Original owner. 280k miles. On cold starts plus low rpm acceleration the engine knocks as if in 3 cylinders. I removed the 0ring on the radiator cap and problem goes away. I’m assuming engine pressure buildup is the culprit. Could it be Intake manifold or other areas besides head gasket? Thanks for any Help.
Welcome to Prius Chat. Some questions: Any dash lights? What are you using to read the codes? Could it be the water pump? Cleaned the egr circuit stem to stern? Good luck and keep us posted.
That's interesting. And sounds vaguely familiar, someone else found the same thing?? A PIP with 280K miles, likely at least half utilizing the engine, Hybrid Vehicle mode? 140K miles is about the time regular Prius start having head gasket failure.
Im surprised it made it to 280k! When my sisters 2010 head gasket blew we replaced it with a 2013 Prius plug-in engine with only 45k. (I saw the car it came out of) after putting about 35k on the “new” engine, it’s head gasket blew. I was and still am a little shocked and disappointed. But it still runs, been running that awful stop leak for over a year. It’s not worth replacing an engine a second time.
Here is a reply to a similar problem reported here some time ago. " Removing the radiator cap o-ring unseals the system, placing less hydraulic pressure on any head gasket leak -- including after shutdown, during the cool down cycle. Not a fix, a palliative." "A possible middle ground is a different cap that seals the system at a lower PSI relief pressure. (I do not know what PSI the OEM cap is rated.) That said, you will still lose some coolant, maybe a lot, depending on ambient temperature and ICE duty cycle."
The OE cap is 19psi. When cars had a conventional metal cap, the final two digits of the part number indicated the PSI. Then Toyota and other automakers used a smaller cap, then came plastic caps and the like. I seriously doubt that you will find a lower PSI cap. Removing the o ring compromises the system integrity as bad as the blown gasket. It needs a mechanic, or some “mechanic in a bottle”.
I checked the under the engine and looked at the head gasket exhaust side. Sure enough the gasket is wet around the edges. Time to R&r the head. 280k miles not bad for a head gasket to live that long.
