| Home |
| Search |
| Today's Posts |
|
|
|
#1
|
|||
|
|||
"Dan Olstad" wrote
the manual recommends straight 30W oil. Why not a 20-40W or a 20-50W? The manual says that's ok if straight weight is not available but it is not recommended. Can anyone shed any light on this for me? Disclaimer: This is free advice and you get what you pay for. My understanding is that the reason single grade oils are recommended for boats is to reduce internal corrosion in your engine. Because a single grade oil is thicker at lower temperatures than an equivalent multigrade oil, it sticks to the bits and pieces inside your engine better after you shut it down and things in there cool off. Now, about those Ws. Your manual probably recommends an SAE30 and those multigrades you're looking at are probably 20w40 and 20w50s, not number-numberWs. The W stands for winter and what it's all about is the temperature at which the viscosity rating applies. If there's no W, the viscosity rating is measured at a high temperature, probably something like 212 degrees Fahrenheit. If there's a W attached, the rating is measured at a cold temperature, like maybe zero degrees Fahrenheit. A 20W oil has 20 somethings (what that number actually means is kind of mysterious, at least to me, so I like to just think of it as a relative thing) at zero degrees and would be less viscous, ie lower number, at 212 degrees. An SAE20 (with no W) oil would be more viscous, ie higher number, at zero degrees than a 20W. At any rate what 20w50 means in oil lingo is that at zero degrees Fahrenheit it has the characteristics of a 20W oil and at 212 degrees Fahrenheit it acts like an SAE50. They make all that happen by adding polymers that wrinkle up or stretch out depending on the temperature, making multigrade oils thin out less as their temperatures rise and thicken up less as their temperatures fall than single ones do. This is great for cars, especially in cold weather, because it gives you a relatively thin oil at startup, so it circulates nicely around the cold engine, and then it stays thick enough once the engine warms up to keep things nicely lubricated. And since car engines are typically used frequently and seldom sit around in a moist bilge, it's not a terrible problem that the oil drips off of the innards relatively easily when the engine cools off. All of the above may be total BS, but I did get it from a reliable source, I think, but unfortunately that was so long ago that I don't remember who or how reliable that source might have been. |
|
#2
|
|||
|
|||
|
All of the above may be total BS, but I did get it from a reliable source, I think, but unfortunately that was so long ago that I don't remember who or how reliable that source might have been. I think its BS. My Mercruiser manual says to use 5-40. What the hell is that? so 10-40 isn't good enough? Real reason is to cause F.U.D. to discourage boat owners from doing work themselves. John C. |
|
#3
|
|||
|
|||
|
My Mercruiser manual says to use 5-40.
What the hell is that? so 10-40 isn't good enough? Real reason is to cause F.U.D. to discourage boat owners from doing work themselves. no, 5w-40 lubes better upon ambient temp engine startup that 10w-40 and much better than 30w or 40w does. however, the difference between 5w-40 and 10w-40 isn't all that great. In past, 5w-40 didn't hold up as well under long service, and so was seldom sold. |
|
#4
|
|||
|
|||
|
"JAXAshby" wrote in message ... My Mercruiser manual says to use 5-40. What the hell is that? so 10-40 isn't good enough? Real reason is to cause F.U.D. to discourage boat owners from doing work themselves. no, 5w-40 lubes better upon ambient temp engine startup that 10w-40 and much better than 30w or 40w does. however, the difference between 5w-40 and 10w-40 isn't all that great. In past, 5w-40 didn't hold up as well under long service, and so was seldom sold. Thanks all. With all that, I don't see any reason that a 20w-40 or 20w-50 would not be a preferable choice to plain old SAE 20, 30, or 40 which are all recommended in my 1987 manual. -Dan O. Minneapolis |
|
#5
|
|||
|
|||
|
With all that, I don't see any reason that a 20w-40 or 20w-50
would not be a preferable choice to plain old SAE 20, 30, or 40 which are all recommended in my 1987 manual. operating weigh above recommendations can harm seals. thus using 20w-40 in place of 20w doesn't do any good for lubing upon engine startup and can do some harm when the engine is warm. some people are under the mistaken impression that multi grade oils "thicken up" as they warm up. they don't. they just thin out less as they warm up. |
|
#6
|
|||
|
|||
|
|
|
#7
|
|||
|
|||
|
ben, that is utter bull****.
a 30w oil will keep its viscosity over a much broader temp range then a multi weight oil. 30w oil viscosity ***changes*** over the entire temp range. |
|
#8
|
|||
|
|||
|
ben, that is utter bull****.
just to clarify jax a 5w-40 oil is 40 at rest/cold therefore will take more time to pump anywhere being theoretically 25% thicker then a 30w oil. 5w-40 is ***5w*** at cold temp. kriste on a crutch, ben, 14 year old boys know this. |
|
#9
|
|||
|
|||
|
bennie, I own a mid-80's Fiero and right on the oil fill cap if embossed the
directions to use 5w-30 oil. That means for 20 years at least the manufacturer GM has recommended multi-weight oil. in fact, GM has recommended multi longer than that, since the 1970's go ahead. tell us it was a GM plot to sell us more cars. manufacturers dont make recommendations for no reason, follow them and you will never have any trouble. if you are having trouble finding a 30w oil any volvo dealer will sell it as a lot of volvo equipment uses that grade. |
Hybrid Mode
