low tension piston rings the reason for lower viscosity oils?

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JHZR2

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Hi, Had my 98 Chevy S10 in for service and was talking to a very knowledgable technician. One thing I asked was about oil viscosities, and if he thought something like a 5w-40 would be better for the L35 4.3L V6 in my truck. I told him that I wondered about using heavier oils because my sources have stated more or less that tolerances and clearances havent really changed at all in a long time. He said that the reason for this was that engines now use 'low tension piston rings', which have less friction and less pressure against cylinder walls. Since there is less pressure, a thinner oil can be used and still provide an adequate (or sometimes better) film. Also inferred that bearing tolerances should always have an adequate flow of oil to provide a good protective layer, so long as oil pressure is sufficient, and the fuel isnt too thin, i.e. diluted with coolant or fuel, etc. He said that the 5w- oils are mainly for fuel economy in cold engines, and for these engines a 10w-30 oil (particularly synthetic) would be the best protection, although 5w-30 is preferred for all climates. 5w-40 would do nothing but rob HP. So a lot of what he said is exactly what we have been saying here for a long time. However, I notice that most of the discussion is about bearing tolerances and oil weights, when he seemed to suggest that piston rings, and their respective pressures on the cylinders, etc. were an important factor. Any comments? I know it seems that the LS1 engines have been successful with 40wt oils, and I know my 4.3 is essentially a 350 with two cylinders cut off. But Id bet the designs of a lot of things are different, particularly because one is a car engine, the other for a truck. I had a good analysis one time using rotella synth 5w-40, as I got 8.5 ppm after 3000 miles on this all iron engine. But I did feel like power was a bit less. Im thinking of going to M1 10w-30 next, as I know this is a highly regarded oil, but we shall see. That 0w-30 racing looks good and is probably a bit thicker than the m1 30weights that tensd to be quite thin. JMH
 

JHZR2

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Thus my question... But his point does make sense, because if the piston rings arent pressing as hard on the cylinder walls, then a thinner oil can sit in there and lubriate well without being forced out, as it might be if there was a lot more pressure against said cylinder walls.
 

tpi

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Combustion pressures force piston rings outward toward cylinder wall by design. The maximum force on the piston ring against wall is not brought by the spring tension. My guess is 20 wt. is sufficient for at least reasonable wear, and has been all along. It was recommended in the '50s and '60s for summer use. Today's engines benefit from much finer fuel mixture control between cylinders, less likely to ping or detonate, better and more controlled warmup fuel ratios, unleaded fuel, less likely to have vacuum leaks or other life shortening problems, and frequently better temperature regulation. Throw in superior oils and you get longer lasting engines. Judging by the long life of old design engines currently in use (SB Chevy, Buick V6, Jeep inline 6) most likely all the '50s designs would give outstanding service today given modern fuel management, hardened valve seats, and today's oil. [ January 30, 2004, 10:55 AM: Message edited by: tpi ]
 
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For the last thirty odd years there has been a water cooled four cylinder VW in our garage. I have kept all the factory shop manuals from that first Rabbit in 1975. Bearing clearances have remained essential the same for all models. Since the advent of 'low tension piston rings' some clearances in the ring pack have actually increased. Example piston ring side clearance is greater than twenty years ago. VW's used to use 20w-50 in all climates above freezing. Apart from valve stem oil control problems, VW's had bullet proof bottom ends and had NO OIL BURNING ISSUES with rings. Today is totally different and VW owners are running out of oil as it is being consumed in some cases as much as 1 litre per 1000 kms. If you own a modern VW, you had better check your dipstick on a regular basis.
 

Patman

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quote:
If you own a modern VW, you had better check your dipstick on a regular basis.
A friend of mine has a girlfriend who bought a 2002 VW Golf brand new, with the 2.0 engine and it burned a liter of oil every 2000 to 3000km, so he complained to VW and they rebuilt the engine. This was last year that it was rebuilt, and now the engine is burning oil yet again! (at about the same rate) I don't know what the heck is going on at VW, but it's definitely a problem. Another guy I know in my car club said his wife's Beetle also burns about a liter every 2 or 3000km. [I dont know]
 
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As far as "heavier" oil robbing HP, I think the only way to verify that one way or another would be a carefully controlled engine dynometer or chassis dynometer test. My Uncle, who used to be a mechanic on HD equipment and cars until he retired in 1985, claimed that 30 or 40 was used in summer, and 20W-20 or 10W in winter. Sometimes you had to mix kerosene in the 10W to get it working good at temps colder than -15 F. These were the "good 'ole days?" No thanks! I ran Mobil 1 15W-50 and Delvac 1 5W-40 in my 1990 Toyota 4Runner and had NO difference in fuel economy compared to a 5W-30. Much quieter too. I've heard of the VW oil burning issue too, a friend of mine in Salt Lake City bought new a 1996 VW Golf, then in 2001 traded for a new VW Golf, both with the gas motor. He claims the European VW's don't use oil but the American ones do depending on how they're driven and how they're maintained. He immigrated from Switzerland and refuses to run a "light" 5W-30 except in coldest winter. Like most Europeans, his idea of a "short" OCI is every 6,000 miles. After much research he ran Mobil 1 15W-50 in summer and Mobil 1 5W-30 from Nov to Feb. He did the initial service at 3,000 miles, after using about 2 quarts of factory oil. He drives the bejeezus out of his Golf's, especially rodding them up steep grades on I-80 from SLC to Kimball Junction and Park City, and has never used more than 1 quart every 6,000 miles on 15W-50, 1 quart every 3,500 miles on 5W-30 in winter. I'm not sure if his aggressive driving helps "seat" the rings or if Mobil 1 15W-50 helps control oil consumption. Any thoughts?? Jerry
 
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given the fact that cylinder pressure forces the rings against the cylinder walls, like terry said, i would think that low tension rings do not provide any friction reduction during the ignition stroke. it seems to me that low tension rings would only be beneficial during intake and exhaust stroke, however this would be where you do not want low tension rings, as they would be more prone to leaking? same with the compression stroke.... i would rather have high tension rings and lose half a mpg.
 
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quote:
I wonder if gapless rings will ever make it to production cars?
I use them on my Dodge 2.2's and 2.5 Turbos. My 84 Unturbo Shelby had NO blowby and on a crompression test was at 215 Lbs on all 4 dry and 220 with a shot of 20w oil. With the only change being the rings and main bearings it picked up 4/10's in the quarter mile. I am installing them on my 78 Dodge Little Red Express trucks 360. DaveJ [ January 30, 2004, 10:59 PM: Message edited by: DaveJ ]
 
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quote:
Originally posted by Patman: [QUOTE] I don't know what the heck is going on at VW, but it's definitely a problem. Another guy I know in my car club said his wife's Beetle also burns about a liter every 2 or 3000km. [I dont know]
And the problem is that it is impossible to find out. Up here in Canada we have the VW personnel gives us some amazing reasons when customers complain. The favorite is : "The rings have not seated yet. come back in another 20,000 kms" " You did your first oil change before 7,500 Kms" Thats a no-no!!! " You are using synthetic oil?. Well no wonder the rings have not seated" " All cars burn oil. It s perfectly normal" And it goes on and on. [ January 30, 2004, 12:35 PM: Message edited by: Nosmo King ]
 
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Ring tension must be matched with the engine design and I'm no builder but 'lower" tension oil control rings help improve HP production but at the expense of oil control depending on the pressures involved and ventilation etc. A more chemically stable and POSSIBLY higher vis oil may help. My daughters 1999 2.0 L VW/AUDI engine uses 0 oil but I run M1 10w-30 with LC at 2 ounces per qt currently using 10,000 mile drains. Same one she drove 16+ miles with no coolant recently. [No no] It is a remanufactured engine as the last owner ran it out of oil and destroyed it.
 
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Lot of good information here. At first I was thinking about combustion pushing the rings against the cylinder wall, but as I read on I began to wonder if the low tension rings are more easily pushed against the cylinder wall because they flex easier in both directions.
 
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quote:
Originally posted by Terry: My daughters 1999 2.0 L VW/AUDI engine uses 0 oil but I run M1 10w-30 with LC at 2 ounces per qt currently using 10,000 mile drains. Same one she drove 16+ miles with no coolant recently. [No no]
[Off Topic!] Terry, I'm planning on running Chevron Supreme with an ARX treat for the next OCI on my Wife's Corolla. The car has ~23k and although it is still very new, we know ARX seemed to have done a good job in my Z. Anyway, afterwards I plan on running M1 5W-30 and LC for 10k or more, just like your daughter's. As long as I have it, might as well run some LC in the Z too [Roll Eyes] [Wink]
 
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