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My 2002 4.0 5 speed (NV3550) will be getting some fresh fluid in the trans tomorrow (If I can escape from work). I can get the Royal Purple Synchromax from the local pep boys. Any recommendation on this oil either positive or negative. I am getting up in miles (148k) and not sure what the prior owner had done. Starting to get a little bit of grinding and tougher than normal shifts. Any other oil I should consider? I'd go with redline MTL, but that seems like it needs to be shipped.
Thanks.
 

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Synchromax is a good choice for your NV3550. Don't expect any miracle fixes of grinding which is a synchro problem, unless perhaps the wrong lube was used before. :)
 

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I have the same transmission as Kevin, but 100,000 less miles. It shifts so much smoother when cold in morning (20-30 degrees F) than later when warm. Is there anything that I can add to keep it like this all the time?
 

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KMG 365
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I do not know that transmission very well. If it has two plugs one for draining and one for filling remove the fill plug first.
 

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KevinNJ said:
My 2002 4.0 5 speed (NV3550) will be getting some fresh fluid in the trans tomorrow (If I can escape from work). I can get the Royal Purple Synchromax from the local pep boys. Any recommendation on this oil either positive or negative. I am getting up in miles (148k) and not sure what the prior owner had done. Starting to get a little bit of grinding and tougher than normal shifts. Any other oil I should consider? I'd go with redline MTL, but that seems like it needs to be shipped.
Thanks.
I just put Royal Purple in my nv3550 and can't say there is a huge difference. The transmission seems a little quieter but still shifts about the same.
 

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Here's my tranny fluid story:

I changed my trans fluid last Dec and put in Pennzoil Syncromesh. I bought the Jeep used and didn't know what was in it when I bought it, but wouldn't be surprised if it was the Mopar fluid since there were only 29K miles on it. Since the maintenance history was unknown to me, I was changing out all of the fluids as a matter of course.

Anyway, I ran the Pennzoil fluid for about a month [Dec-Jan] and noticed quite a bit of grindy and notchy shifts when cold [30 deg F], especially from 1st to 2nd gear. Once warmed up though the trans shifted normally.

So, I switched to RP Synchromax and the cold shifting really didn't get any better. Seemed about the same to me as the Pennzoil product - fine once the trans was warmed up.

So, I went and bought the Mopar fluid at the dealer and presto, no more cold shifting issues and the trans was back to shifting smoothly even when cold.

I wouldn't have thought that there would be as much difference as there is, and I probably wouldn't have believed a post like this one saying that there was a difference between those three choices, but for me there was so I'm posting my story FWIW. Note too that the Mopar fluid really wasn't any more expensive than the other two, maybe even less expensive.

All in all though it was an expensive exercise overall. So, if anyone wants a gallon of Pennzoil Synchromesh or RP Synchromax with almost no mileage on it let me know...:)
 

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I just did this myself with same setup as you. I used mopar nsg 370....about 2.5 quarts.
 
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