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Fuel Mileage comments? 2007 Mustang GT

1879 Views 14 Replies 10 Participants Last post by  GTBob985, 
C
Hey everyone, so this might be a dumb question to ask and I really don't know why this is happening. My 07 GT 5-spd has 21k on it, and is driven roughly 30-40 miles a day on average. Recently did an oil change with Amsoil 10W-30 Dominator Racing oil and cleaned out the throttle body. Results were a much better throttle response and overall "cleaner" feeling engine, if you know what I mean...

Yet, before this, even with tire pressures lower, I check them weekly now, I was averaging at least 19.3 mpg, now I can't get past 18.6-18.7 and my driving habits haven't really changed much..

Also, gears are stock 3.31 (yes I Know, 3.73s planned in the spring) and only other mods are FRPP mufflers, k&n drop in and hurst short throw..

Any comments as to what I can do? Thanks
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RSalamon
I'm not sure what to tell you. I get 22MPG driving around town with routine oil changes and being light on the throttle. Freeway driving I see between 27 and 28 MPG depending on how much of the go go pedal I push down :). This is with really tall gears and such.
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Muckerpuck
That's not the correct weight oil for your car to start. The oil weight can effect the cam phasers and timing, so your car may not be using the variable valve timing properly. And many say the vvt in the mustangs is very sensitive to oil weight and you should just run stock. Just a thought.
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C
Hmm..I've been doing some research into this, many people say that you will experience a drop in mileage with a higher viscosity, but in fact leads to longer engine life? I mean if that's true then it kinda makes sense..?
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My_White_Horsey
I've seen as low as 12-14 in San Francisco city driving and 25-27 on the HWY. 18-19 seems about right for mixed use driving.

Stock 2009 GT vert 5sp with 3.55's
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markag
your oil is too heavy. 10W30 is going to give lower gas mileage then 5W20. As far as longer engine life with a 30 weight oil... all I can say is that ford would not have called for an oil weight that would lead to premature engine failure. Use the rated oil and call it a day. That's what I say ;)

Also, lower tire pressure is going to burn more fuel. Higher pressures have less rolling resistance and give better fuel economy.
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JBert
clutch22 said:
. . . Recently did an oil change with Amsoil 10W-30 Dominator Racing oil and cleaned out the throttle body. . . . I was averaging at least 19.3 mpg, now I can't get past 18.6-18.7 . . . . gears are stock 3.31 (yes I Know, 3.73s planned in the spring) . . . . . . Any comments as to what I can do?
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Yeah, keep the 3.31's! . . . if you're concerned about gas mileage. I recently went to 3.73's from 3.31 and the car is more fun to drive, but the mileage did go down maybe 1 MPG or so. With the 3.31's you can always downshift; with the 3.73's the car feels more responsive and quicker but is always running around at slightly higher RPM.

I like synthetic 5W-20 because I feel like it offers good protection (synthetic) plus good cold flow and *maybe* better MPG ; your 10W-30 might have something to do with the MPG decrease.
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07GTStallion
Put 5w-20 back in that car right now! Too thick of oil is going to cause issues down the road. Maybe sooner than later. That motor was designed to run 5w-20 for a long list of reasons.
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themangeraaad
Seeing as it's getting into winter months... did you start warming up your car in the mornings before leaving the house?

During the summer I can typically get 22-23mpg mixed city/highway but during the winter this drops to 18-19 if I let the car warm up for 10ish minutes each morning... and I have a 70 mile round trip commute. If you warm up your car for 5-10 minutes and then have a shorter commute it will influence your perceived fuel economy even more.
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C
This oil was put in on the recommendation of a master mechanic who has been working on muscle cars for over the past 30 years, I do trust his word..

I have been looking around online and many owners run 5W-30 upto 10W-30 with no problems at all, in fact the spec'd 5W-20 is only due to Ford's CAFE standards, as this same engine abroad is spec'd to 5W-30.

And yes I do let the car warm up for a couple of minutes in the morning, but I will say this though, it has helped calm down the "ticks" I used to hear. I live in NJ, if that helps, the range of temps we get are all over the place and this winter has been mild so far..
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JBert
clutch22 said:
This oil was put in on the recommendation of a master mechanic who has been working on muscle cars for over the past 30 years, I do trust his word..

I have been looking around online and many owners run 5W-30 upto 10W-30 with no problems at all, in fact the spec'd 5W-20 is only due to Ford's CAFE standards, as this same engine abroad is spec'd to 5W-30.

And yes I do let the car warm up for a couple of minutes in the morning, but I will say this though, it has helped calm down the "ticks" I used to hear. I live in NJ, if that helps, the range of temps we get are all over the place and this winter has been mild so far..
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Today's mustang engine is a lot different from muscle cars of 30 years ago, but if you want to trust that guy over the manufacturer's recommendation, that is up to you. And today's synthetic motor oils are a lot better than the dyno oil of 30 years ago; I'm pretty sure if you look at the technical data today's synthetic 0W-20 lubricates and protects better than good ol' 50 weight.

Also remember that it is winter now, so that lower number is important when you start the car -- when cold, 10W will not flow as well as 5W . . . by roughly a factor of two. When I start my car, I'd rather have my moving parts oiled instead of dry.

I don't think there are any other answers to your question beyond what we have already suggested ; good luck with it.
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topbliss
1/2 mpg difference is well within normal day to day tolerance. Don't worry about it.
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themangeraaad
Well if you are driving 30-40 miles per day and let it warm up for maybe 3-5 minutes every morning that's probably your reason right there.

I let my car warm up maybe 10 minutes in the morning but do 70+ miles per day and have seen a ~3mpg decrease in fuel economy. If you're seeing less than 1mpg decrease and warming up the car for a few minutes? There's your answer.
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markag
It may have been said already, but the variable cam timing was designed to run off with 5W20 oil. That's a big reason right there to run 5W20.
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GTBob985
I run 3.73 gears and 50% of my driving is in the city. Mileage actually went up 1 mpg


Sent from my iPhone using AutoGuide.com App
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