I Asked About My Oil Dilemma At Bob the Oil Guy. - A40 Is the best?

[Hib Halverson]

Contrary to the opinion of many, 1G LT5s do not require high amounts of ZDDP because, while they are flat tappet engines, they are not pushrod engines, thus their valve spring tension is less than is required by an OHV engine which has to control not only the valve, retainer, locks and lifter but also the mass of a pushrod and part of the rocker arm mass. If valve springs have less tension, there is less need for the extreme pressure lubricants in ZDDP. Less ZDDP means longer cat converter life. IG LT5s can do fine with 800 or so PPM ZDDP but many of the engine oils ZRoners tend to buy (ie: Amzoil, some blends of Mobil 1, Driven and Red Line) are about 1000-1200 PPM.

If I still had my C4 ZR1 today, I'd use a 0W40 oil, either Red Line 0W40, Driven DI40 (also a 0W40) or, in a pinch, Mobil 1 0W40 ESV.

The reason I would have used a 0W40 over the 10W30 I used I had kept "Barney" my Purple '95 is that 1) oil technology advances, just like many other things and 2) the main advantage of a 0W vs a 5W or a 10W on a cold start is the 0W gets to the bearings and valve gear quicker than does a 5W or a 10W. A large proportion of engine wear occurs during cold starts in the time between when the rotating assembly starts to move and when oil pressure has built to the nominal level. I'm not making that up, either. When GM went to 0W40 in all Corvette engines for 2019, part of why that happened was research GM did on how quickly oil pressure built in various parts of Gen 5 V8s showed there was a clear durability advantage in a 0W oil over a 5W or 10W during cold starts.

Today I use 0W40 in the LS6 in our C5 ZO6, in the LSA7 in our C6 ZO6 and the 2G LT5 in our C7 ZR1.

For those who still prefer M1 10W30, but best prices I've seen on it is at Costco.