One would have to look up the info, but "synthetic" is known in the US as a marketing term. So, as an exmaple, Shell Rotella T Synthetic is actually a Group III petroleum. No manufactured product like one would think is man made. Very, very good oil, as are other Group III oils, and they might even be found in actual synthetic oils as part of the proprietary manufacturers' mix.
I think something that is a "synthetic blend" might only have 1-3% of the part that is "synthetic".
Longer drain intervals are going to have to be related to additive packages and the sheer strength of the oil itself.
At one time, I was sponsored by one of the real synthetic oil companies, and they recommended a specific petroleum oil for break in stating, "It has a higher film strength than most synthetic oils available."
I think buying "blend" oil is probably not a good idea, partly because you don't know how much percentage is which, and partly due to cost. Instead, I'd just mix it myself.
I remember being 17 and buying "Castrol Syntec Blend" 20W50 thinking I was doing my aging car a favor. I don't know if my bad choice (20W50 is way heavier than was recommended for the car) contributed to any of the engine problems I had, but I doubt it.
Don't tell me you put 20W50 in the caddy with an aging 4100 V-8. That may have been a large part of your problems right there. The 4100 wasn't a strong engine to begin with, and using oil far thicker than was intended probably burned up the bearings.
Well, at least you are older & wiser now. 20W50 may have been fine for an aging 350, but not a 4100. The thickest oil I have ever used is 10W40. I started out doing what my dad had always did. I used 10W30 in the winter, and 10W40 in the summer. In the mid 90's I made the decision to use nothing but 10W30 year round. ~2000 I decided to use nothing but synthetic. Currently I'm using Mobil1 Extended Performance 5W30 in the Buick, Mobil1 High Mileage 10W30 in Rusty, and Mobil1 Advanced Fuel Economy 0W30 in The Beast.
That is exactly what I did. Well, I was a dumb kid...
Maybe you were mis-instructed like me. I remember my mechanics teacher in High School saying "When you have an older car (75k +) you should start using higher viscosity oil. As the car ages the clearances increase so you need to compensate with thicker oil."
Looking back at it this is why I think my Volvo's bearing's went a few months after I bought it. That and I drove it like a typical 17 year old.
Now that I've drove Honda's ever since 75k ain't nuthin'. 75k isn't much on any properly maintained car.
...At twenty five hours I changed the oil with Honda motorcycle full synthetic ..
Yup definately use only motorcycle synth or if you use a regular make sure it doesn't say 'Energy Conserving' on it. That means there'd actually be friction modifiers that would (supposedly) fairly quickly render your clutch useless.
I read up on that stuff ad nauseam when I wanted to find a synthetic for my motorcycle.
Also my father has always used 10W40 year round. I'm really not sure why. Of course his vehicles are all trucks or caprices with 350s, on the Oddessy he uses whatever Honda says, I think 0W20. I remember on one of our newer caprices it says 5W30 oil only and he was like, wow didn't realize anyone would put such a light oil in a V8.
I've run that in my truck for a while and was suprised when oil change shops didn't have 10W40 and kept calling it diesel oil, since then I've been sythetic all the way, mostly for the pour point and -20F winters.
I would completely agree. My old 74 Chevy truck went over 300,000 miles on dino juice, and when I sold it the truck still didn't burn or leak any signifigant amount of oil. It had 190,000 miles on it when I bought it, and I kept the oil changed with Valvoline 10W30 every 3,000 miles. Until I bought the Beast it was the best running vehicle I had ever owned. In some respects I wish I still had it.
I remember my mechanics teacher in High School saying "When you have an older car (75k +) you should start using higher viscosity oil. As the car ages the clearances increase so you need to compensate with thicker oil."
That was probably true with engines and oils available in the 50's & 60's, but with modern vehicles and lubricants I don't think this applies anymore.