The reason to change oil is that it gets contaminated. When the oil is "new/fresh", it is almost clear in color (especially if you view it on a dipstick). As soon as it loses that clear color, it is contaminated. At that point, the contaminates in the oil are acting as sandpaper, wearing down the moving parts of your engine. THAT is why you change your oil frequently. How frequently should you change it? As soon as it is contaminated. Yes, that could be as little as 100 miles. But literally...the way to tell if the oil needs to be changed is to check the color. No longer clear? CHANGE IT.

But the above assumes that you wish to keep a car on the road forever. For the average car owner who maybe puts 200K or maybe even 300K on an engine, then the car manufacturer's recommendation is probably sufficient. If that's 3000 miles or 5000 miles or even 10,000 miles.

The key to keeping your car running correctly is not the type of oil (as far as synthetic or regular) but HOW OFTEN it is changed. If you religiously change at exactly 5000 miles, then you could save a ton of money by switching from synthetic to regular. With no impact on performance or longevity of your engine.

The dangerous message is that synthetic oils (and salesmen) want you to believe that synthetics will perform for a long time, in terms of mileage. Such as "good for 100K miles", or implying that the synthetic oil will last much longer than regular oil will. While that may be "technically" correct, it also assumes that the oil will never get contaminated. Which is an incorrect assumption.

doing your own oil change on a conventional oil doesn't save any money... it not worth the hassle if youre doing conventional unless you are just real peculiar about things. Doing it yourself on synthetic costs about half as much as a lube shop.

high mileage oil will have conditioners in it for the seals. you should be using that.

IF you switch to conventional after using synthetic, the gas mileage will just be a tad less because the oil is heavier.

if your vehicle is consuming oil, switching to conventional will help with that somewhat. the interval just depens on how hard the miles are. Freeway miles are easy on the oil and car. Stop and go and climbing hills, towing, etc.. is hard miles that would require shorter change interval. If the vehcle is getting used hard like police, taxi, newspaper delivery or other fleet/delivery vehicle, oil change should be once a month or about 1500 miles.

The best filter is Napa Gold. I like the napa gold filter or the OEM filters and I just give those to the lube shop when I go get oil change... they will use a filter you bring.

Synthetic oil lasts a lot longer than conventional. Synthetic can go up to 15,000 miles.

I used to live thru the COLD northeastern Ohio winters, & I used synthetic in the winter & regular oil in the summer.

If its a cost thing for you why not try a synthetic blend? They only cost slightly more than regular oils. Also look for a store brand synthetic. Big store chains usually rotate through various brands to be on sale each month. If you watch you can usually catch your brand on sale or if its like the Napa in my area when their brand goes on sale the synthetic is cheaper than the big names regular.

I have always used synthetic in my cars. I guess I'll use my high mileage outback as an example. I have an 02 Subaru outback H6. I have always run synthetic, and religiously change it at 5000 mile intervals and it has 215000+ miles. Would it be bad if I switched to regular? I do my own oil changes and even doing it myself, I feel like I'm spending a lot more money than necessary. I am considering switching to regular because Eric the car guy on YouTube said it wouldn't be a bad idea. I trust that, because he knows his stuff (seriously if you don't watch his videos you should, their great) but the video covered going from standard to synthetic, not vice versa. Also will I need to reduce my oil change interval to 3000 miles?