Just some evaporation from the overflow bottle. Top it off and forget about it.

 

And that was my expectation. Still, this is the first time I've had it come up in such a short period, so I'll stay, shall we say, casually watchful.

 

Several people have noted that their Subarus need more topping off of the coolant reservoir, more often in hot dry weather.

 

Disappointed the OB still has an outdated unsealed reservoir, rather than a sealed system, like most vehicles nowadays. So yes, there's going to be evaporation from that kind of system, unfortunately. Especially with the ridiculous heat some (or a lot of) us are experiencing lately. It's been over 110F here for a lot of days. At any rate, all new vehicles have air in the system, needing a top off the first few months. I'm going to top off my coolant with the factory 50/50 super coolant for the first few months. But after that, I'll probably use distilled water if needed, as not to increase the percentage of coolant, since only the water evaporates.

 

But after that, I'll probably use distilled water if needed, as not to increase the percentage of coolant, since only the water evaporates.

Interesting thought. I've got a refractometer, so I'll just check the coolant sometime in the next few days. Then, if it drops again, I'll check it then to see if it's gotten more concentrated.

 

I am curious about why the new Subaru tends to evaporate more because if I'm not mistaken, all coolant overflow tanks have a tiny hole to let air escape as it fills with fluid. That hole is so tiny that the evaporation is normally negligible and in my other 3 Subarus there was not much evaporative loss.

Normally the hot coolant that enters the reservoir will try to evaporate moisture like any hot water would, but it will condense on the cooler walls of the overflow reservoir and not come out.

If the overflow reservoir has not much head space, then I think evaporation is much worse.

 

I am curious about why the new Subaru tends to evaporate more. In my other 3 Subarus there was not much evaporative loss.

Ditto. I can't recall adding coolant to my 2005 LL Bean in the whole 16 years I drove it. You gotta believe that I did at some point, but I don't remember doing it.

Sniff. Now I'm getting nostalgic about the 3.0 H6 and the 5EAT. What a nice powertrain.

 

As the engine warms up, expanded coolant enters the reservoir and pushes vapor saturated air out into the atmosphere.

When the engine cools off, coolant contracts in the engine and coolant is sucked out of the reservoir back into the engine and it is replaced with dry outside air.

So this repeated pumping action of air in and out of the reservoir can cause some evaporative loss.

 

I've not had to do mine yet, and it has been hot of late in Georgia, but I do keep Subaru coolant in the garage just in case. This is after 15,600 miles too.

 

Our 19, 20, and 23 all need coolant added periodically. What's interesting in our case is the 23 is a turbo that needs less coolant added, the 19 and 20 are both 2.5's that need at least half a reservoir added every 6K miles. Yours is the first turbo I have heard of that needs that much coolant added, certainly more than our turbo. Just continue to keep track and you'll be fine.

 

Driving from NY to Florida this week... Maybe I should check my coolant. Just had the 24,000 mile service. Hopefully it was checked but never can be sure these days.

 

Had to top off my 2021 too after approx 14,000 mi; I ordered the Subaru brand from Amazon. Surprised that it was low but honestly, it just wasn't a level I'd paid attention to, like I do now

 

I just checked coolant with my refractometer. First, fresh 50/50 premix Peak Asian Blue, straight from the jug. It tested at -25F, even though the jug says -34F. Then, I drew some from the radiator. It came in at -40F. What's unknown at this point is how it might have tested before two cycles of evaporation and refill.

If I need to add coolant again, I'll check with the refractometer first. If it's lower than -40, I'll just add distilled water. Living in Memphis, I don't need protection below -40. I do need good cooling, so there's no point in running a mix with too little water.

 

Well today I learned...

I've driven Volkswagens / Audis forever, and they have used sealed / pressurized coolant systems for decades (at least back to the early 1990s off the top of my head) and I didn't realize that any manufacturer would use a non-pressurized / sealed system.

 

I didn't realize that any manufacturer would use a non-pressurized / sealed system.

For lurkers and future readers, the Subaru cooling system is pressurized. It is the overflow tank that is not.

Someone help me understand why this is a big issue. Is it just because it results in having to check the coolant level in the overflow tank a few times a year due to the potential of evaporation?

 

As long as the coolant level never goes below the 'low' mark when dead cold, and above the 'high' level when hot, this normal behavior. When hot, the coolant expands and partially or fully fills the overflow reservoir. When it cools, the coolant is pulled back into the engine from the reservoir, going back to the 'low' level, completing the heat cycle. I see this cycle on my 2018 OB 2.5L. Mine typically drops to the 'low' level when cold, and to the 'high' level when hot. Never goes beyond these limits in 6 yrs, 60k. No need to ever add coolant if it stays within these limits.

 

We deal with the same thing on my 2019. Sometimes it even smells like coolant after driving. Husband has put the pressure tester on it and it holds pressure just fine. Even watched the dealer put their tester on it and holds pressure. They say it's normal......we just keep an eye on it.

 

Late to this thread, but my situation is similar to yours. Have '24 OBW with same engine. I've topped off twice, once at about 8k miles, and just the other day at around 16k. Each time, I added perhaps a cup. I have no indication of any leak or consumption internally, e.g. head gasket failure. Car runs well. I'm assuming evaporation from expansion bottle.

 

All three of our Subarus have been like this. Each 6000 mile service my dealer refills the overflow tank. The amount that disappears each 6K miles is about the same as the distance between the low and full mark.