0w or 5w-20 for gas mileage?

[Man In Black]

Why don't car companies make lighter (but still strong) cars with better aerodynamics to save gas instead of pouring lighter oil into them?

Actually I guess it is because the American car-buying public doesn't want those kind of cars. They want pickups, SUVs, and sports cars.

It also sounds obvious you can use lighter oil in order to gain fuel economy, but it also appears protection is lost. How can a 20 wt. oil hold up like a 30 wt. or heavier oil as time passes when speeding or pulling heavy loads or when there is a lot of heat, etc.?

 

[Triple_Se7en]

Is the 5W-20 Mobil-1 thinner at operating temps than 0W-20?

 

[Gary Allan]

quote:

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Originally posted by TRDUSA2002:
I would rather sacrafice using a thinner oil for engine protection any day of the week.

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Do you need a 70+ weight oil at ANY TIME in the universe for protection? So if you did 5 mile commutes you would rather spin motor honey instead of the 40 weight that a 5w-20 will be at?

What condition is your engine in to require that high a visc

 

[Clyde65]

Gary, I understand your point about parasitic loses due to higher viscosity, but what about power loses due to friction? Can 5W-20 reduce friction in all engines the same way it does for an engine designed for 5W-20? An oil needs to fill the space completely between surface (A) and surface (B) in order to eliminate friction. This is the reason oils are available in different thicknesses - I assume.

 

[sjlee]

quote:

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Originally posted by Man In Black:
Why don't car companies make lighter (but still strong) cars with better aerodynamics to save gas instead of pouring lighter oil into them?

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They are starting to. In the past the public didn't mind not getting the best possible gas mileage because gas was relatively inexpensive.

One downside to having lighter vehicles is that the ride won't be as smooth over uneven surfaces. On less than ideal road surfaces, you'll also lose traction.

 

[sjlee]

quote:

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Originally posted by TomJones76:
Also, speeding isn't hard on your engine or oil. If you drive fast enough to really tax your engine, you're either driving a vintage VW Bug or you'll lose your license within the week.

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Actually, it's the engine speed (RPMs) that makes the most impact.

 

[b_rubenstein]

Clyde - read this: http://www.iantaylor.org.uk/papers/IMechEFE2000.pdf by a lubrication research scientist.

 

[b_rubenstein]

quote:

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One downside to having lighter vehicles is that the ride won't be as smooth over uneven surfaces. On less than ideal road surfaces, you'll also lose traction.

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Nonsense. Ride quality and traction (related to uneven road surface) are dependent on the sprung to unsprung weight ratio of the wheel/suspension to vehicle and the spring rates and dampening charteristics.

 

[Clyde65]

quote:

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Originally posted by b_rubenstein:
Clyde - read this: http://www.iantaylor.org.uk/papers/IMechEFE2000.pdf by a lubrication research scientist.

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What I found very interesting so far while reading your link is that on page 4, the power loses from valvetrain friction were the lowest with 20W-50 in the Mercedes 2.0L engine compared to 10W-30 and 15W-40. Thanks for the link. I have a lot more reading to do.

 

[Gary Allan]

quote:

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Originally posted by Clyde65:
Gary, I understand your point about parasitic loses due to higher viscosity, but what about power loses due to friction? Can 5W-20 reduce friction in all engines the same way it does for an engine designed for 5W-20? An oil needs to fill the space completely between surface (A) and surface (B) in order to eliminate friction. This is the reason oils are available in different thicknesses - I assume.

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Sure ..but there's some assumption that a 5w-20 is somehow inadaquate for this task. It's mostly irrational in origin. That is, there's no supporting factual basis for the "fear factor".

Somehow ..for at least the past 25 years ..millions of cars have run 5w-30 oils that have sheared to 20 weights and lived to tell about it ...for well over 100k ..even those neglected.

Sure there are different weight oils for different engines/services. Yet we have people towing with 5w-30 spec'd in the manual. Only the duration of use is altered. We have high powered Euro alloy that spec's only synthetics of the 40 weight variety.

..but for your average appliance

...

So, no, you wouldn't "blindly" just say that 5w-20 is the next best thing to sliced bread and will be an "oil for all seasons and reasons". For the vast majority it would be.

Especially the OP

 

[steven88]

wow, this thread came back from the dead...lots of information being thrown around!

Gary Allan, what would you suggest? I'll break it down for you one more time, just so I didn't leave anything out

- Short city (stop & go) miles (about 5 each way)
- Occasional wide open throttle runs (maybe twice, 3x a week?)
- A/c blasting everyday, cuz darn So Cal is hot!
- VQ35DE engine that calls for 5w-30 in owners manual (the owners manual says you can go up to 10w-40 if weather permits)

I've been running 5w-30 oils since day 1 of buying this car...And most recently, I switched over to GC Green 0w-30...I heard this is a THICK oil...even though its listed as 0w, I heard it's pretty far from actually being a 0w...funny thing is, I noticed no drop in MPG with this thicker GC oil...my previous oils were Torco SR-1 synthetic 5w-30...all I remember is the CST @ 100 is 11.1...which I believe is average from 5wt?

What do ya think Gary?

 

[Gary Allan]

My offering is simply due to your service profile. You're surely not anywhere near full warm up in 5 miles ...unless it takes you about 15 minutes to go 5 miles. As far as your occasional sprints ..they will subject the engine and oil to rapid thermal soaking ...but it's all relative to the service profile. You're not flogging your ride like a teenager.

Take someone towing. They're going to elevate their oil temp to above normal levels ..do they "worry"? No, they change it more often because they're up against the other end of this curious debate. They can't, practically anyway, go too much heavier (let's say they use HDEO 5w-40 which appears good enough for diesels that have 250-275F oil temps). They have full confidence in their "thinned to a 20 weight" 40 weight oil and go on in a bliss that can only be duplicated with fairy dust and vaporous mists.


FYI: Someone using a 15w-40 with a 100C visc of 15.8 is running a 7.7CST visc @ 275F. The difference between this oil (a 15w-40) being a (barely) 30 weight and a 7.7 CST 20 weight is 19 degrees F (256F-275F).

Yet ..these same people ..tend to think that REAL 20 weight oil ..not subjected to those extremes in temperatures are destructive (do you see the irrational "fear factor"

).

Here's what I would do. I would do an OCI with the 5w-20 and track your fuel economy. If you see no gains in fuel economy that are truly measurable, then go back to whatever you're using. You're not going to shorten the life of your engine with one OCI. If you DO see fuel economy gains ..then do a UOA to determine if there are any out of whack wear markers. This is the cheapest way to save money (that statement must fall into some literary oddity). That is, it kinda defeats the purpose of trying the new oil if you're spending $20 to find out that it's okay to use ..but doesn't save you a dime in fuel usage. OTOH, if you do save $20 in fuel ..you can go to the trouble of finding out if it's okay to save fuel this way.

 

[TomJones76]

quote:

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Originally posted by sjlee:

quote:

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Originally posted by TomJones76:
Also, speeding isn't hard on your engine or oil. If you drive fast enough to really tax your engine, you're either driving a vintage VW Bug or you'll lose your license within the week.

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Actually, it's the engine speed (RPMs) that makes the most impact.

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I'm trying to digest that.
Your engine is going to heat up based on the power produced; engines don't run at over 210 Fahrenheit because they're being efficient. They run high temps because waste energy from the combustion builds up in the engine.
The power an engine is creating is a variable most closely tracked by gallons per hour being poured into the engine, not by RPM.
If I go 55 and knock my Taurus from 4th (around 1.6 GPH) to 3rd (around 1.9 GPH), there's only a 15% increase in fuel consumption, despite the fact that my RPMs go from about 2K to about 3K, and my cooling system has no trouble keeping up.
If I was busy punching it and cruising along at 120 MPH, my biggest problem would be that I would be burning 7-8 GPH, not that I was in 3rd gear instead of 4th, and to be honest my car wouldn't be running a whole lot cooler if I was running 120 MPH in 4th gear... calculations show I'd be at 6.5 GPH anyway, which isn't a huge drop.
Help me out here. What were you trying to get at?

 

[TomJones76]

by the way, Steven88,

For what you're doing 90% of the time, that 5 mile trip, NO WAY your oil is getting hot... like, no way at ALL. Guys here sometimes say it takes 30 miles before their oil temp hits its stable maximum temperature.
As a result, during those trips, you're actually churning oil that is substantially thicker than *ANY* oil made for passenger cars is supposed to be at operating temperature.
Bottom line, even with 5W20, you're STILL driving to work or school with oil in the crankcase that is thicker than the automaker expected you to be running when you're at operating temp.
With your driving, you have the opportunity for *substantial* fuel savings on a % basis from using thin oil.
On the other hand, you're spending almost NOTHING in gas driving to work/school in that car, so it isn't a huge deal. If you're going broke on gas, it ISN'T your daily commute doing it.
PS-- I think yours is probably expired, but if you're under warranty, STICK TO 5W30.

 

[Man In Black]

quote:

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Originally posted by Gary Allan:
FYI: Someone using a 15w-40 with a 100C visc of 15.8 is running a 7.7CST visc @ 275F. The difference between this oil (a 15w-40) being a (barely) 30 weight and a 7.7 CST 20 weight is 19 degrees F (256F-275F).

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Interesting. So if the engine running 5W-20 was to overheat, there is a very good chance the oil would fail. Since the thicker oil takes more temperature, it can therefore take more heat. Correct?

 

[Gary Allan]

quote:

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Originally posted by Man In Black:

quote:

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Originally posted by Gary Allan:
FYI: Someone using a 15w-40 with a 100C visc of 15.8 is running a 7.7CST visc @ 275F. The difference between this oil (a 15w-40) being a (barely) 30 weight and a 7.7 CST 20 weight is 19 degrees F (256F-275F).

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Interesting. So if the engine running 5W-20 was to overheat, there is a very good chance the oil would fail. Since the thicker oil takes more temperature, it can therefore take more heat. Correct?

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What would make you assume this? Cars overheat all the time and don't experience oil failure ...oil fatigue, surely.

Then again ...we do have a declining level of sensible wisdom among our population ..so sure ..someone will drive overheated engines to the point of seizure. Now can you tell the difference between a seized 20,30, or 40 weight engine

I truly enjoy the "well if you wired C4 explosive to it and slammed a brick wall ...would your 20 weight have the guts to take it?" type stuff.

I have no love for 20 weight oil. If it doesn't serve me in a superior manner to other weight oils ..I would not use it.

But using any higher viscosity than is necessary just has no legit presence in any rational thought process.

 

[steven88]

wait, are you guys tryin to tell me that a 20wt oil will be THICKER than it is when it reaches operating temp? I don't understand, I thought the first # indicates how heavy the oil is when it's cold..and the 2nd # incidates how heavy the oil is when it's hot?

My driving does consist of 5 miles per way...it does take about 15-20 minutes to reach one way...only cuz the stop and go...and heavy california traffic...I sometimes throw in highway miles in there...but it's usually very short itself...if anything, in a tank of 300 miles, I never surpass 100 miles WORTH of highway miles...in other words, I never travel more than 33% highway

 

[Man In Black]

Well I couldn't tell you the difference between a seized 20, 30, or 40 weight oil engine, but it would make sense that the engine with the 20 weight oil would be more likely to seize than the others if the temperature gets hot enough would it not? Oils get thinner the hotter they get. Would not a 20 weight oil therefore be thinner than a 30 or 40 weight oil at the same temperature?

 

[Gary Allan]

No. Yes. Yes ..but not by much.

Are you of the persuasion that would drive a car in an overheated condition? If so ..then no oil will save you from such behavior, correct??

 

[Man In Black]

Gary I am not so sure. Using Mobil 1 as an example, 5W-20 is 8.8 cSt @ 100º C while 5W-30 is 11.3 cSt @ 100º C. That is a pretty big difference.