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Re: fuel economy Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Sun, 20 Apr 2008 16:34:24
In Reply to: Re: fuel economy, felixf, Sun, 20 Apr 2008 16:10:27 Members do not see ads below this line. - Help Keep This Site Online - Signup |
1- Let's not start oil wars, but it's always a hot subject. I have to come down on the side of changing oil sooner.
Heat from the engine breaks down the oil. It also breaks down and uses up the additives in the oil. Buffers to neutralize acid, viscosity improvers, etc. So the longer the oil sits in the engine, the more it degrades.
It used to be that they recommended oil changes ever 3K miles (5Kms). Oil has gotten better, and engine push less in the way of combustion products into the oil. So the interval increases. The tough part about increasing the interval is that short of actually doing oil sampling to determine when the oil is worn out, it's a guess. Car manufacturers have recommended longer and longer intervals, because it makes their cost of ownership seem less. At 10K miles (15Km), you'll do 10 oil changes in 100K miles; that's a savings of 10 over half that interval, which can be $400. The bad news is that strategy bit most manufacturers in the butt in the late '90s and early '00, as engine sludge problems cropped up. Saab, but also Honda, Toyota, and many US firms started getting early engine failures due to sludge.
The other thing oil does is remove particles and 'gunk' from the oil. Theoretically the filter then removes that, but filters only remove particles down to a certain size. And filters don't remove acids and other nasty chemicals that build up over time. And as engines wear, they push more gunk into the oil. You can run synthetic oil - it resists breakdown much better. But if you've got moisture, combustion products, or just plain metal bits in the oil, it still carries it around the engine.
5K miles (8Km) seems like a good compromise given modern oil. Is 10Km OK? Probably. I wouldn't go over 7.5K miles/11Km. Frankly, I just change the oil at 5K miles/8Km. Yes, oil isn't cheap. But a blown engine is very, very expensive. Since I don't do oil analysis, I play it safer and change the oil sooner.
I like Mann filters. And I believe they may even make them for Saab. What counts the most is (1) changing the filter, no matter what kind. After that, a good brand name filter is a good bet.
Mobil 1 is a good synthetic. Again, we're talking oil wars here, so I won't tell you what is right or wrong. My approach is to use a good quality non-synthetic oil, and change it regularly and frequently. I change it before it has completely broken down, and before it becomes fouled with combustion products, acids, and any coolant that has snuk by the seals. And by changing it I flush those out. If I were running in adverse environments, like very hot weather, heavy loads, or racing, I'd use a synthetic. Personally, I don't, and just change it early and often.
posted by 75.58.113...
, Mon, 21 Apr 2008 17:15:33, Sun, 20 Apr 2008 15:50:01, Mon, 21 Apr 2008 05:19:59, Sun, 20 Apr 2008 16:34:24 <-- Viewing This Message, Sun, 20 Apr 2008 15:27:01
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