High Coolant Temp warning after EGR cleaning

Hi all,

Big lurker here, so first off: Thank you all for all your insightful posts!

I bought my 2010 Prius in 2019 with a little less than 100K on it. Later I read all about the head gasket problems for this car and I was determined to take good care of everything. I love my Prius.

Previous weekend I finally did the 120K preventative maintenance with my son in law (female here), cleaning the throttle body, intake manifold, EGR valve and cooler, and PCV valve at 131K (I did the spark plugs last summer at 120K). The car is running fine but the coolant temp warning light came on right after that.

Also, coincidentally, a tire pressure light because I had caught a nail in my left rear tire, as well as some codes with the Dr. Prius app, P0102 and some more, but these all eventually cleared on their own (and after disconnecting HV and 12V batteries for a reset) and I had the tire fixed.

Of course, starting up the car with thls temp light on can't literally mean the coolant or engine temp is high because I know the engine is still cold. So I wasn't too worried and have been driving it for some 250 miles now, while checking the temps with my Hybrid Assistant app all along.

Everything seems fine, car runs fine (I am seeing some improved mpg depending on how I drive) but the temp light didn't go away so I took it to the dealer today. I had to push for some immediate help so a "really good mechanic" came out 10 mins later. He held my fob near the power button and tried to clear some codes (I guess), opened the hood, then asked me to come listen to the gurgling in the engine coolant system hose near the engine coolant reservoir. He took of the cap off the reservoir and released some audible pressure. This was his quick diagnostic that there is air in the coolant system and it needs to be bled and/or flushed, hoping this will clear the temp light. Cost of flush is $230. Bleeding is less (but they couldn't tell me how much.... "because you don't know what else comes up.").

I took it back home to weigh my options and ask you some questions. Yes, we lost some coolant fluid from the engine coolant system (and inverter system as well). We just filled up the engine coolant reservoir and thought any air would clear out of the inverter system.

Do you have any thoughts on what we mighty have done wrong? Any suggestions of what is going on or what I can or should do?

 

Thanks for the link! I would not have looked for that topic in my situation but I will read more on it. Dealer would do a bleed first, then flush if the bleed doesn't clear the code. I will go by my regular mechanic tomorrow to see what they think.

 

The engine coolant is around 197 at 70 mph, rarely if ever higher. This didn’t mean anything according to the mech. I am not sure if he was implying that the app shows a theoretical temp based on other data? There have been no signs of overheating. I have overheated 2 cars before in my life, I should be scared.

 

Thanks everyone for the detailed info so far. I am going to drain the engine coolant tomorrow and see if that clears the light. If not, I am going to dive into the sensors, and will update this thread with the results. I really appreciate your guidance!

 

@MAX2 Thanks for sharing your chart. The MG temp following this EGR cleaning is actually better than it was back in February and in May, so I guess that's an improvement? I need to find out more about these temps. See attached.

 

I have to double-check which chart I uploaded earlier in this thread. That doesn't look like the right one. Below is the correct temp chart after EGR cleaning. Sorry for that confusion!

Argh no, I am confusing these exports between my phone and laptop.
The one I posted originally was correct, the one I just posted was a shorter trip, so the lower MG makes sense. My MG temp is always high then?

 

I have an OBD reader and use the Hybrid Assistant and Dr. Prius app.
Since the mech said that there was air in the engine coolant, draining it seems the least I should do.
Problem with the sensors is that it's more complicated and I am only slowly learning how to read the Hybrid Assistant data.

From my initial readings well before I posted this topic, I suspected the temp light had to do with the sensors and I purchased MAF sensor cleaner (I had code P0104 which now cleared). And another piece of info, I may have sprayed some brakleen on the sensor that sits on the manifold, not on the electronics but the exterior, but it may have gotten onto the electronics.

If draining the coolant doesn't make the temp light go away, I will sure go into all the info you posted about the sensors, or I will take it to my mechanic and accept this as a lesson.

I am also thinking about getting a 2nd (clean) egr cooler and swap it, because after more reading on the forum I think that I didn't clean mine well enough, so I have to do it again. It should go a lot faster though.

 

@ChapmanF Sooo, I had some time to look around while the oil is draining. Are we talking about this one?

 

My poor son-in-law....
So grateful for your guidance!