Chevy Big Block 427 L72 Spec Engine

Should this Chevy Big Block 427 get 10W-30 or 20W-50 motor oil? (photo credit:

A reader asks: My street rod has a 1967-vintage Chevy big block 427 (L72 spec) with solid lifter cams. This car runs only in the summer and has an estimated 450 horsepower. I would like to run AMSOIL Z-Rod in this engine, but I’m really torn between 10W-30 and 20W-50. There’s so much debate on the internet about which grade to use. Can you offer any thoughts?

Answer: This is a very contentious and well-worn subject, but there is actually no wrong answer. There is no downside to going with 10W-30 or 20W-50 motor oil in your engine. It really comes down to personal preference. As your engine does put out significant horsepower, we would lean toward using 20W-50.

If your engine sees very light duty or is built exceptionally tight, 10W-30 would be fine. But again, if you twisted our arm, we would give 20W-50 the nod for the thicker viscosity.

Regardless of which viscosity is chosen, AMSOIL Z-Rod is formulated expressly for older engines. Packed with 1440 ppm of zinc and 1320 ppm of phosphorous (serious anti-wear additives), Z-Rod is a superior choice for classic engines. These anti-wear agents make Z-ROD Oils especially suitable for engines with flat tappet camshafts.

Motor oils specified for modern cars and trucks are anemic by comparison with zinc and phosphorus levels averaging in the 800 ppm range. Today’s cars and trucks have emissions equipment that do not react well to high zinc and phosphorus levels. Therefore the latest motor oil specifications take a different approach to wear control.

But as emissions equipment are a non-issue for classic engines, this motor oil has no formulation constraints. The 100% synthetic base oil of Z-Rod provides tremendous shear strength and maintains consistent viscosity, regardless of high engine temperatures or hard operation.

There is absolutely no downside to going with a synthetic oil like Z-Rod in vintage engines. You will not see increased oil consumption or leaks. Z-Rod Oils also contain special additives that condition seals to extend their life.

As vintage cars tend to retire for the winter, AMSOIL also gave Z-Rod a healthy dose of anti-rust and corrosion agents. So you can rest well knowing your baby is well-protected whether she’s running or not.

So regardless of whether you opt for 10W-30 or 20W-50, you will have done your engine a favor by choosing the AMSOIL Z-Rod Motor Oil series.

AMSOIL OE Synthetic 10W-30 Motor Oil

Is there any need to switch to 10W-30 engine oil during the summer months?

A reader asks: I use 5W-30 motor oil in my Infinti G35 during the winter and my owner’s manual suggests that it is suitable to use 10W-30 in warmer temperatures. Is there any real benefit to switching to 10W-30 in the summer and back to 5W-30 in the fall?

Answer: There is absolutely no need to switch to 10W-30 motor oil in the summer if 5W-30 is an acceptable grade for your engine. While some car manufacturers still advocate the use of 10W-30 (or even 10W-40) as an appropriate engine oil option for summer use, it is completely unnecessary.

Today’s 5W-30 motor oils provide consistent protection at both extremes of the temperature spectrum. During hot operating conditions, they are resistant to thinning out, breaking down, boiling off and degrading to the point where they might cause deposits. Remember also that a 10W-30 and 5W-30 are essentially the same viscosity at operating temperature, so there is no tangible advantage switching over to 10W-30 for summer driving.

There used to be a time when switching to a heavier motor during the summer was a necessity. Four or five decades ago, engine oil technology was far less advanced and engine tolerances were less precise. Thicker engine oil was needed in summer to combat wear and oil consumption. These thicker grades did not pump well in extreme cold, so a seasonal oil viscosity change was once a common part of regular maintenance. This habit does still linger, but today’s motor oils (especially synthetic oil) negate the need for a seasonal viscosity changeover in either gasoline or diesel engines.

Enjoy the convenience of keeping one engine oil grade on hand and take solace in the fact that using 5W-30 for year round use will not compromise engine protection in the slightest.