Coolant loss from expansion tank

Can't wait for the answer on this one. Maybe then Zeng will issue the first ever Priuschat paycheck as long as the answer is knowledgeable, typical and follows the outline properly.

 

There are several reason for overheating. Checking the easiest things first is quickest.
The waterpumps do fail, as with any waterpump on other cars. They just cost more.
If the pump is turning too slow the coolant gets too hot and will overflow to the tank.
Same if the empeller is not turning. And if the head gasket is leaking.
With what I've seen here on PC, the coolant doesn't seem to leak into the oil, except rarely.

But you've said you're changing the waterpump (and thermostat?) so you'll remove that possible problem.
Hopefully that will resolve the issue. And if it doesn't, and you end up with a leaking head gasket, you won't
have to change the waterpump! Which most people do when they change the head gasket.

 

Let me know if swapping out the pump fixes the issue. I am not yet convinced that the P148F code is a death sentence for the pump. I think the code only indicates a sudden loss of load on the motor causing the motor to speed up faster than the control loop can control it. could this over speed condition be caused by the impeller free wheeling on the motor shaft as some have suggested... it is plausible, however, I think an air bubble is more likely the cause of the code and in my mind an air bubble in the system is not cause to condemn a 300 dollar water pump. I need empirical data indicating that the pump is the root cause of the issue before condemning it. of course, if someone was to send me a brand new Toyota water pump for my Prius free of charge, I would be willing to swap it out and let you all know if that fixed the issue. any takers? I'm not going to hold my breath.

 

If you are the thrifty type, you can always drain the engine coolant loop and investigate the pump.

See how much resistance is there and you'll see our recommendations as to "why".

Or do nothing and deal with those consequences in terms of cost.

Always good to get data yourself sometimes for your situation, but share your findings.

 

Nobody can really suggest that, because there isn't a "motor shaft" for the impeller to freewheel on. The pump is sealed, AIUI; it creates a rotating magnetic field surrounding the impeller, which is plastic and contains magnets, and spins on bearings over a simple fixed shaft.

What happens, though, is the impeller comes apart, and then its water-moving effectiveness is lower, so it spins unexpectedly fast for the power input.

 

Water boiling over is pretty empirical in my book. 250k miles and many easy coolant changes later have never created an air bubble beyond an initial open reservoir burp and certainly no coolant has never escaped with the cap on. This is in Central Texas heat with occasionally blasts down an 85 mph tollway. All while trying to avoid being run over by Truck Drivers, Teslas and Hot Rod Lincolns.

I have proactively changed the radiator fans. Do both of yours work? Have you measured the coolant temp as you drive? It will quickly raise higher than 205f with a failing fan. I am sure you have changed the cap.

Don't wait until you blow a head gasket the old fashion way, eg by overheating. Yes it would be extremely empirical at that point but painfully expensive.

 

It took only half a gallon of coolant?

I just drained and filled my coolant, I put in a bit over 1 whole gallon in there. And that's only the engine coolant, not including the inverter coolant circuit.

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If you pull the impeller out you'll probably see that it is cracked.
Double check the coolant level after drive a while.... Hope the new pump resolved your problem.

 

What is that white layer made up of, and how does it works?
The computer chips detects voltage or amperage current or resistance of this water pump motor as an input?
If short-circuited, why is the water pump still rotates albeit at reduced speed at similar inputs of Voltage/power from battery?

 

When you look at something like that and you don't see "bearings" of a familiar type (ball, roller, etc.), that means that the smooth bores in the magnet/impeller assembly that rotate on the fixed shaft are the bearings, a kind known as 'journal' or 'sleeve' bearings. There is nothing between those moving surfaces and the fixed shaft except for a bunch of coolant molecules, but those are very slippery for the purpose.

This is an excellent kind of bearing as long as its lubricating fluid is present, but can get wrecked very quickly if run dry. Crankshaft and camshaft bearings in the engine work on the same principle.

The chips use one of several methods to determine the rotational position of the rotor and magnets, so as to know what currents to deliver to the (looks like) three phase windings, to create a magnetic field that stays ahead of rotor and leads it to rotate.

You can get a quick idea how it's done from Wikipedia, and if you're looking for more depth, there are a lot of resources on the subject.

I'm not quite sure what you're getting at with "if short-circuited".

The motor is designed to be given a constant power supply between B and ground, and then be told how fast to spin by a separate WPO signal that carries a pulse train. The controller ICs interpret the duty cycle of the pulse train as the requested operating speed.

 

I am not sure why they would need that, when there is already a polished shaft in the center and the rotor spins on that. I would have assumed there's a larger clearance around the rotor's outer surface.

 

Hi Buster,
Good to hear that you seem to have corrected your cooling issue. Update on my cooling issue. I tracked it down to the thermostat not operating correctly. I changed the Thermostat and while in there I pulled the water pump and checked it out. Water pump turns freely and no cracks in the rotor housing. I haven't drove the car long enough to verify that the issue is fixed.
I will update in a couple of weeks when I have more time on the car.

 

Your suggestion of journal bearings at work here makes complete sense now as there isn't a hardware of a shape like that of a typical ball or roller bearing.

However, should there be a 'journal bearing' in between internal bore of rotating rotor and impeller water pump shaft externals, the rotating rotor (being excited and moved by Stator coils) would not be able to cause rotation of water pump impeller shaft, hence no engine coolant circulation is possible, right?

Could the suggested 'journal bearing' interfaces between the outside surface of rotor yellowish white plastics (which is torn in this case) and inner surface of stationary stator ?

If yes, is the inner surface of Stator of a smoothened nature or its undulating winding coils being exposed?

How is the 'torn' plastic teflon affecting the coolant flowrate with regards to rotor magnets/stator assembly winding coils?

Is the engine coolant acting as a lubricating fluid film here ?

Thank you for the links.

By short-circuit , I meant to suggest rotor consists of electrical 'wiring' of differing voltages. This assumption seems to be invalid now and am I right to assume the rotor of the water pump assembly is purely a 'magnet' and nothing more than this?

 

I haven't inspected one closely myself, but these are my assumptions (which somebody who knows it better might talk me out of): that polished shaft in the middle of the pump is stationary, and the plastic rotor, which is also the impeller and contains permanent magnets, is the only moving part, with the coolant serving as the lubricating film as it spins on the shaft.

 

adding to this thread...

My wife's Prius suddenly is showing coolant loss. twice now. so far it has happened once every two weeks or so.

As an aside, i finally got my wife to check her car fluids once a week. so far it has saved her twice already. it took years for her to come around and she is now glad that she did.

back on topic, Since its only been 20+ K Mi. i was thinking either i didnt do something right and its burning coolant or something else is wrong. No white smoke from the tailpipe so it cant be the former (fingers crossed) so i'm looking for evidence of the latter and i think i found it.

We run the HybridAssistant app almost every time we use our priuses and its really useful for realtime data aside from keeping the battery fan on all the time when its hot. In this case it captured this coolant temp spike during that week in one of the run when she was on her way home from work during the afternoon. Spike happened within 9 mins of start from sitting all day. Wife is not an aggressive driver.


i checked other runs during the same week and they are all normal and staying around 192F. no idea what caused it yet. still waiting for more data so im just keeping the coolant topped up since not much was spilled. about an inch height in the expansion tank. I asked her to keep an eye on the temps while she drives.

i kept the old pump and thermostat when i rebuilt the engine. so just in case, i ordered the water pump and thermostat. (Aisin pump price jumped by $50+ since last year!)

Below is a sample normal run.