Maddog, I'd like to clarify what I was saying about dirt getting into the intake system. The oil companies claim you can go 7,500 or 10,000 miles before you need an oil change with synthetics. I don't believe that is completely accurate. Maybe for a select few that drive alot of miles on a freeway like a truck driver or sales person for example, this may be ok. For many of us, I don't agree with a 7.500 or 10,000 mile oil change interval. The largest reason to change oil is not because it has broken down, but it is to flush the contaminants out of your oil system. The excess fuel that didn't burn, moisture, engine wear that leaves particles floating around, and dirt that gets past your air cleaner. I was not saying oil will protect you if sand gets in the engine. I am saying you need to dump your oil to remove the dirt and other contaminants.I don't think I was questioning the value or performance of synthetic oils. Syn is certainly not a new invention. The aircraft industry & the military in particular have been using Syn before the start of WWII. For many of us, conventional oils & blends work just fine. For the rest of us, there is a choice that we can make. Also while Syn oils cost more, no one should accept or reject there use based on cost. Selection should be based on use & need.
I'm not sure I understand some of what you stated. You mentioned the air intake system. There is no question that an air intake system that is not properly filtered or operating correctly will totally destroy an engine in no time at all. But what is the relationship between the air & oil system. They are seperate systems. No lubrication system, including Syn system is going to protect your engine from airborn contamination. For instance, if you suck in some fine beach sand while doing 70mph, there's nothing that's going to prevent tearing up your cylinder walls. At least as far as I know.
You mentioned conventional oils breaking down in the heat & not protecting in the cold. I agree there are extreams. But no one seems to back up their statements with some data as to when & what point this happens at. I mean, how would I know I'm overheating my oil if my engine is running with no overheat issues? And if I'm changing my oil well ahead of the recommended change times, what are the odds? One of the reasons new cars run on 5wt oil is to reduce the friction wear alone caused by heavier grade of oil in engines built with high component tolerences, as well as the thickening of the oil you mentioned due to cold conditions. But there again how cold is cold ?
Lets agree to disagree. I don't think there are any right or wrong answers here. Just personal choice. I'm not in a situation where going Syn is going to improve anything for me. If I thought it did I would jump on it. But maybe a guy down the road from me might see it diffrently for himself.
Contrary to what most people think, an oil filter does not really filter much, which enhances the need for regular oil changes. Your engine has an oil by-pass valve. When the oil pump circulates the oil through your engine, the majority of your oil does not flow through your oil filter for each cycle. Every engine is a bit different, but we're talking 2/3 to 3/4 of your oil doesn't flow through the oil filter per cycle.
As far as when oil breaks down, especially if you over heat it, I have no idea when to know when that is. In all honesty I don't care. It does not apply to most of us. I don't think the majority of us could work our engines hard enough to break down the oil whether it be synthetic or non synthetic. As far as cold weather, I have seen oil jell up at around 0 to 10 degrees. This also applies to transmission fluid, in particular manual transmissions. A good example of this is a few of my cars have had manual transmissions and in the winter they shift hard until the transmission warms up. In some cases they were hard to get into gear. After I switched to synthetic oil in the manual transmission, I could take my finger and poke the shifter into gear when cold rather than jamming with force. I've tried pouring 5w-30 oil that has been sitting in a trunk of a car or a non insulated garage and it takes a while when it is 0 or 20 below zero. My mechanical oil pressure gauge also take a while for the needle to move off zero at these temps. Synthetic 20w-50 at -20 degrees will still pour like water. With synthetic 10w-40 I have instant oil pressure at -20 degrees. Synthetics don't freeze or jell up like the non synthetics will do. As I said, cold weather use is my biggest reason for using synthetics.
I do agree with you, synthetics are not for everyone. I do personally feel they are superior to non synthetics. For many people the decision not to use synthetics is based on the up front costs and I don't feel that is the way to look at it. It should be based on how the synthetics can make something you own work better or last longer. Each person has to scratch their head and see if the switch to synthetics makes sense for them or not. It's a complicated subject with many different opinions. I base my opinion from 22 years of experience as an engine builder and as many years working on vehicles. Let the debate rage on!