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Oil Burning and Oil Weight

Just before my most recent oil-change, I noticed my car’s “check oil level” warning coming on when I would start my car when it was pointed downward on an incline. I was, indeed, at the “add a quart” level. A day or two later, when my mechanic was changing the oil, I mentioned this to him, and he suggested that, instead of using the 10w-30 oil that one is supposed to use in a 2001 Buick LeSabre custom, that I try using 10w-40 oil for the remainder of the summer, hot months.

“The parts of the engine get worn, over time, and the thicker oil will tend to fill in some of the slightly larger gaps.”

My mechanic’s FATHER–they are a father and son in business together, and both extremely good, smart, seasoned, old-fashioned mechanics, who love cars–overheard this, and objected. “I wouldn’t put 10w-40 in that car; in emissions school they told us not to–and it will sludge up the engine!”

This was the first time I heard them disagree about such a matter, but the son said, “It’s what I would do for my own car,” and went ahead to add 10w-40.

My 2001 Buick LeSabre custom has about 133,000 miles on it. Since my oil change, I’ve come accross a number of remarks, on line, from people saying that “down a quart” in about 3000 miles is not at all to be regarded as problematic. (I have always had an oil-change quite regularly every 3000 miles).

My question is: Who is right? Albin, the father, or Justin, the son? Could it be somewhat HARMFUL to disobey GM’s engineers and use a heavier oil in summer? Will it “sludge up” the engine, as Albin suggested? Or, as Justin suggested, in warmer months, might the heavier oil be less likely to burn and be more likely to keep the engine well-lubricated longer?

Use the weight recommended in the owner’s manual or on the oil filler cap. Then, get in the habit of checking the oil level every week or so and topping it off.

Never overfill it. Never run the car more than a single quart low. For the “check oil level” warning to come on, you were likely down about 3 quarts out of 5. If that is the case, start shopping.

You’re not using very much oil, I’d stick with the recommended oil weight and add some when you get low.

Both the father and the son are correct, but it is really not very important. Replacing 10W-30 with 10W-40 will do no damage to an engine of this vintage.

I would point out, however, that I have never seen a 10W-40 oil come out on top in an independent test of motor oils. It takes a lot of tweaking to get conventional oil to have a 30 point viscosity spread. The sludge the father warned of has more to do with additives than with viscosity. At 3000 mile oil change intervals, sludge should not be a problem for you unless you drive nothing but very short trips. All other variables being equal, a 10W-30 oil will perform better than a 10W-40 oil in a test.

Modern cars use their oil as a coolant, and cars with variable valve timing tend to force oil through some pretty small holes. Those are two of the reasons why we are warned to never use oil with higher viscosity than what is recommended by the manufacturer. I don’t use 10W-40, but I would not worry about it.

No one is really right. A Buick with 133,000 miles on the clock and well maintained is expected to burn a quart every 3000-4000 or so. Nothing unusual about that.

On the other hand, starting a car in the morning with 10W40 oil will add to engine wear and INCREASE oil consumption. However, it will not cause sludging, and those two should know that. Sludging is caused by changing oil not often enough!

Last year I rented a new Toyota Matrix, which uses 5W20 oil! It also said in the manual that having to add a quart every 750 MILES!!! was not unususual. In other words, today’s thin oil lubricates OK, and activate the valve gear, but expect oil consumption. In your case, I would stick with a quality 5W30 oil and add as needed. It will mean the cost of a six pack of Budweiser every few months.

P.S. Both father and son need a basic course in the priciples of lubrication!!

I have a 1978 Oldsmobile Cutlass with the 260 cubic inch V-8 engine. The owner’s manual specified either 10W-30 or 10W-40. I thought that the added protection of 10W-40 would help the engine, so that is what I intitially used. However, I kept having trouble with detonation (engine ping) from carbon buildup. About every 90 days, I would have to pour a can of Casite motor tune-up in the gas tank and also pour a can directly into the carburetor. On “Car Talk”, a motorist called in with the same problem. Tom and Ray asked about the oil and the motorist was using 10W-40. They said that certain brands of 10W-40 had polymers that extended the viscosity and would cause carbon buildup. I switched to 10W-30 and never had the detonation problem after that.
Now, your Buick is fuel injected and runs much cleaner than my 1978 Oldsmobile. The 10W-40 probably won’t make any difference one way or the other. However, if it were my car, I would go back to 10W-30 at the next oil change.

I use 10w40 year around in my '88 Escort which is spec 5w30. I’ve been using 10w40 in it ever since I bought it with 146K miles on it except the last oil change when I used some 20w50 I had in the garage. My brother bought the car new and either ran 10w30 or 10w40 until I bought it, I’m not sure which. It currently has 517K miles on it. I did have to remove the oil pan a few months ago and clean the oil pick up screen on the oil pump (first time in over 500K miles), but I think most of the sludge problem was due to driving it on dusty construction sites for the first 12 years 350K miles of it’s life than the use of 10w40. The 10w30 and the 10w40 will both have the same lubrication at start up, because they are acting as a 10 weight oil when cold, the only difference is in warmer temperatures the operating weight will be 40 weight instead of 30 weight. With the mileage and age of your engine, I wouldn’t expect any negative affects from the 10w40. I maintain 7 cars and a motorcycle in my family and use 10w40 in all of them. My newest car is an '02 Ford Escort that is spec 5w20 it has about 118K miles and uses about a half quart of oil between changes (5K miles). For what it’s worth I’d have taken the advice of the son. Most likely if your oil pressure light was coming on it was at least 2 quarts low on oil. I’ve never seen a car where the light came on at only 1 quart low.

If the owners manual states it’s O.K. to use 10W-40 as well as 10W-30, then using 10W-40 would be perfectly all right. If it only specifies 10W-30, I would resort to 10W-40 only if the car burns “a lot” of oil. The problem is deciding how much is “a lot.” If it uses 1 quart per 3,000 miles, most people would agree that it is not a lot at all. I personally think using 1 quart in 500 miles would be a lot. The point is that if the internal engine parts are so worn out that oil is leaking through all kinds of gaps, then it’s time to use thicker oil. If not, then stick with what the manufacturer recommends. Also, check oil often. Find out how many miles it takes to use 1/2 quart and add that much to bring it up to full (but never more than full). Don’t wait to go down by 1 quart to add.

While the thicker oil won’t hurt it, it will give you slightly less gas mileage, and not significantly more protection unless you’re racing it.

Down 1 quart in 3,000 miles isn’t bad at all. There are Audi/VW owners who would be tickled if their cars only used this much oil. Instead of switching weights of oil, perhaps try a different brand or switch to a full synthetic, like Mobil-1. My oil consumption on my old car dropped from a little worse than yours to practically nil after switching to synthetic.