2012 Prius (150,000+ miles) low coolant = water pump replacement?

Head gasket issue more serious than water pump

 

Do you have a garage?
If so do you notice any coolant on the floor?

I would be VERY VERY suspicious of this diagnosos, and I would immediately do three things:

1. Check your coolant level. YOURSELF.

2. Check back in about a week.

3. Get an independent diagnosis from some place that does not sell new cars.

From the Googles:
The average cost for a Toyota Prius water pump replacement is between $1,013 and $1,424. Labor costs are estimated between $161 and $204 while parts are priced between $852 and $1220.

My diagnosis:
Your water pump is fine.
Your dealership needs to be replaced.

 

where are you checking the coolant level?

 

150K miles, presumably with no attention paid to the EGR and intake manifold condition, they're likely getting pretty clogged, engine running hotter, and it could be early stage head gasket failure, allowing coolant to leak into the combustion chambers. I would continue to monitor the coolant. If it's steadily dropping, probably the head gasket. A leak-down test will help to diagnose.

That said, 150K miles, not a bad time to change the coolant pump. But I would make assesment of the head gasket number one priority:

Monitor coolant level, and if it continues to drop, get leak-down test, to verify head gasket failure.

If it turns out to be head gasket failure, you can get it replaced, with a fairly complete replacement of any and all gaskets, O-rings and seals, for maybe $1500~2000, through an independent mechanic. Or (I'd speculate) $2500~3000 through dealership.

Probably best to do the coolant pump at the same time, since the coolant will be drained. And at 150K miles it's about time.

After all that, get the intake manifold and EGR completely cleaned. It's the carbon clogging of those two components that likely caused the head gasket failure.

The sand pounder in all of this: if you're not a rabid DIY'r, lurking on forums, learning all this and keeping on top of it, the 3rd gen Prius is a lemon. An expensive one. And Toyota doesn't want to know about.

Gasket rebuild kit (includes head gasket, and most every gasket, O-ring, seal): 04111-37315
(Engine) water pump: 161A0-29015

 

^
True all.

This means that you may get socked in the wallet for a $700 water pump replacement only to have the head gasket let go a little later on.

My original diagnosis stands.
If you're not a DIY-er it might be a good time to go shopping for a Prime.

 

If the coolant pump isn’t working, the coolant won’t circulate — which is bad. But how does that make you lose coolant?

If there’s no coolant circulating, the engine will overheat and this could blow the head gasket. That would put coolant in your engine oil and could lead to complete engine destruction. If you drain a little engine oil, you can tell whether it’s contaminated with coolant.

But it’s also possible that your coolant pump is fine and something else is causing you to lose coolant. Any puddles under your car? If you’re losing coolant it’s entire winding up on your floor or going into your engine. It has to go somewhere. The coolant pump doesn’t drink it.

 

There would be evidence of coolant leak on the underside of the engine, and/or the top (inside) of the plastic engine under panel. Pink, crusty, crystalline stuff.

 

Based on OP's initial description only ...

Sounds like they are getting sustained coolant loss. I'd continue to top up and confirm that for both coolant systems. Topping up with 50/50 of the Toyota coolant mix, or just distilled water while debugging here should be sufficient. As long as you keep the coolant from running low, there is no urgency.

If you're getting a confirmed continued loss of coolant, from either system (sounds like the inverter coolant is the suspect), next step is to isolate the leak / point of loss.

It could be that the dealer was honestly and accurately identifying the WP due to observed leak residue at that location. On the other hand, dealers don't generally have much incentive to make accurate diagnoses.

To carefully isolate a leak source myself, step one is to clean everything carefully (garden hose, toothbrush, paper towels, whatever it takes, carefully done), then a few days of driving later, observe. Maybe obvious, maybe not. If not obvious, pressurizing the system while it is cold may allow for easier inspection - engine off, cold, safe for removing things for a better look, etc. You can buy or freely borrow pressure testers at most auto parts stores.

If it ends up being a difficult isolation process, fully removing the engine undercover until the problem is resolved may make it easier to inspect things.

 

Start selling car soon

 

is the overflow reservoir a reliable source for gauging coolant loss?

 

Clean your coolant reservoir off and make sure it's not leaking.

Did the car ever overheat? If your water pump stops working I'm pretty sure you will overheat fairly quickly. You can monitor temps with an OBD2 adapter and hybrid assistant app, should typically stay around 190 when fully warmed up.

Is a compression test the best test for a headgasket?

I don't actually know, but seems checking coolant for exhaust gas, leak down, or boroscope would be cheaper and/or better?

Water pump is $250-300 and it's an easy job. Don't know what it's billed at, but if you can buy the part and find someone to put it in you could save a few hundred. Shouldn't take more than an hour for anyone competent.

Those pink crusty's would make me very suspicious of a leak though

 

The coolant resevoir has "Full" and "Low" markings already on it. They can be a bit difficult to read b/c they blend into the opaque container. I'm not a mechanic, but based on your sharpie marking and that you say the shop filled the container to nearly full I think it was way over filled. The crusty pink substance along the outside of it means that it's coming out of somewhere (it looks like from the cap) as it gets hot and pressurized, but I don't think it's going through your headgasket and into your combustion chamber within the engine. It wouldn't show up on top of your coolant tank unless some really wacky things were happening.

I think you should wipe away the pink crusty residue and check the coolant level according to the official markings. The "Full" mark should be just above what looks like a lid edge, along the right side in your photo. The "Low" mark should be maybe four inches below that. If the level is below that full mark, top it off to the mark and then observe it from there once a week. And make sure the cap is tight and secure.

 

As long as you aren't only taking short trips, it sounds like your water pump is most likely OK. As has been said there's no way it's losing you coolant unless it's leaking externally. I wouldn't worry about that for now personally.