# Transmission & RPM vs Road Speed



## JSmith86 (Jan 26, 2013)

I have a 99 Nissan Altima with close to 150k miles on it, I picked it up when it had about 120k. I recently had a transmission pan drop, filter change I believe, and refill with non-Nissan dealer fluid, shop tech said it was equivalent aftermarket but I don't know. I was having some flare on morning cold starts between 1st and 2nd, would go away when warm, and someone recommended the fluid change as a fix. As far as I can tell it's still there 500 miles after change. When the tech dropped the pan he swears it's the original gasket so it's either been reused, which I doubt, or the transmission has never had any service. There was a crapload of gunk on the magnets and also 2 larger shavings according to the tech and he was freaked out by this. I was less concerned but how bad is having a third of an inch shaving in there after all this time? I'm going to assume it's never been serviced. How many miles would guesses out there say this transmission has left.

Also, I got the specs on the transmission and final differential and calculated out my expected rpm vs gear & road speed, and the values seemed pretty spot on, I think the biggest difference I could spot was in 4th around 70mph, it was about 100rpm higher than I expected, so about 3% off. Does a transmission diverge from expected rpm vs speed profiles as it ages, and by how much, or does it pretty much stay on spec till the day it dies.

Also, I'm somewhat worried about the non-genuine Nissan fluid, but he assured me it was fine. I'm not sure because my temp gauge used to sit prett steadily around or under the 1/3rd mark, now it's solidly over 2/3rds. I'm not sure what caused the temp diff, whether it's wrong fluid, something else that might have gotten changed.


----------



## smj999smj (Jan 1, 2006)

I think you're doing a lot of overthinking! I doubt there are many people who calculate their gear RPM versus road speed. The big concerns would be the color of the fluid drained out (brownish color fluid would indicate clutch material in the fluid) and if there is any slippage. The transmission service is usually a drain and fill and there is a drain plug on the AT pan to provide this without have to drop the pan. Nissan transmissions don't use a filter, just a screen that doesn't require servicing. Their thinking is that if there is enough debris in the ATF to clog the screen, then it needs a trans overhaul and not a service. Some metal shavings stuck to the magnet is not a major concern, but the bigger pieces "might" be an indication of a hard part starting to fail. The cold-shift "flare" could be due to clutch pack seals that are starting to get hard due to age and mileage. Even with that, there is no possible way to say how long your trans will last, nor anyone else's. It could last the rest of the life of the vehicle or it could fail next week; the best you can do is give it the proper maintenance and don't abuse your vehicle. As far as the fluid, Nissan does recommend Nissan Type "D" ATF, which is the same as the original formula of Dexron and similar to Dexron II. Dexron III is acceptable to top-off the fluid if it is low, but is not recommended for a full service of the fluid. The reason is that it has a thicker viscosity and has been found to potentially cause valves to stick in the valve body. So, if servicing the fluid, it's best to stick with Nissan Type "D" ATF or an aftermarket fluid that is "recommended" for use in Dexron II applications. Two that work well include Castrol Multi-import ATF and Valvoline Maxlife ATF. If the flare didn't change any after the service, even if the mechanic did use Dexron III, I doubt that replacing the fluid with Type "D" will make any difference. I wouldn't be overly worried about it, however.


----------



## JSmith86 (Jan 26, 2013)

Alright, sounds good. I was just curious if you could judge transmission health by rpm vs road speed. Any idea on the temp difference though? Was steadily at or under 1/3rd now it's rough over 2/3rds on the gauge.


----------



## smj999smj (Jan 1, 2006)

Are we talking about the coolant gauge or do you have a trans fluid temp gauge installed?


----------



## JSmith86 (Jan 26, 2013)

Coolant gauge that's right on the dash and not actually marked with any temperatures.


----------



## smj999smj (Jan 1, 2006)

Maybe a bad thermostat? Are both electric fans working properly? Coolant level full? No restriction of airflow through the condensor and radiator cores? Possible head gasket failure? I can't see another 100RPM at 70MPH making an engine overheat. If the only time it overheats is at highway speeds, this would rule out a cooling fan issue, as the ammount of airflow forced through the core at that speed would negate any cooling benefit from the electric fan.


----------



## jdg (Aug 27, 2009)

Unless the torque converter wasn't locking up maybe?
Might help explain the extra 100rpm at low load cruise as well as the heating up.


----------



## JSmith86 (Jan 26, 2013)

Oh, it doesn't just happen at highway speeds. I don't think it's overheating, just running warmer than before, but I don't know where the temp needle should be. When I bought the car over 2 years ago, no matter what I did the coolant temp gauge never seemed to go above 1/3rd. Right after the transmission fluid change, within about 5 minutes of driving it climbs to a little over 2/3rds and stays there, whether stop & go 30mph city driving or 70mph up & down I95. It just seems like they're related events, but I'm not sure how or if I should be worried. Thanks


----------



## rogoman (Dec 16, 2004)

Maybe the shop tampered with the coolant system. Take the car back to the shop and have them check it out.


----------



## mikeLekan (Feb 27, 2013)

yeah, the best way is to Take it to the shop and let them check it


----------

