P0117 Overheating

Have you checked to see whether you have a bad headgasket? That seems to be one of the more common problems with Gen 3 cars, especially with overheating.

 

I'm surprised it running. Overheating the engine is never good. You "might" get lucky and
and only the headgasket is blown. The head could be warped, and cylinders scored.

 

I think the million dollar question is... besides the leaving the cap off incident, were you ever loosing coolant?

It sounds like a head-gasket, but if the coolant level never drops then there may be a glimmer of hope that you did just ruin the water pump, which has a plastic piece that can get cracked, or put an air pocket in the cooling system or something. How far did you drive with the light on?

 

How many miles?

 

That's a fairly weak design open deck engine setup anyway and you're really putting it to the test I guess mine wouldn't have stood up to it it didn't number two piston tried to roll around in the block and it's bore broke the rod around 220 k oil changes were in effect things were good Head gasket blew first and then the number 2 small end of the rod broke. The engine would still reciprocate without making a huge racket obviously it was running completely out of balance and I didn't know much of this until the engine was pulled and I could see the damage so I replaced the engine obviously and with a low mileage transmission MG1 and 2 also

 

Doesn’t matter; they’re separate systems.

 

I think it's your head-gasket and at this point I would be pretty concerned about the rest of the engine since it's been driven over-temp. Removing the O-ring is putting a band-aid on a broken arm.

 

Was that the one with the bottle of solution drawing up coolant to check for exhaust gas presence? If that comes back negative, it indicates you don't have exhaust gas leaking past the head gasket.

Still, the majority of failures seem to be coolant leaking past head gasket into a cylinder, typically cylinder one and/or two. The head gasket failure tends to be at the wall between those 2 cylinders.

Boroscope inspection of the cylinder can help check for coolant leaks into cylinders.

And for any and all failure routes (IIRC there's eight?): leak-down test.

 

I THINK he's saying that even if it's accurate, it might not be telling the whole story.

 

I believe for the Prius, you won't have exhaust gases in the coolant. Because it doesn't fail that way.
It fails from too much back pressure so coolant leak INTO the cylinder.
So that test ONLY tells you there are no exhaust gases in the coolant.

Do Post #12...
You may get lucky and ONLY have a blown head gasket. But over heating the engine????
Count on warped head and scored cylinder walls and melted piston rings...