2002 Subaru Outback with previous cracked and repaired head gasket about ten years ago. The only thing of note is that it does burn oil a little at a predictable rate. The worst this car has had is a couple of burned-out light bulbs. It has ~86,000 and is typically driven short distances but has done long distances without issue. Oil changes kept up, the only notable thing done in the past year was having the transmission flushed about ten months ago given that the fluid was very old and it felt sluggish. Performance improved and until recently, drove very well.

Coming home about five weeks ago, while at a traffic light, it looked like there was steam escaping from under the hood. It was very fine and this was at dusk - so it showed up due to the headlights of other cars. I drove a couple of blocks home as there was no other place to stop and immediately popped the hood. There was nothing. The temperature was fine, no signs of overheating, no warning lights, no steam after parking, and no signs of anything happening. Thought it was in my head.

Shortly after this, there started to be a periodic smell that wasn't pleasant. Could not source it and it wasn't constant or that overwhelming. Pulling into a gas station a couple of weeks later, I saw the same thin steam escaping under the hood again. I opened the hood and it was gone. The smell was there slightly, kind of like burning but no signs of anything wrong, no steam, no strange noises, no lights, no overheating. I made sure there was coolant, The oil looked fine though it was due to be changed and it was floating at the lower end as it typically does due to the above-mentioned mild oil burning issue.

I wondered if maybe a hose was leaking somewhere and fluid was getting on the engine. I did call the dealer who proceeded to tell me that sometimes when it gets cold there could be steam from the air hitting the engine! What?! It was almost 50 degrees that morning! And I never had anything like this, even on a morning when I had to drive through freezing fog and got ice on the leading edges of the car. They told me not to worry about it.

I took it for its regular oil change and the coolant was topped off. This isn't a car that leaks fluids, and they mentioned they were surprised it was low. It drove alright that morning, but by evening it had that smell, stronger than it had been with the weird whispy steam again.

While driving the next morning trying to sort out a mechanic to take it to, the idle changed. It's hard to describe, it wasn't loud but it definitely felt rougher. The smell was present but the steam was not.

Any ideas of what this could be? Originally, when the head gasket was cracked it had inconsistent symptoms though more typical. Given the age of the car, though it runs really well, I know any part of it could fail.

  • Welcome to Motor Vehicle Maintenance & Repair! Dec 22, 2023 at 21:29
  • White steam points to coolant. Topping it off is a hint. With many coolant lines and major engine repair, either a very slow coolant leak is occurring from old(?) Coolant hoses, loose hose clamp(s) or..........another head gasket issue. If you are comfortable around engines, check and tighten coolant hose clamps, feel and look for coolant stains. As a rule, hoses bulging in diameter larger than its hose clamps should be replaced.
    – F Dryer
    Dec 22, 2023 at 23:13

1 Answer 1


The most likely cause of these issues is a coolant leak. The strange smell could be coolant, which probably smells strange if you've never smelled it before.

You could have a worn-out radiator cap, a hose clamp may have rusted and broken, a coolant hose or the radiator, heater core or a freeze plug (if you have them) could have developed a leak or a mechanical part such as the water pump may be leaking. There are other possibilities as well, such as a failed head gasket or a cracked block.

The easiest way to confirm and find the leak is to pump up the cooling system to maximum operating pressure using a hand pump, usually to 15 PSI, and see if it holds pressure or it leaks down. A pressure test kit comes with various fitting that attach the pump to the radiator. If the test pressure leaks down and the leak is in an exposed location, you should be able to locate the leak by spotting the dripping coolant.

If it leaks down but you can't find the leak, it could be the heater core or an internal leak in the engine. Since you have observed apparent steam, it's probably an easily found leak in an accessible place.

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