My other car is a '99 Nissan Maxima with 141,000 miles. I have noticed that to maintain about 80 mph the car revs at about 3.3k rpm whereas when the car was newer (< 100k miles), it rev'ed at 3k rpm at 80 mph. As part of the scheduled maintenance I got new spark plugs recently. Does anyone have an idea if this is normal? If it is not, why is it happening?

Also, does the brand of fuel make a difference (Exxon/Sunoco/Shell vs US Gas)? I don't think it should. What is your opinion?

 

The only thing (that I know of) that could/would cause that is a different tire diameter. Of course, changing gearing (transmission or differential) would also cause a change in engine rpm but you would have known that immediately.

 

Emthusiast, as Danimal pointed out, it has to be your tire diameter.
Are your tires properly inflated?
You mentioned a difference of 41k miles. Believe it or not, thanks to treadwear, your RPM will actually increase as your tires where out.
300 rpm's is alot, but if your tires had extra deep tread to start with, it could possibly make the difference.

 

My tires are properly inflated. I'm not sure if they were around 70k (the 3k rpm data). They may have been over inflated. I did change tires too around 110k. They were a different make. May be the radius of the new tires (non premium - low speed rating) is less than the old ones (premium tires - high speed rating).

 

By any chance, did you change the brand of rice you use to feed it? Might be the cause.

 

I think you answered you own question. If you changed tires, (even if they are the same exact size) and if they're made by a different manufacture, they can have different dimensions. There is no "standardization" in the tire industry.
I thought you meant that your car was turning 3k rpm's at 80 mph with 100k miles, then at 141k miles it was turning 3,300 rpm's to do the same speed.
Using the same tires.

 

If its an automatic, your torque converter might not be locking, or your tranny is slipping.

 

Its a 5 speed manual.

 

Dang. Did not know tires could make this much of a difference. Well at 150k I will need to replace them. I will get the premiums I think.