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Unread 02-24-2013, 01:49 AM   #1
sean112280
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T-18 question

What fluid do I put in it? I know it's kind of a rookie question but never had one before this jeep

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Unread 02-24-2013, 06:59 AM   #2
ADDZ71
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From a viscosity standpoint it is easy 85-90W Gear Oil. The GL rating is where it gets hard. Older transmissions like the T-18 have some yellow metal parts i.e. Brass. Search and you will see many threads on here and other forums on this issue. From the factory it recommended GL-4 which is only offered that I found at NAPA. You may be able to get it online from somewhere but in town stores will be NAPA and I would call in advance since it is not always on the shelf or not enough. You will need I think just more than 2 quarts.
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Unread 02-24-2013, 08:26 AM   #3
82JeepCJ7
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A T-18 holds 2 quarts. I'm running 50wt motor oil in mine. This was recommended to me by a transmission builder. Normally these transmissions are used in heavy trucks where the stress on the gears requires the heavier gear lube. In light weight Jeeps, that is not the case. Using 50wt motor oil will make it shift easier, especially when its cold outside.
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Unread 02-24-2013, 10:37 AM   #4
only in a jeep cj
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Yep, I use motor oil in all my transmission and haven't had any problems in the 20 years and hundreds of thousand mile later.

But, I haven't had a T18 yet, so tha'ts all I say.
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1975 CJ-6 304 T15 Dana20 30/44 3.73
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Unread 02-24-2013, 11:28 AM   #5
CSP
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50 wt motor oil is about equivalent to a 80wt gear oil. The way viscosity is measured in motor oil isn't the same as gear oil. Some people might think 50wt is too light, but that's why it makes a viable choice. You wouldn't want to use it in an axle application as it wouldn't stand up the pressure a hypoid gearset sees, but it's fine in a transmission.
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Unread 02-24-2013, 11:33 AM   #6
sean112280
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Thanks everyone! I appreciate the help
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Unread 02-24-2013, 11:41 AM   #7
brownbagg
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isuzu trooper transmission take 30 wt, and it works fine
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Unread 02-24-2013, 12:06 PM   #8
roadhog304
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Does the 50 wt oil have any effect on the brass in the trans? Can you also use it in the transfer case?
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Unread 02-24-2013, 12:21 PM   #9
CSP
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No, the 50wt motor oil doesn't have the sulphur based additive that eat yellow metals. Those additives are only found in GL5 gear oils (not found in synthetic GL5 gear oils) and are what allow those gear oils to withstand the pressures that the ring and pinion see.
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Unread 02-24-2013, 03:50 PM   #10
roadhog304
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Quote:
Originally Posted by CSP View Post
No, the 50wt motor oil doesn't have the sulphur based additive that eat yellow metals. Those additives are only found in GL5 gear oils (not found in synthetic GL5 gear oils) and are what allow those gear oils to withstand the pressures that the ring and pinion see.
Thanks. So is it okay to use the 50wt in the transfer case?
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Unread 02-24-2013, 04:21 PM   #11
CSP
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Yes, the tcase is not a hypoid gear case (just axles are) so it's ok there too.
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