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I have a 1970 cutlass olds that had a engine swap to a 455 oversize cam, rebuilt about 6000 miles ago, Castrol said to run 5w/50 this seems pretty thick oil any suggestions?
I take it you live in the PNW, so a10W-30 with additional ZDDP (I use Lucas Hot Rod) should be fine. 5W-50 isn't as radical as it sounds, but would be better in a climate that has more extreme highs and lows.
I take it you live in the PNW, so a10W-30 with additional ZDDP (I use Lucas Hot Rod) should be fine. 5W-50 isn't as radical as it sounds, but would be better in a climate that has more extreme highs and lows.
Curious...did Castrol ask why type of camshaft flat tappet vs. roller and discuss ZDDP levels? I'd bet their 5w-50 is low on ZDDP.
VR1 10w-30 has my vote, or Rotella T 15w-40.
Good luck!!!
Last edited by Sugar Bear; March 16th, 2023 at 06:15 PM.
I have been running the old formula 15-40 CI4+ that does not meet CJ specs, with 1/2 pint of old formula GM EOS. If I had to buy more oil today I would look for stuff with similar specs.
I am going to chime in only because no one has mentioned this choice yet and IMO it is a high quality option and a great value. Mobil 1 15w50 full synthetic. It has 1300 ppm Zinc and 1200 ppm Phosphorus. The Mobil 1 Spec Guide says it is specifically designed for High Temp/High Stress and Flat Tappet applications. This Spec Guide can be found on the Mobil 1 website if you want to check it out. My '67 4-4-2 with 400ci seems to love the stuff during our hot St. Louis summers. It can be purchased thru Amazon or Walmart for only $30 for the 5-qt jug.
Your first concern with any oil is the viscosity. Here's the guidance behind what BangScreech said....
The last number (30, 40, 50, etc.) is the viscosity when the oil is hot. This number needs to be low enough that there is always sufficient flow to bearings and valve parts and that the rings can operate as designed.
The maximum number you should use is baked into the engine design and Oldsmobile publishes that number. For example, look at Recommended Viscosity on page 0-15 in the 1970 Chassis Service Manual. The largest number is 40. So don't run 50 weight in a standard engine.
The first number (0, 5, 10, etc.) is the viscosity when the oil is cold. Using 10 or lower is important to reduce the startup load on the distributor gear that drives the oil pump. You have a non-factory cam and, depending on design, the cam gear can be softer or more prone to wear than a factory cam gear. Don't guess, use a low first number to protect your cam and distributor gears from possible problems. There's no downside to running a low first number in any engine.
Last edited by VC455; March 20th, 2023 at 07:05 AM.
Reason: Spelling
Why are so many people using and recommending 20W-50 for a street engine?
They use 50 weight because their engine is worn out, oil consumption is high, and oil pressure is low.
There's no rationale for using 20W even with a worn-out engine.
20W means in winter weather if flows like a 20w oil. 50 is the viscosity at running temp. The difference between the two is achieved by additives, mostly paraffin, the same thing they make sneakers out of, or thereabouts.
The general consensus is, the smaller the range given, the more stable the oil will be. So TECHNICALLY, a 20W-50 will be more stable than a 5W-50 and so on.
I run 20W-50 in almost everything. Mainly for the bearing clearances I use, as well as making the Hyd lifters work a bit better, sometimes.
The general consensus is, the smaller the range given, the more stable the oil will be. So TECHNICALLY, a 20W-50 will be more stable than a 5W-50 and so on.
Hi Mark.
Your observations are, as usual, right on the "Mark."
And I can add a bit to them. Dinosaur oil has low inherent viscosity index. In other words, a dino oil without Viscosity Improver additives will rate only a single number such as 30, 40, or 50.
It takes a lot of additive to make a spread such as 20W-50 and even more to create 10W-50. As you point out, the additives break down with use. When they break down, the hot viscosity drops, sometimes significantly.
Here's a table that illustrates the viscosity of the different ranges.
The abbreviation cSt stands for centistokes, which is a measure of viscosity.
The thing that jumps out is that cold oil is massively thicker than hot oil.
Lower cold viscosity allows more oil flow, which helps reduce cold engine wear (and puts less load on the oil pump drive system).
For a built engine, it makes sense to balance the viscosity index against the amount of Viscosity Improver additive.
Which range is stable enough to use depends also on the oil base stock.
Synthetic oils have high inherent viscosity index. And it takes a lot less additive to widen the spread.
The boutique synthetic makers such as Royal Purple, Red Line, and AMSOil chose which molecules they want to build their oil with. And, they choose a molecule that will have a wide viscosity index. As such, their oils can lose less viscosity with time because they don't carry as high a load of Viscosity Improver additives.
The synthetic oils from the major refiners are generally made with highly refined dino oil that meets the definition of synthetic. These will lose viscosity faster than the boutique oils because they require more Viscosity Improvers to meet a viscosity index. Their benefit is that they are cheaper.
Hot viscosity comes first when choosing oil for a built engine. And choosing the cold viscosity comes down to a balance between low viscosity and low amount of Viscosity Improver additives.
Bone stock 455 . I run shell Rotella T4 15w-40 . I emailed shell about 3 months ago and asked about the zinc ppm in t4 and they replied it’s around 1200ppm and plenty adequate for flat tappet cams. The car loves the t4 and has better oil pressure and just seems to run smoother/ quieter ,which is probably thanks to the additives in t4 because they car did sit a long time So I’m sure some thing were clogged up a bit . I also just bought some Lucas hot rod and classic 20w-50 I was going to put in for the summer . We will see how that goes . Napa gold 1258 filters as well.
March 16th, 2023, 11:06 AM
