upping viscosity in older cars

[JHZR2]

Hi,

Sometimes I get the impression that it is believed that when a car gets older, the thing to do is increase oil viscosity.
If you arent consuming oil, why do it?
My girlfriend's car specs 5w-30 and we use that (just changed to mobil1, Im not worried about it being light because its an acura, which now uses 5w-20)
My fathers van uses 10w-30 as suggested from the very beginning, its totally fine at 150k on 7500mi dino changes.
My diesel Mercedes should use 15w-40 according to the book, but I have changed to delvac1 5w-40 about 10k ago and are now over 200K... No oddness, or oil consumption.

Is there any reason why I would ever want to consider upping the viscosity? The cars seem to be doing well on their own.

 

[MolaKule]

quote:

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Sometimes I get the impression that it is believed that when a car gets older, the thing to do is increase oil viscosity. If you arent consuming oil, why do it?

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In some instances, such as when it is found or believed that bearing clearances and piston ring/cylinder clearances are going to the far end of service specs, it makes sense.

But if you are not using oil, or don't have unusual engine noises, then I'm with you. As grandpappy said, "don't fix somthin ifin it ain't broke."

 

[JohnBrowning]

I belive that the old API oil Grade/Vis Charts based on temp are much more accurate then current trends buy manufactures when the car is sold in the U.S.! It makes no sense to thnk that a 5w30 dino oil that is ok for a vechile in the winter time and used for short trips is going to protect the engine well at 75-90 MPH speeds for hours at a time in Texas in the summer. I also think that it is funny how engine oil weights recomended for vechiles keep droping even if the engine has not changed at all since 20W50 was recomended. It is even funny to read a book on building up up small blocks with OEM parts with raceing in mind. In the book (put out by a large OEM) it clearly recommends 20W50 but that same engine with oem parts off of the assembly line only recomends 5W30! Owners manuals and oil caps are not the most definative sources of automotive knoldge and are intended to be simple for those people that want simple! The truth is never as easy as one all defineing single answere.