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View Poll Results: Is my transmission running too cold?
Yes, get a thermostat! 1 50.00%
No, leave it alone! 1 50.00%
Voters: 2. You may not vote on this poll

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Old 07-17-2019, 01:16 PM   #11 (permalink)
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Not a ton. From class we had a little tribology portion in mechanical system design and the big weights weren't hugely different. I'm sure you could find a "temp and viscosity thickness" chart and compare different weights at x temp for your reference as it relates to your transmission. Main take away: gas mileage will only vary a small percent wise, but the friction goes up and decreases the life cycle rating if the bearing/wear tolerances are designed to maintain a certain gap /psi rating with the spec weight at x temperature and you put in a thicc er fluid or cool the fluid too much. Think: Toyota doesn't recommend 0w-20 in their 0w-16 designed motors.

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Old 07-17-2019, 02:37 PM   #12 (permalink)
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Quote:
Originally Posted by hayden55 View Post
Not a ton. From class we had a little tribology portion in mechanical system design and the big weights weren't hugely different. I'm sure you could find a "temp and viscosity thickness" chart and compare different weights at x temp for your reference as it relates to your transmission. Main take away: gas mileage will only vary a small percent wise, but the friction goes up and decreases the life cycle rating if the bearing/wear tolerances are designed to maintain a certain gap /psi rating with the spec weight at x temperature and you put in a thicc er fluid or cool the fluid too much. Think: Toyota doesn't recommend 0w-20 in their 0w-16 designed motors.
Thanks. So you are saying that running this cold may actually be harmful to the transmission?
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Old 07-17-2019, 02:42 PM   #13 (permalink)
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Quote:
Originally Posted by EcoCivic View Post
Thanks. So you are saying that running this cold may actually be harmful to the transmission?
reiterate: No probably not. I don't actually know what the spec for ATF would be in your application, but you will lose a couple percent in FE since you're a couple degrees colder than optimal.

I would just plug your lines, and run a test loop with and without and see what the difference was. I used to have a 5 mile test loop I used on the mustang.
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Old 07-17-2019, 07:27 PM   #14 (permalink)
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Originally Posted by hayden55 View Post
reiterate: No probably not. I don't actually know what the spec for ATF would be in your application, but you will lose a couple percent in FE since you're a couple degrees colder than optimal.

I would just plug your lines, and run a test loop with and without and see what the difference was. I used to have a 5 mile test loop I used on the mustang.
Thanks again, I really appreciate your help. I have heard that the torque converter stall speed increases as the oil temp increases because the thinner oil flows through the torque converter easier. Is there any truth to that?

EDIT: Now that I think about it, I could test how stall speed changes with oil temperature pretty easily: Warm up the engine to operating temp, warm the trans up to ~200 degrees, test the stall speed (press the brake, put trans in D, floor it briefly, and see what RPM the engine will rev to). Then cool the trans off to ~100 degrees by spraying the cooler with water while the engine is running until it cools off, and retest stall speed to see how much it changes, if at all. If 100 degrees of oil temp difference doesn't measurably affect stall speed, the difference is certainly negligible.

Last edited by EcoCivic; 07-17-2019 at 07:35 PM..
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Old 07-20-2019, 12:22 PM   #15 (permalink)
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How about a thermostat?
https://derale.com/product-footer/fl...ol-thermostats
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Old 07-20-2019, 01:17 PM   #16 (permalink)
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I edited my post above.

So I had the opportunity to drive the Yukon a couple times the last couple days, temps in the low 90's and the trans stayed at 165, not 180.

I would guess 130F is fine, maybe a little low but from my limited research anything 110 to 180 seems to be acceptable or normal.
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Old 07-20-2019, 01:23 PM   #17 (permalink)
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Originally Posted by ncs View Post
I was wondering about getting one. However, I would prefer to not get one if it would be of no benefit. Like I said before, I worry about the thermostat sticking closed and overheating the trans. But if I install a trans temp gauge I could watch the temperature and make sure it stays normal.
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Old 07-20-2019, 01:31 PM   #18 (permalink)
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I have an update. I discovered that I can not trust my temp readings because my thermometer seems to read cold, at least sometimes. I was idling in neutral for about 3 minutes at a railroad track, and the thermometer dropped to about 90 degrees F, which was about 5 degrees below ambient temp. Not possible. So once I got home (about 30 seconds later) I felt the pipe that I mounted my temp sensor to, and it was hot even though the thermometer showed ~90 degrees. The thermometer was still securely clamped to the pipe. I would guess that the pipe was at least 120 degrees, probably more, so I am going to install a real trans temp gauge.
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Old 07-23-2019, 06:37 PM   #19 (permalink)
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I tested my stall speed cold (~90 degrees F) vs hot (~180 degrees F) and the difference in my stall speed was about 50 RPM. (2650 vs 2700 RPM respectively). I was expecting more of a difference, but now I know
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Old 08-04-2019, 03:20 PM   #20 (permalink)
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Trans oil likes to be warm, not hot. My temps are ~140 when warmed up. It's fine.

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