2006 Subaru Outback, 2.5l NA, ~110k

Had the timing belt, including water pump and some old, corroded hoses replaced about 3 months ago since it seemed overdue. Which I would assume if not a full flush is still a drain and fill of the coolant. And according to dealer (bought car used around 90k) head gaskets were replaced shortly before I purchased, have the service receipt.

Noticed today the engine was heating up much faster than usual, hit about 75% of the temp gauge during normal, commute driving. Checked under the hood and the reservoir tank was completely dry.

No time to wait to cool and check radiator, so just topped up the reservoir tank to the tippy top (as in to near the cap). After a short, 2-mi drive from the gas station to work (with temp gauge quickly dropping to normal levels), checked again and the reservoir tank is now sitting right about the full line.

Never had any particular reason to suspect coolant leak. No puddles, or smoke under the hood. Never smelled anything weird (though hard to say, living in a city, sometimes during commute I get a wiff of gasoline but you can't tell if it's you or the truck in front throwing heavy exhaust smoke).

Before driving home, with the engine cold, might be a good chance to take off the radiator cap and see what level is like inside there. But can't focus right now. I'm wondering if the timing belt replacement was shoddy, if the gaskets are leaking. Just want to see some preliminary opinions of whether this is just something that can happen or a sign of something serious.

  • Hopefully, the cooling system was just filling some air pockets left from the maintenance with fluid from the reservoir and you've topped it up and all is well. Alternatively, the head gasket is bad, or there's a coolant leak somewhere, or something else. Can't really tell from the info given.
    – cory
    Commented Feb 15, 2017 at 21:02
  • Yeah that's what I'm hoping, and it was just low this whole time (since I neglected to check, otherwise 3 months seems too long). Engine cooled off enough and looked under the radiator cap and there's definitely a good deal of fluid missing. Short drive to get some more distilled water/coolant. Will wait again till engine cools off, top off in the actual radiator, and just keep an eye on it every drive. If levels drop off radically again seems I might have a pricey repair coming up :\ just hoping it's not the gasket and something simple like a bad hose or whatever. Commented Feb 15, 2017 at 21:18
  • Or maybe just a bad radiator cap. Commented Feb 15, 2017 at 21:34

2 Answers 2


The Subaru engines are notorious for being difficult to burp. It takes me about 20 minutes to fill a Subaru radiator if I've done a full drain (as per a timing belt replacement).

75% on the temperature gauge is within normal, so you've spotted the problem (missing coolant), and fixed it already. If the head gasket work was shoddy, the temperature gauge would quite literally be past the red mark (as would your own temperature, thinking about the work just done!)

  • 1
    That's what I'm hoping. It's been a week since I topped off the levels in the radiator itself and the reservoir (then ran on idle for about 10-min with heaters on full to try and get everything circulated/burped). I haven't done any major driving besides work commute. The reservoir level dropped a tiny bit more but nothing alarming considering what happened and it might need to suck up a bit more. At this point just going to keep an eye on it but looks like the best case scenario might be likely. Thanks! Commented Feb 23, 2017 at 17:13

Check your engine oil. If it looks like Carmel or has bubbles in it then you have an internal leak. Let your car cool off open the radiator cap and start the car. Turn on the heater full plastic for a few minutes watch the fluid level from a distance wear protective spectacles. Top off as necessary. If all is well just check your reservoir now and again. Be blessed.

  • I did read about that. Is checking via dipstick fine? I haven't noticed any milky-ness or anything. I used to do my own fluid changes but not having a driveway anymore I'll mention it for my next oil change. Commented Feb 23, 2017 at 17:17

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