anti freeze question

The reservoir on the driver's side is a separate system to keep the inverter cool... The one on the passenger side is the reservoir for engine coolant and radiator cap... Both reservoirs need to be kept topped off when you check your fluids. The radiator cap must only be removed when engine is cold and that's the best place to top off with coolant if you're trying to get air bubbles out of the system.

 

The one time I had to deal with that I found that if the fluid was low at the radiator cap and the overflow tank adding fluid at the former location wasn't a great way to fill up the latter, basically it didn't work at all. This came up after a 3 way valve change and running through the burping procedure with the relay and voltmeter. So the first day I added fluid in both places and the next day or two only added it to the overflow tank. (Which had been marked midway with a Sharpie to make the target point more obvious.) When the overflow tank no longer needed fluid added for a few days I checked the radiator and it was full to the top too. I think I also left the "tray" that sits over the radiator off for those days, as it was in the way, and it doesn't do that much in any case.

 

Yea... Any work you do that lowers coolant level in radiator needs to be topped off via radiator cap. The reservoir is just to make sure it stays full once you're certain its full.

 

Same system all modern cars have. The radiator cap has an emergency pressure relief valve and the coolant reservoir allows you to maintain fluid level without removing radiator cap when engine is hot and its too dangerous to remove the cap.

 

When the car is cold? That is absolutely not normal. If the car is warm now let it cool off (until the radiator cap is ambient temperature). While it is doing so obtain a bottle of Toyota's pink coolant from a dealer - the parts desk will know which one it is (same as on almost all their cars). Also get a Sharpie.

Look for signs of a leak. Pink stuff near the water pump or at any hose connection in the complex ICE cooling loop. If you see what looks like a leak, fix that before adding coolant.

Remove the tray over the radiator. Mark the middle of the overflow tank with the Sharpie so that you can see that mark clearly when looking at it from over the passenger side fender. Fill the overflow tank to that mark. Open the radiator. Odds are very high that you will not see any coolant, or at least that it is markedly low. Add coolant until it is up to the hole which leads to the overflow tank. Try to keep track of how much coolant was added. With the cap off the radiator run the ICE. It is better to do this with a funnel stuck into, or clamped onto, the radiator. You are looking for bubbles when the ICE is running. If there aren't any for several minutes turn off the car and put the cap back on. If there are keep adding coolant a bit at a time as the level falls. It should stop bubbling eventually - unless you have a blown head gasket, then it can bubble forever.

Check the level on the overflow tank each morning and add more coolant there to the Sharpie line. If there are no other problems air will work itself out and you should be adding less and less until it is stable and needs no more.

So, why was it low? The main possibilities are:

1. Coolant leak.
2. Leaking radiator cap.
3. Blown head gasket.

Most mechanics have the right tool to test that the radiator cap is sealing properly and that it opens at the right pressure. It is a very fast test and maybe they can do it for you for a small amount? Otherwise you can rent the tool from Autozone and do it yourself, but the deposit was more than $200 when I did that recently for our Accord. If the cap looks worn replace it with an OEM one. (I recently bought a Gates cap for the Accord which was defective, it would not open at pressure. That's a reputable brand but that one was bad. Now I think it is best to pressure test even a new radiator cap.) Note that for a leaking radiator cap there are usually no signs of that leak. The fluid only comes out when very hot and under pressure, and it evaporates instantly, leaving no trace.

 

Gen 3 Prii are even more modern cars that don't have that system. Gen 2 still had it. (I think also Prius c still had it.)

The older system with both a radiator cap and a reservoir cap is a "reserve bottle" system. The bottle just has one hose connecting to the radiator filler neck, on the non-pressurized side of the radiator cap. Coolant only flows out of the radiator into the bottle when it expands and pushes past the pressure cap, and only flows from the bottle back into the radiator when it cools and contracts and gets sucked back in. The rest of the time it just sits in the bottle.

The newer system they went to for gen 3 is a "degas bottle" system: that bottle has more than one hose, and it's a full part of the cooling system under pressure, and the coolant circulates through it. As the name suggests, it helps the system burp itself; air bubbles just get circulated along and end trading places with coolant in the degas bottle. Those systems don't have a separate radiator cap, and the bottle is the only place to fill.

But this is the gen 2 forum, so that's still a reserve-bottle system and you do have to make sure the radiator is full right up to the cap and there is some coolant in the bottle.

 

Take a look in the owners manual, and you will answer your own question.

 

The car has no way to monitor coolant level. It will turn on a "temperature warning light" (an icon on the MFD) if the ECM detects an overheating condition.

If that's happening because of a coolant leak, then it'll likely end up with engine damage.

Posted via the PriusChat mobile app.

 

Not a week goes by that I don't learn about something different in Gen3 than Gen2. So many changes at the height of Prius popularity was a huge risk that created less problems than it could of for the owner, but definitely created problems/more work for the owner's mechanic.

 

I for one like the degas-bottle system. It's simple, there's just one cap to open to correct coolant levels, and I've never had any trouble burping it, seems to work just like the engineers knew what they were doing. Fill 'er up to B, close the cap, run the engine at temperature for several minutes, let 'er cool down, and the extra coolant from FULL to B traded places with the air and now the level is at FULL. Boom, done.

 

It's interesting how removing the cap on a Gen3 Coolant reservoir blows air or sucks air depending on how things are going and is the quickest way to diagnose loss of coolant for the dreaded head gasket failure between cylinder 1 & 2.