jfactor

On my last oil change about 8k ago (I run 10k oci, M1 ext. perf.) I decided to try a napa platinum oil filter supposedly designed for use with synthetic oils. After the oil and filter change I started noticing a gradual decline in the mpg. I was averaging around 25 mpg, even with my heavy foot. Here it is 8k later and my car has worked its way down to the 20-22 mpg range. Has anyone else here had an issue with a particular oil filter causing lower mpg? Is it possible that maybe the flow through the filter is more restrictive causing the engine to have to work harder to pump the oil through causing the lower mpg? I'm thinking I'll just go back to the fram tg or m1 on the next oil change. Is there something else I'm missing that wears out around this mileage?

95 Maxima
224k miles
Mobil1 Extended Performance 5w30
Napa Platinum oil filter (normally use Fram TG)

njmaxseltd

iTrader: (19)

It's not the oil filter, that's for sure.

WendysMaxima

8k miles on one change? Even full synthetic that's a lot. Try changing more often. Clean your maf too

Slamrod

iTrader: (11)

Most certainly not the filter, maybe try seafoaming your car to clean some gunk out? Other than that, pcv valve, air filter, fuel filter, etc etc. Its a big stretch but maybe even the knock sensor?

From what i understand many if not most of the basic tune up stuff can have a significant effect on performance as well as effeciency.

njmaxseltd

iTrader: (19)

The list of items that impact MPG is rather large, but the oil filter isn't on it.
I wouldn't go more then 5k miles on any oil...

AWeb80

You can. Just depends what oil you use. I use Rotella T6 5w-40. The diesel truck guys go 8k on it and their used oil analysis comes back saying they could go farther. I use the oil and love it.

maxgtr2000

iTrader: (29)

If tire pressure is down a psi or so your mileage can change. Air expands in heat and contracts in the cold. Cooler weather can play a part.

njmaxseltd

iTrader: (19)

Do you know how many "gallons" are in a diesel truck motor compared to the VQ's 4.5 qts? My BMW went 7,500 on oil changes, it held 8 quarts. My 4Runner goes just over 5,000, it holds over 1.5 gallons.

I wouldn't let 4.5 quarts of any oil go more then 5,000 miles in our VQ.

AWeb80

Do you know the type of stresses turbo diesels see? Even NA ones see 20+:1 compression. That's a lot of force on rod/crank bearings. They also run a lot hotter.

Do a UOA, I bet you can go farther.

cashoit

Synthetic is supposed to last 10k miles or so. That being sd, after 3k miles I would check the oil color. If its still clean run that bish and check again every 1000 miles. When its dirty replace it

OP:

a clogged filter would mean your engine oil is really dirty and thereby cylinder head and cam shafts could have sludge on them and make the engine work harder and MIGHT decrease MPGs.... But just changing filter brands shouldnt have any effect on MPG

Amerikaner83

iTrader: (17)

a lot of gas stations have begun switching to their winter blend gasolines...with which the addiditon of 10% ethanol lowers your MPG.

jfactor

I seafoam, clean the maf, and replace the fuel filter every time I do an oil change. I replaced the pcv valve at some point over 200k and the air filter is only about a month old. A faulty knock sensor is a very big stretch considering the decrease in mpg is the only problem I'm having. When the decrease in mpg began I replaced the fuel tank sending unit with a new one (old one was cracked) and replaced the sock on the fuel pump while I was in there. Cleaned the throttle body and iacv, got a noticeable bump in performance but no effect on mpg.

jfactor

I've never really seen any significant differnce in mileage on my Max or any other vehicle I've owned in the past for that matter when they change blends and gas has had up to 10% ethanol long as I've had this car anyways.

maxgtr2000

iTrader: (29)

It is over 200k. It won't get the same mileage unless you do an engine overhaul. Try doing a compression and leak down test. Many years and miles of compression and the piston rings are probably worn, that's just how it is if you checked all the other stuff.

jfactor

I was cleaning out my glove box today and came across the inspection paperwork from several months ago. The NOX emissions, which have been really low on past inspections, were a good bit higher on the last test. That coupled with the drop in mpg could point to my catalytic converter going bad. I got under the car and it looks like its still got the original cat on it.

jfactor

So I was looking under the hood, thinking, Budweiser in hand. I though what about the egr tube? They're known to get clogged. After some fighting with the nuts and bolts got it off and guess what, hardly any carbon buildup at all. The UIM on the other hand is another story. The EGR tube hole on the back of it is cram packed with buildup. Looks like it's off to the junkyard this weekend to find one to cleanup and switch out.