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

The reservoir cap is designed to relief over a certain pressure. That's why it's leaking out the reservoir.

The engine water pump is most likely on it's way out. The shaft is plastic and probably doesn't take too kindly to engine over-temperature. According to some experienced PC'ers (@Raytheeagle) it has a lifetime around 150k.

What's likely going on with your car is the engine is overheating because of one or more of the following:
1. EGR system plugged
2. head gasket damaged
3. water pump at end of life
4. thermostat at end of life
5. reservoir cap not holding pressure.
6. Replacing engine coolant with water

Reading DTCs and getting a coolant pressure test, compression test, etc should get you to the root cause(s)

 

This could be your leak. Perhaps the hose clamp, the expansion tank or its cap.

Or maybe someone spilled coolant when filling the tank.

Or maybe the tank was overfilled cold somebody and the expanding hot fluid escaped. Under pressure.

First step: Clean all that stuff up and drive the car until it’s fully heated, then look for leaks. Use care because the hot coolant can scald. A Clorox wipe or two should clean it all up perfectly.

Not certain, but I think the Low and High marks mean Cold and Hot. Somebody will correct me if I’m wrong.

As for the water pump — before the engine is hot, but while running, feel the fat coolant hose. Do you feel coolant circulating inside it?

 

Leak-down test would be better.

Interesting, in the repair manual, the mention "B line" too. To be used for top up during a drain and fill:



I'd think it's the max amount you should put in, during the refill process, assuming air pockets coming out will soon drop the level.

When done, they recommend to top up only to the full line:



And yeah, the marks are hard to see: full mark is practically on a seam.

 

There are headgasket test kits for around US$40 that test the coolant for exhaust gasses. It is a quick and easy way to determine if the headgasket is starting to blow. It is much easier than doing a compression test.

 

Symptoms of a bad head gasket include: rough running/misfiring at low RPMs, starting the engine cold and noticing a plume of sweet-smelling white exhaust, milkshake in oil and/or milkshake in coolant.

 

Another option to add to your list of potential problems is:
0) Nothing is wrong

I'd settle down and move carefully here. Don't believe everything you are told.

Check the owner's manual to settle doubts.

Basically as I said earlier, step one is to set your coolant levels properly. Some more details on that (and again, believe a careful reading of the owner's manual before you believe this, if in doubt):

There are two separate coolant systems. One for engine, one for inverter (electrical device).

Both take the same Toyota coolant, mixed 50/50 with (ideally) distilled water. The 50/50 mix is to optimize heat transfer, heat capacity, freeze resistance, and boiling point increase. It is not critical. So if you want to add distilled water to potentially change the ratio from 50/50 to 48/52, that will be just fine. 30/70 is fine too. 10/90 is probably fine unless you are in real risk of freezing weather in SoCal. Since you may have a leak, and may end up having work done on the system which may involve a full coolant change, it may be wise to top up with water while you find the leak. That's the sort of thing I do.

Both systems have their own separate reservoirs. They should have clearly marked high/low max/min or whatever horizontal lines in the tanks to indicate coolant level. Those levels are generally (for all cars, but check your owner's manual in case there is something crazy going on here) to be checked when the engine+coolant are cold, i.e., in the morning before starting the engine. This is because coolant expands when warm. I would check both tanks carefully, and carefully add water or 50/50 mix to bring the level up to the upper (max) line, and no further.

Make sure the caps and especially any sealing gaskets in there are clean and free of debris that might interfere with a good seal.

These systems are designed to run with a controlled air gap in there, accommodating the thermal expansion of the coolant without exhausting any liquid due to overpressure. But if overfilled, that is exactly what will happen.

^^^ OK, so that's a lot of words to say ... set your coolant levels properly. Really, that's where you start.

Then clean off any residue as cleanly as you can, knowing that in the future you will be inspecting carefully and want to be sure any leak / liquid / crystallized residue is new due an existing condition vs. old due to a mistaken overfill. Most things will be pretty tolerant to spraying with a hose, using a toothbrush, paper towels, etc.

Then use the car normally and inspect on a regular basis to see if you have coolant loss. You should not. If you do, see if you can find the leak. A pro mechanic will be able to put the car in the air to look underneath, will know what panels can be removed for easier visibility, and will know what parts / hoses carry the fluid and are likely failure points. OK, so they will have an advantage, but anyone with good vision, a good flashlight, and some patience may be able to find it as well. Start by carefully inspecting the reservoir caps.

Obvious, but it's important - the leaks will generally flow downwards. They will also generally be blown rearwards as the car is driven. Putting a piece of cardboard under the car may help isolate the leak location (vs. a leak that somehow leaks and evaporates overnight, almost without a trace). Similarly, removing the engine undercover will help visibility if you can jack the car up and get under there.

If you find you need to pressurize the system (two systems, so one at a time) to simulate the pressure the cooling systems see during operation, there are tools to do that, as I mentioned.

I don't know if the mention of pressurizing the system somehow led to the discussion of doing a compression test, but that is completely different at this stage of diagnosis. But yes, if you do have a head gasket issue, a compression test and even better leakdown test will help the diagnosis, as will a "block tester" that checks for combustion gases in the coolant. But based on what you've said here so far, I think those steps are not warranted yet.

 

Fair enough.

Are there DTC's though?

I would expect a temp light if the coolant was getting hot enough to spew out the top of the reservoir.

I AM a strong proponent of water pump replacement at around 150k, I'm just not convinced it's the most likely scenario.

As just mentioned there's hope that nothings wrong and it was overfilled.

 

The water pumps for Priuses are expensive and along that the labor will be more. The cheapest one I found was $400 oem. Just keep searching.

 

On a turd gen?

 

Get yourself a gallon bottle of Toyota Super Long Life Coolant (50/50 pre-mix in the States). It's not a good idea to be topping up with straight water, you're reducing the percent. I would think what he did is just a drop in the bucket, but stick to adding the spec'd pre-mix in future.

 

Yeah, I think a little bit of misinformation crept in, earlier in the thread:

The Gen 1 Prius took Toyota LLC, which came full strength and was meant to be cut 50/50. But starting with Gen 2, the right stuff is Toyota SLLC, which comes pre-cut; you just pour it in from the bottle.

There are a couple of different ways for the cooling system to become so pressurized that coolant spews out.

One is for the coolant to get so hot that it is boiling and making steam pressure.

Another is for pressure to enter the cooling system from somewhere else, such as a combustion chamber (where the pressures get really high).

 

On the first one ... Unless there has been a revolutionary change in how coolant is made, I expect the SLLC straight from the bottle is still actually 50% (close to pure) water, 50% ethylene glycol, and a tiny amount of coloring and additives. So everything I said above related to the criticality of the 50/50 ratio is valid, as far as I know. Is there a completely different type of coolant involved here, or is it just pre-mixed 50/50 without saying that? 100% ethylene glycol would not be a good coolant. Selling 50/50 while getting people to think it is un-cut might gain marketing approval due to the higher pricing potential.

On the second one, these closed coolant systems in general have caps that are not supposed to open under normal conditions. The air gap in the expansion tank (that's explicitly what it's called for some cars = "expansion") is designed to allow for the coolant to expand as it should under normal conditions, compressing the air above the coolant in the tank, allowing pressure to build. None of this requires boiling. But if the air gap is insufficient, for example due to an overfill, as the fluid expands (again, not requiring boiling to occur), pressure will increase to the point where the reservoir cap opens. When that happens, the drop in pressure may trigger boiling and all of a sudden things may rush out the reservoir cap. Or if it does not trigger boiling, it may leak slowly as needed to let the expanded fluid escape.

More simply ... if you were to fill the tank to the very top with the engine cold, once the coolant warms up, where do you think it will go? It would have no choice but to escape the cap, even if there is no failed component anywhere and no overheating issue.

 

No, it is pre-mixed 50/50 totally with saying that, to the point that anybody adding any distilled water to it would be disregarding some rather large print on the jug.



My concern was that a post saying something like:

or

could muddy that fact for a person reading the thread.

The point is, when you buy the Toyota coolant, it's already mixed, and you don't need to have ideals about what kind of water it's mixed with, because they picked out the water for you.

Right. Mendel did post the illustrations of the proper fill levels upthread. The OP's first photo seemed to show the engine coolant at pretty much the proper level, and the inverter coolant just a touch over. But if it had been filled a lot higher than that at one point, that could explain some fluid escaping.

My experience the last time I changed mine was that the engineers really had the refill-and-burp process dialed. I filled up to B, went through the exact prescribed warmup and burping steps, and at the end of the process when I checked, the level was sitting right at F just as exactly as could be.

 

On the "DO NOT ADD WATER" warning there, they are protecting idiots from themselves. The jug contains a 50/50 mix. Interesting how they use approx the same size font on the label to say 50/50, but it is less apparent to a quick glance. I think they are telling people who need to be told that they should not mix it with an equal amount of water (yielding 25/75).

Kind of like my table saw's power cord that warns me not to use it in the bathtub.

But for those that do not need such protection, I can assure you that the SLLC will work just as well at a 48/52 ethylene glycol to water ratio. Maybe better. The heat transfer properties (etc.) vary between 0 and 100% mix, not optimal at 0, 50, or 100. Depending on climate, etc., one could try to pick the best ratio, but just doing 50/50 is so clear and easy and good enough that it is the standard.

And the main point on the overflow is that it could occur with no problems anywhere other than overfilling the reservoir.

 

I'm ok with all of that, as long as we avoid posting that people should buy the Toyota coolant and then cut it with water.

 

Toyota Canada issues super long life coolant at 55%.

 

Isn't a leak harder to find once you pressure wash the area? And isn't a pressure washer a no-no around electrical connectors? Wouldn't the source of leak show as a clean and wet spot, with the distal end of the residue attracting grime the leak is easier to detect without washing?

 

There's not enough information here to make a diagnosis. Please perform all the necessary diagnostic testing and report back with the results. Also please include the results of selecting "on" for the pump in techstream under live testing area.

 

ditto!

I know this is old thread, but i can't believe only Mikey saw the obvious in the picture.