The past month I have been refilling my empty coolant reservoir before each trip.

My most recent trip I noticed every few moments I would lose some performance, the RPM's would stay the same but my acceleration would slow.

I got home to investigate the problem and found the source of the coolant leak, my cylinder head...

Here are my questions:

  1. This power loss I am experiencing, is this coolant leaking into my combustion chamber?
  2. I called a mechanic who recommended I try to use some head-gasket sealants, is this a good recommendation or have I 'passed the point of no return'?
  3. About a month ago, I changed the timing belt and water pump, is there anything I could have done that would have caused the head gasket to blow?
  • 1
    Many mechanics recommend against using sealants, as there's no way to direct them to where sealing is needed, and they can make the inevitable repair more difficult (because the sealant will have to be scraped off, which can be problematic on aluminum heads).
    – TMN
    Jul 5, 2016 at 19:06

4 Answers 4

  1. Coolant can definitely leak into the combustion chamber with a blown head gasket. Whether or not this is the cause of your power loss is hard to say. The amount of coolant going into the cylinder varies due to the severity of the head gasket leak. The head gasket itself is an integral part of the compression system in your engine. With a faulty head gasket, compression is lost in the cylinders causing a loss of performance.
  2. I have never had success with head gasket sealers. This isn't to say that it won't help you though. If you don't want to spend the hundreds of dollars to repair your head gasket right away you could try the sealant and see if it does anything for you. If it doesn't help though, you definitely need to get the gasket replaced. Severe damage can be done to overheating engines.
  3. Head gaskets are just like every other gasket in a car and go bad over time from age and use. The only thing I can think of that you would have affected is if your water pump gasket didn't seal entirely and caused a coolant leak. I would think that you'd notice that though as they typically leak pretty conspicuously.
  1. Quite possibly, because the cylinder with coolant leaking into it will have low compression. When I ran my Subaru with two leaking cylinders, I found that on the freeway, the engine had to run at about 1,000 rpm higher for the same performance. At low speed it ran really badly, of course.

  2. Find a new mechanic; this one's after extra work. Those head sealers only work if you want to sell the car in the next week or so (then the mess becomes someone else's problem). They really clog up a lot the engine, by virtue of the way they work.

  3. No. If you have problems replacing the timing belt, you KNOW as soon as you rotate the engine :) The only similarity is that the gaskets are the same age as the old timing belt, so pretty much ready to go. How many miles on the car?

If you did your own timing belt, and (especially) if you're fine with taking the engine out - 4 bolts on most Subaru engines - you can do the job yourself and save a lot of money.

  • Thanks for the input! The car only has 107k on it. Haven't taken an engine out yet, but I'm not afraid to try and my neighbor will let me use any tools I need. However, I did see some people online pulling the heads without pulling the engine...
    – Calvin
    Jul 5, 2016 at 15:15
  • 1
    Don't even bother to try it without the engine out. Yes - there are some videos on it, but to get the heads off you need to drain all the fluids anyway, You may as well go for the extra few bolts (two engine mount bolts and four engine/transmission bolts) and pull the engine - then you can really get a good look at what you're working on, and replace the valve cover gaskets etc while you're in there. Use a quality gasket (e.g SixStar) and you'll be good.
    – PeteCon
    Jul 5, 2016 at 19:35

These engines are notorious for blowing head gaskets around +/-160,000 miles. It's highly likely you have already warped the head so no matter who does the work make sure the head is resurfaced. On the plus side, as others have mentioned these engines are easy to remove should you tackle this job yourself. You will want to replace additional gaskets when replacing the head gaskets such as valve guides and cam seals.

  • An additional plus is that if you do decide to take it to a mechanic, they've probably replaced head gaskets on a Subaru before, so they'll know exactly what to look for and how to deal with it.
    – TMN
    Jul 5, 2016 at 19:00
  1. Hard to say, but plausible.

  2. I've had mixed experience with sealants but it's never a permanent fix. I had it hold in a 98 Outback for about a year, but then it failed again and more sealant did not help. If there's a chance that could buy you the time you need to replace the vehicle, wait until the weather is pleasant for working on the vehicle, or save up money to use on the repairs, go for it. There's really nothing much to lose beyond the price of the sealant. It will not ruin your engine by gunking it up, but there is a chance it could clog your radiator to an extent that you want to replace it (another $100 or so).

  3. I don't think you did anything wrong. These vehicles are infamous for blown head gaskets. Some people say it's due to the materials not being made to handle fuel with ethanol added, but I don't know whether it's true or not or whether it applies to your model year even if it was true for earlier ones (I heard this for the 98s).

In any case, I did the job in a 98 without taking out the engine, so I suspect that's possible in yours too. Most of the pain was actually getting off the valve covers and dealing with removing/installing the cam shafts while the engine was in the vehicle (necessary on DOHC models from that period, maybe not on yours, to reach the head bolts). Once you get everything else off, though, removing and reinstalling the heads is pretty easy.

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