Years ago I had a '75 Ford van with a 351W engine and 150K miles on it. An Amsoil dealer convinced me to switch to synthetic oil and their system of two oil filters. Within a week, the oil pressure dropped to zero at idle, with bearing knock, and it took a full city block of travel to bring the pressure up to 40#. Evidently, the synthetic oil cleaned the internals of the engine and ran all that sludge through the bearings and wiped them out.
The next Ford van used synthetic oil from the start and after 150K miles, it developed emission problems which were never able to be fixed.
Now, I have a 2007 van with 85K miles and only drive it about 2500 miles a year, usually 3 miles a day. I’d be interested to switch it to synthetic oil, but am afraid the same thing will happen.
What’s your advice about switching to synthetic oil once the engine has some miles on it?