A reader asks: I’ve got a Volvo-Penta marine engine. The recommended engine oil is straight SAE 30. What do you suggest?

AMSOIL 4-Stroke Marine Synthetic 10W-30 Engine OilOur answer: AMSOIL Synthetic 10W-30 Marine Engine Oil would be at the top of our list. The “straight-weight” SAE 30 recommendation is derived from antiquated thinking on motor oil. Some conventional multi-viscosity motor oils could be prone to shearing and thinning when exposed to extended periods of heavy loads. The AMSOIL Marine 10W-30 is highly resistant to shear down, so that simply isn’t a factor. AMSOIL Marine 10W-30 would meet the viscosity requirements of your engine through the entire service interval.

It is important to note that AMSOIL Synthetic 10W-30 Marine Engine Oil contains very powerful anti-rust/corrosion ingredients for marine use. This product was engineered to stand up to all of the rigors of marine use.

Why Is Shearing An Issue With Some Motor Oil Formulas?

One of the main reasons that some multi-grade motor oils are highly prone to shearing is that they may contain “viscosity index improvers”. “VI” improvers expand with heat to prevent the motor oil from thinning out as engine temperatures rise. Imagine tiny springs that expand when exposed to heat. The problem with VI improvers is that eventually they can shear down reducing the overall viscosity of the motor oil. This compromises the oil’s ability to fight wear in extreme heat and contributes to depositing. Some conventional motor oils can contain up to 20 percent VI improvers by volume. They offer no benefits in terms of lubrication.

AMSOIL motor oils do not contain VI improvers. The synthetic chemistry of AMSOIL Marine 10W-30 makes it highly resistant to heat and shearing. That’s why it is the perfect candidate for Volvo-Penta engines that suggest an SAE 30 motor oil.

We do have a motor oil that could be consider a straight SAE 30. AMSOIL SAE 30/10W-30 Synthetic Heavy-Duty Diesel Oil is suitable for diesel and gasoline engines. We would still lean toward AMSOIL Marine 10W-30 because of the obvious benefits of the marine anti-rust/corrosion package.

A reader asks: How long is motor oil usable after the bottle has been opened?

Our answer: Once the seal has been cracked on a bottle of motor oil, the remaining oil should be used up within one year. This guideline also applies to transmission oil and gear oil. Opened bottles of both synthetic and conventional motor oils would have a similar lifespan.

Three Reasons Why Motor Oil Should Be Used Within A Year Of Opening

  1. Condensation- After the seal on the bottle has been broken, the interior is more prone to condensation. Once the oil level in the bottle is lowered, there is more open space for condensation to develop.
  2. Oxidation- As the motor oil becomes exposed to oxygen over time, the chemical makeup of the motor oil changes. Simply put, once the oxidation process has started in motor oil, the capabilities of the oil are severely limited and unpredictable. Therefore, that partial bottle of motor oil that has been sitting on shelf for several years should be used in an oil can or sent to recycling.
  3. Additive Fallout- Over time, the ingredients that make up the motor oil formula can start to degrade. This compromises the capabilities and service life of the motor oil. This process would likely take much longer than a year. This can happen in sealed bottles that have been stored for too long as well.

Motor Oil Storage Tips

  • Store motor oil in dry conditions. Don’t leave motor oil bottles out in the yard or in the back of the truck.
  • Do not store the oil in temperatures below it’s cold-pour-point. If the motor oil freezes and “gels”, this will shorten the lifespan of the motor oil.
  • The ideal storage temperature range for motor oil is between 0°C (32°F) and 29°C (85°F).

Shelf Life Of Unopened Motor Oil Bottles

The shelf life of sealed, unopened motor oil, transmission fluid or gear oil is roughly 5 years. Please note the storage tips above to maximize the shelf life of new motor oil.

PayPal Logo

Image Credit: PayPal

AMSOIL synthetic oil can now be purchased using PayPal as a payment method. This payment option is available with online orders only at the AMSOIL corporate site. We strongly suggest exploring an AMSOIL wholesale account before purchasing. We can certainly help you with that.

This new payment option applies to all AMSOIL account types including catalog customers (buying at suggested retail), Preferred Customers, AMSOIL Dealers, retailer and commercial accounts.

How To Buy AMSOIL Products With PayPal

  • Get a wholesale account (optional, but highly recommended). Contact us for a wholesale price list using the form on this page.
  • If you do not want a wholesale account or if you are buying smaller quantities (just a quart or two), you can buy at suggested retail. For smaller orders, you can start shopping here. PayPal will be a payment option once you checkout.
  • Once you have a wholesale account, contact us for the steps to create an online log-in at the AMSOIL corporate site. We won’t go into the steps for that process here.
  • Do not use the “EZ Online Form”. This is a form that allows you to manually type in product part numbers to build your order. The EZ Online Form is handy, but this option will not allow you to use PayPal to pay for your order.
  • To use PayPal, shop using the online store. To use this option, log-in to your account and then click on “Ordering”. Then choose “Start Shopping”. You can also go to each product page, click on the desired product and add it to your shopping cart.
  • Once you have chosen your products, click on “Check Out”. PayPal will be shown as a payment option.
  • You will then be directed to the log-in page of your PayPal account. You can then complete payment.

Other AMSOIL Payment Options

Aside from PayPal, AMSOIL accepts several other major forms of payment. The following payment methods are accepted for both online and telephone ordering.


  • Visa
  • MasterCard
  • Discover
  • American Express


  • Visa
  • MasterCard


Contact us using the form on this page with questions or to request a wholesale price list.