), the fluid oxidizes, the dynamic coefficients of friction change, and the fluid may start leaving varnish deposits on the clutch faces. Hence, my recommendation for ATF OCI's of ~ 30-35k.

Last edited by MolaKule; 07/29/19 04:07 PM.

"As engineers [and scientists] we are wired to solve problems and to create new things, to challenge the status quo and push the limits..." Ken Hurt, Embry-Riddle University, Class of '97.
Re: What happens to Transmission Fluid When It Gets Hot? [Re: MolaKule] #5174233 07/29/19 07:45 PM
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Originally Posted by MolaKule
Originally Posted by bullwinkle


Entertaining presentation, Mola-so you’re basically saying there’s no such thing as “too big” when it comes to transmission coolers & sump pans, and even in arctic temps-cooler ATF is ALWAYS better?


No, I never said that nor was I inferring that.


Quote
When the ATF becomes degraded from being in the sump too long, or due to extreme heat cycling (insufficient temperature control), the fluid oxidizes, the dynamic coefficients of friction change, and the fluid may start leaving varnish deposits on the clutch faces. Hence, my recommendation for ATF OCI's of ~ 30-35k.
[/quote]

Couldn't get a good front view but this is my 2 large transmission coolers mounted in front of the condenser on my 84 Cutlass. The transmission has about 270k miles on it and shifts perfectly still. I bought it at 115k miles and it towed a 3500 pound boat for the previous owner. I took it to the drag races whenever I could and drove it really hard for the first 10 plus years I had it.

I've started to drive it easier because I feel like my luck will run out eventually. I've broken a couple rear ends behind this transmission but the trans hangs in there.

30k mile flushes plus filter and the coolers are likely the only reason it made it this far.

IMG_20190729_203928.jpg

84 Olds Cutlass - 350 Olds
83 Chevy Caprice - 305 Sbc
05 Silverado 1500 4wd - 4.8/4L60E
79 Honda CX500
Re: What happens to Transmission Fluid When It Gets Hot? [Re: oldhp] #5174319 07/29/19 09:15 PM
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Originally Posted by oldhp
The ideal fluid temperature is under 175 degrees, but as fluid ages it starts to break down and lose its capacity to cool down the transmission. This is when transmission overheating occurs. At 220 degrees, varnish forms. At 240 degrees, seals start to harden. Anything higher fluid starts to burn, clutch plates warp, spools in valve bodies stick. You know, all kinds of bad $$$$$$ things.



Your statements are likely true if your talking about DEXRON III type fluids. Today many AT's the operating temps are 200F.


make the inside of your engine oil cap white.
don't use.
Re: What happens to Transmission Fluid When It Gets Hot? [Re: Fitz98] #5174674 07/30/19 09:45 AM
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On my 80s toyota. When its cold the level is way beyond the top notch last mark, the 4th mark. When its hot and engine is running, ran through all gears slowly and put into P, its 3/4 up from 3rd notch, close to the last 4th notch, where its supposed to be (in between 3rd and 4th notch is the HOT reading).


Kyosho Optima Mid SWB, LWB and Lazer ZX
1991 Proton Saga 1.3S SOLD
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1992 Robinson Pro
Re: What happens to Transmission Fluid When It Gets Hot? [Re: Fitz98] #5174978 07/30/19 03:55 PM
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Hayden 679 on FJ Cruiser

Hayden 679 install.jpg
Re: What happens to Transmission Fluid When It Gets Hot? [Re: Fitz98] #5175113 07/30/19 06:51 PM
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But, just because the overall temp is XX degrees, that doesn't mean that in certain areas the trans fluid isn't hitting hotter temperatures, correct? Hot Spots.

Re: What happens to Transmission Fluid When It Gets Hot? [Re: Gasbuggy] #5175360 07/31/19 04:48 AM
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Originally Posted by Gasbuggy
But, just because the overall temp is XX degrees, that doesn't mean that in certain areas the trans fluid isn't hitting hotter temperatures, correct? Hot Spots.



Thats the reason torque converter always reports higher temps than the pan temps.

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