+4 MPG with MC 5w-30...How is this possible?

[merc80]

My work truck is a '95 F150 w/ a six cylinder engine. It was purchased with about 175k on the odometer. When purchased it had a sticker from the local kwikee lube saying it used Castrol 10w-30. I had been averaging about 14.5 mpg. My first tank of gas after changing to MC 5w30 I averaged 18.78 mpg

I have a real hard time believing that it's due to the oil, but it's the only thing that's changed. The weather has been fairly cool for a couple months now, so a/c use isn't a factor. The same couple of people have been driving it since purchased, so it's not being driven any differently. Anyone else have a similar experience?

 

[lindermant]

Track the #'s and report back after 3-5 gas fillups. If the numbers stay up, then you may be onto something.

Too many variables to consider... did you fill up at the same gas station, the same pump, do you fill up until you can see it in the neck or stop at pumps first click, etc.?

 

[MNgopher]

As stated - give it several more tanks of gas before jumping to the conclusion something wonderful has happened. I'm willing to bet it comes back towards your normal fuel mileage.

 

[Steve S]

Don't think it is possible.

 

[OriginHacker21]

I once gassed up at a tattered Vallero station in the desert. My car got -5MPG+ and had a few hard/startups. I believe different stations = different gas = more or less MPG. It may be my imagination but my car tends to idle softer on different gas stations in different locations. So my opinion = if you fill up at different places then that could be it.

 

[LouDawg]

You definitely need to check several tankfuls and do it at the same place for a period of time, doing everything the same as much as possible, driving patterns, habits, etc. THEN see what you come up with.

I *seriously* doubt that switching from 10W- to 5W- alone is going to net you a 4mpg (almost 30%) increase.

 

[Cutehumor]

some gas station probably cheated you a gallon when it said it was full. I bet their meters are off. causing the difference

 

[rpn453]

Coincidence.

 

[CBODY67]

I have a friend that noted an mpg increase on trips and around town after the Firestone store he gets the oil changed at switched to a blended synthetic oil. His 100K+ mile Neon now gets 38mpg on round trips to far southwest TX from Dallas, which he had done enough before the oil change to know what mpg he got doing that. Something like 2mpg better after the oil change, consistently. He was surprised when he noted the mpg increase, but not displeased in the least. That Firestone store's now got a customer for life, I suspect--at least for oil changes.

I believe the noted change (the Neon and the F-150) can happen from just an oil brand/type change, but it might also be due to particular engines and such too, just as certain engines tend to "like" certain brands/blends of fuel. Unfortunately, I haven't noted such changes in the vehicles I drive (from a change of oil brands), yet.

Just some thoughts,
CBODY67

 

[Chris142]

I'd guess that the lube tech noticed an unplugged sensor while working on the car and plugged it in.

 

[Ray H]

Quote:

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My work truck is a '95 F150 w/ a six cylinder engine. It was purchased with about 175k on the odometer. ... I had been averaging about 14.5 mpg. My first tank of gas after changing to MC 5w30 I averaged 18.78 mpg...

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Water in the gas tank from condensation or a prior fill-up that finally purged on through? (Might wanna consder investing in a new gas cap...)

 

[merc80]

The truck is just about always filled at the same shell station next to the shop. I did the oil change myself, there were no sensor wires unplugged. My initial thought was that maybe the kwik lube place may have not put in what the sticker showed. However, I have a real hard time believing that even a much thicker oil could cause such a drastic difference in mileage. I'll track the next couple tankfuls, but as of now I'm just stumped.

 

[Kestas]

A 30% increase?... doubtful. When the time comes, switch back to regular 10W-30 and report back the results.

Reminds me of a Gomer Pyle USMC episode where Sarge had a car and the guys would discreetly siphon gas from the tank so Sarge would measure poor gas mileage. He then sold the car to his friend, and the guys would discreetly add gas so the mileage would go up and Sarge would feel bad about the sale. Are you sure your friends aren't rippin' on you?

 

[BlueOvalFitter]

Maybe the earths axis tilt is different since switching oil.....