I just did some maintenance on my 93,000 mile 2012 Plug-in: I cleaned the EGR pipe, the MAF sensor and the throttle body. When I opened the throttle and looked in, I saw something shiny. I dipped a Q-Tip in, and it's motor oil. It's pretty far down, well below the throttle plate. Is this normal? If not, what's the cause, and should I fix it?
Yes, It is normal. The Atkinson cycle leaves the intake valves open part way up the compression stroke of the engine and about 1/3 of the air/fuel mixture is expelled back into the intake manifold. This has been in contact with the oil coating the cylinder and a tiny bit of oil gets sucked into the intake manifold. It is far heavier than air and falls to the bottom of the manifold. There is no need to fix that. (not a Prius, but the best explanation of Atkinson Cycle air flow I found on YouTube)
Thank you very much! That's a huge relief! Should I siphon the oil out and clean it up, or will more oil just replace it?
Ours looked like that too. I was a little alarmed, dipped a bit out with a syringe, then gave up. It seems a little lighter than straight oil? Not sure.
The oil and gasoline pooled at the bottom evaporate the next time you drive your car more than a few miles because the intake manifold gets hot enough to burn off this mixture. Most Gen 2s have this issue as well.
Thanks for all of the responses. I also wrote to the experts at Luscious Garage, and they said the pooled oil is normal and they don't remove it. When cleaning the throttle body, they first insert a rag so that the solvent doesn't land in this mixture. But I sprayed the solvent on a rag and wiped the throttle body clean that way, so no fluid dropped down.
