Can Oil Improve Your Fuel Economy?
We had been using Mobil One 10W30 in our Tundra.

The Tundra has a recommended viscosity of 5W30 but we had gone to 10W30 since our supercharged engine puts a bigger load on the engine’s bearings. This also means that our oil choice has more viscous drag than stock so a change of oil might make a bigger difference.

Our super low friction oil is Idemitsu ZEPRO 0W-20. This blend of energy saving Idemitsu oil is fortified with Molybdenum which protects against wear.

ZEPRO 0W20 had been formulated based on Idemitsu’s rich history and knowledge of developing the first factory fill 0W20 for Hondas and the Sky Active powered Mazdas. As we stated before, this oil was our power champion in our last dyno test.  It was designed for cars using start-stop technology, the feature that shuts off the engine at lights to save fuel.

Since a lot of an engines wear occurs during starts due to the engine running momentarily with low to no oil pressure as it cranks up to speed, the moly works to provide extra film forming lubrication during those times. We figured that the moly would also work great to protect engine parts under hard use and for performance applications.  ZEPRO 0W20 is a high-quality synthetic and has the normal full complement of friction modifiers and extreme pressure additives in addition to the moly to provide great lubrication even with the extremely low viscosity.

For our fuel economy test, we first did a baseline test of driving the Civic and the Tundra by driving over 1000 miles of combined city-highway driving, trying to keep the driving cycle consistent in everyday commuting to and from the office. In addition, we racked up over 300 towing miles in the Tundra.

In our baseline, the Civic did 27.2 MPG while the Tundra averaged 12.2 MPG in regular driving and 9.95 MPG while towing.

With our baseline established we changed the oil to ZEPRO 0W20 and drove another 1000 miles on both vehicles and did just over 300 tow miles on the Tundra.

The results were impressive, Civic averaged 28.7 mpg, a 6.7% improvement! The Tundra averaged 13 mpg, a 6.3% improvement!  In Towing the Tundra averaged 10.8 mpg for a fuel economy improvement of 8.3%.  This is a really impressive gain from just an oil change.

As a control, we put ZEPRO in a new late model Civic for its first oil change, replacing the factory fill oil.  In this case, there was no change in fuel economy since ZEPRO is the Honda factory fill.

We also analyzed the value of going to Idemitsu ZEPRO 0W20.  When compared to Mobil 1, a typical synthetic oil, Idemitsu’s street price of about $35 for 5 quarts vs $22 for the same quantity of Mobil 1 is definitely more expensive. However, depending on what sort of mileage your car gets, that price difference is made up in 3 to 6 tankfuls of gas. After you go through that much fuel, you are putting money in your pocket as you have amortized the cost difference between the oils and contributing less to pollution if that matters much to you.

We did have some concerns about running such a thin oil in our high performance, hard use Tundra and we did notice a slight difference in a lower hot idling oil pressure on the factory oil pressure gauge but the Tundra seems ok so far after about 3000 miles of use.  We were also concerned about an increase of oil burning with the low viscosity oil but we have not seen an increase in oil consumption on either vehicle.

With great gains in both power and fuel economy, we are very impressed with Idemitsu ZEPRO 0W20.  We can definitely recommend it for any late model car designed for low viscosity oil. For older vehicles, as long as oil pressure can be maintained, ZEPRO would also be a great oil to consider.


Idemistsu Lubricants 



  1. the civic test isn’t really fair comparing a dino oil vs a synthetic oil… same with the tundra going from a 10W-30 to a 0W-20… its basically a rigged test.
    a real test would be to compare it to other synthetic 0W-20 oils. for an even better picture you can also compare it to Mobil 1’s “Advanced Fuel Economy” 0W-20 since the ZEPRO is branded “ECOMEDALIST”.
    I know it sounds like I’m a Mobil 1 fanboi, they’re just the only other brand that makes eco oil. Personally I don’t use Mobil 1, I go for max protection over max eco. I’d rather know my engine is getting good protection over saving 2-4 bucks at the pump (assuming your 3-6 tanks to make up the 22 to 35 dollar price difference holds true)

    basically what I’m saying is lets compare apples to apples and not apples to oranges and tangerines

  2. Rigged is a matter of your opinion. We are comparing the Idemitsu oil to a high-quality mineral oil like what would be typical of what someone would put in an old Civic. We even did a cost breakdown analysis of when your break-even point would be.

    We did test Royal Purple for power gains on the Civic and it did help but not nearly as much as the Idemitsu oil. You can search and find that article here for both power tests. Also, the Mobil One oil in the truck is what we used and we are testing the gains over that oil. We are testing the gains of what a typical user might experience when switching to the Idemitsu oil. A rigged test is if we lied about what the comparison was.

    We also don’t know what the wear and protection differences are, we didn’t test that and that is a difficult test. You might assume, less friction equals less wear. The Idemitsu oil has some moly based EP additives that are formulated help cars with the auto start/stop function wear less. A lot of wear occurs during starting due to the engine running with little oil pressure and the Moly is meant to reduce this. We talked about this before so it is an assumption that this oil has less protection. I don’t know either way. If I was running a late model NA car in a close to stock race class, I would not hesitate to run this stuff under race conditions.

  3. maybe rigged is too strong of a word, but its definitely not apples to apples. I didn’t mean rigged as in cheating, I meant rigged as in predictable result. I’d expect a similar result from a test between a dino 5W-20 and whatever other brand high quality synthetic 0W-20 oil. maybe not to the same degree, but who knows, maybe even better from other eco focused synthetic oils. but I could have told you which oil would perform better just knowing the weights and dino or synthetic without knowing which brand is which.

    the typical civic owner… sure, so it makes a bit more power and gets a little better mpg. but whats to say thats coming from specifically the ZEPRO oil and not the fact that you’re going to a synthetic oil… or that there aren’t better suited oils out there to get even better mpg than the ZEPRO. and I only saw the cost breakdown break even point for the Tundra when comparing to Mobil 1 cost, not the cheaper dino oil cost. Although based on the math it should still end in favor of the synthetic oil.
    as for the truck, you compared a 10W-30 vs a 0W-20… again, sure maybe typical owner… but not apples to apples… you could have tested it against a 5W-30 ZEPRO… which would have been a much closer test

    I wasn’t really saying that ZEPRO “is bad” for the engine, just that its focus is mpg and hp… I prefer and oil which has the focus of engine protection. I’m not willing to take that risk

    as far as royal purple goes, I learned that lesson the hard way on an RSX my sister owned since new and used royal purple from prolly about 10k or so. by 80k it was eating more than a quart of oil per 1000 miles… mostly highway commuting miles too. thats not typical of a K20. I bought a used RSX years later with over 100k on it and it ate less than a quart of oil every 3k or so with a few track days on each oil change. A few of my friends has similar results in other cars. I’m not saying that ZEPRO is the same charlatan act (well maybe not charlatan, I don’t remember their ads saying anything about engine protection, just hp gain) as royal purple, but I’ll let someone else be the guinea pig for this one while I use normal synthetic oil focused on engine protection.

    that being said, I’d love to see an apples to apples test of the ZEPRO vs another synthetic eco oil of the same weight (not royal purple)

  4. The power gains are more than a little power, 11% it’s more than what a typical cold air intake might do and a little less than a set of headers. The break-even point for mineral oil like we used in the Honda would be something like 5 to 8 tanks of gas.

    Although not typical, many K20’s experience oil consumption like your sister’s car does. Did you perform a compression and leak down test or just assume the problem was some sort of wear issue with the rings and cylinder walls? Did you do an oil analysis? That would be interesting.

    A few years ago, a major manufacturer of racing engines including F1 stuff did extensive testing of many oils and Royal Purple was among the highest performing in their tests.

  5. well its 11% between a dino oil and a synthetic oil… (you’re talking civic only right? I don’t remember seeing a power test on the Tundra) I’m sure that gain would be smaller if compared to another quality 0W-20 synthetic oil… but to me personally, even if it was 11% between the 2 synthetics, my RP experience scarred me enough that I won’t be using “power gain super oil” till long term engine protection is proven. speculation about how it “should” still provide great protection thanks to it high tech this that and the other isn’t good enough for me. Although I might run it for a track day or 2 in my Miata’s current engine when I’m ready to do my engine swap… as long as it doesn’t blow up on be before that, haha

    I didn’t do any sort of oil analysis mostly cause I didn’t know that kinda thing existed yet…

    what would a compression or leak down test tell me about oil consumption? (not being a smart ass, genuine question)

    I guess it is a more or less anecdotal evidence, but a few of my friends that also used royal purple extensively also had the same experience. and its my personal experience, so I’ll never be using it again…

    well F1’s parameter’s are different… they’re not looking to make their engine run over 100k… they’re looking to make as most power as possible for the number of races required by F1 rules, right? I completely believe royal purple would excel there. also, were they running off the shelf street car multi weight oils for this test? or race grade single weight special stuff? Also, do you know where I can take a see this test? I’m curious how other stuff scored too…

  6. Compression and leakdown testing is the easiest and fastest noninvasive way to test your ring, valve guide and valve seat wear. Nowadays F1 has limited engines and its all about wear and durability. Regardless of mileage, the piston speeds, bearing loads and bearing surface speeds are orders of magnitudes higher than any street car. The demands on the oil are very high. Wear and friction reduction go hand in hand. No, unfortunately, you can’t know the company or the test, it is all highly secret. They used whatever oil was best for their fill and customer allowed use, street oil or not.

  7. ok, so where else would an engine consume oil from? I mean its gotta be one of those or an oil leak.. right? and the car didn’t have any oil leaks.

  8. point I was trying to make is that a compression / leakdown test is kinda redundant if an engine is consuming oil, not leaking, and you’re not planning on doing anything to fix the oil comsumption (engine rebuild wasn’t in the cards for my sister at the time)

  9. Possibly the PCV system as well but that’s usually the result of blowby from the rings. If you look at Honda Forums some K20’s have severe oil burning issues from new.

  10. it was a gradual progression… I wish I would have figured it out sooner, but hey, I was 18-20 at the time… I just liked vtak noises with the AEM V2 intake 😀 (the only engine mod on the car)

  11. Recommend doing an oil analysis for each and noting level of bearing wear material; will give a good idea if the 0w20’s efficiency comes at the cost of wear.

  12. you could also just drop in some Moly or CerraTech from Lubro-Moly. It’s a really great German manufacturer of oil additives, that truly work.

    1. Interestingly enough, when we did our power testing with this oil, I tried an additive that worked pretty well in producing a little power on the dyno in the past and it actually lost power when combined with it.

  13. hey for all those who are worried about oil consumption with synthetics, the Mini Cooper is slated to take a QUART EVERY 3000 MILES…if you’re under that, I say you’re good. That’s a factory specification, BTW. It’s making it’s way past the seals, obviously, because it has much more lubricity.

  14. @joe
    I’m not worried about synthetics, just super thin synthetics that seam to value mpg and more power over engine protection. Like I said above, idk if this oil doesn’t provide enough protection or if it does, but after my experience with royal purple, I’m not taking the risk

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