Using gear oil instead of ATF for NP231 transfer case
10-26-2014, 07:59 PM
#1
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Year: 1988
Model: Cherokee
Engine: 4.0
Using gear oil instead of ATF for NP231 transfer case
My NP231 transfer case has been real noisy and the fluid in it was shot. Doing a little research, it seems that some folks had good success using 75w-90 gear oil rather than the recommended ATF.
I filled it with the gear oil and it is way quieter and smoother running.
Should I expect any drawbacks to using the heavier weight lube? (I am OK with losing a tiny bit of gas mileage...)
I filled it with the gear oil and it is way quieter and smoother running.
Should I expect any drawbacks to using the heavier weight lube? (I am OK with losing a tiny bit of gas mileage...)
10-26-2014, 08:03 PM
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Year: 1988
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The rear seal on the case is leaking too, and the thin ATF just oozes out of it. My hopes are that the heavier gear oil won't ooze out of the seal so quickly...
10-26-2014, 08:54 PM
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Year: 1999
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People have had success using *engine oil*. Gear oil is WAY too thick! The oil pump cannot move nearly as much of it versus the factory specified ATF. I see you're in Prescott - have you seen how thick gear oil gets at 30°F? The planetary gears are ALWAYS turning and the oiling passages in the main shaft aren't exactly generous.
Why not replace the output seal? The rear seal is cheap and easy and increasing internal wear is not a good trade-off.
On second thought... if your transfer case had a noticeable reduction in noise when you changed to a thicker oil it needs a rebuild anyway...
Why not replace the output seal? The rear seal is cheap and easy and increasing internal wear is not a good trade-off.
On second thought... if your transfer case had a noticeable reduction in noise when you changed to a thicker oil it needs a rebuild anyway...
Last edited by salad; 10-26-2014 at 09:03 PM.
10-27-2014, 06:11 AM
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Year: 1999
Engine: 4.0
People have had success using *engine oil*. Gear oil is WAY too thick! The oil pump cannot move nearly as much of it versus the factory specified ATF. I see you're in Prescott - have you seen how thick gear oil gets at 30°F? The planetary gears are ALWAYS turning and the oiling passages in the main shaft aren't exactly generous. Why not replace the output seal? The rear seal is cheap and easy and increasing internal wear is not a good trade-off. On second thought... if your transfer case had a noticeable reduction in noise when you changed to a thicker oil it needs a rebuild anyway...
10-27-2014, 11:31 AM
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Year: 1999
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Yup you took one easy problem to fix and went to a complete rebuild needed now or at least replace with another used one.
When there is one type of fluid stated to use by the car company for an application its for a reason...........You just found out why
When there is one type of fluid stated to use by the car company for an application its for a reason...........You just found out why
10-27-2014, 02:20 PM
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Year: 1988
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People have had success using *engine oil*. Gear oil is WAY too thick! The oil pump cannot move nearly as much of it versus the factory specified ATF. I see you're in Prescott - have you seen how thick gear oil gets at 30°F? The planetary gears are ALWAYS turning and the oiling passages in the main shaft aren't exactly generous.
Why not replace the output seal? The rear seal is cheap and easy and increasing internal wear is not a good trade-off.
On second thought... if your transfer case had a noticeable reduction in noise when you changed to a thicker oil it needs a rebuild anyway...
Why not replace the output seal? The rear seal is cheap and easy and increasing internal wear is not a good trade-off.
On second thought... if your transfer case had a noticeable reduction in noise when you changed to a thicker oil it needs a rebuild anyway...
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10-27-2014, 03:34 PM
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Yep. It was published by Rockland Standard Gear in 2003 on how the NP231 has a habit of evaporating ATF. This is why so many wind up running dry and eventually failing. Pages 5 & 6 of this PDF: http://www.rsgear.com/articles/2003_10.pdf
10-27-2014, 05:37 PM
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I had to change the output shaft seal on mine (twice) because the vent was clogged. be sure to check this when you do yours. it took the new seal leaking for me to investigate further. what sucked is that it leaked out the back and got thrown onto the cat. talk about a terrible smell. it had gear oil in it when I first addressed it, most likely because it was leaking due to the vent. gear oil burning on the cat is a horrid smell. I put synthetic atf in mine. I had to add about half a quart after 35k miles for unknown reasons, it is not leaking. perhaps there is some solidarity to the evaporation claim.
10-27-2014, 05:54 PM
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I had to change the output shaft seal on mine (twice) because the vent was clogged. be sure to check this when you do yours. it took the new seal leaking for me to investigate further. what sucked is that it leaked out the back and got thrown onto the cat. talk about a terrible smell. it had gear oil in it when I first addressed it, most likely because it was leaking due to the vent. gear oil burning on the cat is a horrid smell. I put synthetic atf in mine. I had to add about half a quart after 35k miles for unknown reasons, it is not leaking. perhaps there is some solidarity to the evaporation claim.
10-27-2014, 06:46 PM
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Year: 1999
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Yep. It was published by Rockland Standard Gear in 2003 on how the NP231 has a habit of evaporating ATF. This is why so many wind up running dry and eventually failing. Pages 5 & 6 of this PDF: http://www.rsgear.com/articles/2003_10.pdf
The one I had/have was different but also proclaimed the use of motor oil in TC's was the way to go.
10-27-2014, 06:52 PM
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Year: 1999
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I had to change the output shaft seal on mine (twice) because the vent was clogged. be sure to check this when you do yours. it took the new seal leaking for me to investigate further. what sucked is that it leaked out the back and got thrown onto the cat. talk about a terrible smell. it had gear oil in it when I first addressed it, most likely because it was leaking due to the vent. gear oil burning on the cat is a horrid smell. I put synthetic atf in mine. I had to add about half a quart after 35k miles for unknown reasons, it is not leaking. perhaps there is some solidarity to the evaporation claim.
Pics.
10-27-2014, 07:11 PM
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Yep. It was published by Rockland Standard Gear in 2003 on how the NP231 has a habit of evaporating ATF. This is why so many wind up running dry and eventually failing. Pages 5 & 6 of this PDF: http://www.rsgear.com/articles/2003_10.pdf
