2023, 27k miles - car appears to be consuming coolant?
 

Anyone else experienced this?

A few days ago I decided to check my oil and noticed that the coolant level was low in the overflow container. Barely anything in there, in fact.

I had just a little bit of Subaru coolant left and I was able to fill it up to the LOW line.

Got some coolant 2 days later, it was back to barely anything in the overflow bottle. Filled it up to full. Drove it to work, gym, and dinner with girlfriend. Probably 40 min of driving total. Next morning (today), it's down to halfway between FULL and LOW.

Before anyone asks, I am only checking and filling it in the morning before starting the car. Engine is dead cold.

I'm a bit concerned. It's a new car. Cooling system has never been opened up or touched. I am not noticing any smoke from the exhaust or smell of coolant (good), but not sure where it could be going other than a leak (which I'd smell) or being burned (which would make smoke).

Anyone else noticed anything like this?

The radiator is covered by the bumper, so I suppose next step is to pull the bumper to see if there's any evidence of leaks. But that would be a pretty big leak which I would imagine would make quite the smell.

Totally normal on these cars, especially if you daily drive this car at that current mileage without checking. If you've checked the radiator hoses for any leaks, then you might have a leak issue and might need to replace something.

During the hot days or Summer, the coolant starts to slowly evaporate since it is a 50/50 antifreeze and water fluid. As for filling up to "FULL", you may fill it when the engine is cold. The hoses expand once the engine is at operating temp, so it's best to fill it when it is at operating temp. Make sure to fill some in the coolant reservoir bottle as well.

Evaporate? Isn't it a closed system?

And nothing about the situation OP described sounds normal, ESPECIALLY for a 2 year old car with only 27K on it. :thumbdown:

Yeah, it is a closed system if everything is sealed properly. Evaporation only occurs in the coolant reservoir bottle because there is a vent hole, and it evaporates out the vent hole over time from the amount of heat under the hood, especially with the number of miles of daily driving, even if you don't have any leaks or problems with coolant hoses.

Disagree. The line from the rad to the overflow reservoir is sealed, the cap to the reservoir is pretty tight fitting and does not have the vent hole you mentioned. I just went out to my car to inspect and reacquaint myself with the parts.

If anything, what you are calling evaporation should be called a leak.

@gnarjunkie have you figured anything out?

It's hidden underneath the radiator support. The vented hole is in front of the reservoir bottle to prevent the build-up of coolant pressure when pushing your car, depending on your driving style. Evaporation happens at a "very slow rate", whether you are driving your car hard or live in an area that is hot/humid.

https://www.mishimoto.com/media/mage...-installed.jpg Attachment 227829

This conversation is insanity. This is why AI can't be trusted for car stuff.

The overflow bottle on our cars is not sealed. The cap is just a dust cover without any sealing function. This isn't like a lot of American and German cars.

The rest of the cooling system is a closed system. It should not lose coolant naturally in any significant amount within the normal service cycle.

The overflow functions as either an overflow or a vacuum return depending on if the pressure in the cooling system allows the radiator cap to open so that the hose can either put coolant into that tank or draw it out. Since coolant expands when it's hot and contracts when it cools, the system vacuum returns coolant to coolant system as the car cools down if it is losing coolant elsewhere.

So, if you are constantly overflowing that tank then that means that your cooling system is over pressurizing and generally indicates an issue with excess pressure coming via exhaust gasses. In this case (and one I've experienced personally), the issue is a head gasket or warped head allowing exhaust gasses to enter the cooling system. I did not lose coolant in this situation but the car fails the coolant combustion test.

If you are losing coolant and there is no obvious evidence around the radiator cap then you are likely losing it somewhere else if it is a significant amount. I would recommend doing a coolant combustion test to determine if you have a head gasket leak of some sort.

I'm guessing/hopeful that you've checked the oil to validate that there is no coolant there. There is also a possibility that you have a hot pressure leak on one of you coolant hoses that only leaks when the car is hot and under way. You could be losing a small amount of coolant in that scenario. So, again, check your hoses while the car is hot.

So, do these things:

• Get a coolant combustion tester and test for combustion gases in your coolant.
• Get a coolant system pressure tester to check for leaks in the coolant system.
• Look for leaks while the car is hot.
• Change your radiator cap. (This should be considered a last ditch effort since your car shouldn't be losing coolant at that point without obvious evidence.)

I was thinking that reading this too lol. I don’t think I have had fluid in the expansion tank in my car for 10 years. It evaporates out pretty quickly due to how hot the engine bay gets and not being sealed.

Regardless of the fact that the overflow reservoir isn't sealed, that's too much fluid to lose over a single drive.

I track my car and rev it out all the time, hot climate. At best it goes from full to low maybe once every 6 months.


If you don't find any fluid in your expansion tank, chances are you're running your fluid under capacity and pulling air into the cooling system (not good)

My fluid level basically never changes. I fill it from the rad cap about 1/2inch below the top. That’s why I never bother with my overflow bottle. Sometimes it pushes a tiny amount in a hot track day but that’s it.

My own recent experience with a situation like this happened after adding FI and it looks like I have a failing head gasket at the least. I'm not consuming coolant but the system was over pressurizing which ended up forcing the lower coolant hose to pop off and then made the problem official. That led me down the path of all of the methods of checking for leaks, combustion gases and other failures.

Wow, this got a lot more responses than I realized! Sorry for not checking back sooner.

I am confident now it was just evaporation. Someone pointed out to me that if the overflow bottle was that low, the radiator was probably a bit low too and so it was sucking in from the overflow bottle. I filled the rad up to full, then the overflow bottle, and the level has not moved at all since then.

It makes sense. I live in a desert, it is extremely dry here. I've had the car for 3 years and not checked coolant levels once. The whole system was low probably a cup or two of liquid total... if I left a cup or two of 50/50 water mixture out in a mostly sealed bottle for 3 years... it makes sense it would evaporate.

Looking around online, there are a very large number of people reporting similar evaporation amounts from Subaru engines in many different models. I'm guessing some people see it and some don't because of where people live. Around here you could be completely soaking wet and if you stand outside for 10 min in the sun you and everything you're wearing will be bone-dry.

It also makes sense as I'm very confident the car does not have a leak and is not burning coolant.

Looking back now, it's a funny situation. My car before this was a 450+ whp STi that saw track use constantly. Had that car for 8 years and I checked everything constantly... I'd literally be checking fuel lines once a week to make sure they hadn't worked loose.

Guess I got a little lazy with a brand-new car with an unmodified engine and stopped checking the basics :bonk:

Well I stand corrected lol!

Thank you for posting pics of the overflow bottle @ZC6_STi

Thank you also for bringing an end to the insanity @RT-BRZ

and finally thank you to @gnarjunkie for following back up and letting us know your conclusion!

:thanks:

I guess the one thing we can all agree on is to check your coolant level in the overflow tank somewhat regularly if you live in a dry climate. I was not aware of that since it is really humid where I live.


:respekt: