I have a Jetta with a 12v VR6 that hasn't ran for over 3 years. I have no clue as to what oil it was running, synthetic or conventional.
It has 106,000 miles. I know switching to synthetic at higher mileage can cause leaks, but it's also better for our engines. So I have a dilemma. I don't want to spring leaks everywhere, but I want this thing to last once I get it going.
Worst case scenario, where am I likely to get leaks? Head gasket, valve cover gasket, anywhere else? I need some opinions, is switching to synthetic worth the possible oil leak repairs in the future?
Chemically, there isn't any difference between "synthetic" and dino oils anymore like there was when PAO was the typical base oil in synthetics. PAO does and did shrink seals, so esters were added to counteract the shrinking. PAO isn't used any longer, with few exceptions. Dino oil and the hydrocracked derivatives are basically seal-neutral, and all API oils pass a seal compatibility test.
Seals can be damaged from becoming varnished-over from the inside and drying out. Varnish can be dissolved away, rewetting the seal and stopping the temporary leak.
So, no, it doesn't matter, even if synth oil was used before. HiMiles oils work effectively, pick a brand you like and start w/a 10w-30. Go up or down from there depending on climate and consumption. VR6 runs hot, so keep an eye on oil temps. If you exceed +100c, move up to a 40 weight.
If I had to pick, I'd grab the Shell Rotella 10w-30 HD Semi-Synth, WalMart has it. It's a thick 30, plenty of additives like the old engine designs require. If you really prefer synth, the Mobil 1 High Miles is essentially made for euro engines.
Since it hasn't run in a while, and the history is unknown, a few short runs of cheap HD oil is a good start. Maybe toss in a quart of kero (or ideally biodiesel) in the oil before you change it, idling for 10 minutes and dump it. Intake cleaning and esp a piston soak, along with a PCV check-up or modification.
Marvel Mystery is a good product for old engines, esp in the gas. Good luck, idk much about VR6.
"Synthetic oil can be made—synthesized—from many sources, including crude oil. If you see a couple guys in white lab coats wrestling on the ground, they’re probably oil-company chemists arguing the pros and cons of crude-oil-based synthetics versus PAO synthetics.
Here are some of motor oil fallacies that may, or may not, have been true in 1942 or 1982, along with the current truth.
It’s bad for my engine to switch between synthetic and conventional motor oil.
Today’s synthetics are totally compatible with conventional oil, and other leading synthetics. Switch back and forth all you want. Some who live where temperatures plummet well below zero use synthetic in the winter for its protection during cold starts and extreme temperatures and then switch to lower-priced conventional oil for warmer weather.
Synthetics are bad for engine seals.
Today’s synthetics are designed to play nice with all engine seals. While 30 years ago some synthetics reacted differently with some engine seals than did conventional motor oil, chemists for oil companies long ago cured that issue."