jyeung528

i thought the problem was at warm idle, not cold idle.

Apex1.0

My UOa indicates amsoil 5w30 had a higher viscosity than m1 10w30. Fwiw.

Amsoil sheared a bit less.

rpg51

If your bearings are worn and you use thicker oil to get a higher pressure reading, will your engine get proper lubrication? Or do you need to deal with the bearings?

rrounds

For most 5/40 oils the cSt@100c is lower than 10/40 oils
Take Valvoline 5/40, its cSt@100c is 13.1 while thier 10/40 is 15.1@100c
The 10/40 100c number is little more than 15% greater than the 5/40, so the 10/40 should give him a little more oil pressure than the 5/40 would at idle.
Its all about the numbers(cSt) at 100c

ROD

rrounds

If its normal wear, then yes a thicker oil like a 10/40 will help. What a thicker oil does is it keeps the crank from touching the bearings. If you have crank walk and the bearings are shot, then its best to rebuild it.
Both Ford(Mustang) and Chevy(Corvette) say if you track it(drive it hard) use a 5/50 for the Ford and 15/50 for the Chevy but if you just drive them around on the street like an old man then use 0/30 or even a 0/20 and all will be good. Most of these new cars pull power when the oil gets to hot(thin) so the engine doesn't eat itself. Our S doesn't have that, so its safer to be a little thick than a little thin.

I've read about way to many blown engines on here in the last 8 years and I know my S likes 10/40 from my uoa's. After spending 23 years driving trucks and changing more gallons of oil than most on here(with more than 40 uoa's on my trucks) I go by numbers, both the virgin oil numbers and my used oil numbers.

ROD

rpg51

How do your uoa numbers differ when you use 10/40 v. oem spec?

Chuck S

I don't think any of us have sufficient test equipment to determine oil flow vs oil pressure. I suggest using 90 grade oil if you want a lot of oil pressure. Lubrication will be poor, of course, 'cuz very little oil is flowing. Serious suggestion? Nope, but the oil pressure will be nice and high. The oil flow is the critical part, not the pressure.

Oil pressure spec for an engine is based on the oil spec. Too thin or too thick oil will show bad numbers. If using in-spec oil and getting low oil pressure I suggest there's an oil pump problem, not an oil problem.

The number before the W is only for low engine temperatures such as on startup. Even 0W is still too thick but becomes thin enough faster. I looked at the oil spec of my other car(s) and 0W was that number My 5.4 Ford V8 oil spec is 0W-20 for example. The number after the dash is for the engine at operating temperature. Honda wants 30 wt here with 40 being acceptable.

-- Chuck

jyeung528

i'm guessing both uoa's would be good with no discernible difference between the two.

rrounds

I have four uoa's on our S
We bought our S('06 with less than 20k miles) out of state, so we flew there and drove it 1200 miles home.

Unknown oil was told it was 10/30 and uoa said its close to a 10/30-on the thin side with a wix filter, wear numbers were over universal averages for the miles on the oil said to be around 5800 miles
First oil I used was M1 10/30 with a new Baldwin filter, wear numbers came down to avg. 7500 miles on oil
Second oil change is when I went with 10/30 H/M M1 with a can of Liqui Moly(did not change the Baldwin filter), wear number came down to under U/A for 7500 miles on the oil.
Third oil change is when I moved up to M1 10/40 HM with a can of Liqui Moly with a new Baldwin filter, wear numbers came down but not much.

The reason I went to H/M oil is because most H/M oils had a better anti-wear package. If you don't want wear you need a strong a/w package in the oil.

My numbers are just that, for my S and the way we drive. That is why I say go by the numbers(your numbers), what works for me might be to thin for someone with F/I or some one that gets his oil hotter than me. One thing I do know is 10/40 is not to thick for any S. Even if you live where it gets down to -10F if you start it and let it idle for a few min. no harm will be done. Now if you start it up and go play Johnny racer you will hurt any engine and it will hurt any engine even if you start it and run it hard at 80/90*f, you have to let the oil get to NOT(that goes for the trans and rear end too).

ROD
Oh, I use a mix of Red Line in the trans and a 50/50 mix of M1 75/90 and 75/140 in the rearend.

rpg51

I don't understand why those numbers lead to the conclusion that 10/40 oil is best for you. There are variables other than oil weight changing for each analysis and the changes in your numbers are minimial. What am I missing?