I'm a synthetic oil fan but mind you most hotstreet vw engine cases get cracked open for maintenance frequently.
I dont think I've ever really heard of people scoring main bearings due to the use of 20w50 or other thicker oils. If you choose to use that oil its entirely upto you. I dont think oil starvation will occur from thick oils but logic will \"hopefully\" tell you not to use thick oil in the cold winter months due to oil pressure spikes as you start up the car in the cold.
I'm a rotella T fan just because of its oil additive package with alot of zinc. The oil is just a regular mineral group1 oil but its additive package is what is appealing to flat tappet engine owners.
Silas, ya gotta remember in Vancouver we are living in a moderate climate with no extreme cold or hot weather. 10w30 should be absolutely fine. The use of straight weight oils is old tech and it pours thick cold and retains the lubricating qualities of 30 weight when at operating temps.
I've been using European oil: ELF excellium 10w50. Its PAO based group4 synthetic and my reasoning is that it pours thin when cold and has lubricating qualities of 50 when at operating temps. When I beat the snot out of the engine I am praying its helping. Bruce mentioned how potentially the oil cct may divert the oil away from the cooler due to the thickness of the oil at operating temps. The stock plumbing is assuming thick oil is \"colder not requiring to flow completely to the oil cooler.\" Since I'm full flowed the oil is constantly flowing through my 96plate/ B&M supercooler so my ass is covered.
Just remember if people are running rich and contaminating the oil the viscosity goes down hill quickly. Fuel wash in the cylinders will eventually go past the rings and your 10w30 or whatever your using will soon be thinner. So yes change your oil.
In stock engines with no full flow I'd suggest sticking with 10w30 so that your plunger/springs work as VW intended. This will assure your oil is being cooled when the hot oil is being diverted to the cooler when it hits a certain temperature. Thats what I gather how the oil system works in the flat 4. Use whatever oil that doesn't let the dummy oil light to flicker in the hot summers and you should be fine. So the \"owner\" must determine what is good viscosity for the condition of the engine. Worn out engines with more oil clearance should use thicker oils to compensate.
I'm not a fan with all this new 5w20 oils in the newer cars(water cooled). Alot of manfacturers are recommending oil change intervals at 8000kms!!!!! with the use of the thinner oil I see it a great way of wearing engines alot sooner. Water contamination(short trips not getting full operating temps) will contaminate the already thin oils. 5w30 is probably more suiteable for all new cars but the car manufactures are also trying to achieve higher gas mileage for bragging rights. Blind faith believing the car manufacturers knows best in some way or another.
5w20 oils are usually higher in quality like a group 3 hydrocracked mineral oil or at least a group2 so its gonna mimic the charactertics of a real synthetic. Petro canada's 5w20 Supreme is a group3 to my knowledge so its equivalent to the Castrol Syntec products. So hopefully in a flat4 the oils will have good shear strength to handle Bruce T's abuse to his engines
Sometimes I think lifter bores is gonna benefit from a thicker oil but thats speculation on my part. I just noticed on my brutally abused 2110 had a quieter startup with 20w50 than a 10w30 oil. Thats got to do with the cold characteristics of 20w in the 20w50. Damn worn lifter bores!!!! mind you I had an easy 15,000kms with splat/scat lifters with my w125 cam.
holy crap do I write alot!!