A few years back Mendel and ChapmanF were involved in discussions on bypassing a gen 4 Prius exhaust heat exchanger. I performed this mod in August after losing coolant through a leak into the exhaust. Subsequently, the engine has tended to overheat after 10 miles from cold, with zero heater function. The lower radiator hose has remained cold and changing the thermostat has not helped. The diagnostic on the water pump is that it is over revolution (P148F-00). Would you recommend removing and examining the water pump as the next step? I have heard that sometimes a seized water pump can give a false overspeeding diagnostic code, or the impeller can detach from the (speeding) spindle. Of course, there's quite a lot of work to remove the water pump on this car. A second clue comes from diagnostic code P2681-9C (Engine Coolant Bypass Valve Low/Insufficient Flow). This could fit with no hot water being pumped to the heater, if the water pump was not working. I'd appreciate your thoughts.
No, for two reasons: (1) diagnostic trouble code P148F00 might have been stored during the earlier coolant leak, if the overspeeding was due to lack of coolant rather than a failure of the pump itself; and (2) even if this DTC returns after having been cleared, since replacing the pump is such a big job (as you correctly observe), the Repair Manual (more info) recommends a functional test first. See the “Inspect Engine Water Pump Assembly” step in the procedure for DTC P148F00 and the “Perform Active Test Using GTS (Activate the Electric Water Pump)” step in the procedure for DTC P26819C; both require a Toyota Techstream (Global TechStream, GTS) diagnostic system or equivalent. The latter procedure also has a “Visual Inspection of Impeller” step, but it’s reached only if the problem hasn’t been found with easier steps. If you do have to replace the water pump, be sure to use a current version of the Repair Manual—the procedures have been revised to avoid the need to remove the engine assembly.
As far as I know, yes. “Engine assembly with transaxle” just sounds like a lot of work to me, even if it doesn’t come out completely.
Clearly, this is related to your coolant bypass mod. You don't say, but was it the U-shaped coolant hose mod removing the heat exchanger circuit from the system? Regardless, you may have introduced air into the coolant circuit, and this may have made its way to the coolant pump causing cavitation. The pump may simply be spinning air, not coolant, causing the overspeed and subsequent lack of coolant flow.
That idea always makes me scratch my head. The pump is in near the lowest point of the cooling system. Not the sort of place air tends to remain if the system is full enough to have coolant above it.
Thanks Gentlemen for your helpful comments. I can go no further now, having no access to a Toyota Techstream (available at my local dealership). Their opinion is that the water pump has failed, and they propose to change it. This will take 4 hours of labour plus the part costing around £400 ($500) at UK main dealer prices. Remarkably, included with the cost of my annual service is warranty cover for the car (which excludes anything in the exhaust system) but does cover the water pump. Hallelujah!
I own 2016 Prius Two. At 46K miles(sept 2022) dealer replaced 170171P Exhaust pipe assembly (said it is recall fix) and service record says followed T-SB-0135-19 Now my engine gave up. Dealer is saying it is overheating and needs replacement these are the codes P00B111, P011511, P148F AND P319000
