Doing remote prognostication on my dad's 2009 Legacy (base 2.5L).
Had, along with the pertinent maintenance, the water pump replaced at a shop he's had a long good relationship with. Noticed later that the coolant looked a little low (below "low" mark on the reservoir cold), and eventually stopped by the shop to ask about it. They put in a pint or so, and everything seemed dandy.
But after very little driving it went back to the former below-"low." Then it stops and goes no lower. That suggests it's not really a worry to me, though I wish they'd get those sorts of things to line up.
I'm guessing that's just where it sits and purges anything beyond that, but curious about whether that's just what Subies do, or whether that's unusual.
He's going to ask the shop (I'm a little puzzled they didn't just clarify when he popped by for the top up), but I said I'd ask the hive, too.
I'd recommend that you keep topping it up and see if it continues to decrease after a few more heat cycles. A car should only lose maybe 50~200ml per year of coolant to evaporation if it has rubber hoses (more for silicone as coolant can be lost THROUGH the hoses). If the decrease stops soon then nothing to worry about. If it continues it may have disappearing coolant due to the usual Subaru head gasket issues...
If it stays at that level and never goes lower I would look at the radiator cap and hose to the reservoir. That generation should have the round 1 way cap on the radiator and the 2nd more traditional cap on the coolant neck thing on the engine. If the 1 way cap (which only allows coolant out for expansion) is leaking it will not recover coolant from the overflow when the system cools. But once it got the coolant out due to expansion at operating temp it would never push more out, just air.
Same thing would happen if their was a cut or leak in the 2 way cap or line to the overflow. Here when the system cooled it would just suck in air.
I've had caps loose seal on the rivet In the middle and cause this problem. They will Bubble the caution do not open hot sticker if equiped when the car warms up and sometimes will have water on the rivet recess.
Thanks, guys!
In reply to nocones :
I believe he's checked it cold a few times since the top-up, and the radiator itself remains absolutely full (no head space air); that suggests to me that it's not doing the thing where it fails to draw coolant back in as it cools and contracts? Really wish I could find a good diagram of the plumbing and caps and their functions. Am I correct in thinking that the 1-way cap on the radiator is not the way coolant returns as things cool off, and that it has to do with the unusually large number (3?) of hoses attached to the reservoir in pics I can find? Totally weirded out by the notion that the reservoir is... pressurized? And plumbed back into the rest of the cooling system in places other than the radiator overflow? I am behind the times on coolant systems (among other things).
I'm thinking this is another follow-up with the shop, but thanks for the specifics to check!
In reply to GameboyRMH:
I guess the weird thing is that it seems to be purge-and-done. After just a couple of drives, then stops. I agree that topping it up again to see what it does is the right first step, but if it purges to the same point and stops, that doesn't sound like either evaporation or anything head gasket related, as those wouldn't stop, right?
In reply to Jesse Ransom :
That's right.
Didn't realize this was a pressurized coolant overflow bottle with multiple connections to the main system, that makes things a lot more interesting...
I wonder if there is air trapped behind the new thermostat or somewhere in the system and it keeps self purging a little at a time.
As mentioned, I would keep topping up and see if it stops at some point. I might also run it with the heater on for a bit.
The coolant reservoir is not pressurized, it is just an old school puke tank.
If you are seeing pictures of a pressurized tank on a Subaru with multiple hoses going to it, you're looking at the coolant tank on a turbo model. Which only serves as a high point in the cooling system, they still have an unpressurized puke tank for overflow.
In reply to Pete. (l33t FS) :
Thanks! I hate remote diagnosis... and shooting myself in the foot with bad assumptions. I think I conflated nocones' description of a one-way cap at the radiator with a need to have some other return path.
It would be worth the peace of mind to sniff the oil on the dipstick to make sure it doesn't smell like coolant.
In reply to ShinnyGroove (Forum Supporter) :
That's a new one on me! I've heard of looking for the crankcase milkshake, but I didn't know you could expect to make out coolant scent in the oil...
I'll pass that along, but I'm also pleased to report that the most recent top-up/drive/cool cycle has the coolant right at the Low mark. Starting to hope I've managed to create an entire thread over "totally stock car with recently opened cooling system needed one more burp." But I learned some stuff, so that's cool!
