3rd gen Prius where is upper radiator hose???

At the risk of repetition, what P261B means is that the ECM thinks the WP rpm is less than 900. Whether the ECM is right about that is one of the things the human needs to find out.

 

I know it's been loong... but were you able to figure out the problem?

 

Hey @ChapmanF

I've a Gen3 R&D car I'm making plans for regarding how cool I can keep the enginge running and I'm going to add an additional water temp gauge in the dash that's hardwired to a sensor that screws into a coupling and I'm thinking the best place to put that additional sensor is in the pipe that you highlighted in red? Would that be a location that other sensors don't cover?

Basically trying to figure out where all the temp sensors are and where there's gaps in the data... What would you suggest? Someone told me monitoring water pump temperature might be useful...

 

Just two temperature sensors. One on the cylinder head near the water outlet, and one at the top of the hose coming back up from the EHRS exchanger.

 

So where would you want more temp data from within this system?

 

The two you already have are really all you need. Right now you have none on the dash unless you have an obd2 monitor.

Taking another temperature from the input or output of the reservoir is not that useful. It would essentially be the same as the block sensor except there is no flow through the reservoir hoses until the thermostat opens.

The reservoir input flow is from the block output and returns to the radiator output which is flowing to the thermostat. It does not flow through the main radiator tube and fins.

A possible third temperature might be at the thermostat input from the radiator. You could then monitor the effectiveness of the radiator to reduce coolant temperature once the thermostat opens. This would not be that useful unless you already had overheating and needed it for diagnostic purposes.

The normal method to reduce engine operating temperature is to install a reduced temperature thermostat.

 

Well, these engines get hot and have a history of blowing head gaskets at 200K miles. And assuming you have a clean EGR and crappy short-lifepspan pistons and rings are not contributing to headgasket failure and the problem is heat, you and @ChapmanF have made clear that monitoring water temperature is adequate. And by process of elimination that leaves poorly designed electric water pump as weakest link of heat related head gasket failures?

I've definitely talked to plenty of people with headgasket failure soon after they had pump warning codes and people replacing electric water pump early as preventative...

Perhaps monitoring the temperature of water pump motor, as well as monitoring details of water pump voltage/amp load reading directly rather than depending on OBD2 would be the way to own a Gen3 without headgasket failure before 300K miles?