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Older vehicle, heavier oil in the Summer?

I was told by a mechanic that I should use a heavier oil in my 2000 Blazer in the summer months because of the mileage. (200,000+ miles) The manual says to use 5W30. Which I have used since I bought it in 2009, with 112,000 miles on it. Should I do as suggested? Or continue as usual?

The maker of your vehicle knows more about it than the mechanic. Keep doing what has got you to 200,000 miles.


Have you got 112K on this Blazer, or 200+K miles? Where do you live? How hot is hot? Nothing wrong with 5W30, but why are you asking? Are you burning lots of oil? If you add 1 or 2 quarts of oil between 5K oil changes that is pretty good.

You can use heavier 10W30 or 20W50 in hot summer weather, but if you live in an area that gets below freezing in the winter you’ll be back to 5W30 in the cold weather.

What is the reason your mechanic is recommending “heavier” oil?

durning the summer mounths i won’t use anything j=heaver then 10w-30 but put 5w30 back in her for the winter

Your mechanic is likely an old-timer, since this advice was universal a couple of decades ago. Some folks still follow that method, especially on older cars.

For your 2000 Blazer, with 200K miles, it may be a good idea. 10W-40 in summer, 5W-30 in winter. Or you can stick with your current weight oil year-round. It hardly matters.

10/30, 10/40 or 15/40 may offer some added protection during the summer months and then again, they may not…Switching to one of these grades certainly won’t hurt anything…

I love living in Mexico. But, the culture does have its peculiarities concerning cars.

I was trying to buy 5W30 Quaker State for my Sienna. The shops which sell oil tend to mostly stock 20W-50. I went into a shop and asked for 5W-30. The kid in there, told me that was not good, that 5W-30 would allow the motor to burn up. Sigh.

Even Autozone in Tehuacan does not always stock the correct oil. I assume because no one will buy it.

I finally found a shop which had the correct oil. I assume this bad information gets passed on generation after generation, and it is a waste of time to say a word to them.

I agree with Uncle Turbo. These old engines with high mileage could use 10W30 or heavier in the summer; if OP is towing a trailer, I would recommnd 15W40 mixed-fleet oil. This oil is suitable for both diesels and gasoline engines. I’ve used it a lot in the old Chevy small block engines when trailering.

Agree with irlandes; in tropical countries 20W50 seems to be the standard stuff at gas pumps and grocery stores.

I dont have any 20w50 in my store got lots 5w20, 5w30, 10w30, and 10w40 i am in the sothern half of NJ

Do you use much oil? If it’s running fine, I’d keep using what you’ve been using.

Who are you going to believe, your local mechanic or the manufacturer? I’d bet the manufacturer knows more and has more experience with those Blazers than any mechanic.

I find it silly to do things like this based on mileage rather than symptoms. Is it losing a small amount of oil? Well then, maybe a higher weight oil is appropriate, no matter how many miles it has on it. Is it not losing any oil? Then why fix what isn’t broken, even if it’s got half a million miles on it?

I disagree with everyone who says the manufacturer knows best… They do on a new car, and honestly even then THEY WILL sacrifice some ware and tear in the name of fuel efficiency and CAFE… However with 200,000+ on the car they can care less, and they don’t know what your car needs… Look at all the BMW/Mini owners who followed the 15k service cycle, and are out of warranty with sludged up motors.

With that said as others have said you surely will not hurt anything putting in a 10-40, but if you are not having issues with the 5-30 why change it?

What difference does summer make? You may need a thinner oil in winter to start the vehicle, but that does not mean you need a thicker oil in summer. Your engine has a liquid cooled, thermostatically controlled cooling system, its running temperature is the same in summer or winter.

There are several different lubrication demands in engines and the correct viscosity is the best compromise that the oil people can develop relative to all possible conditions. Cylinder wall/piston ring wear will cause excessive oil consumption and thin oils are best suited to quickly coat the pistons and protect them from wear but when worn those thin oils are more prone to blow past the rings and into the combustion chamber. At the other extreme is the camshaft and the cam follower/lifters which must have a lubrication film heavy enough to withstand the impact and heavier weights with extreme pressure additives are needed there. In tropical climates straight 30w is possibly the best choice. But there is way too much voo-doo and mystique in the recommendations and advertisements.

If you are not burning any oil I would not change. If you are burning oil I would consider it. If you are burning oil the extra viscosity can help, and you end up on the ever increasing treadmill of higher oil weights due to piston ring wear.

Either oil would probably be fine year round unless you live in an area where has very cold winters where it gets extremely cold and stays cold for long periods of time. I use 10w40 in all my cars year round and live in an area where temperatures sometimes get 0 to -10F, but normal is 10’s to 30’s for lows. Summertime high’s are often 90-110. One of my cars has over 500K miles, two near 200K miles, two between 125-150K miles, one near 100K miles and one under 50K miles. The only one that uses more than a quart of oil per 5K mile change is the one with over 500K miles, but I’m sure the rings and bearings have some wear with that many miles, it didn’t begin using enough oil to show on the dipstick until between 250-300K miles. The manufacturer recommends 5w20 or 5w30 for all my cars. I have a stock of about 20 cases of 10w40 in the garage so I’m going to be using it for several years to come.

The oil consumption seems to be due to leaking oil cooling lines. (Which are being replaced this week.) Prior to this, it didn’t seem to use any oil between 5k mile changes. I know the school of though for summer vs. winter oil weights is an old one. However, Steve F, this mechanic is under 40 years of age.

Thanks for all the words of advice everyone. I’m thinking I will stick with what is working.