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| [GMCnet] Trans temp [message #31284] |
Wed, 24 December 2008 15:17  |
David L Greenberg
Messages: 899
Registered: January 2004
Location: Port St Lucie, FL
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On Wed, 24 Dec 2008 12:35:26 -0600 Randy <Acrosport2@hotmail.com> writes:
> To those who have a trans temp gauge, how long does it usually take
> to see a rise in temps and what is a normal idling temp and
> operating temp with moderate (60-80F) ambient temps?
> --
> Randy
> 1973 26' Painted Desert
> Ahwatukee (Phoenix) AZ
>
With my Ragusa pan and the probe in the pan, I rarely moved off the peg
unless I was climbing hills (always towing a 2600 lb Saturn SW2 loaded to
the gunnels) and then it was rarely over 150*
David Lee Greenberg
Port St Lucie, FL
Dedicated to the Preservation of the Classic GMC Motorhome
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| Re: [GMCnet] Trans Temp [message #155371 is a reply to message #31284] |
Wed, 04 January 2012 11:09  |
Gary Casey
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Registered: September 2009
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The idea that the radiator coolers "regulate" and "heat" the engine and transmission oil is a myth that has been around forever. I think the original reason they were incorporated is that it was cheaper than producing an oil-to-air cooler. But maybe it was because the design engineers believed - or maybe even created - the myth. Keep in mind that the radiator has a hot and a cold tank. The cold tank is on the right side and it houses both coolers. While the thermostat is regulating the engine temperature (after the engine warms, but isn't overheating) it restricts the flow through the radiator. Let's start with a very light load on the engine or on a cold day. The hot side will be at essentially engine (outlet) temperature because there hasn't been any opportunity for the air to cool it. So that will stay at, say, 200 degrees. However, the coolant flow rate through the radiator is very low and the air cools the coolant a lot, and
therefore the cold tank will be at maybe just a little above ambient. Then as the engine is asked to produce more and more power the coolant flow increases as allowed by the thermostat. The hot tank stays at the same temperature but the cold tank temperature increases because of the higher flow through the radiator. This progresses until the thermostat is wide open and the coolant flow is at its maximum. The normal design temperature drop through the radiator (hot day, high power) is about 15 degrees. So now the cold tank will be at about 185 degrees. Take it a step further, climbing a hill and on the verge of overheating - the hot tank will be at 240 and the "cold" tank at about 225.
Bottom line is that when everything is cold and not working hard the coolers provide very, very little heat to the transmission and engine oil. When everything is very hot the coolers provide very little cooling. I remember doing tests on this very thing and the cold tank temperature changes at about twice the rate of ambient. Cruising along at 0F the cold tank might be at 10F. Cruising at 100F and the cold tank will be at 210F (I fudged the numbers to make it come out even :-).
Conclusion: The radiator coolers should be put in the hot tank - at least then they will actually warm the oil. And the cooling on a hot day won't be much different. The overall cooling capacity of the radiator will remain the same. My PO eliminated both coolers and added external coolers, but he was towing a big race car trailer on hot days. I'm towing nothing, so I put the original coolers back in the system. According to my argument above, the wrong thing to do, but.....that's what I did and everything works just fine. I'm not going to be doing much driving on cold days, so I'm not too concerned about heating the oil.
Gary Casey
'73 23'
since the trans goes thru the radiator and if it was to cold the radiator
would warm it.
there is your answer, as long as you heat your engine with a thermostat,
it is going to heat your transmission .
and
it depends upon where you measure the temp, Manny says in the pan, all else
is transitory.
and
our TCs run all the time, (no lock-up) so it is not possible to get the
tranny too cool while it is running.
gene
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| Re: [GMCnet] Trans Temp [message #155385 is a reply to message #31284] |
Wed, 04 January 2012 14:11 |
Richard Brown
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Registered: May 2009
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Someone please correct me if I'm mistaken, but at one time didn't transmission cooler manufacturers sell a thermostatic bypass valve that would open at a pre-determined temperature to send the fluid to an auxiliary air-cooled cooler when the temperature exceeded a certain temperature? Do they still make them? If so, that sounds like what I'd do. Let the fluid go to the radiator in normal operation & divert to the aux. cooler under heavy load. If I recall, some heavy-duty trucks with auto transmissions used to use a similar set-up. The return from the aux. cooler was teed into the return line back to the transmission. It's been a while, but I remember seeing a 1-ton Dually set up that way.
Richard & Carol Brown
1974 Eleganza SE
"DILLIGAF"
Lindale, Tx. 75771
903-881-0192
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1974 Eleganza SE
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Murchison, TX. 75778
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| Re: [GMCnet] Trans temp [message #155390 is a reply to message #31284] |
Wed, 04 January 2012 14:44 |
JohnL455
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Registered: October 2006
Location: Woodstock, IL
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Found this on the web so it must be right, right?
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.
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: [GMCnet] Trans temp [message #155413 is a reply to message #155390] |
Wed, 04 January 2012 16:32 |
emerystora
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Registered: January 2004
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John
It would also depend on the fluid. The fully snythetic fluids will take a much higher heat before breaking down.
That is why Manny has always recommended Mobil 1 fully synthetic transmission fluid.
I have been using that for years now.
Emery Stora
On Jan 4, 2012, at 1:44 PM, John R. Lebetski wrote:
>
>
> Found this on the web so it must be right, right?
>
> 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.
>
>
> --
> John Lebetski
> Chicago, IL
> 77 Eleganza II
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| Re: [GMCnet] Trans Temp [message #155437 is a reply to message #155371] |
Wed, 04 January 2012 19:35 |
Bob de Kruyff
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Registered: January 2004
Location: Chandler, AZ
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""our TCs run all the time, (no lock-up) so it is not possible to get the
tranny too cool while it is running.
""
That's not totally true. A converter without a locking clutch will still approach hydraulic lock up at higher RPMs.
Bob de Kruyff
78 Eleganza
Chandler, AZ
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| Re: [GMCnet] Trans temp [message #155458 is a reply to message #155390] |
Wed, 04 January 2012 21:49 |
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Matt Colie
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Registered: March 2007
Location: S.E. Michigan
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| JohnL455 wrote on Wed, 04 January 2012 15:44 |
Found this on the web so it must be right, right?
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.
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John,
I don't doubt that you read that, but the fact is that all dino based lubricants (with some very few - expensive - exceptions) actually disassociate at 305°F. This is not a time/temperature thing, when that molecule gets to 305°F it comes apart and is not longer lube oil. Unless you have a system with really terrible lube oil flow differentiation (lots where it isn't needed and little where it is), even 200° won't start to cause any degradation. I never start to worry until I see temperatures over 250° and like to have everything stay over 225 just to keep the condensate from doing damage.
Matt
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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