Changing to 10W40 won't give you any benefits unless your doing some long hard driving. If your oil pressure is still good run what ever the manufacture calls for.

the oil is all 10 weight when you start the engine, if its a 10 oil, the 40 is what the oil becomes after it heats up, it increases viscosity at temp.  manufacturers advise 5 weight for an easier start up given the tighter tolerances in newer technology engines.  personally given the nice loose engines i have, a 15 40 or even a 20 50 is more my style.  i had an old motor in my toe truck that i used to run straight 40 weight, the engine died when i put some 10 30 in by mistake.

Visit www.Bob is the oil guy.com. Open "Oil 101". All engine oil thins to a 10 weight when it reaches oil operating temperature!
Read the part about oil pressure and oil viscosity and the reading on your gauge. A zero or 5 weight oil is best for starting the engine. Flows better cold. Semi-synthetic flows better still, Full synthetic flows best.
Make sure you run a ZINC & PHOSPHATE additive in your engine. TKO is the highest zinc content of ALL of them. Shop around.
By the time you finish reading OIL 101 you will realize how many people don't have any idea about oil and base their "Knowledge" on rumours and wives tails. Oils truly are an area where "they were better in the good old days".

Your grandfather put 38,000 miles on his old car and then parked it behind the barn, about 15 years after he bought it, ALL MILES PUT ON WITH AN HIGH ZINC AND PHOSPHATE OIL. You put 20,000 to 30,000 kms per YEAR on your car That's 13,000 to 19,000 miles PER YEAR! Your Hot Rod gets 3,000 to 5,000 miles per year and the new oil is CRAP! ALSO READ THE PART ABOUT OIL ADDITIVES.

I don't care what John Force says, he's not running a 30-50 year old car with flat tappet lifters. Everything he runs has roller cams and new oil EVERY PASS! and he still replaces parts at an unbelievable rate. If you have his level of sponsorship pour anything in,
If you're like me (hip pocket financing) be careful and read LOTS!

Mercury Marine runs roller cams in their engines. They insist you run Mercury Marine Brand oil if you would like to have warranty. This is because most oil is garbage. They have boosted the zinc & phosphate level in their oil to prevent cam failure from inadequate protection of the cam lobes. Are you familiar with Quaker State "ENHANCED DURABILTY" oil? It's in red containers. It is the closest thing to the oil our cars require, that Quaker Stae sells, short of "OFF-ROAD ONLY" Oil. (no catalytic convertor) Why don't they promote that one?

Did anybody ever see anything from any oil company about the reduction of zinc in oils? How the the Governments that MANDATED the reduction of zinc in oil to stop contaminating catalytic convertors, anything from them? The governments want us to be buying NEW cars/trucks because they need the tax money. They don't want our old cars on the road, because we are not paying enough taxes on them.

Before you dismiss "Bob is the oil guy" read his credentials, see what he uses to test oils and who has contracted him to do research.

One last thing. Read the part about ALL the 305/350 cams that ground down the lobes still passed ROCKWELL Hardness tests after the lobes were worn off. How did that happen?

It's your car and your money.

the Kid.

exactley, you must let the heavier goo work its way thru the engine or stuff it full of bananas and sawdust, for the kijiji sale