How does coolant get in the Oil????

Re-reading your question, I don't have a definitive answer. The cylinder head does contain both oil passages (to lubricate the cams and operate the VVT) and coolant passages (to cool it), and both pass through the head gasket from the block, but I don't know how likely it is to pass coolant directly between those passages. It is certainly common for coolant to leak into a cylinder, and from there, find its way into the crankcase.

 

One of my favorite graphics: 6 different ways a head gasket can fail. Notice: Blown to coolant port, water in oil.

 

I don't think piston rings make perfect seals ... for one thing, they have end gaps. They're good enough for blocking most of the pressure and the oil while the engine's running, but I imagine if you leave coolant standing on top of a piston for a while, some's going to get in the crankcase. I could be wrong.

 

Agree

 

Some would say use a compression test but if you already have a blown head gasket differences in compression may not be definitive. A slightly bent rod may not immediately cause problems but the piston will press the cylinder unevenly leading to a larger failure later. So a mechanic will check the tdc heights very carefully after the head is removed. If necessary he can then change the affected piston and rod although on a Prius it requires pulling the engine.

 

Yes what you show is possible(and might account for coolant in the oil). however if you have engine "shakes" (misfire ) on cold startup then it is fairly certain that you have coolant leakage into the cylinder. It can hydrolock and damage the rod anytime that the amount of liquid in the cylinder is equal or greater volume than the combustion chamber size at Top Dead Center. Might happen next month, or next week, or who knows.

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The five stages of head gasket failure acceptance?

(Google “the five stages of grief”.)

 

I thought the OP was already at the acceptance stage in post #1 ("I think its a blown head gasket"), but just trying to pin down in what way it might have blown.

 

Point taken.

 

Something else to consider, If the engine gets too hot with coolant in the oil, the mixture can react and turn into a lacquer. Then when you let the engine cool down the lacquer will set and freeze the engine beyond any hope of repair. This historically has been a problem with mineral oil. I do not know what polyalphaolefin-based (synthetic) oils will do in a similar situation.

 

Knock Knock Who's There?

Stage 1
Spark Plug and Coil Change
Clean EGR
Monitor Coolant
Try Head Gasket Sealant

Stage 2
Order a Motor from Japan
Arrange Killer Install Deal

Stage 3
Question Motor from Japan

Stage 4
Decide to Change the Head Gasket

Stage 5
Reconsider Motor if yours might have a Bent Rod

 

I wonder could we include spark plug and coil change?

Killer board game?

 

Revised above

 

You can check for a bent rod by inserting a dowel (or other suitable straight stock) in a cylinder, rotating the crank to the top of the piston stroke, mark the dowel, then rotate the crank to the bottom of the stroke, and mark the dowel. Then use that for comparison across all 4 cylinders.