Intermittent thermometer (beep, red triangle of death, problem, thermometer)

Check the coolant level in the radiator, do not rely just on looking at the reservoir. You need to remove the large black plastic panel over the radiator for access to the radiator cap.

Also look at the inverter coolant reservoir when the Prius is READY. Do you see fluid turbulence which shows the inverter coolant pump is working?

 

Make sure you check all vital fluid levels. But it does sound like your problem is coolant/temperature related. You'll need to read the codes on the car to pinpoint the issue. Maybe a bad thermostat or air trapped in the system since you last serviced the coolant 1000 miles ago

 

How long has it taken to put on the 1000 miles?

If you don’t do much freeway driving then did a trip for the first time since the change in pumps, there might be air in the system.

Was the thermostat replaced along with the water pump?

 

You can ask it for a Health Check, and see what codes (current and/or historical) come up.

Beyond that, you can go to either the Engine or the Hybrid Control screen and pull up the Data List, and watch the temperatures (engine coolant or inverter coolant, respectively) while you warm the car up. Just to see how it behaves. For example, does the engine coolant temperature rise fairly steadily up toward 85 or 90 celsius, and then slow down and level off around 90ish as the thermostat opens?

Somebody else may have to chime in with how the inverter coolant temperature behaves normally. One nice thing is there are multiple temp sensors in the inverter and transaxle, so you can see if there's a hot spot in one particular place, for example.

If you have a passenger to watch Techstream while your eyes are on the road, you can see what the temperatures do while driving. (You can also have Techstream record them while you drive, and graph them later.)

-Chap

 

What version of Techstream do you have?

There are plenty of temps that you can monitor, but from what you are reporting here, the temps seem elevated.

I’d have someone else in the car with me and then they could watch Techstream while you drive so the behavior can be noted.

Next step I’d do if the temps confirm high would be to pull the thermostat and check it’s functionality.

Keep us posted .

 

That’s much higher than normal.

I’d be looking into the thermostat.

Should run around 195 F.

Keep us posted .

 

Yes, that's alarmingly high. The car should have something like an 85 or 90 degree (Celsius) thermostat (that's about 185 to 194 Fahrenheit). (I think the lower number might have been for Gen 1.) If the temp continues to climb above there, the fans should kick on around 95 C / 203 F. Is that happening? At 250 F you should definitely have fans on full blast.

I wondered for a long time what could even lead to a thermostat failing closed, since it's really a pretty bulletproof bit of technology. Turns out the one possible cause of failure is some severe overheating originally caused by something else ... thermostat opens as wide as it can, further temperature increase splurches out the expanding wax, then it's an ex-thermostat. Then if you fix whatever caused the original overheating in the first place, you still have overheating because of the now-splurched thermostat.

-Chap

 

Since it has been so hot in NC lately you probably have not used the heat in your car since the coolant replacement. Simple thing that could be tried would be to run the heat at max temperature. Would circulate coolant and if there is air in the system, that would hopefully purge it.

Confirm that the correct coolant was used, if there was something different in there before, or put in after it could have gummed things up. Mixing coolant types can do this, and enough is left in the engine loop after a drain to cause problems.

 

The standard, pleasingly low-tech test for a properly operating thermostat is to twist some wire around it and hang it from a utensil across the top of a pot of water on the stove, so the thermostat is hanging down in the water. Start heating the water, stick in a thermometer (capable of reading up to 100 C / 212 F without damage). The 'stat should be full open at the temperature stamped on it. That either happens or it doesn't; if it doesn't, you've got your culprit.

-Chap

 

250's will cook the motor. It will warp the aluminum cylinder head. It should never run hotter than 190-200.

You have alot of air trapped in the engine coolant loop. Turn on the car's heat and listen for gurgling sounds under the dash. You never said who did the engine coolant change but if they opened the engine block drain they are in for a long day. At the very least the CHS motor has to cycled by TS to purge any trapped air. Seen this post a thousand times on this site.

I did a full coolant dump years ago and it sucked. It was a real pain to get all the air out. Its a modern car issue where now the cylinder head is actually higher than the rad and that tends to trap air bubbles in the worst place possible the aluminum cylinder head. Which is really easy to damage with high heat. Compounded in this car by the coolant heat recovery canister not allowing coolant flow.

Be very careful here because you can easily toast the motor on one good overheat which you are already seeing. There is no temp gauge so driving around and waiting till the thermometer to pop up with be very $$$$.

The trapped air needs to be bled by ts cycling of the canister and bleeding using the rad petcock.

 

If the thermostat is relatively cheap purchase, I'd get a new one, just since you're going to all the bother of pulling the old one out. Then, hang both in a pot of water and slowly bring up the temp, watch the difference in performance. Also compare the condition of the rubber gaskets on both.

Basically you make a "race" of it, and the differences between the new and old are very easy to tell.

Doing that exercise decades back, for starters, I noted the rubber gasket on the old thermostat was definitely more frayed/brittle, with a few bits missing. And hanging in the bath, the old one opened a lot sooner. In my case the old thermstat was overcooling.

 

That was the version I had prior to going back to 10.30.029.

The 10 version for me has the utility menu in addition to all of the other ecu menus working.

Something to consider .

 

If you get the thermostat changed, I'd suggest asking for the old one back. Then you can stick it on the stove and boil it and see what temperature opens it. If it shows as definitely failed closed, then you can be confident it was your problem and that your car is probably fixed. If it performs well, you'll know it wasn't your problem, and you're not out of the woods yet.

In general, if the reason for changing the water pump is that it failed and the engine got way hot, then changing the thermostat makes sense, because the wax might have splurched out.

If the WP was changed for some other reason (noise, bit of seepage, etc.) and the engine never overheated, and you're not having slow warmup problems like Mendel with his early-opening one, the old thermostat is probably still fine. Something built out of a spring and some expanding wax just doesn't have all that many ways to go bad.

-Chap