How much coolant loss is normal?

In ten years, mine hasn’t changed

 

That's a good question.
It's hard for me to believe there wouldn't be slight normal loss. Otherwise would require that the pressure release cap never vents due to thermal expansion, and that all coolant hoses and gaskets are absolutely impermeable to water vapor.

 

Should be none, if the car is in good order and not leaking.

 

Our 2010’s coolant reservoir levels, both engine and inverter, both gradually dropped during the first few years ownership. When they were near low line I topped both up. In the ensuing nearly seven years they haven’t budged.

question in my mind: with the 4th gen replacement heat recovery units, was there any revision, to avoid a repeat?

 

I'm more or less with bisco: I can't say "no change for ten years", because I don't go that long without changing the coolant. But in between deliberate changes, it tends to stay right on the line where I filled it without noticeable loss.

In a degas-bottle system like Gen 3, there is plenty of headspace in the bottle that can be compressed as the fluid expands. It does not rely as much on the pressure cap venting as the older recovery-bottle systems like Gen 2 (where fluid gets expelled through the vent cap and slurped back in on every drive cycle) did.

On the other hand, it doesn't surprise me in the first week or so after a fluid change if the level changes slightly, with some last bubbles of air finding their way to the degas bottle.

 

Has the outside temperature changed? The coolant level will change with lower outdoor temps.

 

None

 

According to the TSB there was a change in the design (if I remember right).

 

You are right; @Elektroingenieur posted:

TSB: Coolant leakage at front exhaust pipe (Prius & Prius Prime) | PriusChat

 

If it's just a little then I would keep an eye on it but wouldn't worry about it. Any leaks would be noticeable on one of the levels....the left coolant tank, I believe, is for the engine and radiator while the right tank is for the traction engine cooling. Which one looked a little lower?

If the level does go down more, you can use a flashlight to inspect all around the radiator for anything pinkish in color. Follow the hoses all around looking for signs of anything pink or red. If nothing, you'll have to get underneath, remove the large cover, and inspect all down there paying especially to the heat transfer which is on the muffler.

Keep us updated!

 

I'd agree to "none".
However, service work 5 months/ 12k mileage ago, just perhaps there were air trapped/ bubbles that settled over time.
Only recently the coolant level was noticed.
FWIW
Prudently I would use some light/ lamps and trace all the coolant lines to rule out a leak.
Weather temperature could be a valid diagnosis.
Lastly, no joke, inspect the coolant cap gasket - can evaporate and leave no traces.
I'd top off, continue to monitor and not worry at this time.
Good luck.

 

I'd agree to "none".
However, service work 5 months/ 12k mileage ago, just perhaps there were air trapped/ bubbles that settled over time.
Only recently the coolant level was noticed.
FWIW
Prudently I would use some light/ lamps and trace all the coolant lines to rule out a leak.
Weather temperature could be a valid diagnosis.
Lastly, no joke, inspect the coolant cap gasket - can evaporate and leave no traces.
I'd top off, continue to monitor and not worry at this time.
Good luck.

 

Zero

 

Maybe said already, could be stray air pockets working out, post install.

 

in a thread from today, poster said the car over heated and blew the head gasket some time after the heat exchanger tsb was performed.
i'm wondering if the fix doesn't always fix it

 

Perhaps the replacements are still failure prone? You’d hope not…

 

Yeah. I suspect that after the supposed fix, either there was a leak that was overlooked until too late, or else the pump wasn't pumping for some reason. Or possibly the engine was already ruined before the tsb was performed.