1 FMF

iTrader: (1)

http://www.machinerylubrication.com/...?articleid=779

in case you don't know the bearings in your engine are journal bearings- the mains which support the crankshaft and also the rod bearings which support the rod around the crankshaft journal. And these bearings are of the babbitt type as shown in figure 2 of the article.

1 FMF

iTrader: (1)

Demystifying sludge and varnish

http://www.reliableplant.com/Article.aspx?articleid=259

so you think using a synthetic oil is best ?
not always!

sergo

interesting reads.

Daryn

iTrader: (19)

very good reads! .. low weight oils are a killer for cold start up on ur bearings

joecar

I don't think you can get a low enough weight oil for that to happen... for example, 0W40 has sufficient cold flow ability to be able to get to all the bearings during start up while at the same time being having sufficient cold lubrication properties to protect the bearings...

lower weight oil actually protects the bearings during cold start up by virtue of being able to flow easier while it's cold... (did you read about cavitation with heavy weight oil in that article...? During cold startup heavy weight oil has a high resistance to flow... the pump may cavitate and the bearings will be starved).

gun5l1ng3r

"A generally accepted minimum viscosity of the oil at the operating temperature for journal bearings is 13 cSt, although some designs allow for an oil as thin as 7 or 8 cSt at the operating temperature. The optimum viscosity at operating temperature is 22 to 35 cSt, for moderate-speed bearings if no shock loading occurs. The optimum viscosity may be as high as 95 cSt for low-speed, heavily loaded or shock-loaded journal bearings."

The above quote from the OP was somewhat scary. If you take a look at most of the oils for sale with the GM recommended weight of 5-30W, you will see that the manufacturers rate their oils at about 9.8-11.5 cSt at 100*C, which would be close to operating temp.

Does the LSx family of motors fall into the catagory of machine that is designed to operate a journal bearing with proper amount of lubrication at an oil cSt as low as 9?

I would hope so...


EDIT:Further in the original quote, it says that optimum viscosity is around 22-35 cSt, where, as previously stated, typical oils are around 9-11 cSt. Does the pressurized nature of the system change the bearing's needs?

Does this mean 20W-50 might be a better choice (even though I know its low temperature flow characteristics are probably not good to bearing wear on cold starts)?

LS6427

iTrader: (2)

20w50 is what I use in my 427ci. 120,000+ miles...still perfect. I understand the cold start-up thoughts....but I just don't buy it to the extent that some people think it hurts bearings. I agree the cold start-up is probably where bearing "wear" will happen...but its just not all its cacked up to be. I'd rather have heavier oil for when my engine is at operating temp, running around all day or racing, and spinning like crazy for 30 minutes at a time....rather than worry about the .10th of a second my engine takes to start-up. My oil pressure needle jumps up before my engine is actually started, by the time I release my fingers off the key the oil pressure is rising, so its getting oil flow almost instantly.

The thought that lighter oil will flow easier than heavier oil, thats only common sense. But another thing that is alos common sense is that 20w50 and say 10w30 are very very close as far as how thick they are when cold. They pour out of the bottle the same. Its not like one pours like honey and the other one pours like water...............

Good articles though.


.

gun5l1ng3r

I had a thought about the start-up issue and wondered if an Accusump would be a solution to get the oil flowing before the engine is cranked over.

If the Accusump can provide this at start-up, 20W-50 might be a great oil to run...

joecar

When hot, 0W40 is not that much thinner than 20W50.

1 FMF

iTrader: (1)

(a) the recommended (required for warranty? ) weight of 5w-30, is not just GM, it is by every automaker that sells cars & trucks in North America and it is not because the automaker has decided it is best, it is because they are all inherently forced by the government under CAFE and EPA to meet fuel economy, and emissions, requirements if they want to sell their product. And the primary way they meet the fuel economy requirement is by lowering the oil's viscosity globally, not just at operating temperature. The majority of the fuel savings is when the engine is not hot, and the oil is colder than operating temp which can be a significant amount of time. Operating temp is considered to be 100C or 212F, basically the engine temp where the coolant thermostat is 190-200F. (if you know how heat transfer works, heat goes from hotter areas to cold areas, so if the coolant at 190F is taking away the heat, then where the heat is coming from must be hotter than the coolant temperature).

(b)well if you use logic, your owner's manual says so so then it must. sarcasm aside, there are millions of cars on the road running 5w30 that do just fine. And don't forget there is 5w-20 oil recommended (or required) by ford, chrysler, and others, which all around is a lower viscosity oil than 5w-30. But don't forget the temperature variable, you can run any weight oil theoretically if you can control temperature.

(c) good question. I don't know, maybe to some extent but i think it would be marginal to insignificant compared to other factors such as loading and speed, film strength, and additives in the oil.

(d) if you provide a temperature then an answer can be given. If the oil temp is < around 180F then no it's not a good choice, you would be losing efficiency because the oil is too thick and not gaining anything in terms of wear prevention. But if the oil temp is > 220F then yes it is a good choice, you are gaining a great deal in terms of wear prevention compared to a lower viscosity oil of the same oil base stock and same additives. And to be more accurate you should also give the speed and loading which the bearing would see. The real answer is knowing what temperature range the oil will see, and deciding what is an acceptable trade off of wear to fuel economy. Except for cold starts, or once oil is flowing adequately, a thicker oil does not cause more wear.