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Discussion Starter · #1 ·
I recently had an oil change, using 100% synthetic (as is usual), but this time, I noticed a decrease in the highway mileage from 32 mpg to 24 mpg.
Could that be the oil, lack of changing the filter...or, winter gas?

Thanks for your input!
 

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I don't think Oil would have an impact, I did mine early spring time last year and didn't notice a difference. What did cause a difference was due to Winter Mixture to Summer Mixture for gas. I think it was about 2-4 impact if I remember right. I also noticed depending on where you go, I also get slightly better gas depending on the brand of gas station I go to. I didn't notice it before since I normally went to Meijer or Speedway, but my last trip back to my parents place outside Chicago, had to fill up with Mobil1, and noticed I got like 2 mpg better comparatively to Meijer and Speedway (by extension sam's club). I think I've seen similar posts confirming this regarding Shell or BP but it could also be a pseudo-effect. But assuming that I keep my driving fairly consistent post tune now (basically I just keep the car in Sport/Sport+ and let it do its thing), I don't think its my driving.
 
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Discussion Starter · #3 ·
I don't think Oil would have an impact, I did mine early spring time last year and didn't notice a difference. What did cause a difference was due to Winter Mixture to Summer Mixture for gas. I think it was about 2-4 impact if I remember right. I also noticed depending on where you go, I also get slightly better gas depending on the brand of gas station I go to. I didn't notice it before since I normally went to Meijer or Speedway, but my last trip back to my parents place outside Chicago, had to fill up with Mobil1, and noticed I got like 2 mpg better comparatively to Meijer and Speedway (by extension sam's club). I think I've seen similar posts confirming this regarding Shell or BP but it could also be a pseudo-effect. But assuming that I keep my driving fairly consistent post tune now (basically I just keep the car in Sport/Sport+ and let it do its thing), I don't think its my driving.
Thanks for your input. I use KWIK Trip gas, exclusively, but you may be right on the Summer to WInter gas mixture. I also noticed a bit of exhaust smell, which I hadn't before.
I drive the Stang in "old lady mode" consistently. LOL I will get braver this summer :)
 

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Thanks for your input. I use KWIK Trip gas, exclusively, but you may be right on the Summer to WInter gas mixture. I also noticed a bit of exhaust smell, which I hadn't before.
I drive the Stang in "old lady mode" consistently. LOL I will get braver this summer :)
Lol Everyone gets braver once winter ends so no worries there. I forgot to mention that the Octane rating will also effect the mpg as well so if you're stock and switched from 93/91 down to 87, the combo of that plus the winter mixture could in theory cause an 8 mpg max difference. But this is also highly dependent on a person's driving style.
 
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Discussion Starter · #5 ·
Lol Everyone gets braver once winter ends so no worries there. I forgot to mention that the Octane rating will also effect the mpg as well so if you're stock and switched from 93/91 down to 87, the combo of that plus the winter mixture could in theory cause an 8 mpg max difference. But this is also highly dependent on a person's driving style.
Well, Hubby always used 87 Octane. He tried higher and didn't really notice much difference. My driving style is fairly conservative, always a bit over the speed limit and I do let it 'run out' once a week to get that catalytic converter to clear. When we first got the car, he had me drive down those 13 switchbacks at Devils Lake in sport mode...OMFG! I MAY try that again, now that I am more familiar with the road. I really don't think the Stang is getting enough exercise, like all of us in the Winter. ;)
 

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Well, Hubby always used 87 Octane. He tried higher and didn't really notice much difference. My driving style is fairly conservative, always a bit over the speed limit and I do let it 'run out' once a week to get that catalytic converter to clear. When we first got the car, he had me drive down those 13 switchbacks at Devils Lake in sport mode...OMFG! I MAY try that again, now that I am more familiar with the road. I really don't think the Stang is getting enough exercise, like all of us in the Winter. ;)
My recommendations for when you go back to said switchbacks then, try out the summer 93 mix if its available, you'll probably need to do two fill ups to get the octane in the tank up to that rating (since we don't drive till we are completely empty so you'll need multiple fill ups to get a full tank of 93). Flip it into sport/sport+ and enjoy pushing the car. As for winter since I noticed that yours is a drop top, I don't know what your willingness is for driving it in winter, but I will say, I was skeptical of winter tires, but now my only regret is not getting winter performance tires instead of the Nordic/Snow ones I currently got (Michigan has currently been getting a stupid mild winter and haven't been getting much snow in my area, when we do it melts away within one-three days time). Mine is my daily driver tuned with Ford Performance, and it loves the winter (minus the excess dirt).
 

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Discussion Starter · #7 ·
My recommendations for when you go back to said switchbacks then, try out the summer 93 mix if its available, you'll probably need to do two fill ups to get the octane in the tank up to that rating (since we don't drive till we are completely empty so you'll need multiple fill ups to get a full tank of 93). Flip it into sport/sport+ and enjoy pushing the car. As for winter since I noticed that yours is a drop top, I don't know what your willingness is for driving it in winter, but I will say, I was skeptical of winter tires, but now my only regret is not getting winter performance tires instead of the Nordic/Snow ones I currently got (Michigan has currently been getting a stupid mild winter and haven't been getting much snow in my area, when we do it melts away within one-three days time). Mine is my daily driver tuned with Ford Performance, and it loves the winter (minus the excess dirt).
Sure, it's worth a try with the higher octane. I love to drive in the winter. The tires are Y-rated All-Season Continentals and it very stable on the winter roads, although I don't enjoy driving in a blizzard. You are right about the lack of snow this Winter, though...ours has been minimal, but enough for them to salt the roads. We still have about 6 inches on the ground as the 'warm' weather has melted a lot of it. The Stang is my only car and it is a CAR and does what cars are expected to do, even in the Winter. Since I am retired, it doesn't get enough road time. That being said, after my cross country trip to Oregon and back last year kind of took the white line fever out of me for a while.
 

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Discussion Starter · #8 ·
This is what hubby said about winter driving:
Ahhhh, I suppose you are wondering how do I drive it in The Winter.
The car is rock solid on the snow and ice. Put it in Snow/Wet mode, and it does better than any other car I've owned. You can high center it if the snow is to deep,
as in the first time it happened to me. The snow was 14".
 

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I don't think Oil would have an impact,

Not entirely true. If its the same weight then no it won't. But oil weight/viscosity can definitely have an impact on mpg. The lighter the oil the better the MPG. If OP put in a higher weight oil. MPG would drop. But definitely not by 8mpg. Maybe upto 1-2mpg depending on how much more weight.

Many factors can be creating the lower MPG. The colder temperatures alone in the winter. Both from warming the car before driving to defrost the windows and feel comfortable. To the colder more dense air allowing the ecu to inject more fuel and create more power as well as less knock and timing being pulled at other occasions. Are just a few of the factors including a winter mix as mentioned.
 

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A lot of factors can go into why your milage has gone down. Definitely stay away from cheap gas with a high ethanol content. STROKERCRATE brings up great points. Hopefully, your car has an oil catch can to keep your intake valves from getting carbon build up. This can also affect mileage.
 

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I don't think OP needs to worry about the Oil Catch Can subject. From what I've personally read, catch can's required when you are running high boost builds/or track builds (ie anything at or above 400whp). Given OP's state is in Midwest, what the catch can will end up doing is getting mostly filled by condensation which would mean one extra chore for maintenance (a lot of people do forget to check oil levels regularly in the catch can which can screw up the car).
Given OP is currently using 87, they're on stock tune, the stock HVAC system should be more than adequate (again based on posts I've seen touching this subject). At the end of the day the best way of preventing carbon build up is either modifying to port injection and/or using TOP TIER gasoline (TOP TIER™ Gasoline Brands) (not sure if this is the latest list) and Oil that has been certified that it can help prevent oil build up (
) (generally from what I've seen Full Synthetic meets said criteria).
Also thanks Strokercrate, I forgot that oil weight could impact it as well. Again it's probably a compounding effect of various things, especially given how much snow is in said photos lol.
 

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Discussion Starter · #12 ·
Not entirely true. If its the same weight then no it won't. But oil weight/viscosity can definitely have an impact on mpg. The lighter the oil the better the MPG. If OP put in a higher weight oil. MPG would drop. But definitely not by 8mpg. Maybe upto 1-2mpg depending on how much more weight.

Many factors can be creating the lower MPG. The colder temperatures alone in the winter. Both from warming the car before driving to defrost the windows and feel comfortable. To the colder more dense air allowing the ecu to inject more fuel and create more power as well as less knock and timing being pulled at other occasions. Are just a few of the factors including a winter mix as mentioned.
There is so much to know in maintenance of the Stang. It is no ordinary car and I wish to take the best care of it that I can. I appreciate your responses to these 'simple' questions. You all are my 'go to' people, since I have no others in my house who know of these things. Thank you :)
 

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You said HAD the oil changed, so there's really no telling what some kid at "Oil Express" put in there. A really heavy weight oil in the winter cold will surely drag down your mileage. Going from a 5W-30 to a 30W-50 in the cold would really put a drag on the engine. Also when it gets cold, the air pressure in your tires goes down increasing your rolling resistance and increasing drag. Got to keep checking those tires for proper pressure. The Tire Pressure monitor is fairly accurate enough to see a drop of 5 lbs, and that is enough to slow down your mileage too.
 

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There is so much to know in maintenance of the Stang. It is no ordinary car and I wish to take the best care of it that I can. I appreciate your responses to these 'simple' questions. You all are my 'go to' people, since I have no others in my house who know of these things. Thank you :)
Tbh it's actually pretty easy. One of the easiest cars I have worked on to change the oil. Even fitted a FMIC in a mini Hurricane. The hardest thing so far has been trying to fit the damn front light bulbs. Jesus christ. Have fun with that one
 

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I don't think OP needs to worry about the Oil Catch Can subject. From what I've personally read, catch can's required when you are running high boost builds/or track builds (ie anything at or above 400whp). Given OP's state is in Midwest, what the catch can will end up doing is getting mostly filled by condensation which would mean one extra chore for maintenance (a lot of people do forget to check oil levels regularly in the catch can which can screw up the car).
Given OP is currently using 87, they're on stock tune, the stock HVAC system should be more than adequate (again based on posts I've seen touching this subject). At the end of the day the best way of preventing carbon build up is either modifying to port injection and/or using TOP TIER gasoline (TOP TIER™ Gasoline Brands) (not sure if this is the latest list) and Oil that has been certified that it can help prevent oil build up (
) (generally from what I've seen Full Synthetic meets said criteria).
Also thanks Strokercrate, I forgot that oil weight could impact it as well. Again it's probably a compounding effect of various things, especially given how much snow is in said photos lol.
I thought direct injection engines need an oil catch can, sorry. I'm not extremely knowledgeable when it comes to this stuff.
 

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I thought direct injection engines need an oil catch can, sorry. I'm not extremely knowledgeable when it comes to this stuff.
You don't NEED one. It's not going to hurt if you don't have one. The engineers at Ford and just about any car maker would put one on as standard if it was that important.

I can tell you I'm FBO with custom tune and had one in for 3 months now DD the car and have nothing more then a thin oily film in the catch can.

I was also told that I must change my cam belt every 10k in the Skyline. They squeek like fuck expensive to maintain insure and fill with petrol and were very unreliable. Yeah na DD'd that ***** no more or less then any other car I had. Driven tonnes more fun and even out performed most cars and 4x4 in several inches of snow every winter. Still have it in storage in the UK been 12 years now. I miss her.
 
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I was also told that I must change my cam belt every 10k in the Skyline. They squeek like fuck expensive to maintain insure and fill with petrol and were very unreliable. Yeah na DD'd that * no more or less then any other car I had. Driven tonnes more fun and even out performed most cars and 4x4 in several inches of snow every winter. Still have it in storage in the UK been 12 years now. I miss her.
Man of culture I see, what trim is your Skyline? GTR? GTST? GTS4?
 

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R33 GTST type M ( all where type M's ) spec 1.5 (Sun roof side skirts and high rise spoiler all standard) and the Velour interia before that changed to the crap stuff. Amazingly the HICAS still worked when I bought her and is absolutely brilliant when it works. I modified her too approx 400bhp all the usual bolt ons and a tune from Rising Sun performance
 
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Discussion Starter · #19 ·
You said HAD the oil changed, so there's really no telling what some kid at "Oil Express" put in there. A really heavy weight oil in the winter cold will surely drag down your mileage. Going from a 5W-30 to a 30W-50 in the cold would really put a drag on the engine. Also when it gets cold, the air pressure in your tires goes down increasing your rolling resistance and increasing drag. Got to keep checking those tires for proper pressure. The Tire Pressure monitor is fairly accurate enough to see a drop of 5 lbs, and that is enough to slow down your mileage too.
The oil was changed at the dealership. NO way I would take my Stang to one of those kinds of places. I use 100% synthentic, year round. And, I had the tires pressured to 32 for the Winter.
The display on the dashboard lets me know if the pressure is varying at all...very handy, too. Thanks for your reply, Jim.
 

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There are so many variables. Ambient temps, drive style, trip lengths, tire pressures. You really need to track it over more than several tanks to get some kind of average. And don't trust the dash, it is notorious for being inaccurate. I typically fill at the same station, usually the same pump, pull the hose when it clicks off (no topping up). I take a picture of the dash (digital) so I get the mileage and the computer economy for that tank, and the engine running time. Cost, quantity and dash info goes into a spreadsheet. Easy to see the variance between tanks and track the average over the long haul.
 
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