A Primer on Motorcycle Oil — Without the Controversy

/, How-To Articles/A Primer on Motorcycle Oil — Without the Controversy

A Primer on Motorcycle Oil — Without the Controversy

There’s always been confusion and conflict when it comes to any discussion about oil, which is of course, the lifeblood of our beloved motorcycles. And I’m probably not going to bring world peace to this topic with anything I’ll say in today’s blog post. Truth be told, this topic has created more debate on our Riders Forum on the J&P Cycles website than any other subject.

In fact, I’m mostly going to stick to the facts in this post, steering away from the controversies for the most part. First off, let’s explore the function of oil in an internal combustion engine — the educational portion of this segment. There are five different tasks that oil has to perform.

1. First, it must lubricate and reduce friction.

2. Next, oil helps cool your bike. Harleys are indeed air-cooled, but oil removes quite a bit of heat. As oil flow over the hot parts, heat transfers and is carried away. The “dry sump” oiling system utilized by Harley-Davidson aids in this cooling process because oil pumped out of the engine travels to a remote tank, thus affording more cooling time.

3. Another function of oil is “sealing.” The surfaces of the piston rings, ring grooves and cylinder walls are never completely smooth. There are microscopic hills and valleys that can reduce engine efficiency by allowing combustion pressure to escape into these low-pressure areas of the crankcase. The job of motor oils is to fill in these hills and valleys on ring surfaces and cylinder walls, thus allowing maximum combustion pressure.

4. Oil’s next task is to protect against rust and corrosion. This is pretty self-explanatory.

5. And finally it’s up to oil to keep the inside of your engine clean. Whew! Talk about multitasking!

Motor oil is the primary determinant in the durability of an engine. Oil change interval is a hotly contested subject, as is the great dead dyno versus synthetic debate. Until recently, the Harley-Davidson Motor Company was staunchly opposed to synthetic oil. But today the company offers a synthetic product that is marketed as Syn-3.

Let’s discuss the differences between the types of oil. Consider first that oil contains two basic components: base stocks and additives. Base stocks can be made of petroleum (dead dinosaurs); chemically synthesized materials; or a combination of synthetics and petroleum (called para-synthetic, semi-synthetic or synthetic blend). We’re not going to get into the third type in today’s discussion. What’s important to remember is that additives provide anti-wear, anti-foam, corrosion protection, acid neutralization, and maintenance of viscosity, detergency and dispersion.

Let’s talk about what causes oil to get dirty in the first place. Many factors contribute to a motor oil’s demise, but essentially it’s the accumulation of contaminants in the oil and chemical changes in the oil itself that make a motor oil unfit for further service. It’s inevitable that oil will be contaminated by dirt or sludge, or succumb to the extreme pressures or temperatures found inside an engine.

One of the biggest killers of oil is extreme heat. In a Harley, the operating temperature of oil should ideally be in the 180- to 220-degree Fahrenheit range. Anything much beyond this leads to breakdown of the oil, which adds oxidants to conventional oils. Synthetic oils withstand much higher temperatures before this process starts.
Today’s Twin Cam engines have higher operating temperatures than engines of years past, and it’s not unusual for a Twinkies’ oil temp to be in the 220- to 260-degree range. This increased running temperature is why Mother Harley jumped firmly onto the synthetic bandwagon.

A good way to monitor the heat issue with your bike is to invest in an inexpensive temperature dipstick. If your temp runs over 220 degrees on a regular basis, an oil cooler or a change to synthetic may be in order. Another oil assassin is not getting your bike up to full operating temperature. The combustion process has many byproducts, one of which is condensation (water), and unless you get to full operating temperature, the water produced can dilute your oil. That’s because water doesn’t usually hang around once you’re up to temp. It boils off.

Other byproducts of oil include acids that also act as contaminants. Water and acids lead to sludge, rust and corrosion. Soot and carbon create sludge and varnish and can lead to clogged filters. TC engines use a 10-micron filter; the difference is due to how the filter is positioned in the system. The 10-micron filter removes more contaminants, but is more restrictive. Someone might think, “Let’s use a TC filter on my Evo since it removes more junk.” That’s not your best thinking. Don’t do it! I’ve seen situations where a more restrictive filter increased oil-carryover in an Evo motor to the point the engine was ruined due to lack of oil. In one case, I would have bet the rider would have done something before it got to that point, but he didn’t. Goodbye engine. So be sure to use the correct filter for your application.

Decade following decade, HD has always recommended that your oil be changed every 5,000 miles. Personally, I change mine every 2,500 miles and I use dyno oil. It’s been my experience that “oil’s cheap, engines aren’t.” With today’s synthetic oils as high priced as they are, this is something you will need to determine for yourself. The bottom line is this: Use whatever oil you’re most comfortable with, as long as you keep the oil clean and the filter changed at the correct intervals.

By |2015-04-14T16:19:47+00:00January 12th, 2012|Categories: Editorial/Commentary Articles, How-To Articles|24 Comments

About the Author:


  1. Steve James December 20, 2015 at 11:16 pm

    I can’t find any parts on your site for my Moto Guzzi, yet you have parts for Buells. What’s up with that?

  2. Jon October 3, 2014 at 8:14 am

    Some excellent info, however, I feel one aspect of an oil’s performance has not been addressed fully.

    When you buy a multigrade oil, the numbers tell you how the oil will perform. A 20w-50 will behave like a 20 weight oil when cold, and like a 50 weight, when hot .

    The ‘cold’ number, (the one with a ‘w’ for winter after it) is actually rated at 40 degree C (105 deg F)…which is the temperature of a hot bath. On start-up, all oils are MUCH thicker than when at the ‘winter’ temp. For a 20w-50, the numbers mean it behaves like a straight 20 when at 105 deg F, and like a straight 50 when at 220 deg F

    ALL engines are designed to lubricate and cool properly with their oil at the viscosity it is at when the engine is at full working temperature. This means around 100 deg C…(220F)

    It is often said, and it is quite true, that the vast majority of ALL engine wear occurs when the engine is cold, during the first few miles of starting.

    What that means in practice, is that if you do long journeys most of your total miles will be when the engine is hot, and very little engine wear will occur. if however your typical journeys are short, under 20 miles, your ‘cold’ miles will form most of your total miles and wear will be high.

    This is why ‘I use Walmart 20w-50 and I have 150,000 miles on my bike’ type endorsements are meaningless because that person’s typical riding habits may be dramatically different from yours..

    If it’s 150,000 miles of 5 mile commutes it is a stunningly good achievement for the engine, and a real endorsement of the oil, however if it is five hundred 300 mile journeys it is less impressive.

    As a reference, a 20w-50 is over 200 times thicker at 32 deg F than it is at the correct working temperature of the engine, so it pumps slowly, fails to take heat from hot spots, overheats locally and so allows huge amounts of wear during the first few miles….As much as 90% of the total wear your engine experiences over it’s lifetime.

    That engine’s life expectancy will therefore be MUCH shorter.

    At 105 deg F a 20w-50 it is still ten times thicker than the engine is designed to use…

    A 0w-50 however is only about twice as thick at 105 deg F than it is at full working temp, which mean s the more sophisticated (and almost certainly synthetic) multigrade offers hugely better cold engine protection…During which at least 80 percent of ALL engine wear occurs.

    Basically, if you don’t do enormous journeys every time you ride, an oil with a low ‘first’ number and the manufacturers recommended second number will offer massively better protection and longevity to your engine.

    The fact that such an oil is likely to be a synthetic and will also effortlessly deal with higher working temperatures is a bonus.

    I use a fully synthetic 0w-50 as I do many 5 to 30 mile journeys….

  3. Dazza March 20, 2014 at 10:29 am

    I ride a modified 1980 ironhead roadster and in OZ we cant get your amsoil or V-twin Mobil so I use Penrite HD OIL 50-70/SAE 60 (Mineral) which was recommended to me as – supposedly – synthetic oils glaze the internal workings of the old school motorcycles. HD Oil is a premium, heavy duty, high performance mineral, SAE 25W-70, non friction modified, 4 stroke engine oil. It contains a superior anti wear and cleansing package package of FULL ZINC (exceeding 1750+ ppm levels) for ultimate engine, gearbox & clutch protection and special detergents and dispersants for protection in the harshest of on and off road conditions for older and classic motorcycles.

    HD Oilis primarily recommended for use in classic motorcycles where SAE 50 & SAE 60 monograde oils were specified. It is also equally suitable for use in transmissions with wet clutch systems where engine & gearbox oils are combined. It has optimum clutch slip prevention in these systems.

    HD Oil is particularly suited to be used in pre-Evolution (1984) engined Harley Davidson motor cycles. Specific models such as –

    1000 cc / 1200 cc Panheads (1948 – 1965)
    1200 cc / 1340 cc Shovelheads (1966 -1985)
    1200 cc Electraglides (1978 – 1985)
    1000 cc Sportsters & Roadsters (1978 – 1985)
    All side valve models to (1903 – 1969)

    HD Oil is also suitable for other large V-Twin bikes such as Ducati, Hummel, Indian, NSU, PUCH, Henderson & early Buell. It is also ideal oil for Classic British motorcycles such as Norton, AJS & BSA including single cylinder 350 to 500cc low revving engines like Enfield and 500 to 650 cc Parallel twins. This oil is the “Ducks Nuts” down here in Australia and I change oil & filter every 5000 Klm’s (3100 miles). Costs about aud$55 per 4 litres.

    • Boston Jim March 22, 2014 at 6:15 pm

      Hey Dazza, that was a great post ! But, what was your point ? We can get AMSOIL & V-Twin Mobil, & oil, that any “ole” Harley needs, right hear in the “GOOD OLE USA”. Don’t need to be ordering any Penrite from 10,000 miles away, thank you very much, for the kind thoughts, “gah day”!

  4. william May 26, 2013 at 4:52 pm

    I mixed primary case oil and engine oil in the oil tank do I started it are is it going to ruin my engine please help

  5. Nice and fine oil give new life to engine and parts works properly.

  6. Dave Scott December 8, 2012 at 4:02 pm

    Nice to read some detailed info, yet nobody is being ‘preachy’ about which oil to use. I just purchased my buddy’s 2006 Softail Deluxe with the 103. It’s been running with synthetic but I’ve been thinking of going back to mineral oil. The only thing I see here which makes synthetic a draw is that it tolerates higher operating temps. I’ve had several bikes and like many others, I change my oil and filter on time. The bike does have an oil thermometer so I can keep track of the temp in the hottest part of summer. (I’m in the Toronto area, so we ride here in a wide temperature range) I don’t have a specific question regarding oil use but if anyone reads this who is knowedgeable and thinks I’m ok with my reasoning (or not) please feel free to comment. It’s December as I write this so I’ll take a bit of time to check things out before changing fluids and storing it for the winter. One comment I did read mentioned the use of a different weight of oil in the primary to make shifting smoother. Like to know more about that if anyone has more info…

    • boston jim February 4, 2013 at 8:43 pm


  7. fedrick miaroni June 23, 2012 at 7:27 am

    plz what about the premier 125cc

  8. Jim Mulanix February 15, 2012 at 9:14 am

    Not everyone worships at the sacred alter of Harley-Davidson. My Suzuki uses a slightly different oiling system than the Harleys (great bike, mucho dinero). I would love to hear the experts discuss the metrics along with the Harleys. Please don’t mistake this as a knock at the Harleys, I don’t mean it as that. I would just like info on my bike as well. Thanks and by the way good article.

  9. Don Gunritz February 11, 2012 at 5:49 pm

    I use Harley syn.oil in my 5-speed [Transmission & Primary chaincase oil,only in my trans.] it seems like 20-50 can’t find the wt.In my Primary I use 10-40 mobil1 syn. Let the bike warm up,And away I go,This produces a nice smooth shift and The only time it cluncks is when it is still cold.I use 20-50 Mobil 1 in the engine [Syn.] Still want to try Amsoil! I put the bike up the winter with the old oil,then when spring comes around I warm it up real good and change the oil then.

    • boston jim February 4, 2013 at 8:23 pm

      75W-110 GEAR IN TRANS, FACT !

  10. OLDEVO February 7, 2012 at 4:08 pm

    My ’95 ( built ’94) EG classic is up over 225,000 kms and never had the heads off. Change oil and filter by the BOOK. meaning HD 20/50 oil and HD std filter. Runs just fine and only consumes one extra qrt per change.

    • boston jim February 4, 2013 at 8:16 pm


  11. matt mccann February 7, 2012 at 3:50 pm

    i own a 2000 fxd and use mobil v twin syn 20-50 with agood quality filter. since i change my own oil i save enough to justify using syn. and i only ride 2-3k miles a year any way so i change it once a year before winter storage . that works for me.

    • boston jim February 4, 2013 at 8:10 pm

      HEY MATT, you know the 99/00 had the cam bearing problems, & all pre 2007 have serious cam chain tensioner problems, check-out j&p blogs nov & dec 2012, 600+ comments, save your motor. You did right, changing oil & filter, before winter storage. Theres alot of bad crap & acids in dirty oil. boston jim,
      http://www.fatzusa.com, AMSOIL #1, MOBIL V-TWIN #2

  12. ultraboy January 13, 2012 at 3:46 pm

    Scott, great article! As you know, when I’m not building trikes, my real job is oil filtration. While the filters and systems we manufacture are used in power plants and other large reservoir applications, my customers will always want to talk “Mineral vs Synthetic.” It’s a tough question. The answer is not as simple as “yes” or “no”. A better question would be: “Is synthetic oil the best choice for this application?” All types of synthetic base oils can be the best choice for certain situations. The trick is identifying those situations where they make sense or provide value.
    First, let’s set the record straight. No lubrication problem due to poor system design, poor PM practices or lack of fundamental contamination control can be solved by the use of synthetics. The notion that selecting a different lubricant can somehow magically make up for inattention to lubricant condition or an inadequate breather or filter is fundamentally flawed.
    There are plenty of potential benefits to using synthetic oil vs. mineral oil, but that doesn’t mean that synthetics are necessarily better. In order to get value from using a higher-priced synthetic oil, you have to be sure that you are using the potential improved performance of synthetics. To be able to figure that out, you need to understand the conditions that allow synthetics to provide that value.

    Like Scott, I’m going to discuss the most common of the synthetics, polyalphaolefins or PAOs. These oils are often called synthetic hydrocarbons, and are the most common type of synthetic base oil used today. They provide excellent performance and have few negative attributes.
    PAO base oil is actually similar to mineral oil. The advantage comes from the fact that it is built, rather than extracted and modified, making it more pure. Practically all of the oil molecules are the same shape and size and are completely saturated.
    The potential benefits of PAOs are improved oxidative and thermal stability, excellent demulsibility and hydrolytic stability, a high VI, and very low pour point. Most of the properties make PAOs a good selection for temperature extremes – both high operating temperatures and low start-up temperatures. In my opinion, those are the conditions that favor PAO selection. Typical applications for PAOs are engine oils, gear oils and compressor oils.
    The negative attributes of PAOs are the price and poor solubility. The low inherent solubility of PAOs creates problems for formulators when it comes to dissolving additives. Likewise, PAOs cannot suspend potential varnish-forming degradation by-products, although they are a bit less prone to create such material.
    Many people waste money on expensive products that for a number of reasons don’t improve reliability or anything else. One other important thing to remember is that I am discussing the properties of base oils, not finished lubricants. It is quite possible for a finished lubricant using a mineral basestock to offer better performance than a similar product utilizing a synthetic. As far as the price is concerned, oil suppliers have a much higher profit margin on synthetics, so they tend to over-blow and over advertise their advantages.
    But can the additional cost for synthetic oils be justified? The answer to this question really needs to be “it depends.” For example, imagine being able to extend the oil drain interval using a high-quality PAO synthetic-based oil by a factor of six or seven simply by purchasing a product that is five times the cost.
    From this perspective, it would appear that the additional cost is money well spent, particularly when you consider the additional costs associated with an oil change. But if the oil change interval is driven not by base oil degradation, but rather due to additive depletion or the buildup of certain contaminants such as water, particles or soot, then perhaps the cost of a synthetic-based oil cannot be justified.
    For example, there have been numerous studies showing that the poor solvency of certain types of petroleum-based synthetics can result in a greater tendency to lay down varnish in high-temperature applications because the oil does not have the solvency to keep the oil-wetted components clean.
    So, back to the original question, is synthetic oil better? The answer is yes … and no … or maybe. You’ll have to decide. Personally, and this is just MHO, I use 20W/50 mineral oil formulated for air-cooled big twins, and good quality filters, on the intake and oil in my Twinkie motors. Like Scott, I’m pretty religious about changing oil and filter, and am going to do it every 2500-3000 miles anyway, have oil coolers and watch my oil temperature, so I don’t feel the added expense is worth any perceived improvement.

  13. Scootrbum January 13, 2012 at 12:27 pm

    I’ve been running Mobile 1, 15-50 in both my Harley’s, year round, for more years than I can remeber. I change oil around 5K and haven’t had a problem with either of my engines or primaries, a quart goes in there also.
    You can spend all sorts of money on motorcycle specific oils but it’s waste of money.
    Oh yeah I live in Northern Illinois and ride year round, so I see extreme heat and cold.

    • boston jim February 4, 2013 at 7:58 pm

      Your using mobil 1 car oil ! I PITY THE FOOL WHO BUYS YOUR USED BIKES ! Car oil has friction modifiers, that HARLEY clutchs don’t LIKE. Why is it a waste of money to use the correct oil in your AIR COOLED Harley ? Only the Sportster takes a qt in combo trans & primary ! AMSOIL IS #1, MOBIL V-TWIN #2, FACT.

      • Gary August 29, 2013 at 5:45 pm

        Some PAO formulas are blended with esters to correct the PAO limitations. These are Group IV and V basestocks. One thing for sure that you want to look for is the MA & MA2 rating for wet clutch compatibility. A lot of Synthetic oil is now a Group III, highly refined petroleum oil. Good but not as good as the Group IV. My HD mechanic told me he can always tell the bikes that run AMSOIL because there is never any fuzz on the magnetic drain plug when he changes oil. Same with the shock oil. No goo at the bottom of the shock after a few years of hard riding. But each to their own. I’m not afraid to spend a little extra for my high priced ride. And I still can afford to eat out.

      • Jon December 21, 2015 at 9:04 am

        Not fact at all!

        Mobil 1 15w-50 is not ‘car oil’ and has no extra friction modifiers. The only oils that do are specially formulated eco oils usually with a car makers brand on, and are almost always low viscosity…Like a 5w-30 or similar. They are low viscosity and have friction modifiers to reduce drag and so improve economy. Oils like Mobil 1 and such are simply motor oil, nothing more or less. They are GUARANTEED to be direct replacements for old school oils which is what all the letters and numbers regarding the spec mean.

        The only ‘danger’ in using a good synthetic is that the superior detergents in them can clean the built-up gunk away from badly fitting casings and promote leaks…But that only happens on tired old heat stressed or poorly assembled engines

        I’ve been using similar in wet clutch bikes since the early ’80’s and use it in an auto-clutch Honda at the moment. One bike I had, a Husqvarna, was required to use Mobil 1 as the race shop that built the engine wouldn’t warranty the motor with anything else in!

        • boston jim December 21, 2015 at 10:30 am

          Hey Jon, I think you are totally wrong on most of your comments. Mobil1 15W-50 is not an air cooled motor oil. & it has extra friction modifiers ! It was designed for water cooled race cars. If it’s NOT a car oil, WHAT IS IT, it’s Not a Diesel oil, or a bike oil ? Mobil V-Twin 20W-50 was designed for air cooled Harleys. You wouldn’t put the V-Twin oil in your car, unless it was an air cooled Porsche !
          On the flip side, Erik Buell was using AMSOIL 15W-50 race car oil, with friction modifiers, because He was looking for extra HP. Amsoil’s 20W-50 MCV, NO friction modifiers, is your best bet for 1984 to present Harley’s. Great for your wet clutch, Good for 10 K miles ! You don’t know, what you don’t know ! Merry Xmas, Boston Jim

          • Jon December 22, 2015 at 1:45 pm

            Sorry mate, but you are wrong. There are no extra friction modifiers in Mobil 1. While it is true that oils WITH friction modifiers are almost always synthetic, and are specifically for cars, that doesn’t mean all synthetics have friction modifiers, in fact only very specific oils, so marked have them.

            The trouble is, there ARE car oils with friction modifiers, and they ARE synthetic, but that doesn’t mean if it doesn’t say ‘bike’ it is a car oil.
            It is this confusion that has created the myth that you are perpetuating.

            I’ll say it again…I have been using fully synth motor oils in my bikes since 1982, and I’m an ex dispatch rider, covering over 70,000 miles in a year, so I’ve done some miles and in the last 34 years have had about twenty bikes, mostly wet clutch and often small hard revving hard working designs. My last one, an air-cooled 650cc twin was bought from new in 1999 and ran 0w-40 synthetic exclusively throughout the 15 years I had it. It was thrashed mercilessly to the red line and ridden absolutely flat out for entire tankfuls of petrol without the slightest hint of clutch issues…In fact I only sold it because the carbs were getting problematic due to crappy modern fuel and were quite time consuming to get too every time.

            My current daily ride is a 40 year old 750 airhead BMW which runs 0w-50 synthetic…I could ( and would) run friction modified oil in that one no probs because it has a dry clutch, but THEY DON’T MAKE ONE THAT ACTS AS A 50 WEIGHT WHEN HOT…So I can’t!!!

            As regards the air-cooled thing. The only difference between an air-cooled engine and a water-cooled engine is that an air-cooled engine suffers greater extremes of temperature but if you look at the specs of ‘bike’ oil…It has the same temperature range as the motor oil it is repackaged from. Not that IS a fact!

            Incidentally, the original Mini car ran its gearbox inside the A series engine sump ( along with the Austin 1100, 1300, Riley Elf, Wolesley Hornet Innocenti Mini, and Mini Moke) the gears ran in engine oil and that engine was designed to use standard 20w-50 so the supposed extra shear resistant properties of bike oil are also unnecessary….Ordinary engine oil has been coping with gears as well as engines for 65 years….AND with 5-10,00 mile service intervals.

            I wouldn’t use any 20-50 in any engine irrespective of the base oil stock anyway. It takes far too long for a 20w-50 to warm enough to thin down to the engine manufacturers required working viscosity and the whole time it is too thick, the motor is suffering wear. Now, I know Harleys rev slow, so the cold wear problem is lessened, which is why even short hop Harleys wear well…Much like cars, but smaller engines, which have to work harder at normal traffic speeds need their oils to be cooling busy engines ASAP.

            Ever wondered why back in the 60’s American car engines would often go over 100,000 miles when Brit stuff would be worn out by 50,000 ?…All down to cold start wear and hard working high revving little engines running 20w-50

          • boston jim December 22, 2015 at 5:26 pm

            Hey Jon, good report, But, I won’t be following it, Walmart Oil ? I’ll stick with the Official Bike Oil of Sturgis, Daytona, & Laconia; AMSOIL ! Happy Holidays, Boston Jim

Comments are closed.