Oil weight

Okay, Let’s see if this makes sense.

You’ll use an oil that flows slower at a cold start which the 10W oil will do over a 5W oil? And then have the same protection once the oil hits a hot component?


I have the original owners manual for my dads 1948 chevy, I was reading which oil to use as they were just straight weight oils then …If I remember it said use a 20 or 30 weight in the summer, then for winter said a 10W…Now the kicker is, if the outside temp drops to 10 or more degrees below zero, to mix 10 % kerosine to the winter oil !! YIKES ! No wonder the engines of this era had a short life.

@jaspn here’s my take on the oil viscosity

I’m fairly certain that 10W30 was one of the most common viscosities for gasoline engines in 1982

5w30 didn’t become “commonplace” until several years later, perhaps in the 90s.

I say stick with 10w30

My 1978 Oldsmobile Cutlass with the 260 cubic inch V-8 called for either 10W-30 or 10W-40. I thought 10W-40 would be better. However, the polymers to give the 10W-40 the viscosity range also caused carbon buildup on the pistons. Every 2 months or so I would add a can of Casite Motor Tune-up to the gas tank and pour a can through the carburetor. I then heard that certain brands of 10W-40 in certain GM V-8 engines would cause this condition. I switched to 10W-30 and the carbon buildup problem disappeared and there was no oil consumption. The first car I owned that specified 5W-30 was my 1985 Ford Tempo. However, the manual did say that 10W-30 could be used if 5W-30 wasn’t available, but at the next oil change 5W-30 should be used. My guess is that 5W-30 wasn’t common in 1982 when your Chevrolet was made. I would guess that the correct oil by the manual would be 10W-30.

My opinion, use either the 5w30 or 10w30 and your engine will be fine. I would not use 10w40, but I might be behind the times on this a little. In 1982, if you used 10w40, the top of the engine would sludge up real bad. I had seen engines at that time that used 10w40 ruined in 40 to 50k miles, especially GM engines.

The 10w40 oil back then would start to sludge up at around 295°F and the oil in the GM V8 engines at the time would run at around 305°F. But even 10w30 at that time had a lower temperature at which breakdown would occur. Today most 5w30 and 10w30 oils can take around 350°F so the 10w40 may have also been improved, I just haven’t seen any figures on it lately.

This is Phoenix. Does it really matter what you use ? Maybe a 5 or 10- 40w for summer consideration but other then that…

Maybe 10W-30 made 1982 held up better in the heat than 5W-30 from back then,
but today’s oils are so much better than both.

Even 0W-20 would protect as long as oil pressure didn’t drop too low,
but then there’ could be more consumption and leaks.

The chart for your car says " Above 11 degrees= 15w-40, above 0 degrees= 10w-30, above 20 degrees= 20w-20, 20w-40, 20w-50, below 60 degrees 5w-30, above 39 degrees straight 30 weight". All temps in fahrenheit . These are the specs for your car, not an opinion.

@circuitsmith my relative’s 2004 Grand Cherokee 4.0 calls for 10W30 in the owner’s manual.

And that car is much newer than OP’s car. Plenty of other cars were calling for 5w30 back then. Yet Jeep specifically called for 10W30.

Are you suggesting that a manufacturer would say it’s okay to use a thinner oil in an older car?

I think somebody from the oil industry needs to chime in.

Ur motor has flat tappet lifters so it likes high zinc oil. Been told 10w-30 has better wear properties than 5w-30. I would like to use 0-30 for cold weather starts but syn oil is pricey. Is ur motor fairly quiet at idle? Any lifter noise?

I wouldn’t think that 10W40 would be an issue anymore, especially if you use some kind of synthetic. The same goes for 5W40 and 0W40. Many of the European cars specify change intervals much longer than domestic vehicles and they can use 0W40 for up to 10K or longer. These do spec very high performing oils to prevent sludge and breakdown as well as larger filters for these long change intervals. I have a car that specifies 5W30 but am using a European spec 0W40 in it. These oils simply didn’t exist 25 years ago when the car was made but help with cold weather starts, all while providing greater protection than in the past. If you want to use the cheap store brand oil on sale, staying with 10W30 might be best. If you want to splurge a little and get synthetic, I see nothing wrong with a slight change in the weight.

Several people I know like to run the Rotella T6 5W40 synthetic diesel oil in their gas cars. This is good oil and provides extra wear protection for hard working diesel engines. On the other hand, the additives can foul emissions sensors, the cat, and such, especially if you are burning some oil. I think nothing of using this oil in non-emissions gas equipment like mowers, etc. You can usually get 5 quarts of the Rotella T6 at Wal Mart for like $20 so that seems like a pretty good deal.

What kind of driving are you doing with your 1982 Impala?

If you are doing interstate driving, towing a 2500 pound trailer and traveling 80 miles per hour, then go with a heavier oil. If you are doing local driving, 10W-30 should be fine.

Many of the European cars specify change intervals much longer than domestic vehicles and they can use 0W40 for up to 10K or longer.

And some of those vehicles (like BMW) are having major sludge problems with under 50k miles. Personally I’d stick with a shorter change interval and try to keep the engine running good as long as I can. Since I keep my vehicles over 300k miles I’m not going to take the chance on 10k oil change intervals.

Well, it “feels” ok. Motor has not blown up. So manual says use 5w-30 but something else is “ok” cuz it works? You going to tell me a new BMW OHC motor has same bearing clearances as my 33yr old push rod Chevy? It works for BMW, so it has to be good for Chevy?

Mike, I used to go about 11,000 miles between oil changes on my 02 Saturn when I used the cheap Walmart SuperTech synthetic oil, At around 80k, I switched to conventional oil and run about 5500 miles between changes. I have 255k on it now, but since I have retired, I don’t drive it all that much so I don’t know if I will live long enough for it to see 300k, but if I did drive more, I have no doubt it would make it.


“You going to tell me a new BMW OHC motor has same bearing clearances as my 33yr old push rod Chevy?”

You might be surprised at the answer.

@MikeInNH Agree, but the Eurpean oils also have a lot more additves. Just the same, 24,000 miles between oil changes for a Vauxhall in England is insane. However, the car will run till at least the end of the warranty.

Pushrod (stove bolt) Chevies had very large clearances. Any new engine designed today is much “tighter”; my new Mazda 3 uses 0W20 synthetic and in 4000 miles has yet to show any drop in the oil level. A stovebolt Chevie would have gone through at least one quart already with that oil…