That would be an interesting discussion , but I doubt that it matters much. If he ran the engine out of oil (or low enough that the oil pump was sucking air and the engine started to clatter) then he may have scored the crankshaft and bearings. Cylinder walls may also be scored. The oil pump could have also been damaged. In hot weather if the oil isn't thick enough the oil pressure could drop to the point where more damage will occur. Also a heavier oil may reduce oil consumption.
-jim
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Thicker oil may increase the indicated pressure on the gage, but the overall result might not be as desirable as you think. The gauge is measuring pressure at the beginning of the oiling system shortly after the oil pump. BUT - What is happening further downstream in the oiling system when you use thicker oil? Certainly the thicker oil may leak out of bearing clearances slower, but there will also be greater pressure drops through oil passages. The flow to rear main and rod bearings, cam bearings, etc, might be reduced. High pressure / low flow might actually be worse than low pressure / high flow. Thicker oil can provide higher oil film thickness in bearings (usually a good thing) but if the oil flow is too low because the higher oil does not flow well, you can actually starve bearings further along in the system.
OK so he shouldn't get carried away and use pure STP or pure MotorHoney or axle grease in his crankcase. 10-40 is not so thick it won't flow thru the oil passages. The oil temps in an engine are higher in summer than winter that affects the viscosity of the oil. When the engine reaches a point where it is worn enough it is a good idea to compensate for that loss of viscosity in hot weather.
-jim
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I agree than 10W40 will not cause oil flow problems. However, it probably won't fix his problem either.
As for the oil temperature - as long as your cooling system is in good shape, the "hot" oil temperature varies a lot less than you would think from summer to winter. The temperature of the oil actually varies a lot more with continuous engine load than without outside temperature. Towing or high speed driving in New York in the winter will heat up the oil a lot more than driving the car unloaded in the Arizona desert in the summer (assuming your cooling system is in good shape). One of my Audis had an oil temperature gauge. I used to be amazed at high steady it was most of the time. However, if you drove for a few miles at WOT, the oil temperature just kept climbing. I wonder how they got away with this in Germany where people can drive for miles on the autobahn at WOT. After looking into this, I found that in Germany the car had an auxiliary oil cooler. I guess Audi felt this wasn't needed for the US since we had relatively low speed limits. And I guess they were right since most of the time the oil temperature varied very little once the car warmed up.
The OP reported that the increased oil consumption was due to running the engine low on oil. The particular type of damage that occurs under those circumstances and considering that his oil consumption is around 1 qt. every 350 miles is likely to be small scratches in the cylinder walls, pistons, crank-bearings and bearing journals. Those scratches are the main cause of the oil consumption. Aside from the minor scratches everything else in the engine could well be pretty tight and in good shape. Using 10-40 instead of 10-30 may reduce his oil consumption and extend the life of the engine far into the future.
-jim
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You mean like you think no one has ever felt an oil pan in summer and winter?
Why is there something wrong with your cooling system. You just said in the previous paragraph that the oil stays the same temp if your cooling system is working. The reality is there is a lot of surface area like oil pan and valve covers that shed a lot more heat when it is 20 below than when it is 100F. That means all else being equal the oil will run cooler when its 20 below.
One of my Audis had an oil temperature gauge. I used to be
Yeah well I thought the discussion was about the OP's engine not yours.
He shouldn't use 10-40 in the winter because it will make the engine easier to start if he uses 10-30 and lives where it gets cold. If he lives in Hawaii then he can use 10-40 all year. He said he does only city driving so there is no need to bring the Arizona desert or towing or the autobahn into it.
If 10-30w is the recommended oil for his engine then previously (before he had his little accident with running it out of oil) the pressure regulator is what maintained oil pressure. Now, it is likely that when the oil is hot (like on a hot summer day) the oil pressure is not as high as it used to be and may fall below the limit set by the pressure regulator.
-jim
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Back in 1971, I was in Atlanta.I was looking around in the Atlanta Underground.I saw an ad in a freebie handout newspaper about a guy in Lawrenceville, he had a 1957 Ford Thunderbird car for sale.At the time, I owned a 1968 Ford Mustang car.I traded my car plus $350.00 for the T Bird car.About every nienty miles, I had to stop and add a quart of oil to the T Bird.That T Bird car was slap worn out.The exaust leaked so bad I didn't dare drive with the windows up, a bunch of things.When I got back home with my T Bird car, a front end lineup shop had to put in no telling how many shims to get the front end reasonably lined up.
Later on, I saw an ad in Hemmings Motor News magazine about a 1931 Model A four door car for sale in Sublette,Kansas.I put a hitch on my T Bird car and an old buddy went with me to Sublette.I paid $700.00 for the
1931 Model A Ford car and towed it home behind my T Bird car.Making those sharp left and right hand turns, the old hardened grease in the Model A tie rods wouldn't let the Model A steering straighten out.I had to stop and twist the Model A steering wheel to straihten it out.About a year later, I traded my Model A Ford car to a local area guy for his
1939 Ford car.Later on he told me he had to go to dodging because of the brakes on the Model A.
One time, one evening when I was mowing my front yard, a guy from Indiana stopped and he asked me, How much do you want for that car? (my old T Bird) I sold the T Bird to him for $2,000.His pretty peroxide blonde wife wanted the T Bird. cuhulin
I don't see why the flash point would matter since any oil that finds it's way into the combustion chamber will be burned. I had always assumed that the conventional wisdom was that viscosity oil would resist being sucked into the chamber as readily which would reduce oil consumption.
Heavier oil does get consumed more slowly by worn engines, within limits. The upper number isn't as important as the cold viscosity, though; 15W-whatever will work better than 10W-40. For the same reason, there is little advantage in going from 10W-40 to 10W-30 for Winter, because it's the starting viscosity that matters most in cold weather.
You obviously have never poured 10-40 and 10-30 when it is -20F outside. If you had you would have noticed that there is a significant visible difference in viscosity no matter what the API might say. At that temperature, it makes a noticeable difference in engine cranking also.
-jim
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I shouldn't have used that example, because the wider the spread in viscosity, the more likely you are to find the oil behaving wrong, especially with non-synthetics. I never use oil with a 30 weight 'spread' anymore. 10W-30 seems to be just fine for Summer driving, so
10W-30 in Summer and 5W-30 in Winter (if the engine isn't worn) is probably the best way to go for normal driving.
No, because that's basically the DEFINITION of the API rating. If there's a huge difference in cold pour characteristics, then the oil really isn't meeting its API rating. Which, to be fair, is entirely possible especially for bargain oils, and high viscosity spread oils.
So the answer is yes you just read about it. You didn't read very well. The cold pour rating is not for -20F. When it is -20 there is a noticeable difference.
-jim
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Ask the manufacturer for a plot of viscosity versus temperature.
The various API ratings require the viscosity to be in a certain range over a certain temperature range. But once you exceed the rated temperature range, all bets are off.
If you buy an API SL grade oil marked "10W-30", you know according to the standard that it will be a 10 weight (7Pa) oil at -25'C and that it will be a 30 weight (2.9mPa) oil at 150C. But you have no idea what the oil is going to do outside of those two points. And when things get really cold and really hot, the viscosity improvers get weird sometimes.
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