Loss of inverter coolant.

When are you checking it? When the car is cool, the coolant will be at the low mark. When the car warms up, the liquid expands and will be at the high mark. The level should only be checked when the car is warmed up.

 

You have to drive the car for the inverter coolant to warm up. You are only warming up the engine.

 

What bedrock8x said is correct. You must drive the car or at a minimum, put the car in D with your foot on the brake and give it gas. The inverter is not working much during initial warmup.

 

It took ours, both engine and coolant circuits, about 4.5 years to get from top to bottom marks. They went pretty much in tandem. I topped both up in early April, neither has moved to speak of since. I see little if any variation in level, cold or hot.

It seems to me you've got a leak. I'd just tell them what you're seeing, hopefully they figure it out.

 

Look around in the engine compartment for dried residue. That leaked coolant had to drip on to something. I wouldn't volunteer that information to the Service Writer as the mechanic should be able to see it as well as you can. If they say they don't see anything then ask them about what you found.

My inverter coolant was low (probably since the beginning). The dealer didn't top it off so I did. So, like Mendel, one "fill" in 5 years.

 

There could be some variation on ours, hot vs cold, I'm not that attentive. Not a lot though I think, maybe 1/8" variation. I think you're on right track, just continuing to monitor a bit longer.

I'd still bet something's up though.

 

Me too.

 

I had to add coolant recently so I want to clarify that the manual says to check the level and fill when cold:

"The coolant level is satisfactory if it is between the "FULL" and "LOW" lines on the reservoir when the hybrid system is cold. If the level is on or below the "LOW" line, add coolant up to the "FULL" line."

I have a certified used 2010 that I bought in 2013. I noticed earlier this year that the engine coolant was just below LOW, and the inverter was right at LOW when cold. I filled them (10 oz engine, 1 oz inverter) to FULL (cold) and they haven't budged in the six months since. I can't be sure that they were never topped off before I bought it, but based on the levels not moving in six months since I filled them, I'm guessing it took five years for the levels to get low. The level does go somewhat above FULL when hot.

So I'd say if your cold level drops at all in weeks or months it should be checked for a leak.