Blended Synthetic or Petroleum, That Is The Question

[RagTop]

I bought some Castrol GTX High Mileage for my '69 vert. I figured that, even though it only has 47K miles on the engine since I rebuilt it, it has been running around with 3.55 gears and a C4 3 speed, so it probably has more wear than your average 47K engine. I've been using Castrol GTX 10W30 in the engine since I bought the car 17 years ago and it has never had an oil consumption problem. I failed to notice that the green bottled high mileage product was blended synthetic instead of the good old dinosaur juice. I have always heard that synthetic, due to its smaller molecular structure, finds every potential leak opportunity in an old technology engine. My 308 (302 .040 over) has never had an oil leak problem of any kind. Should I switch over to the blended synthetic or try to return it from whence it came and stay with the petroleum based stuff? Opinions please.

 

[Midlife]

If it ain't broke, why fix it? Go back to what you've been running.

 

[RyanG85]

Whatever oil you are running, make sure it has enough zinc in it. I switched to Valvoline VR1 racing oil for that reason. Most oils today are not designed for flat tappet engines.

 

[GypsyR]

I'd run it and not worry about it as long as you're comfortable with the lower ZDDP levels it has. Like about every other oil at the parts store) versus a higher ZDDP content oil like RyanG85 uses. I've had pretty good luck with synthetic blend. With my engines that are well past break-in I don't worry about it. That said, I'm not running any high lift cams or high pressure valve springs, stuff that might put extra load on cam lobes. If I were, I would run nothing but "racing" oil.
Wish oil companies would come off what their blend ratios are. "Blend" could mean about anything, even their data sheets give not a hint. I'd suspect it's mostly regular oil with a dash or two of more expensive synthetic. Castrol claims the oil you bought has some kind of seal conditioner to help prevent leaks. That should allay fears of the synthetic oil leaks. That do happen, but tend to be only on very elderly and high mileage engines. From what I've heard the "high mileage" additive package happens to be very well suited to our older engines, even if they are low mileage.
If you want more info and opinions than you can probably stand, you can learn a lot more at bobistheoilguy.com. LOTS of good info there.

 

[MD69Boss]

Whatever oil you are running, make sure it has enough zinc in it. I switched to Valvoline VR1 racing oil for that reason. Most oils today are not designed for flat tappet engines.

Valvoline VR1 is ok for the track, but for a driver, you need detergents in your oil which that racing oil lacks. Brad Penn Racing oil has plenty of ZDDP content and has detergents. Their 10w-30 is what I run in the Boss...

 

[KBMWRS]

Agree with the ZDDP additive....I use the additive but will change over to Brad Penn next time.

You also should realize that you stated it was a blend. That's dino and syn together. I've used a blend in my motorcycles for over 30 years no problem.

The initial fear of changing over to full syn has been rebuked.

Also realize synthetic oil is great. I mean great. It can do all the things your vehicle will probably never encounter if you change at 3k or there abouts. Syn was developed for the military for extreme usage which our cars most likely never need. So its basically a feel good thing for the buyer. If that better feeling is worth the extra cost then go for it.

 

[RagTop]

I chickened out and took the blended synthetic back. The car is back on good old Castrol GTX 10w30.

 

[zray]

I chickened out and took the blended synthetic back. The car is back on good old Castrol GTX 10w30.

Been using full synthetic Mobil 1 15w-50 for about 19 years on numerous classic cars, Shelby's, Mustang's, Trumph, Jaguar E type, other Fords, etc. No leaks. No measurable engine wear, etc. plenty of zddp too.

Z