I have never experienced any kind of engine failure on any of my cars even though by today's standards I abused my car. For the last 45 years I run cars into the ground so I think I have a modest sampling. My cars ranged from 165,000 to 275,000 miles. I suspect my average mileage on my cars was about 200K. Many of these cars went 10-15 K between oil changes. In the olden days we used to change oil in the spring and fall whether or not it needed an oil change. I might add that I drive manual transmissions and rarely rev my cars above 3,000 RPM and all my cars were either German or Japanese. Does anyone know why I got so much mileage out of them with so much 'abuse'? I now change oil ever 5k whether or not it needs a change but I only use normal oil. Is 3K between oil changes a trick to have un necessary oil changes?

'...Does anyone know why I got so much mileage out of them with so much 'abuse'?...'

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I do. The explanation is low expectations.

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The range of 165,000 to 275,000 miles doesn't really qualify as 'so much mileage' for many German and Japanese cars. It isn't even in the upper range for many reliable models.

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Mercedes manufactures badges for affixing to cars when they exceed 1,000,000 miles.

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My first car was a 1976 Datsun 280z that had been in the family, but maintenance had been severely neglected (oil changes were typically the result of my father realizing that the person who was supposed to be taking care of oil changes, wasn't; at least once it was discovered that there was essentially NO oil in the crankcase) before I received the car with a little under 200k on it. It never had the straight 6 rebuilt and when I sold it with close to 300K on it was running fine, though it was starting to burn a little oil. In retrospect, I wish I could have kept that car.

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Anyway, the point it, those aren't results that surprise me for the type of maintenance you have indicated.

All I stated was I got rid of those cars at those mileages without any engine problems. That year and model Accura had exceptional mileage. I have heard of one lasting 500k. The point I was trying to make is if I was changing the oil on these cars at 10-15k miles between changes and there was no engine problem in 180k to 275k miles. I can also add the cars I tested had like new compressions. How critical is the oil? I got the same mileage out of Penzol that you are getting from synthetic with possibly the same result. Granted the cars never went low on oil and the engines were well made. Maybe oil is more important in cars with poor engines.

My point is, if that year and model can last for 500k miles, then saying that yours lasted, at least, just a little over 1/2 that mileage, doesn't tell us much about how much using conventional oil and changing the oil every 10 - 15 k miles effects the engine.

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It tells us that in one instance 10 - 15 k mile conventional oil changes did not reduce the engine life more than 45% compared to another example of the same year and model.

I have been using full Synthetic oil since the late 80's,both in my private & company cars. Even whenI lost cooling water on one engine, no damage resulted.

Most of the engines were Turbo diesel which are very hard on the oil, far,far harder than any petrol/gas engine can be.....

You only have to try the "old frying pan test" with both normal oil and synthetic,to see and understand which is best...

Also, due to the inreased mileage between oil changes you not only save time and money,but you alsoreduce the amounts of waste oil that need to be disposed of in some correct manner!!

I change at about 20,000 miles both the oil and the filter.....ONCE!! Someone doing it at say 3,500 miles has bought 6 oil and filter changes!!!!Plus the labour if he doesn't do it himself!!!

There is simply no comparison.

I buy a top quality Synthetic made by a small German company, sold on ebay....it has passed all tests and is far far better than any "normal" oil.....it costs about twice that of standard oil.....it has passed all the VW/Mercedes oil tests.

My VW engine was never designed for normal oil anyway.....

Also, none of the cars ever had an engine failure and were sold on in a running condition with ofter more than 300,000 miles on the clock.....even with abuse..... All of these cars pulled heavy trailers for much of the mile driven.

Generally a VW Diesel will achieve at least 450,000 miles before any major work is needed. Many achieve far more.....there are plenty of other diesels around at least as good if not better.....though I do not personally know of any modern diesel running on standard oil....All synthetic. There has to be a reason for that!!!

I call it reliability.

Even if the only advantage of Synthetic oil was longer running life between oil/Filter changes, it would be still a big saver of money and time.....but it is far, far more than that!

2 of my cars were Diesel Rabbits. One was totaled in a car crash the other, I was getting an Accura for next to nothing so I dumped the diesel, I sold it at 180K the buyer figured the car only had 80K on it because it wasn't all that old. He commented on how like new the car was for having so many miles on it. The Accura lasted till 275K when it had a fuel injector iissue. The car had a blue book value of $300 and the repair had a low end of $900. The car had no AC in an area were it is a must. It was old enough to use the original freon so repairs were problematic.

TDi is a great engine and you are right, diesels are hard on oil. Checking my oil just a day after I change it, it is noticeably darker.