why am i getting worse gas mileage?

[efgh]

I put 265-r-75-16s on my truck, it had 245s on it before. Acording to the GPS the speedo was off 1/10 of a mile in one mile. So in a 100 miles it was off -10 miles. mileage on the speedo is the same when I fill up with gas, gallons the same as it was before so I think I am getting more miles per gal.

[Macgyver55]

All I'm saying is i have not seen an issue with cottage cheese looking oil. I figure I have done approximately 22,000 oil changes over the years. If mixing or compatibility were an issue I would have had to run into it by now?

Add another 25,000 or so for me over my 35 years and I havent seen it yet either. In fact, the worst case of sludge I've ever seen was with a regular Pennzoil user. You could scoop it out wit a spatula.

Its pretty common for mileage to drop some with new tires, especially if they are taller. Rotating mass takes more throttle/effort to get rolling, and even a small difference in circumference will show up as lower mileage because it is turning less revolutions than the originals would over the same distance. Throw in more drag due to more surface area on the road and it all adds up. Even going from a road tire to an aggressive tread of the same size will cut mileage.

[Dave S]

I made the jump from a P245 to a P265 and went from a B to C load rating and lost atleast 3 mpg overall.

[tonkapat]

Also remember that tires of different brands (the same size)get different mileage.

[tonkapat]

I made the jump from a P245 to a P265 and went from a B to C load rating and lost atleast 3 mpg overall.

Thats not enough info to establish your tire sizes. A 245 could be larger than a 265

Example 265/50 vs 245/70

[CAMAN]

I'm not saying that the problem didn't occur, I just have a hard time believing the oil was an issue. What brand of oil, what kind of car, The integrity of the motor, the service life, driving habits, etc.

When I bought my truck the dealership gave me 6 free oil changes, after using them up I decided to change my own oil, and so I didn't have to do it all the time I switched over to Valvoline full synthetic. I drained the oil, changed the filter and added the full synthetic. About 1000 miles later I checked the oil and it was slightly milky, didn't worry too much since I had just driven it, but kept it in the back of mind. I kept an eye on it for the next 1000 miles and it got worse and worse. Checked the coolant, nothing wrong there. I decided to drain it and lucky I did, it came out in blobs, not a steady stream like I'm used to. Called a 'car guy' buddy and told him the issue and he asked if I flushed the old oil out by filling with full synthetic and running for 100 miles draining and refilling. "Should I have?" he says "YUP!!!". Tells me to go pick up a can of motor flush ($30) and use it.

Since then I have had ZERO issues with the oil and I frequently run 10,000 miles between oil changes on my full synthetic now.

I guess I can't be 100% certain it was the oil but with it never happening again and the timeframe in which it did happen my conclusion is pretty good that it was the oil.

So after all that, I was out $30 in oil that turned to cottage cheese, $30 in motor flush, another $30 for the flushing oil, and finally another $30 for the final fillup. Not to mention 3 oil filters at $5 each. $135 later I finally had a complete oil change. Thankfully I saved that much from the free oil changes the dealer gave me.

I may be the one in a million guy that this happened to, but I'd rather other people learn from my mistakes than they need to go through same the hastle I went through.

[fishnhuntnboy]

Thanks for all the replies guys. The tires i use to have were P26570R16 and switched to P26575R16. So its just a taller wall by a couple inches. I turned my gps on and when i am at cruse at either 65 my gps says 68 and at 75 its 78. So my spedomiter shows that I am going 3 miles slower than my gps. So now i kno im going faster than what i thought i am. With the oil i never did the flush and i dont think i have noticed a difference. I guess it wouldnt be a bad idea to look at it. One thing i did notice is that it was a little milky under the cap but was told that its common in the winter because of the colder temps and if you drove a short distance and caused a little moisture there. Now I am hoping that all my oil isnt the milky [PoorWordUsage] and will be checking prolly tomorrow.

Also i didnt kno that it was ok to switch back and forth from synthetic to conventional oil. I always thought once you switch you cant go back to conventional. Even tho i switched i am going to stay with the synthetic. my truck has 124,000 miles on it and am try to take care of my truck as much as possible so it will go a looooong ways. Right now i have got mobil one in, is there a good high mileage oil? I kno amsoil is great but idk if i can fork out the dough for that right now.

thanks for all the info

[fishnhuntnboy]

ok so after further inspection...a little bit, i just went and looked under the oil cap and it is full of filthy milky gunky [PoorWordUsage]. Now if its that bad under the cap, will it be that bad through-out the engine? Should i be conserned or is it just a winter thing?

[CAMAN]

ok so after further inspection...a little bit, i just went and looked under the oil cap and it is full of filthy milky gunky [PoorWordUsage]. Now if its that bad under the cap, will it be that bad through-out the engine? Should i be conserned or is it just a winter thing?

Yup, same thing happened to mine.

[Dave S]

Thats not enough info to establish your tire sizes. A 245 could be larger than a 265. Example 265/50 vs 245/70

All other stats stayed the same. Only one that changed in size was 245 to 265. Sorry I didn't clarify earlier.

[Dave S]

Thanks for all the replies guys. The tires i use to have were P26570R16 and switched to P26575R16. So its just a taller wall by a couple inches.

If my math is correct, your increased sidewall height is less than an inch (13.25MM). I'd trust airjer or MacGyver before me though.

[Macgyver55]

Here is from a tire size calculator I use. Gives all the numbers you need.

Original tire 265/70/16

Sidewall: 7.30 in

Radius: 15.30 in

Diameter: 30.61 in

Circumf: 96.15 in

Revs/mile: 658.95

New Tire 265/75/16

Sidewall: 7.82 in

Radius: 15.82 in

Diameter: 31.65 in

Circumf: 99.43 in

Revs/mile: 637.23

[spearchucker]

When I bought my truck the dealership gave me 6 free oil changes, after using them up I decided to change my own oil, and so I didn't have to do it all the time I switched over to Valvoline full synthetic. I drained the oil, changed the filter and added the full synthetic. About 1000 miles later I checked the oil and it was slightly milky, didn't worry too much since I had just driven it, but kept it in the back of mind. I kept an eye on it for the next 1000 miles and it got worse and worse. Checked the coolant, nothing wrong there. I decided to drain it and lucky I did, it came out in blobs, not a steady stream like I'm used to. Called a 'car guy' buddy and told him the issue and he asked if I flushed the old oil out by filling with full synthetic and running for 100 miles draining and refilling. "Should I have?" he says "YUP!!!". Tells me to go pick up a can of motor flush ($30) and use it.

Since then I have had ZERO issues with the oil and I frequently run 10,000 miles between oil changes on my full synthetic now.

I guess I can't be 100% certain it was the oil but with it never happening again and the timeframe in which it did happen my conclusion is pretty good that it was the oil.

So after all that, I was out $30 in oil that turned to cottage cheese, $30 in motor flush, another $30 for the flushing oil, and finally another $30 for the final fillup. Not to mention 3 oil filters at $5 each. $135 later I finally had a complete oil change. Thankfully I saved that much from the free oil changes the dealer gave me.

I may be the one in a million guy that this happened to, but I'd rather other people learn from my mistakes than they need to go through same the hastle I went through.

If this is true, it wasn't the lack of flush that caused your problems. With a flush, how do you get all the flush out? You can't! Whenever you switch oils you are going to have a small amount of oil left over to mix with the new. You can switch oil every day if you want. It may not be the best idea, but it won't hurt anything.

[spearchucker]

ok so after further inspection...a little bit, i just went and looked under the oil cap and it is full of filthy milky gunky [PoorWordUsage]. Now if its that bad under the cap, will it be that bad through-out the engine? Should i be conserned or is it just a winter thing?

The milky colored film is condensation. This is normal in a MN winter. It will be worse the colder it gets and if you take short trips because the oil doesn't heat up to burn off the moisture.

[mechanico]

that's a fact spearchucker. sometimes it looks like moche. I'm still wondering about the clumping when caman draied the oil. i've never seen that, except when I clean out my oil pans with acitone...that clumps. ?

[spearchucker]

that's a fact spearchucker. sometimes it looks like moche. I'm still wondering about the clumping when caman draied the oil. i've never seen that, except when I clean out my oil pans with acitone...that clumps. ?

I'm not calling you a liar, but SynPower is good oil. Any oil isn't going to cause that unless something else was going on.

[fishnhuntnboy]

Here is from a tire size calculator I use. Gives all the numbers you need.

Original tire 265/70/16

Sidewall: 7.30 in

Radius: 15.30 in

Diameter: 30.61 in

Circumf: 96.15 in

Revs/mile: 658.95

New Tire 265/75/16

Sidewall: 7.82 in

Radius: 15.82 in

Diameter: 31.65 in

Circumf: 99.43 in

Revs/mile: 637.23

So with this my guess is that tires are not my issue with getting worse mileage. Now i have another topic on here with my #2 cylinder missiring. Will that cause me to lose mileage? It seems to be happening more and more often and i did replace all plugs and that coil pack cause all my plugs have there own coil pack.

[mechanico]

I agree spearchucker. You're right. The milky stuff almost has to be water condensation. It happens here in the mid-west too when you make lots of short trips. That's the hardest thing you can do to your car... I was just trying to find out what the "clumping" thing is.

I always use valvolene, but I don't use the synth. It cost too much, so I have only limited experience with it. All I see when I change the oil is black nasty smellin' liquid. I have, and have had several cars approaching 200k miles, and the ones I used valvolene in performed the best with the least chatter from the valve train.

[Macgyver55]

Now i have another topic on here with my #2 cylinder missiring. Will that cause me to lose mileage?

Absolutely!

Is this on the same vehicle?

[Scott K]

There you go!

[mechanico]

hey fishnhuntnboy, ya know you have at least three topics goin' on. anyway, here's a link for tire measurements: http://www.miata.net/garage/tirecalcold.html

i used it first to see how wide i could get tires and still match the circomference...which is what you want to know. sorry, i didn't read the whole thread so someone may have already told you that the taller the tire is, the more power it takes to turn it. so you can drop your gas mileage by putting taller tires on it. it tells width, diameter and circumference and compares it to another size. kinda cool and makes it simple

[skolfoppa]

Problem solved. A misfiring cylinder trumps slight tire variations. Good luck. Skol.

[spearchucker]

Get an injector cleaning if the miss stays on #2 after coil swap.

[fishnhuntnboy]

I will have to move the new coil pack that is on that cylider to another and see if i got a defective one or if it is something else. Im still trying to put my finger on it on whats causing it to misfire. I hope i can figure it out this weekend. I have tried the fuel injector cleaner and it doesnt seem to work. Maybe use it more often like every other fill up and see what happens?

[PurpleFloyd]

Tire width and tread pattern can also have an impact on gas mileage. Wider tires can increase the rolling resistance ( I believe that is the term) and thus take more power to turn as compared to a thin tire.

Some of the new generation rims like 22's and 24's get by with a very short sidewall height which reduces rotational mass and keeps the circumference down compared to a tire with a traditional sidewall height on the same rim.

I would agree with the guys above that the culprit causing the cottage cheese look in oil would be a contamination issue and not an oil compatibility issue.