Trans temperature gauge

Mark Kovalsky wrote:
That chart isn't 20 years old. It's more like 50 years old. It is useless for the modern world.
I've run modern ATF as high as 320°F in testing. The seals didn't harden, the clutches didn't burn, varnish didn't form, etc. This chart is plain wrong for a modern transmission.

+1 :)

That chart isn't 20 years old. It's more like 50 years old. It is useless for the modern world.
I've run modern ATF as high as 320°F in testing. The seals didn't harden, the clutches didn't burn, varnish didn't form, etc. This chart is plain wrong for a modern transmission.

partsman01 wrote:
Here is one chart I have.

Everybody - here is one of those twenty year old charts mentioned earlier. It has nothing to do in today's reality. Gm says Dexron 6 to 275 degrees-and they have even had the fluid up to 285 degrees.

Here is one chart I have.

Mark, I yield to your expertise with no issue. I agree that the trans fluid will be the coolest if it goes through the vehicle radiator first and then through the trans cooler. This is great to control the upper temperature in hot weather. Apparently this is not the best overall solution in cold weather or modern transmissions would not come with bypass circuits to maintain a minimum trans fluid temperature. However, on older non-bypass transmission fluid circuits I would have to conclude that the maximum trans fluid temperatures were more of a concern to the manufacturers than minimum trans fluid temperatures.

DougE wrote:
If you search some you will find most sources state that the design operating temperature of automatic transmissions is 175*. You will also find that most life vs. temperature charts for auto transmissions do not go below 175*. This is the reason behind installing an auxiliary cooler prior to the radiator cooler. This allows cool trans fluid to be warmed up to the correct temp as the outlet of the engine radiator is ~175*.

The engine radiator is NOT ~175°F. It usually is MUCH colder than that. Have you ever measured the temperature in the cold side of the radiator? I have, in ambient temperatures from -40°F to +115°F. When towing heavy in high ambients the temperature drop across the radiator can be as small as 15°F. But in cold weather, running lightly loaded the cold side of the radiator is within a few degrees of the ambient temperature. If it's 0°F outside you can expect the cold side of the radiator to be around 5-10°F. How well is THAT going to warm your ATF?

The correct routing for the ATF flow is from the trans to the radiator cooler, then to the aux cooler, then back to the trans. This is the way all of the auto companies route it because they understand how the system works.

But you are right, the designed operating temperature of the trans used to be about 175°F. It has moved higher in recent years to improve efficiency. Newer fluids and materials in the trans are designed to live at those temperatures.

Those charts that are floating around the internet that talk about trans death in feet instead of miles if the trans ever gets above 200°F are based on 1960's technology, or just flat out lies.

Today - max temp of 30 degrees. Tranny temp on the way home was only 100 deg F. Just not enough load on the tranny to heat it up. I have a diesel and an Allison so it may not be a good comparison.

I have a F150 (7700 series) with 4R100. Extra oil oiler and temperature gauge in the oil line going into the rad. Oil temperature in winter never goes about 100° unless I'm in town. In the summer it runns about 140-150°F pulling our 24 ft 5th wheel. Only time I have seen it go 170 or higher was stop and go traffic or parking or going up a couple of grade in the White Mountains in July. The temperature will go back down the minute the torque locks up. Their is a temperature bypass in the $R60 and 100 that will not allow it into OD unless the tranny is at operating temperature.

Don't many transmissions have a thermostat that bypasses the cooler until the fluid comes up to a certain temp? Don't know about the 4L60, but the 6-speed in the F150 in sig below must have one. It'll warm up to 195 and stay there despite the outside temp. The only time I saw it get higher was while towing the TT up Wolf Creek Pass in Colorado (10,700 feet). It went up to 204 then, and went back to 195 quickly on the way back down.

bmanning - I'm not disagreeing with you. My primary point was to recommend against trying to run trans fluid at too low of a temperature as it is not necessary. If you run too cool you never boil off any condensation that has collected inside the trans. Most, if not all, trans cooler sellers want you to mount their cooler after the vehicle radiator. Looking, I suppose, to get the most cooling of the fluid and thus make their cooler look the most effective or to mitigate other cooling system problems that should have been addressed first. I agree with you that modern fluids can operate successfully at higher temperatures than in the past. The '91 Class A I had previously would easily generate temps above 250* on long uphill runs and benefitted greatly from a quality plate trans cooler.