Fuel Economy Analysis...

[N0DIH]

My Pontiac 455 from a 70 Hearse had a 7 blade tight flex fan on it, at 2500 rpm it was still biting hard. Roared like crazy. But kept it cool.

My question is still, how much of what your thinking on oil is just oil company brainwashing? Slick 50, Amsoil and Mobil 1 and the like have brainwashed (you know, like you HAVE to change your oil every 3000 miles...) everyone into thinking that at cold start you are running your engine dry and it is self destructing. In reality, is it? The big semi's run 15W40 year round, they crank slow too, so the pump is going slow, and it is pumping oil to a LOT bigger crankshaft and rods and just plain pure volume than our puny ittle car engines. In the Army we ran 15W40 year round, even in the 6.2L diesels, and these engines would go a week before they would crank, so they soaked cold in the winters of Germany and those engines run in there for 10-20 YEARS with that sort of use, not even high miles. They go 500K to 1M mile overhauls (Army trucks would go 200K or so on overhauls). So, why do we need something so much better (thinner)? This is starting to sound like the oil conspiracy theory!!

My oil pressure gauge on my 301 Turbo took around 2 seconds to read 80 psi at 0F with 20W50. 80 psi! It had to take time to build up, so that means 40 psi in 1 second, 20 psi by 1/2 second. Works for me. Do I need something that flows FASTER than that? Your engine does not drain its oil out. The oil gets there FAST, when it is cold, how long is the oil light ON after you crank it? That is oil pressure below 6 psi. The galleries don't empty, they keep some oil in them, and the oil pupms are positive displasement pumps, so if they are turning, they are moving something. Not like a water pump, more like a roots blower. The owners manual doesn't say that the cars warranty is void if you run the wrong weight oil for that temp range does it?

So, in reality, how fast do you need it? Only our ex resident expert can tell. I know I mentioned in in posts (spars?) with him on it.

How much of the oil specs are for fuel economy vs for engine wear? We don't know. And unless you work for a car company, likely no one will ever know.

Our old expert said in the oil pump blow off tests they measured no block wear with the spec'd oils going from a cold soak (12+ hours @ -20F or so) from cold crank to redline in a second. Honestly, if it is that good to protect an engine, why not leave it alone? I might go 10W30 for some testing of fuel economy for the winter, but I haven't decided yet. I was pondering the 5W40 Rotella T, and see if there is any validity to the claims of better fuel economy, as at hot temp it is still a 40W. So that keeeps one variable the same.

Originally Posted by BluEyes

It's the cold start lubrication I don't like there. 15W is really thick on those cold mornings and doesn't flow really well. Being as the vast majority of engine wear is right at startup, that 15W is going to take awhile to get around everywhere.
On another car that I have run 5W30, 10W30, and 20W50 in, I definately saw the oil pressure rise faster with the lighter oils. The oil pressure sender on this car is first thing in the oil path after the filter, so I hate to think how slow pressure was to build further down the line...
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[vlrench]

This is interesting stuff, I am greenbelt also...

I was thinking about other variables that were not mentioned such as:

Air Cleaners (K&N makes some claims)
Different Thermestat temps
Engine Timeing

The next items would be a little harder to do, but I think they do effect mpg. I know drag racers adjust this stuff, so there has to be something here....

Front end allignement (toe in or out, but keep within specs)
Shift points
Brake adjustments (effects safety, so I wouldn't mess with this)

The ultimate goal would be to come up with a ultimate set up that generates the best mpg. Each change may effects mpg in a small way, and my feeling is that all of these adjusments together may make a large improvement.

Keep up the good work.

[N0DIH]

K&N or one similar is next on the agenda, haven't pondered much on thermostats, and being this is a LT1 and the ECM controls the works, I don't get much control of timing or shift points. Being I have a opened up air box now, it would be interesting. Local Walmart even carries them now. They were carrying the Air Hog by Fram, but now are not. Anyone have any opinions on the 2 to compare?

My alignment is needing to be checked. I can't compare my way to an alignment rack easily (maybe I can calc it), but I use 2 7 foot aluminum bars as straightedges to give me killer resolution on my toe settings. For me, 0.02 degrees toe in (as the Hunter rack said) was around 3/16" toe in @ 6 foot distance. So my resolution is pretty good. But it is worthy to add to my DOE. I need to write it up formally.

Am I using the best chart to look at it? I can send you my Minitab project if you want to look. I am updating the charts everytime I fill up, so it is ongoing.

Another thought would be to get LT1 Edit or the other PCM editor and increase timing to force 92 octane, and run it for a while, say 6000 miles. Enough to get a decent sample.

My concern is that ambient temp is changing seasonally and that my data might get some error to it. I track temp, so it is one of my variables. It doesn't ahve a huge impact though, interestingly enough. It might if I drive shorter trips.

[N0DIH]

Another plot. Scatterplot of MPG vs temp, grouped by AC on/off.

The MPG was climbing until AC got turned on. So overall over the course of the summer, mpg from cold to hot remained more or less the same.

Further proof that AC does hurt mileage.... (But we all knew that...)

[N0DIH]

Yet another analysis to look at.

Trying to make a correlation of Ethanol fuel vs not Ethanol, vs temperature in respect to mpg.

Interesting. It seems as temps get hotter, Ethanol tends to get better mileage, while worse at low temps. Where gasoline seems to get better cold, and worse as temps increase.

BUT, note that I do not have a lot of Ethanol (E10, not E85!) fuel usage in my car when hot. As the summer hit, gas prices where there was no Ethanol were more stable, so I filled up there exclusively.

So the mix here may be somewhat tainted.

I have a vague understanding on why fuel economy testing is somewhat difficult. There are SO many variables, it is hard to tweak one and keep all other things constant. Even from day to day, temps, pressures and humidity changes. You would need a fantastic environmental chamber that would be able to control all those variables to be more definitive on your tests and results.

I will continue to do the best I can (assuming anyone cares....) and post my findings and theories (as warped as some may be...).

[N0DIH]

Well, started next experiement. 5W40 Rotella T. I know, the old bobster would be ragging on me. For me, it is soley fuel economy experiment. With all the data I have so far, what will it do? Soon I am going to try a low restriction air filter like K&N, Amsoil, etc. I have looked at an Air Hog and they look like they would pass more dirt than a vacuum cleaner with a hole in the bag. You can SEE the holes in it that are big enough to see significant light through. I won't subject my engine to that. Anyone have opinions on the K&N when held up to a bright light? How many holes do you actually SEE the light through?