Choosing which 5w40 is best

Feb 18, 2022
So I normally run Castrol GTX 10w40 in my '89 Chevy 1500, with a bone stock 350. Being that the temperature is going to start cooling off in a hurry where I live, and Montana Winters have a tendency to be anywhere from flat out bitter to downright brutal, I figure my next OC should be a 5w40. It will also be the first time I've experimented with full synthetic in my pickup as well.
Right now I'm stuck between choosing Castrol edge euro, or Shell rotella T6. I've learned toward the Rotella due to it being a diesel oil and being high in zinc, but I've also heard euro oils are great for these older American V8s as well, so I'm here to consult the experts.
T6 hands down. I’m a diehard Schaeffer guy but for an experiment or even long term, T6 is hands down the easiest to find.
If you don't mind spending a little more i'd use Mobil 1 0W-40, excellent winter oil.
Current prices at Wal-Mart on this side of the pond:
Rotella T6 5W-40 - $24.73/gallon, works out to $6.18/quart
Mobil 1 FS 0W-40 or 5W-40 - $24.47/jug, works out to $4.89/quart
He can have a better oil for less money, win-win in my book.
I try to run Euro rated oils in all my vehicles with liquid-cooled engines. From little scooters to V8 workhorses, and all 1/4/5/6 cylinder engines in between. Until recently it was almost exclusively Mobil 1 0W40, but now I'm switching over to Quaker State Euro 5W-40, due to better price and availability in my area.
Here is what Mobil said about higher zinc in a Q&A with a customer.
“For an older, flat tappet, performance motor with inherent cam wear issues is there any benefit to mixing high ZDDP Mobil 1 Racing™ 4T 10W-40 to Mobil 1™ High Mileage 0W-30 oil? The 15W-50 creates TOO MUCH oil pressure. It would be nice if you had a product for 'Classic' cars, high ZDDP, 0W-30 and 0W-40. I have used nothing but Mobil 1™ oil for 15+ years.”
Bill McCauley, Tallmadge, Ohio
Mobil 1™ FS 0W-40 oil already contains a higher level of ZDDP (1,000 ppm) that could benefit your flat tappet engine. We also have a Mobil 1™ High Mileage 10W-40 (1,000 ppm).
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I'd go with either the mentioned Mobil FS 0W-40 or Castrol Euro 0W-40. They are both excellent winter oils, and will easily outlast any winter season (at least 7500 to 10,000 miles) in your old stock workhorse 350 V8. Otherwise, the your mentioned T6 5W-40 sounds fine as well.

Run a good filter as well, such as a Fram XG3980, Mobil M1-201, Bosch 3430, Wix 51036 or NAPA 1036 and you'll make it the full distance. :)

My 2006 Alaskan Chevy Silverado 5.3L will have a remainder shelf stock combination of Mobil and Castrol 0W-40 rotated poured into her before the snow flies here.

Happy trails out west!
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Mobil 1 FS Euro 0W-40 will be right up your alley. The 0W rating is perfect for your Montana winter, it's still a 40 grade, and has ~1000 ppm ZDDP which the older engine will likely enjoy.
I currently run Pennzoil Euro 5w40 Synthetic in my 2008 3/4 ton Suburban 6.0 LS engine with 233,000 miles. Most the mileage was with Pennzoil 5w30 Synthetic, but upped it to 5w40 about a year ago. For winter I have Pennzoil Euro 0W30 on tap. It gets a cold start every day at work, with temps as low as -5 F occasionally.

By the way, I often go to Eureka, Montana to pick up things I get sent to Montana Shipping, a freight forwarder in Eureka. Sometimes it’s cheaper to ship things there rather than across the border. I also pick up some of that cheaper American Gasoline at the local Exxon. ;)
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