I have a question regarding changing a high mileage engine over to synthetic oil. My previous experiences with this is based on 30 years ago. At that time changing over was not recommended because the higher detergent/particle suspension qualities in synthetic oil would wash the dirt and sludge out of the ridges and convolutions in the block (gasket mating surfaces) which had previously been slightly pushed apartby the packing of the dirt, causing a leak at just about every gasket mating surface in the engine. I actually saw this happen on several occasions, and the only remedy was to replace all of the gaskets. My question is has technology changed enough to allow a change in a high mileage engine and not have an oil sieve? I should add that my previous experiences were with stationary engines, and reciprocating air and gas compressors. A lot of heat development due to constant running that isn't there on an automotive engine.

 

The "bad result" being an engine with still a lot of life left in it slobbering oil all over the place and having to be torn down to replace gaskets. You might as well rebuild it which costs money that isn't necessary yet. When it's time to rebuild then after break-in put it on synthetic by all means and everything is great. But in high mileage engines you might as well wait to rebuild. That was the general idea back then, remember that synthetics were just comming out at that time, so poeple were just switching over and finding problems. What I "knew" was from some bitter experience. Watching an engine that had no previous leaks turn into an oil slobbering POS almost over night is not a plesant experience even when it is only your employer's or customer's and not yours. Ever since then I have run Dino oil if I didn't know what was in it previously. Just wondering if dino detergents have changed enough to get away with changing in mid-stream, because changing every 5,000 miles is getting expensive, but not expensive enough to justify a complete overhaul when it isn't ready for one yet.

 

I know you think that this is a lie, but I saw that "myth" with my own eyes, and I know it was from the oil change-over because it happened too many times right afterwards for it to be anything else. Oils were generally changed at 150 hours sometimes 200 hours if we couldn't get to it fast enough. These engines ran 24/7, so they weren't cold for very long. I might add that with the synthetic oil the change interval went to 500 hours based on sample analysis. I will try it like you suggest though, but first on an engine that is a little closer to the need for overhaul than my Mercedes. Thanks for your input.