Poor MPG after 60k DIY service - Plugs or gear oil?

Did the 60k service to my taco last week:
Replaced all plugs with OEM Denso (3491) FK20HBR8
Front & Rear diff oil replaced with Valvoline 75W90
Engine/Cabin air filter replacement
Oil & filter change with standard Valvoline 0w20, OEM filter
To my knowledge the diff oils and spark plugs were original before I changed them

I'm seeing a 1.5-2mpg decrease on the highway despite the truck feeling fantastic otherwise. Is it possible that this difference is in the SLIGHTLY higher gear oil viscosity from stock, or do you guys think it's an issue with the plugs? I did bump one of the plugs side electrodes on the valve cover during install (front drivers side cylinder), but I doubt it was enough to change the gap... Plus it's running fine? Planning on pulling the negative terminal to reset the ECU this afternoon. 6MT if that means anything.

 

Sounds like your foot got a little heavy from the excitement of saving a couple hundred bucks!

Let it ride, nothing is wrong.

 

Ha Ha Ha…
Just double check everything you did like hoses, clamps etc.
With everything being equal and it’s feeling fantastic otherwise, your right foot is really happy too.
Just drive it and enjoy it.

 

If that was the case I’d be getting about 8 mpg with 85/140 dino I’ve been running for the last 2 months. Just drive it and have fun.

 

Nothing to worry about. There are so many variables when it come to MPG.

Fuel quality, ambient temperature, and of course the routes you travel will all contribute to short term variability.

 

I plow snow with my 2011, I have a scan gadget it gets 8 MPG plowing snow, 18 plus on the road.

 

Don't rule out the 'blend' of gas coming out of the pump.
Oil companies do everything they can to make a few extra billion per day, ... baby needs a new pair of shoes right?
Changing the 'blend' is all part of the scheme.

There's the Winter blend and the Summer blend, in theory the different blends produce less emissions -
But I don't believe a word of it.

 

^not true^

Seasonal blends of gasoline are mandated by state laws, namely California - not because oil companies want to change their formulation seasonally. Remember, California state fuel economy and emission regulations practcally dictate what the rest of the USA does. NY, WA, OR, NJ, CO and other liberal states all follow California state laws by reference.

Oil refineries would much prefer to produce a constant, steady supply of gasoline that does not have seasonally changing specifications.

(I worked for 30 years as a petroleum engineer for Big Oil, including in the state of CA. So I know this to be true.)

Because it is safer, more reliable, and actually more profitable than having to change out equipment and additives and cracking and blending procedures seasonally for no good reason. You would also experience lower prices at the pump and gasoline in greater supply, things politicians actually don't *want* you to have.

They want to shove an $70,000 EV down your throat that requires a $15,000 battery pack replacement every 5 years and drives your electric bill to skyrocket.

Friendly reminder: Your EV still runs on coal.
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Here are the state of California regulations regarding gasoline, much of of devoted to seasonal blending. This is a stupefying 154 pages of gibberish and I challenge you to read it. TITLE 13 (ca.gov)
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Oil companies have opposed virtually every gasoline regulation promulgated by insufferable politicians since the 1970s.
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There are so many examples of bad gasoline laws enacted by politicians who know nothing about science that I could write about this for days on end.
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* Remember way back in the 1970s when scientists determined that lead in gasoline (and paint) was harmful to human health? And there was some early research that Methyl tert-butyl ether (MTBE) was a promising gasoline additive that possibly could replace lead as an 'anti-knock' additive while also increasing octane.

Actually, it was a great additive in terms of reducing knock and boosting octane.

And so California, before the scientific research process was completed, mandated its use.

Only to discover just a few years later this MTBE chit causes CANCER and is SOLUBLE in water. Earth to everyone: these are the two worst characteristics for a gasoline additive you could possibly imagine.

And so, after all the gasoline refineries in Californa spent BILLIONS to re-tool their refineries to blend MTBE in their fuel, only to result in MTBE being BANNED just a few years later?!?!
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Don't even get me started on EVs and ethanol and oxygenates.

 

I'd say the MPG drop is "coincidental".
I don't see new plugs or the gear oil being the cause of the drop in MPG.

Give it 4 tanks full and see if the MPGs settle back down.

 

It's probably the new plugs making the gas burn more efficiently. So it's burning more gas.

 

I've seen people running the 140, any reason behind that other than finding a deal on heavier oil?

 

maybe its maybelline

 

We need a sub forum for folks who want to talk about MPG's and engine oil.

 

Fresh everything. Truck senses that and now it has to adjust maps to those small changes. As sensitive these trucks are the maps are always changing on every start up. I know the maps are in the teens. So maybe it sensed all those changes and now it trying to find an old map to run the most efficient. You almost want to reset all the learn values when you do any tune ups. Just some thoughts

 

Great advice. Reset the ECU and let it idle with no loads for 10mins so it could relearn. Seeing higher MPG's than before the tuneup now, but the test will be a frequently done highway trip this weekend with cruise control.

 

A lot of us run the 85-140 because it's recommended by ECGS after re-gearing the diffs. https://eastcoastgearsupply.com/ft-2536-ecgs-gear-oil-recommendation.html

I ran it for a while but found that I was hearing less diff howl with a lighter oil, however paradoxical that may seem.