Can a 20 weight oil protect as well as a 30 weight?

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Staff member
May 27, 2002
Guelph, Ontario
With the trend on some new engines to go with a 5w20 oil, I'm wondering if it can protect the engines as well, or is it another ploy to simply get more fuel economy out of the cars to meet CAFE? Has anyone seen any oil analysis data on 5w20 oils? I also notice that a lot of 10w30 and 5w30 oils are dangerously close to being 20 weight oils even when new (such as Mobil 1) and often will shear back to a 20 weight after a short time. What effect will this have on longevity of the engine? I for one wouldn't want to be running a 20 weight oil in my high performance engine.
For what it is worth, I had a fuel dilution problem a while back that thinned my oil down to 20 weight specs. and the wear metals remained very low. [ June 02, 2002, 11:17 AM: Message edited by: GW ]
I remain very skeptical of 5W20 oils. We know they were developed for CAFE reasons, I don't believe there is any debate about that. The question is, do they protect as well as 5W30 and 10W30 oils? My answer to that is I doubt it. I have seen testing that suggests that they do ... but I question the test's real-world correlation and their overall duration. For example, I don't think any of the tests go past 150,000 miles. Doesn't one brand of 5W20 oil say on the bottle something like: "Only for use in engines requiring the use of 5W20 oil." ? [Confused]
What I don't understand is that company's like Honda started specifying 5w20 on their engines, but the previous year they said 5w30, yet made no changes to the engine at all. I'd be especially wary of using the thinner oil in a situation like that.
It's about US CAFE standards and thats it!. Don't expect Europe or downunder to touch it. Mobil Oz told me the 0W-30 will never be availabe here, just not up to it (0W-40 is). 30W synthetic as low as I'm going and only for winter use.
Good Morning Patman : [Smile] Ford did the same thing. They have not re-tooled anything. I know GM was asked if they were going the 5W20 route, but they declined. They are seriously think about recommending 0W30 though, and I can live with that. I could live live with the 5W20 if it was a good ester based synthetic with an extremely good addivite package. I heard some talk some companies were doing some research on a 0W10. [Confused] Now wouldn't that be something to talk about.
You guys say you don't like 5W20 (and as you can tell from above, I agree) but you like the 0W30 and 0W40 formulas? You really like oils with an even thinner base oil and more reliance on vicosity improvers? [Confused]
<b>Bror Jace:</b> You bet. Most of the 0W40 oils are spec'd for the European market autos. If an oil can pass the MB, BMW, VW, and Porsche test (especially Porsche) you have a good product. With the right VI Improvers there is no problem. I have seen some of the brands tested up to 8,000 miles with very little viscosity loss. Even if you lose a little it will show better results than the 5W20. Like everyone else, it's the 20 that bothers me.
The auto mfgs are having a real problem meeting the CAFE standards as they become more and more strict with every passing year. Using a lighter weight oil is an easy way to gain mpg, without any extra engineering on their part at all. So what, if the engine wears out prematurely (as long as the warranty has expired). This just increases the sales volume even more, when the cars have to be replaced. I am not a fan of these lighter weight oils. Call me old fashioned and cynical... My wife does... [Roll Eyes]
You'd have to go to Mobil's website, but different cars require different grades. Mobil 0-40 for new Porsche's (local dealer says 15-50 for older models), M-B AMG, 5-30 is used for the Vette and I believe the Aston, 10-30 for the Viper, and 15-50 for the Cobra R...
Johnny, I stopped using Castrol Syntec 5W50 years ago after I had learned about wide-spread oils and how quickly their polymer viscosity improvers break down. Since that time, the widest spread I’ll ever use is 5W30. But you are saying the engines which have used this stuff (high-revving motors, right?) over several thousand miles have not sheared all those polymers down? [Confused] Sprintman, as for what those expensive cars use as their factory fills, that is a sponsorship deal not unlike race cars with colorful logos all over them. Mobil paid those manufacturers a fee to use their oil in their crankcases and that fee also allowed those cars to be mentioned in Mobil 1’s advertising. The oil may be decent … or better than decent … but please don’t believe the hype at 100% face value. Any oil specified by the manufacturer will have to be widely available across the globe. Nearly every store that sells oil will have a version or two of Mobil 1. That alone would be a reason to specify that stuff. As for what is recommended in Europe (in general), I’m sure their short-sighted eco wizards had a hand in crafting the guidelines that call for extended drain intervals, even with oil of an indifferent quality. Europeans want to import less oil and deal with less used/waste oil. If that means their engines self destruct shortly after the 200,000 kilometer mark (about 125,000 miles) their bureaucrats just don’t care. I guess those junked engines, used parts and prematurely worn-out cars which aren’t worth fixing are not much of an environmental problem. [Roll Eyes]
Bror Jace- I think you'd find that the reason the Europeans can recommend extended drain intervals is that their oil spec requirements are much more severe than are the US specs. Some years back the only two US oils which would meet the European specs for volatility were AMSOIL and Mobil 1. Of course, the Europeans pay for quality, too. Last time I was in the UK, Mobil 1 was about $17 (US) per quart! I do know that GM started using Mobil 1 in Corvettes to solve a design problem. At the time, Mobil had the factory fill contract (non-synthetic). When GM awarded a contract to another company for the non-synthetic, they kept a contract for Mobil 1 for certain engines. I'm sure they are getting a decent price, but doubt that Mobil is paying them for the priviledge of providing one of the few oils which can solve their problems.
Originally posted by Dick in Falls Church: I do know that GM started using Mobil 1 in Corvettes to solve a design problem. At the time, Mobil had the factory fill contract (non-synthetic). When GM awarded a contract to another company for the non-synthetic, they kept a contract for Mobil 1 for certain engines.
Wow, are you missing the point. GM isn't trying to solve a DESIGN PROBLEM with the corvette's engine (I know, cause I've seen LT1's, LT4's, LS1's, and even LS6's run fine on dino and synthetic for years, including mine). The reason Mobile 1 is spec'd in the corvette, but not in the Pontiac Trans Am and Chevy Z28/SS is that it's not really nessesary. There is NO design flaw. The REASON the synthetic is spec'd for the Vette engine (with the same HP and design as the F-body's) is 2 fold: 1) image. Corvette wants to be America's Porsche, and complete against the likes of Vipers, Ferarri's, and even BMW M3's etc... They all use synthetic, so the vette should too right? If you're selling to a regualr media-product Joe Smoe, thats what he thinks. 2) Intended use. Obviously, anyone whose about to buy a new Z06 with 400hp and can hand a Viper, Ferrari (or even some motorbikes) their ass in the 1/4 or on a track, stands a good chance of occationally running it hard. Running a 400hp car HARD at a lap day can (and does) result is HIGH oil temperatures. If you make a car that is without doubt BUILT for the track, and its on warranty, you better give it an oil that can survive for an hour or so at 5000-6000 rpms on an Arizona road course. Need proof? ok. Ever hear of a 2001 Z06 owner complain about oil loss? GM did. Turns out that the handful of pussies who complained about it drove this car like a corolla. Result? the engine never hit the elevated temperatures it was designed for and the piston slugs didn't expand as much as was designed for so the rings would stay a bit loose and oil comsumption would go up. (this is the same reason cold engines, or those with excessive wear have piston slap BTW) So what was the fix? Well, GM's 2002 Z06 has slighter harder pistons (less expansion) and likewise can use tighter tolerances. GM dealers have reccognized this and are now installing 2002 Z06 pistons (and the newly designed rings) in 2001 Z06's that arn't driven hard and the customer complains of piston slap and oil consumption. Synthetic is spec'd becasue the car is DESIGNED to be driven hard. (honestly, some people's BS [Roll Eyes] )
Just so you know, the LS1s will still burn oil even if not driving gently. I know quite a few guys with LS1s that drive very hard, and get the oil consumption. It's not driving gently that causes this. And the 2002 "fix" didn't take, I know 2002 owners that burn tons of oil too. [Frown]
Dick, for the record, I know my summation of the reason for those cars (the 'Vette among them) was a bit simplistic (and I never said each of the cars had the exact same reason) but the face-value argument that: "Mobil 1 is used by the most advanced cars in the world, therefore it is the best oil in the world and you should use it too." is a bunch of nonsense and really irks me. I know the info on US oils failing to meet Euro specs used to be true but I'm not sure that's the case anymore. As for the price, the taxes over there are so much more than they are here, even if the formula is the exact same. Oh, and according to Castrol, Mobil 1 in Europe used Group III stocks ... at least for a while. [Wink]
I've been messing with synthetics for 25 years now, and try to keep BS down. GM did in fact have a design problem with the engines--the oiling holes were small, and non-synthetic in cold weather would not flow rapidly enough to lube the cam. While they researched the problem, all sales were put on hold. Mobil 1 solved this problem, and was much cheaper than pulling the engines down and reworking the parts. After the use of Mobil 1, GM found the engines ran cool enough that they could design out the oil cooler in the next model. And that made savings even greater.
Originally posted by Patman: Just so you know, the LS1s will still burn oil even if not driving gently. I know quite a few guys with LS1s that drive very hard, and get the oil consumption. It's not driving gently that causes this. [Frown]
Interesting... since the oil consumption loss is a LS6 issue, not an LS1. Only the Vette's Z06 model gets the LS6, F-body and other platforms only see the LS1 which has a much differnet block design.
And the 2002 "fix" didn't take, I know 2002 owners that burn tons of oil too. [Frown]
Ok, hang on a second, how many 2002 Z06 owners do you really know? The oil consumption issue in the 405hp 2002 LS6 does NOT amount to "tons" or even close. What we're talking about here is about 1/2 a quart over 5000 miles or so, or so I've been told by Z06 owners.
The LS1 and LS6 have shared the same short block since the LS6 came out in 2001. Before that, the LS1 had a different block of it's own. To simplify production, they just went to one setup for all LS1/LS6 engines. I know this for fact, as one of my cousins works at the plant that casts the block and heads for these engines, and his brother is the engine test engineer at the plant that assembles them. They also share the same intake. The LS6 gets it's extra power through better heads and a more agressive cam. LS1s usually make about 300-310rwhp, LS6s are about 340-350rwhp. The 2002 owners I was referring to were 2002 LS1 f-body owners, not Z06 owners (although I do know a few Z06 owners too, but nowhere near as many as I know f-body owners). As I mentioned before I'm a moderator on and and I see posts almost daily from LS1 owners complaining about oil consumption and have seen quite a few new 2002 owners pop into the forums for the first time and complain about consumption. I talked to one owner yesterday who burns a quart every 500 miles. Another part of the problem is the PCV system, it often causes consumption because it shoots oil into the intake at huge rates. Some guys have had success with modifying their PCV setup (they call it the vertical PCV mod) BTW, I just found yet another 2002 owner who burns oil: [ June 08, 2002, 06:23 AM: Message edited by: Patman ]
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