My wife’s 2014 Prius V has ~181,000 miles. Last week she said there was a large rattle / clunky sound followed by an immediate CEL when she was sitting at a light heading to work. She said it went away a few seconds later. She has a long commute so it was around 50 miles before she got it home. When she got home I pulled the codes and it came back with Cylinder 1 misfire. Her plugs have around 80k on them with the original coil packs so I changed all 4 spark plugs and coils and cleared the code. Cylinder 1’s spark plug was pretty wet with oil but the other 3 were dry. I reset the check engine light but clunky sound didn’t go away during startup, it was hit or miss though. I figured it was leftover oil in the cylinder. We waited a week (around 300 miles) and the startup rattling still hasn’t gone away, but the CEL is still off. I re-ran the code reader anyway and it’s now reading 3 “pending” codes. - Cylinder 1 Misfire - Cylinder 2 Misfire - Random Cylinder Misfire Today I noticed her left hand coolant tank only had about 1-2” of coolant in it (WAY below the low line). The engine was still hot so I waited for it to cool down and I topped it off to the max line and I plan to keep an eye on it. I pulled the engine dip stick and fill cap - no sign of milky residue - the oil looks very normal (translucent brown). I’m not sure what to check next - I thought about pulling the plugs again to see if they are still wet and if so, maybe look into replacing the valve cover gasket. My other thought was a blown head gasket but the oil looked fine. I don’t want to replace this unnecessary but I’m not really sure how to pressure check it from home either. The low coolant is concerning though. Here is a video of the sound:
Your mileage and symptoms point to classic Gen 3 head gasket failure. You need to use a borescope to check for coolant leakage into cylinder #1 and #2 while the cooling system is pressurized. Search this forum for much more information on doing the borescope inspection.
Exactly. Almost too common to count. Oil is rarely if ever contaminated, combustion gas coolant test will pass as will leakdown or compression tests. The real question - is it an oil burner as well. With the right vin you would have revised pistons and rings reducing oil burning. If it's an oil burner a rebuilt engine is the best solution. The coils were unnecessary but age might justify the plugs. Excellent Borescope Footage at 6:50 This is not a Prius but gives you the idea. A cheap borescope is not good enough and it requires pressurized coolant. A prius normally has one cylinder with an occasional drop.
