Hey Mechanics…help…oil question?


My old timer mechanic is telling me to run 10w 40 in my 89 Chevy that has 87,000 miles. It calls for 5w 30 in the manual.
I don’t presume to know more than my mechanic…but seems to me it would call for 10w 40 if 10w 40 was okay. It had a small leak that I had him repair (O ring from distributer plug).
He…

I own a shop, and if I were you I would read the rest of the manual. If you read it, you may be surprised at what it says. 5w-30w is the recommended weight for room temp. This is worse than the debate over the tire pressure. Most people do not understand what viscosity even means. New (modern) engine’s are no different than older (classic) engines. They don’t build them out of special metal or anything like that! Thinner oil was introduced to the market due to gas mileage, and had nothing to do with some technical answer spewed out by over zealous mechanics with no experience. My friend purchased a vehicle that had a lot of miles on it, and decided to change the oil. I told him to put thicker oil in it, and he wouldn’t listen. On his way to our next gig, the engine locked down, and he showed up 1/2 hour late to play. An engine with thin oil gets better gas mileage, but the protection is not there. The bearings inside the engine get thin, and oil is what the crankshaft runs on, as it takes up space. Thicker oil remains in the bearings longer, thus thinner oil drains away quickly. Sit two bottles of oil outside (when its 10 degrees) one 5w-30w and 10w-40w. Open them up and try to pour them out. You will see the difference, but this is not where the oil does the most work. It’s when the engine is at operating temp, and isn’t this where the engine runs the most at? Base your oil on what the book says, higher viscosity for engines with a lot of miles on them, and add the temp outside. This works out to be what your “old” mechanic says. When an engine blows, a good mechanic will want to know what did it, so he can steer his customers away from problems. Read the instructions on the oil bottles, as well as your manual, and you will see he is right. Just because the manual says one thing, doesn’t mean it applies to all places. If you investigate the use of viscosity when applying the grade to use, figure in the climate you live in, and apply the wear on your engine, you come up with the CORRECT answer. Ice Road Truckers have to use the thin oil to even get the engine to start, but vehicles in the desert will smoke & knock when thin oil is used.
Glad to help out, Good Luck!!!

10w-40 won’t hurt your car. Manufacturer’s routinely specify 5 weight oil, because it slightly improves gas mileage, but it’s hell on your engine. It makes winter starting easier, but 5 weight oil is like water and nomatter what anyone says, just doesn’t lubricate as well as equivalent 10 weight oil. When the oil get’s hot in both cases it has the viscosity of hot 40 weight oil, so the main problem is in the first 5 minutes of operation…..but that’s when most of the engine wear takes place. Smart people use 10-40 from the beginning. It will help your older car, but making up for some wear and helping the compression stay OK. Won’t do any harm.

If you live North of the Arctic Circle however, better stick with the 5w-40, to get morning starts…otherwise switch to 10w-40.

The type of oil depends on the weather. Ifs it warm out side, then you use the 5w and if its cold, u use the 10w. Using different types of oil will not hurt the engine. All types of oil protect the engine, some more than others. But mixing oils is OK, it will not mess up your car.

no the 10w-40 won’t hurt it as it’s a heavier oil and if your car is using a little oil it will help it to not use as much but if it doesn’t use any oil I would go back to the 5w-30 as it’s a lighter oil and flows better in the engine and will give you better gas mileage.

I owned a few chevys and my 92 called for 5W30 and my mechanic told me that it wasn’t it a good idea because the oil was too thin that 10W40 or 10W30 was better for it. He also mentioned that there were a few engine failures due to the 5W30. You may want to ask around about that also.

Oil weights are important, but your mechanic is probably right. It has more to do with the normal operating temperatures in your area than anything else.

Go with what the manual says, you older mechanic is stuck on 10W40 because that was the standard oil from 1930 until 1990……

10 w40 is fine on that motor with the mileage.The parts have more wear and need a higher viscosity oil.

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