Originally Posted by wavsine
The main concern with a GDI engine is intake valve carbon fouling. A Used Oil Analysis will not
show you that is happening. You may have no fuel dilution whatsoever and still end up with intake valves that look like this because of oil vapor coking the intake valves. Picture is of a Mazda DI engine.
Ford recently did a live teardown of an Ecoboost engine. Notably absent is a picture of the intake valves although the crowns of the pistons are pretty coked. The irony to the use of a "torture tested" engine for evaluation of intake valve carbon fouling is that an engine run hard and at full throttle is likely to have less
carbon fouling than one that is driven at low rpm. Why? Because high rpm equals high heat and high intake air velocity which helps to burn the carbon off the valves. Ford ran the engine at high speed for 24 hours straight
. That would qualify as the ultimate Italian tuneup. I would like to see them do a teardown of a GDI motor driven in a more typical fashion with stop and go city driving and extended idling.
The reason I use a low volatility (low NOACK score) synthetic oil is to try to minimize this. 5W-20 synthetic oils with notably low volatility include Amsoil and Pennzoil Ultra.
Gotcha! Good info.
I never did like those high RPM tests. First off, 24 hours is nothing. The marketing wants you to think it's a lot, but it's not. If you drive 100,000 miles, you could expect upwards of 2,000 hours on your engine (perhaps even near 2500 or more depending on how much idling and/or highway high speed driving you do). Second, constant RPM's (even high RPM's) are easy for engines. It's starting, stopping, idling, taking off cold, hard acceleration, cruising with fluctuations in speed, etc., that's hard on an engine over it's life.
Let's see ford put 2,000 hours on an engine with various starts and stop, allowing the engine to cool, applying load to a cold engine (as many people do when they start it up and immediately take off), etc., and do a teardown. Marketing convinces you that they 'tortured' an engine by running it at high speed for 24 hours, but they didn't do anything the engine wasn't designed to easily handle. Look at piston airplane engines that spend most of their life at the upper end of their RPM range (especially fixed pitch prop planes). Engines that routinely have thousands of hours on them. 'Overhauls' (rebuilds) are typically done around 2500 hours. So, to put that in 'car years', imagine a typical airplane is like driving your car down the interstate at 75mph in 3rd gear for 150,000 miles. Even those 'overhauls' are done with way less wear than a typical car engine is rebuilt at, but of course, engine failures in the air are mighty inconvenient, so it's a 'better safe than sorry' case there.
Anyway; off topic bit over- good info on the intake valves. I suppose I misunderstood you before. Personally, I run Amsoil in mine. Just performs well. On my motorcycle, the transmission shares oil with the engine. After a couple thousand miles with various other brands of oil shifting gets clunky and sticky. With Amsoil, it's still smooth and 'clicks' into each gear all the way up until I change the oil. That's no replacement for UOA's or even evaluating wear, but it should be an indicator that Amsoil performs consistently. Often people mistake things like UOA's as being a 'good time to change' when it's out of spec. But that's just not right. When the oil is worn out or out of spec, it's way too late.
Oil needs to be in-spec 100% of the time in your engine. That's precisely WHY we change it.