Overheating going up inclines is it time for a new thermostat?

Would I ?
No. You have already put more time and money into a 10 year old car than I would have.
A LOT more.
Didn't you say a few posts back that an underbody pan was missing ?

 

No...mine is missing for 3 years now and no problems at all.

 

Probably not. But it might depend on whether or not something else down there is bent, missing or out of place.

IF.....there is more than one coolant temp sensor on these vehicles, then ONE of them is LYING to you, most likely.

 

Several things come to mind....
Bad replacement.
Bad install.

Waitaminute...
HUH?
You have particularly bad luck with picking mechanics, but some of this is on you.
If I'm understanding this They PRESSURE TESTED the cooling system, and it came back with "no issues" and yet they recommended that you change the radiator?
Unmmmm
Why?


What I would do next is replace the engine.
No wait...that's probably what your mechanic is going to suggest when he or she is plumbing the depths of your checking account.

What I would do is put the car in maintenance mode (It's the "Prius line-dance" at 3:30 on the video I sent earlier) and take the coolant reservoir cap off and see what happens after about 5 minutes of run time.
If your fans kick on and you have positive flow in the coolant reservoir, and if your heater blows really really hot - them I'm guessing that your thermostat is opening and your water pump is pumping and your fans are fanning and if you have pink coolant at the appropriate level in your reservoir and no pink fluid leaking out anywhere then your coolant system is doing everything that it's supposed to be doing except pressurizing (because you have the cap off.)
If everything is working as it should then the only thing you haven't really looked at is the engine coolant temp sensor.

If you have a $5 Harbor freight meter and a Ninth Grade reading level (which....isn't guaranteed if you're a product of LAUSD!!) you can actually test this component out yourself before you commit to buying one HOWEVER (comma!) since removing the sensor is MORE than half the fun, I'd go ahead and replace it while I was digging around in there.
As mentioned in the video, the labor rate for this is 2.something hours at $150-200 per hour.
I looked it up and the sensor itself is about a $20 item that the dealer will probably charge you $50 for.

Your call......
It's cheaper than replacing a radiator that you didn't need to replace and LOTS cheaper than a used engine!



(repair manual attachment shameless stolen from @Mendel Leisk post)
[Solved] Engine Coolant Temperature Sensor location? | PriusChat

https://attachments.priuschat.com/attachment-files/2016/09/112768_2010_Toyota_Prius_Repair_Manual_-_Engine_Coolant_Temperature_Sensor.pdf

 

Probably because a cooling system pressure test is looking ONLY for leaks.
It will not pick up a plugged radiator core.
BUT.....recommending changing the radiator is irresponsible advice IF the thermostat hasn't been changed first.

Then......if there is only ONE engine temp sensor, how about offering a theory about why/how the scan gauge is showing 210 and yet the temp warning light is coming ON ??

Given the age of the vehicle, maybe he SHOULD just drive it and not obsess.
As long as it only happens going up steep grades.
Maybe.

 

Scan gauge isn't OEM equipment, and so it could be, literally, many things.
It's always hard to 'digitally' troubleshoot but the described symptoms keep pointing back to this being an "instrumentation" problem rather than a "real-world" overheating event, and it's relatively easy to test.
As YOU probably already know sometimes thermistors can fail open, or act erratically and sometimes it's not the thermistor at all but a flaky spot in the wiring - like a broken conductor making a marginal connection that shakes loose when you're climbing up a hill - or a high resistance short to ground that occurs for the same reason.

I saw a billion dollar submarine welded to the pier one time for a few days because of a carbon filament in a light bulb that failed in such a way that it shorted out against the metal base of the bulb causing an instrumentation problem rather than a real-world failure.


Despite what you hear on TV, the carbon filament was developed by Lewis Howard Latimer, while the bulb itself was invented by Tom Edison.
I think Tom used tungsten originally, making his bulbs kinda 'spendy.'
BUT......that's a story for another time.
.....in another place.....


We've discussed thermistors ad-nauseous before:
Any way to adjust outside air temp reading? | PriusChat

 

There is still some room for the hypothesis to be further fleshed out, though, given that the decision whether the car is overheating or not is made by the same ECU that is converting the thermistor resistance to degrees, which is the same ECU that is reporting that number to the ScanGauge.

 

Drive yours uphill for miles going 70 mph like the subject of this thread then report back.

 

No need to report back...I've been to the mountains of NC several times and it's been fine. I pick up 75 gallons of spring water while I'm there and although coming home is generally coming down the mountains, there are many several mile stretches of uphill with the extra weight....never a problem.
There are those that say missing the "skid pan" ups the gas mileage too, but I still average 54 summer and just under 50 winter.

 

Drove car to Arizona. At the steepest point on the grapevine, Scangauge water temperature topped out at 210 degrees. As it leveled off again, water temperature came down to 180s - 190s.

Got to Arizona with no problems other than the 1-1/2 hour delay on the 210.

 

I'm having this same issue with hills and in addition to the temp light, I'm getting a bit of coolant being spit out onto the top of the reservoir. The last time it happened the check engine light came on. The obd at the auto parts store gave me -- P0117, Engine coolant temp circuit low input.
I purchased the new ECS and will be installing it soon.
2 questions,
- Does anyone have a recommendation on which obd I should purchase? I'd love to see the temp while driving. I've seen a Bluetooth one that connects to an app.
- What other replacements/preventatives can I address when changing this sensor? Since I have to take the wiper cowl off to get to the sensor, I would like to do as much as possible while I'm in there

 

Scangauge

 

I have the Top One Bluetooth plugged into mine. It’s compatible with Dr Prius app for monitoring battery, and I use the free version of the Car Scanner app for temp and other monitors.

 

Thanks, I'll look into it!

 

Took note of the bikes on the back in your Avatar.
You need to be careful to NOT have one of the bike tires directly in line with the exhaust outlet.
It can burn the tire and warp the rim.
Yes......from experience.

 

Not everything in the car is monitored electronically so that it "throws a code" when it fails.
Or when it is just starting to fail.

 

I wrote and still maintain a cooling system blog for BMWs that's known worldwide and one of the top viewed posts/links/blogs on the subject.

I'm not familiar with the Prius cooling system but the concept is pretty much the same for all cars when it comes to cooling. Cooling an engine is really elegantly simple. Do not overthink the concept.

Assuming a healthy running engine (no headgasket leaks and/or other leaks or broken parts, effective cooling boils down (no pun) to:

1) Bubble free water and/or coolant. This means a properly bled system void of any leaks. The car should also have enough coolant/water.

2) Uninhibited flow of said water/coolant. This means no internal blockages anywhere in the loop, and a healthy water pump with all fins in tact and flowing as designed.

3) Proper air flow over the heat exchangers (radiators). This means both FANS working properly and clean radiator fins with no debris or other trash, and no obstructions in or around the front bumper.

4) Signals. This means any and all sensors responsible for the closing and opening of the flow of water, e.g., thermostats (if applicable) or sensors to monitor and/or trigger fan switching. Basically all your sensors that are cooling and/or water and/or temp and/or fan related. There shouldn't be that many and they should be fairly inexpensive.

From my brief skimming of the comments here, it seems OP's car is barely on the edge of its intended thermal operating envelope due to the deficiencies within his system. This is assuming any sensors responsible for reporting the coolant temp are doing the job as designed.

As mentioned, the car really should not overheat if operating correctly, regardless of conditions.

Essentially if water is continually flowing and being cooled by fans (at a stop) and/or incoming rushing air (highway speed), you should in no way overheat unless there is a condition which breaks the chain. Think of a cooling system as one big chain that has to keep moving, uninterrupted.

I'd start with sensors and also make sure the system is bled properly. Make sure thermostat is working properly too and don't rule out a bad replacement thermostat--it happens. They're known as "soft fail" thermostats where they can be partially stuck causing just enough blockage to where you're near overheating but not really. Don't assume a new part means it's good.

 

Im having the same issue always catching up speed on the Highway, after 5 minutes from a cold Start, temperature light, and water spill on the Overflow Tank Cap