Possible myths

[Capa]

1) I heard somewhere that if I switch to synthetic oil that my RPM's will go down in correlation with the speedo. Well, I've switched to 0w30 and the RPM's are the same---at 70 mph my RPM is still 2200. Has anyone noticed a change?

2) I also heard that my engine would run cooler on synthetics. The needle is on the same exact spot, however, it might be running 5 or 10 degrees cooler, it is a needle after all. I suspect that the difference is minimal at best.

3) I've also heard stories about increasing horsepower. This one might be true but, again, the increase is minimal (possibly 1% or 2% at best).

4) There are also rumors of better mileage. Mobil 1 Advanced Fuel Economy synthetic only claims a possible 2% increase. This is negligible and would be difficult to verify with the way most of us measure our gas tanks. A 2% increase would mean if I can go 400 miles on a tank, now I can go 408 miles (yeah, not that impressive and very difficult to measure).

5) I've heard that gas mileage drops in the winter. Can someone explain to me why this would be with more oxygen in the air? I've heard rumors of a winter blend of gas. What is this and does all 50 states get it or not and why exactly might it hurt mpg?

 

[JHZR2]

1) Completely wrong, other than MAYBE in a loust-set-up AT that is not locked-up, and even then slight.

An engine is geared, and so the RPM at, say, 60 MPH are the RPM at 60 MPH.

2) The engine may run cooler, the cooling system is designed to maintain a certain temperature. The small difference in temperature may be noted (and maybe not) in oil temp, but definitely not in coolant temp. if your coolant got colder, the thermostat would restrict flow to keep it at the right point.

3) Right, minimal at best - you wouldnt notice it via normal driving.

4) Right, very difficult to measure, and not statistically significant until proven over at least 5-7 full fuel tanks. Still, makes sense, but operating viscosity differences amongst different oils, conventional or synthetic can have the same effect.

5) Number of reasons why it drops, including the fuel blend, longer time to warm up, etc. More oxygen in the air I would not necessarily say, but for a given displacement, e.g. an engine displaced 2.0L, denser air will have more oxygen molecules per volume of air. Volume is not temperature dependent. I believe gas blends vary by state/region, and it seems like these days all areas get 10% ethanol, though don't quote me. WInter gas is, I suppose, a bit more volatile too, so it will aide cold starts, but dont quote me on that either...

And...

 

[PT1]

1) I heard somewhere that if I switch to synthetic oil that my RPM's will go down in correlation with the speedo. Well, I've switched to 0w30 and the RPM's are the same---at 70 mph my RPM is still 2200. Has anyone noticed a change?

Complete horsehockey

2) I also heard that my engine would run cooler on synthetics. The needle is on the same exact spot, however, it might be running 5 or 10 degrees cooler, it is a needle after all. I suspect that the difference is minimal at best.

air cooled engines will run cooler..water cooled are well water cooled
3) I've also heard stories about increasing horsepower. This one might be true but, again, the increase is minimal (possibly 1% or 2% at best).

True but less than .001

4) There are also rumors of better mileage. Mobil 1 Advanced Fuel Economy synthetic only claims a possible 2% increase. This is negligible and would be difficult to verify with the way most of us measure our gas tanks. A 2% increase would mean if I can go 400 miles on a tank, now I can go 408 miles (yeah, not that impressive and very difficult to measure).

very minor usually span>

5) I've heard that gas mileage drops in the winter. Can someone explain to me why this would be with more oxygen in the air? I've heard rumors of a winter blend of gas. What is this and does all 50 states get it or not and why exactly might it hurt mpg?

 

[tig1]

In the old days,Iv'e used synt. oil for 32 years, a carbarated engine would decrease in RPM at say 65 MPH, by as much as 75 RPM. I saw it on every engine I put it in. But with computer controled engines there will be no differance.

The crank case temp. may decrease at times with synt as it reduces friction a tad. However your water temp most likely will not change on the gauge.

Also years ago synt. oil would increase MPG over dino noticeably but not so much anymore because dino has improved so much.

 

[lenjack]

In the old days,Iv'e used synt. oil for 32 years, a carbarated engine would decrease in RPM at say 65 MPH, by as much as 75 RPM. I saw it on every engine I put it in. But with computer controled engines there will be no differance.

Can't happen!!!

 

[Nyquist]

Originally Posted By: JHZR2
Volume is not temperature dependent.

Careful! Volume IS directly proportional to temperature under constant pressure and mass according to Charles's Law and the Ideal Gas Law.

 

[SlowGT]

Originally Posted By: tig1
In the old days,Iv'e used synt. oil for 32 years, a carbarated engine would decrease in RPM at say 65 MPH, by as much as 75 RPM. I saw it on every engine I put it in.


presumably all with ATs? the only other explanation could be the possiblity of some oil on the tach drive causing a little slippage...

you could fill it up with peanut butter and it won't change the relationship between engine RPM vs MPH. at least not with a stickshift. can't speak for an AT cause convertor slip is still a mystery to me.

 

[JHZR2]

Originally Posted By: Nyquist
Originally Posted By: JHZR2
Volume is not temperature dependent.

Careful! Volume IS directly proportional to temperature under constant pressure and mass according to Charles's Law and the Ideal Gas Law.


Volume of a specific mass or moles of matter is. Displaced volume by an inanimate object is not. A 2L engine will displace 2L of volume whether at 0F or 200F. Thus a 2L engine, for example, will move more molecules of denser air (yes, on a mass basis of air, there is less volume) in displacing 2L than of less dense air... Mass changes, more oxygen present, but still 2L of volume is displaced.

 

[Nyquist]

Originally Posted By: JHZR2
Originally Posted By: Nyquist
Originally Posted By: JHZR2
Volume is not temperature dependent.

Careful! Volume IS directly proportional to temperature under constant pressure and mass according to Charles's Law and the Ideal Gas Law.


Volume of a specific mass or moles of matter is. Displaced volume by an inanimate object is not. A 2L engine will displace 2L of volume whether at 0F or 200F. Thus a 2L engine, for example, will move more molecules of denser air (yes, on a mass basis of air, there is less volume) in displacing 2L than of less dense air... Mass changes, more oxygen present, but still 2L of volume is displaced.

Just wanted some clarification to that statement since it seemed ambiguous between an actual physical property of air vs the engine displacement. I'm all for solid fundamental physics and chemistry

 

[labman]

By the way, it is absolute tmeperature, starting at -459.69 F. Thus an ideal gas expands by a factor of 560/460 in going from 0F to 100 F.

 

[EagleFTE]

Originally Posted By: JHZR2
1)

2) The engine may run cooler, the cooling system is designed to maintain a certain temperature. The small difference in temperature may be noted (and maybe not) in oil temp, but definitely not in coolant temp. if your coolant got colder, the thermostat would restrict flow to keep it at the right point.

Right, and as PT1 noted if you were to use different oils in an air cooled engine (as many of us do) you will see some decrease in temps. Sometimes by a surprising amount with the GIV and GV oils. This has been demonstrated quite a bit by monitoring the oil temp gauge on near identical runs. All that said in a liquid cooled engine I suspect that in certain localized areas or components of the engine (hot spots) these oils may reduce those local temps in hot spots but you won't see that much of a change on your coolant gauge as the overall system is working to maintain a semi constant temp via the thermostat. But I have to admit I have seen some decrease in deflection of the needle on some past cars that I attributed to what is in the crank case.

 

[NHHEMI]

I heard somewhere that if I switch to synthetic oil that my RPM's will go down in correlation with the speedo. Well, I've switched to 0w30 and the RPM's are the same---at 70 mph my RPM is still 2200. Has anyone noticed a change?

No. Your RPM's are a function of tire size, axle gear ratio, and transmission gear ratio

2) I also heard that my engine would run cooler on synthetics. The needle is on the same exact spot, however, it might be running 5 or 10 degrees cooler, it is a needle after all. I suspect that the difference is minimal at best.

Yes, this is 100% possible and I have seen it myself when using a gauge with numbers or a digital gauge where you get a more accurate reading than the factory gauge. It can drop engine and coolant operating degrees by reducing friction. While a water cooled engine does have a thermostat the actual fully warmed up operating temp of the engine and coolant is not exactly that temp at which the t-stat opens. You can have a 160, 180, 190, etc... rated t-stat BUT all that means is that is the temp at which it opens and starts letting the coolant flow.

The actual operating temp of the engine is much higher. Especially on today's modern engines which are designed to run at well over 200 degrees. So, synthetic oil can reduce the temp by reducing friction because there is a lot of difference between the t-stat's opening temp and actual operational temp of the engine. The engine runs cooler and thus the coolant does not get as hot as a result.

You usually need a temp gauge with more detail than a typical dash gauge on a vehicle to notice it. However, when I make the swap to RP synthetic oil and also use their coolant additive I actually notice a difference on the factory dash gauge. Just oil and it is not noticeable on a actory gauge though.

3) I've also heard stories about increasing horsepower. This one might be true but, again, the increase is minimal (possibly 1% or 2% at best).

Yes a small HP increase is possible, by reducing power robbing heat and friction, but it will not be an increase that is noticeable to you. If you swap over your entire drivetrain to synthetics you can see a small power bump( synthetics do not add HP they free up existing HP )and increase in smoothness so you might notice it a little for a day or two before you get used to it and no longer can tell.

4) There are also rumors of better mileage. Mobil 1 Advanced Fuel Economy synthetic only claims a possible 2% increase. This is negligible and would be difficult to verify with the way most of us measure our gas tanks. A 2% increase would mean if I can go 400 miles on a tank, now I can go 408 miles (yeah, not that impressive and very difficult to measure).

As with the HP question above I will answer yes. Just adding synthetic oil can give you a small MPG gain but it will more than likely be a barely noticeable( if at all )MPG increase. Swap your entire drivetrain over however and it can show a real gain. I have seen 1-2MPG gains by swapping an entire drivetrain on 4WD trucks over to RP fluids( not pimping RP - just saying that is what I use ).

5) I've heard that gas mileage drops in the winter. Can someone explain to me why this would be with more oxygen in the air? I've heard rumors of a winter blend of gas. What is this and does all 50 states get it or not and why exactly might it hurt mpg? [/quote]

Yes, MPG does go down in winter( depending on where you live )for a variety of reasons. If you live in a cold climate like I do in NH the morning( or even all day )temps can be well below freezing or even zero for months( it has not broken 30 degrees here for over 2 weeks ). It takes longer for the vehicle to warm up and while it is getting there there is more fuel being dumped in( cold vehicle = more fuel / warm vehicle = less fuel being added ). If you let the vehicle sit and warm up you waste a lot of fuel. Even if you start driving pretty quick it takes longer for the drivetrain fluids to heat up. Until they do they are thicker and thus it takes more power( and thus more gas )to get the vehicle moving. All add's up to more gas being used.

Yes, winter blend gas generally is highly oxenegated. Not all areas see it( I do here in New England )but those that do will see a drop in fuel economy from it. It is done for emmissions reasons but because of it's different chemical make up vs summer blend fuel it results in a less efficient product.

The reason for summer and winter blend gasoline is the Reid Vapor Pressure of the fuel. RVP deals with the volatility of gas. The more volatile the gas is the more likely it will evaporate as the temperatures rises. Evaporating gas adds to ozone and smog levels so they formulate it differently for the high temps of summer and low temps of winter( in areas with those conditions ). Summer blend gas has a low RVP and is less likely to evaporate when compared to the high RVP winter blend.

Summer blend gas contains more energy than winter blend gas. You get more power from the summer blend gas and thus less pedal is needed to achieve your desired speed so you get better MPG. Winter blend gas, due to it's different chemical composition vs the summer blend, produces less energey and thus you need more pedal to achieve speed so you use more fuel.

NOTE - according to the EPA winter blend gas produces 1.7% less energy( per whatever unit the measure it by???)than summer blend gas.

Couple the above with the longer warm up time required and the two add up to a pretty significant drop on fuel economy when winter blend gas is being sold. I see almost a 2 MPG drop during winter.

 

[Capa]

NHEMI,
thank you for the elaborate response on winter blended fuels. This was the one area where I was completely clueless. I don't know if we get that type of fuel in Oklahoma. We get below freezing temperatures but almost never below 0. I seem to get less gas mileage in the summer than in the winter, but that's because of the AC running all of the time. I will say that when it is cooler my car seems more peppy than when it is hot---but the butt dyno can't always be trusted.

 

[Jim Allen]

When my area finally went to the mandated summer blend E10, I lost one solid MPG. My Shell distributor here says that they raise the RVP for winter by adding butane, or some other similar volatile component. to help the fuel ignite better in a cold engine. that reduces the specific heat of the fuel and MPG.

 

[Capa]

Yeah, I think with the 10% ethanol mpg drops around 4-5%. In Oklahoma the gas stations that have it are required by law to have a sign that clearly indicates it. That's what I put in my van. However, we also have a few gas stations that advertise no ethanol and that's where my GS400 gets its premium fuel.

 

[gizzsdad]

Originally Posted By: tig1
In the old days,Iv'e used synt. oil for 32 years, a carbarated engine would decrease in RPM at say 65 MPH, by as much as 75 RPM. I saw it on every engine I put it in. But with computer controled engines there will be no differance.


I could possibly see this with much older automatics. But with the advent of lock-up torque converters I'm sure no change would be seen these days.

 

[mechtech2]

1. You might get a change in RPM/speed with an older automatic trans without a lockup torque converter when using a different fluid. It would be a minimal change - tough to note.

2. Fresh clean oil could feasibly make an engine run cooler. Thinner oils of any type run cooler due to less shearing and better heat transfer away from metal parts. There is less residual oil film on parts to retain heat as the engine is running, as well.

3. More HP comes with thinner oil. This is why NASCAR cars often use 5W oil for qualifying. For a dino/synth comparison, it would be up to the additives each oil contains.

4. M1 AFE oil is good for fuel economy because it is THIN, not because it is synthetic.

5. Gas mileage drops in the winter because your coolant sensor reads colder longer, and the computer calls for a richer mixture to the injectors for a longer time until warmed up. Oil and lubes are thicker when cold - a lot. This makes much more drag. This includes the engine, trans, differential, wheel bearings, C/V joints, power steering, etc.. Also, many of us idle more in winter, either to warm up the car, or idling while scraping snow and ice off of it. Rolling resistance is increased with cold and less flexible tires. Air resistance is greater at highway speeds - [not a factor at slow speeds]. If you DO step on the gas all the way, the denser oxygen will allow a bit more power, and more subsequent fuel use than in summer.