Viscosity v. Temp

[Robert Brennan]

This from a friend trying to ween me off 20/50W Valvoline VR-1:
http://www.bobistheoilguy.com/motor-oil-101/
Does he have a point or will it result in even bigger puddles under the TC and TR3?

Bob Brennan
S. Freeport, ME

[Steve Simmons]

I think he has a point. One thing I've learned is that not all oils are alike. The high-temperature viscosity of the 15W-40 oil I now use is higher than the 20W-50 I used before it, according to the spec reports on each. I have not noticed additional leaking, they leak large quantities with either! The quality of the viscosity modifiers in an oil appear to make a big difference though.

[Robert Brennan]

My '66 Chevelle SS-396 friend adds:
"Bob the oil guy mentioned that if you have leaks you should repair the seal/gaskets and that the 20/50 shouldn't have anything to do with that end of it.
It's hard to get the old school thinking out of the HEAVY is BETTER thinking. The thin stuff flows (psi) better from what I understand. Quieter lifters -better mileage (as if that matters) but more impt from what I read is THE START UP. Once it's all up to op temps they are all equal. Glad you posted it and we';ll see what the Brit guys think after reading Bob's thesis. I"m looking for a 5/40 wt that has the high zinc etc. in a conventional, or an 0w40. It's made me rethink the HEAVY is BETTER idea. The hot rodders with old and new engines are all getting on board, but very slowly."
Clearly, Bobtheoilguy hasn't a clue regarding oil leaks and ancient English autos.
Bob Brennan
S. Freeport, ME

[Rick Waters]

Every time I bring up the idea of using 5-40 or something like that, the old timers all look at me like I'm crazy, and tell me that 20-50 is the only choice for an XPAG. I am going to try something like a 5-30 or 5-40 synthetic, and watch the oil gauge on start up.

I do remember being shown some diagrams of just how oil lubricates, and remember the words hydrostatic wedge, (best of my recollection). It was explained to me that the principle is precisely the same as that which underpins waterskiing. The oil between the bearing and the journal forms a wedge due to the rotation of the journal, and this wedge keeps the two metal surfaces from making contact. If this is correct, then obviously, one would want to have as much oil in the journal area as quickly as possible, so as to cause this wedge to form.

If Bob the Oil Guy is correct, the "clinging" is inconsequential, and further, the clinging does not appear to be related to the "weight" of the oil used.

I'd love to hear from anyone on the group that has run with lighter oil, or with synthetic.

[madhuParoor]

Hi Rick, viscocity 40 or 50 is defined. The first digit 0, 5, 10 or 15 says at what point the oil will freeze. ( You can google it.) The are lot of points to be checked and compared for good quality oil.
madhu

[mike k]

Hemmings motor news puts out a motor oil for classic cars containing the high levels of zinc and phosphorus. It's available in 10W30, 20W50 and 15W50. check link for more details. www.hemmings.com/classicoil

[i.thomson]

I tried 15/40 once on the grounds that the original spec was for a straight 30 grade. As 40 was still higher (thicker) than this I supposed this would be OK. I took it out sharpish when the the oil pressure dropped by 10 psi. And this on a newly rebuilt engine. Reading the oil piece, a difficult job considering the problematic language and grammar, I have to ask why does he contend that all oils are the same at operating temperatures. Surely the hot figures must mean something. I will stick to 20/50 even if it is getting more difficult to get...and more expensive!

Ian Thomson
Notts. UK

[Robert Brennan]

More weekend reading from my thin oil friend:

http://speedtalk.com/forum/viewtopic.php?t=30483

Bob Brennan
S. Freeport, ME