Just got a 2006 Taurus. 3.0 Vulcan pushrod motor. Seems to run ok. 140k miles. Trip computer says 31 mpg avg on 60 mile commute. Which seems a bit high. I had an 01 last yr that got 25mpg avg? Checked plugs today and all 3 front plugs were loose. That is odd. Motor does seem a bit raspy when cold. Seems to quiet down when warm. Plugs look fairly new. Iron head taurues’s are not known for plug issues like the tritons?
No these engines aren’t known for plug issues that I know of. What brand of plugs? Maybe he car’s not happy with X brand plugs. I had a Honda I put Bosch plugs into. They would loosen up if run hard, everytime! Switched back to Denso plugs and the problem went away. Makes no sense to me but there it is.
Trip computers are notoriously inaccurate. The only way to be semi-accurate with mpg calculations is to fill the tank and then divide distance traveled since last fillup by how many gallons you put in. And even that is subject to error because you’re relying on the gas pump actually having dispensed the amount of gas it said it did, which doesn’t always happen.
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I’ve seen many post that opinion/experience here. I’ve not had that experience on trip computers in a number of cars. GMs, Saab and Fords from my first in an '84 Corvette (scary accurate!) to my current Mustang (MPGs are correct, miles to empty, VERY conservative!) I check that stuff with miles between fuel stops and gallons added just so I can trust what it tells me. Much like running until the car throws the yellow Low Fuel light and comparing how many gallons you add to the tank size.
I’ve even checked out a phone app, Torque Pro, that will calculate MPGs and miles-to-empty from the real-time OBD2 stream. Its accuracy is pretty good if you fill the tank and then TELL the app it is full. It does poorly with partial tanks on mile-to-empty.
Obviously you and others have had poor experiences with your cars. Has anybody else had good experiences with their GM or Ford trip computers or is it just me?
Well, I’m not saying they report 12mpg when you’re really getting 40, but a 6mpg difference is not out of the realm of possibility.
My Acura’s trip computer is usually 2-3mpg on the optimistic side. My SO’s Veloster’s is more like 5mpg off.
Wow, that’s still quite a lot! 5 mpg out of 30 maybe?
I was astounded how good the '84 Corvette’s trip computer was. I drove it until the gas gauge read “X miles On Reserve” which I knew to be 2 gallons left. It said I was getting 20 mpg at the time and I drove until the message said “19 miles on the reserve”. I put 18.9 gallons in the car!
Saw similar behavior in a '88 Corvette project car from work for shock absorber development car although Chevy changed the protocol a bit. Still was eerily accurate for 1988.
Remember that big stink a few years back where Hyundai screwed up their mpg calculations and ended up having to pay its owners because they overstated the mileage? Yeah, that was us. 
The bad news is that we only get 36-38mpg, not 40+ as advertised. The good news is that we send Hyundai our odometer reading once a year and they cut us a check which usually totals more than the extra money we spend on gas over what we should have spent if the cars got the advertised mileage, and we’ll get that for as long as we own the car.
But the car’s computer is calibrated based on the bad calculations, so it always thinks we’re getting much better mileage than we actually are.
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Aside from the trip computer, some cars perform better than their peers. Had an 84 T-Bird 6 cylinder, could not believe it but got 35 MPG in combination high desert/mountain driving. Car was totaled. Replaced it with an 86, same equipment as the 84, the 86 Got 25 MPG. Was just lucky with the 84.
My daughters 2012 Chevy Cruze LS is accurate. When she first bought it, I suggested that she check gas mileage the old fashioned way and see how well it matches the trip computer. She said the trip computer was so accurate that she saw no reason to calculate it herself.
finally looked at rear bank plugs. they are platinum and look ok. while the front bank plugs are not platinum. i think the last mechanic decided to not change the rear bank plugs? once you remove simple wiper cowl it is easy to reach rear plugs
I think you’re correct
Presumably, the car is supposed to have platinum plugs, and those platinum plugs on the rear bank were still the factory parts
The guy doing the maintenance apparently installed 3 incorrect non-platinum plugs on the front bank, and neglected the rear entirely, perhaps because he didn’t feel like removing additional components to gain access. If that’s what happened, that would imply a degree of laziness
The stated DTE on my 2016 Mustang is like you stated, very conservative. When it reads “0” there’s still around a gallon left in the tank. As for the average MPG. It’s slightly optimistic. It usually overstates the hand-calculated figure by about two tenths, but it’s in the ballpark.
After verifying my MPG multiple times with hand calculations, I found that the MPG readout on my Outback’s dashboard was consistently .4 MPG gallons optimistic. This slightly optimistic readout was so consistent that I see no need to continue to do hand calculations.
I’m going to do my first test of the mileage calculator on my new Accord at the next fill up. It’s rated at 36mpg on the highway, and that’s what I appear to be getting. That’s great news in these times of high gas prices.