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Is the engine coolant used in any ways to cool the HV battery?
Engine coolant is just for the engine. HV Battery is air cooled only. There's a separate coolant for the inverter though.

I also had the engine coolant run low on me in the reserve tank 2 years ago. I'm assuming loose cap from the factory because it stayed the same since the top off.
 

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Discussion Starter · #42 ·
Thanks @andrew28 -- OK I think we are getting closer to the problem.

First thing: I checked my OBD logs from previous long trips, engine coolant temperature NEVER exceeds 185°F, so 200°F is definitely abnormal.

Then, I looked at the EVAP on OBD logs and there you go, the valve was weirdly opened at 20% (instant of a short 100%) for all the time the engine was running at idle. See the left of the logs below, from 18h44 to 18h46.

Andrew I know you mentioned the EVAP before, good call!!

OK now maybe a theory:

1- I am on the highway, engine coolant is low so engine is running too hot, let's say 215F, but not hot enough to throw a check engine light
2- while the engine is piping hot, the EVAP cannot happen, for some reason
3- I get off the highway, the engine has time to cool a little bit
4- when the engine cools to 190-ish, the EVAP starts but because the engine is still too hot, I can only do a 20% EVAP over a long time, instead of a 100% rapidly
5- EVAP is done, engine is cooled down further, engine can now run and stop normally.

Now, what does it have to do with the battery? Maybe nothing, and maybe these fumes just needed to get out of the canister and the "Battery Temperature Too High" is bogus?

Thoughts?


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Discussion Starter · #44 ·
haha I love how the 12v gets blamed for everything.

In my theory, now I wonder why the radiator fan did not kick on to cool the coolant... unless the coolant level was critically too low but then why was no error thrown.
 

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haha I love how the 12v gets blamed for everything.

In my theory, now I wonder why the radiator fan did not kick on to cool the coolant... unless the coolant level was critically too low but then why was no error thrown.
If you are on the highway - the radiator fan would not help as there is enough air flow already running through the radiator.
 

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yes -- but the problem happens off the highway at very low speeds or idle.
Ok, your really grasping at straws with this theory. It seems like you are looking for problems in areas that would be totally unrelated to a too hot battery message. Radiator fans generally do NOT turn on until the coolant exceeds around 220ish. So, at 203, I would not expect to find the fan on. Your car can’t possibly be critically low on coolant with no warnings. For a car to be low on coolant, it would need a leak, which you would either see with unexplained puddles under the car or smell the very distinctive sweet smell of coolant coming in the vents. And even if you did have a coolant leak, it would have absolutely nothing to do with the HV battery getting hot. While the coolant tank shouldn’t be low, it only represents the reserve overflow. The radiator, hoses, pump and engine block holds the vast majority of the fluid. Top it up and monitor the level.
As for the EVAP purge, it’s not just open or closed. The ECU determines when and how much to open the valve. If the valve was not operating correctly, you would get a code for that, as well as potential engine running issues. Your problem is with the battery control system/temp sensor, not the engine.
 

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FWIW, the last three Honda we've bought ('18 Civic, '19 Insight and '21 Insight) all arrived with coolant below the minimum line in the reserve tank. I added Honda coolant when I realized this. None of the cars had any drivability issues. As @Carfreak09 stated, it's an overflow/reserve tank. There was enough coolant for the cars to run fine. As well, I concur - engine coolant has nothing to do with the HV battery.
 

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Honda Type 2 coolant must be added to the engine reservoir to a level close to the upper (maximum) mark in the reservoir (but not higher). For one thing, check the level in the tank of the inverter.
Let me express my opinion on the problem with overheating of the high-voltage battery.
There are two things to check first:
1. Correct operation of the high-voltage battery cooling system. And these are its temperature sensors and the operation of the battery fan itself.
2. Correct operation of the 12 volt battery charge. Moreover, both the charge mode (it may not charge correctly), and check the consumption load (there may be excessive consumption).
With a high probability, the problem is in these places.
Have your Honda dealer check these subsystems. In fact, your protection system is triggered (real or erroneous - they need to find out) overheating of the high-voltage battery. And if the temperature really rises, then this negatively affects the elements of the high-voltage battery and they degrade faster.
 

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Discussion Starter · #50 ·
Ok, your really grasping at straws with this theory. It seems like you are looking for problems in areas that would be totally unrelated to a too hot battery message. Radiator fans generally do NOT turn on until the coolant exceeds around 220ish. So, at 203, I would not expect to find the fan on. Your car can’t possibly be critically low on coolant with no warnings. For a car to be low on coolant, it would need a leak, which you would either see with unexplained puddles under the car or smell the very distinctive sweet smell of coolant coming in the vents. And even if you did have a coolant leak, it would have absolutely nothing to do with the HV battery getting hot. While the coolant tank shouldn’t be low, it only represents the reserve overflow. The radiator, hoses, pump and engine block holds the vast majority of the fluid. Top it up and monitor the level.
As for the EVAP purge, it’s not just open or closed. The ECU determines when and how much to open the valve. If the valve was not operating correctly, you would get a code for that, as well as potential engine running issues. Your problem is with the battery control system/temp sensor, not the engine.
I agree with what you're saying... unless the message displayed on the dashboard is wrong. How would I be sure that the HV battery actually overheats? The battery fan is working very well on the highway so maybe the battery is just fine. If the battery was really overheating, come to think of it, it wouldn't get charged to 100%.

I did top off coolant reserve yesterday, it was completely dry. Filled it to the max line. Radiator level seemed fine though. I have many highway trips in the coming days, I'll keep an eye.
 

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Discussion Starter · #51 ·
Honda Type 2 coolant must be added to the engine reservoir to a level close to the upper (maximum) mark in the reservoir (but not higher). For one thing, check the level in the tank of the inverter.
Let me express my opinion on the problem with overheating of the high-voltage battery.
There are two things to check first:
1. Correct operation of the high-voltage battery cooling system. And these are its temperature sensors and the operation of the battery fan itself.
2. Correct operation of the 12 volt battery charge. Moreover, both the charge mode (it may not charge correctly), and check the consumption load (there may be excessive consumption).
With a high probability, the problem is in these places.
Have your Honda dealer check these subsystems. In fact, your protection system is triggered (real or erroneous - they need to find out) overheating of the high-voltage battery. And if the temperature really rises, then this negatively affects the elements of the high-voltage battery and they degrade faster.
I... really can't tell these guys at Honda what to do. They are very defensive. And I am quite a polite dude. Last time I tried the advisor was like "yeah yeah we'll figure it out".
 

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Discussion Starter · #52 ·
FWIW, the last three Honda we've bought ('18 Civic, '19 Insight and '21 Insight) all arrived with coolant below the minimum line in the reserve tank. I added Honda coolant when I realized this. None of the cars had any drivability issues. As @Carfreak09 stated, it's an overflow/reserve tank. There was enough coolant for the cars to run fine. As well, I concur - engine coolant has nothing to do with the HV battery.
Unless the message on the dashboard is wrong. As a reminder, this is the message that appears when pressing the EV button. I doubt they put their finest engineers on that... they really just need to tell something - anything really - to the driver as of why EV mode won't happen.
 

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I... really can't tell these guys at Honda what to do. They are very defensive. And I am quite a polite dude. Last time I tried the advisor was like "yeah yeah we'll figure it out".
Sometimes you have to get a little firm. Video what happens when you press the EV button and show it to the service advisor. If he seems dismissive, ask to speak with the service manager. When talking with him, explain that you haven’t received a fix to this issue and something is obviously wrong if it keeps popping up this message and ask if you can please show the video to the actual technician and explain to the tech when it happens. At the very least, get it DOCUMENTED in the papers given to you that you have brought this issue up more than once so that if an actual failure happens later, there will be no hemming and hawing from Honda on fixing it under warranty.

The message is tripped by the temperature sensor. There’s one of 3 possibilities: Despite the fan working correctly, the battery or inverter is getting momentarily too hot due to an internal short somewhere or from being charged rapidly by slowing down from high speed on a lengthy exit (The second part is the likeliest explanation). The temp sensor or its wiring is shorting out, triggering a false message. OR the battery/fan control module has some sort of internal short/failure. Electronics can be VERY finicky.

Personally, I would just not press the EV button under these circumstances. I’ve only used the button once since I’ve owned the car. The car’s battery is too small to really get much electric only range out of it so it seems silly to force the car to run on battery only unless your slowly cruising in a 25mph neighborhood. If the car is operating fine otherwise, is it worth your sanity to worry about this erroneous message (assuming the dealer is unable to find anything wrong after a second time)?
 

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I... really can't tell these guys at Honda what to do. They are very defensive. And I am quite a polite dude. Last time I tried the advisor was like "yeah yeah we'll figure it out".
I recommend you speak to Taylor, she's one of the service managers at Honda Everett. She's always been very helpful if I had an issue that wasn't able to be solve after my first visit to the dealership. As suggested by @Carfreak09, record a video of your problem and request to speak to a tech. Show the tech your problem and that you might think it's a faulty battery temp monitor or fan. Don't pester them too much what you think the solution might be and let them do their job.
Unless the message on the dashboard is wrong. As a reminder, this is the message that appears when pressing the EV button. I doubt they put their finest engineers on that... they really just need to tell something - anything really - to the driver as of why EV mode won't happen.
I remember reading a Honda service bulletin a few years ago sent to Honda certified body shops. They had a reminder to body shop mechanics to not rely on icons/errors that show up in the dash. Do a full diagnostic scan with a Honda provided tool after all repairs. The reason is because it's not possible for Honda to fit all the icons and possible error messages they want behind the dash. Hence you've things like a loose gas cap could trigger a check engine light.
 

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Discussion Starter · #55 ·
Thanks guys for the advice. I'll see next week if the issue went away with the coolant filled (probably not), lots of highway trips. Otherwise I will need to get an inspection in November and I will bring it up if it still bothers me.

@Carfreak09 agreed, I actually never press the EV button. The only reason I pressed it is because I knew something was wrong and I wanted more info :)
 

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Discussion Starter · #56 · (Edited)
Update:
After refilling the coolant, and one week of many highway trips:
  • the problem did not occur
  • the coolant temperature never exceeded 190ª in the engine and 170° in the radiator (OBD gives you both actually) (so the other day's 205° was definitely abnormal)

To be 100% fair, I did not drive at fast as the times it occurred.

Also, I also noticed that:
  • the EVAP purge valve is opened 100% pretty much 100% of the time the ICE is spinning
  • thermostat opens at 172°
  • the fan works perfectly well on the highway, it's on 100% of the time pretty much, so I don't think the HV battery was actually overheating.

I am coming up with two possible conclusions:
- 1 - this was simply a coolant issue and the message on the dashboard was wrong. The engine was too hot after exiting the highway: less air hitting the radiator, so the ICE stayed on to recirculate and cool the coolant.
or - 2 - it's not a problem but "normal operation" and the message on the dashboard was wrong.. A google search indicates other hybrid users (prius, acura) are having the same issue. Especially this guy (ICE wil NOT shut down... - Electric Vehicle Forums) where somebody says it is to "fully charge, equalize and calibrate battery cells".

I believe that is enough for me to stop worrying about it 😁
 

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Oh my. That post was from 15 years ago. I'm guessing the technology has changed a bit since then. :) I think you nailed it with your first thought. Did you try to figure out why you were so low on coolant?
 

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Discussion Starter · #58 ·
Oh my. That post was from 15 years ago. I'm guessing the technology has changed a bit since then. :) I think you nailed it with your first thought. Did you try to figure out why you were so low on coolant?
haha a little old indeed. According to other posts, it's rather filled low at the factory. Maybe it leaked a tiny through the cap over the years? It was a little rusty.
 

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Discussion Starter · #59 ·
The "phenomenom" is back. Straight off the highway (fast speeds) to a plaza gas station. Engine stayed on and charged battery. Didn't have OBD meter. Engine coolant full.

So yeah. I imagine there is just too much residual heat and it needs to go away.
 
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