Subaru EJ25 Head Gasket Replacement – Part One

Hi folks, today we are looking at what’s involved in replacing the head gaskets on a 2010 Subaru Forester. While the vehicle for our tutorial is a 2010 Forester, these instructions will be relevant for all EFI EJ25 Non-turbo Subaru engines.

We elected to remove the engine from the vehicle to do this job, mainly for ease as there is little room between the chassis rails and we have lifting equipment available to us, however this repair CAN be done with the engine still in the vehicle. There is a good writeup of doing it in-car here –, I can’t say it would be my choice to do it this way but if you don’t have access to the gear it will get you out of trouble.

As usual please read all the steps listed before attempting the repair (this is going to be a loooong tutorial!), making sure you understand each step and have the tools required. If you do get stuck though leave a comment at the bottom of the article and we’ll do our best to help you through. Oh and be sure that you’re diagnosis is confirmed as a blown head gasket, you don’t want to go through all of this work to have the issue being caused by something else! There is a little bit of info on the steps we went through to diagnose this particular Subaru here –, although not exhaustive, it may give you something to go on when doing your diagnosing.

NOTE – The harmonic balancer has to be removed at some point as the timing belt needs to be removed to separate the cylinder heads from the block. Deciding how you are going to do this now instead of it becoming a road block halfway through the job is a good idea. The bolt has a 22mm head and it will be tight. If you have an impact gun and are removing the engine, no problem, but if you don’t have air tools or aren’t removing the engine you have another couple of options.

The first is to make up a Harmonic Balancer Locking Tool (yes, that will work with the EJ25 too) to prevent the crankshaft from turning and loosen the bolt with a socket and bar OR remove the starter motor and lock the flex plate up as best you can and do the socket and bar thing again.

And finally, and not really recommended, but done more often than not, is to use the socket and bar again but put an extension on the bar (piece of pipe etc) and lay it on the passengers side chassis rail or inner guard (being sure to keep it clear of anything that could get squashed or damaged) and hit the key momentarily. The starter will kick into action and all going well the socket and bar will stop the bolt from turning and you’ll have a loose balancer bolt. I didn’t tell you how to do this though 🙂 . It’s not the recommended way to loosen a balancer bolt as there is potential for starter motor gear damage or flex plate damage and you could imagine the damage that could occur if the socket bar comes loose and starts spinning around wildly…..

Another noteworthy item is fuel pressure. As the fuel lines have to be removed from the engine it is wise to reduce the fuel system pressure so you don’t have fuel spray around the place when you remove the supply line. With the car in it’s final position where you are going to do the repair take the time to remove the fuel pump or efi fuse or relay and crank the engine until it won’t fire anymore, effectively reducing all fuel system pressure.

Ok, with that out of the way let’s get on with it. First off we need to drain the coolant. I find the easiest way is to jack the car up and put it on stands, remove the belly plate underneath (a mixture of 12mm, 13mm and philips head plastic screws on our Suby), and remove the bottom radiator hose at the radiator end and drain the coolant into a large container. The more coolant you get out at this point the better so it’s a good idea to remove both heater hoses now also (they have to come off at some point anyway).


Next up I suggest taking the radiator out. Even if you aren’t taking the engine out you will need the room to remove the balancer/bottom pulley. The top radiator hose can come off and the electrical connection for the fans can be disconnected.


At the bottom of the radiator there is a heat shield that has to be removed to get to the transmission cooler lines (auto only of course). Once removed the cooler lines will leak some fluid so I suggest blocking them with a bolt or similar. Up top again and there is 12mm bolts securing the radiator brackets, remove these and the radiator can be lifted out, while trying not to pour coolant or trans fluid over yourself 🙂


Next up the air intake can come off –


And the air filter box and intake pipe. There is a 10mm bolt and 10mm nut to remove the air box –


And air flow meter electrical connection and hose clamp to remove the intake pipe –


Next remove the 10mm bolt from the drivebelt cover and remove it –


The negative lead should be removed from the battery next. I actually removed the battery from the car at this point to give a bit more room, but it’s not absolutely necessary to do that. NOTE – Always remove the negative terminal first. If you remove the positive terminal first you have the chance of arcing the spanner out on the still-earthed body which can cause electrical and ecu issues.

Next we can remove the air box from the throttle body. It has two 10mm bolts, a hose clamp to the throttle body and two PCV hoses which can be removed there or at the tappet cover ends.


Next up remove the wiring associated with the alternator and a/c. The green connector on the left has to be undone, the 12mm nut removed and the plastic clip opened on the main lead. The small connector for the a/c power needs to be undone also.


Now we can remove the alternator belt and alternator, the air conditioning belt and compressor and the power steering pump. Both the a/c compressor and power steer pump can be removed from the engine and left in the engine bay with their hoses still attached. To remove the alternator belt loosen the bolt on either side of the alternator and then wind the adjuster bolt down in an anti-clockwise direction.


On the later model EJ25 the air conditioning belt is a single-use belt that requires no tensioning. If you have no a/c belt tensioner cut the belt off and budget for a replacement! With bolt belts off you can completely remove the two alternator bolts and remove the alternator from the engine. The right hand side bolt has a nut that can go back on the bolt once it is out.

I found the easiest way to remove the a/c compressor from the engine was to leave it attached to it’s bracket and remove the bracket from the engine block. There is one 14mm on the right –


And three 14mm bolts on the left – 


The compressor can then be carefully moved to the passengers side of the engine bay out of the way. Just be careful not to kink or squash either of the hoses 🙂

Next the power steer pump can be removed. For this we have three 12mm bolts, two at the front and one hidden away at the back and an electrical connection to undo –




While on that side of the engine you can undo the two oxygen sensor connections and remove the clips from where the wires are attached to the bracket –



On the drivers side again but towards the back we want to undo the large main harness connector. To do this first push down on this part of the clip –


And then lift up the grey part of the clip which will seperate the halves of the connector.


Then remove the 10mm bolt and bracket to remove the car section of the loom from the engine.


Then we can slide the clip on the brake booster hose back and remove it from the manifold. Twisting the hose while pulling back is the easiest way to remove them without causing any damage.


Now over to the passenger side of the engine and the two fuel hoses can be removed. Once again the twisting while pulling action is best 🙂


NOTE – The next two steps are for auto only. Next up we can remove the throttle body to give access to where the torque converter bolts can be undone. On the throttle body there is two coolant hoses, one electrical connection and four 10mm bolts that need to be undone.




With the throttle body removed you should be able to see a rubber plug. Pull the plug up and out and then you’ll have access to the torque converter bolts.

You will need to rotate the engine to find all four 12mm bolts and possibly have an assistant hold the crankshaft while you undo them. Be careful not to drop any!!

When you are on the fourth one I suggest when it is halfway out to push the head of the bolt back towards the ring gear as much as you can so that the torque converter is pushed back into the transmission as far as it will go, typically it will move around 10mm back into the transmission bellhousing and this will help to ensure that it stays with the transmission when the engine comes out.

Now we can start on the bellhousing. First up remove the starter motor, 14mm bolt up top and 14mm nut below.


And there is a 14mm bellhousing bolt just below the starter motor aperture –

And on the drivers side there are two 14mm bolts to remove –


Now there is two more 14mm bellhousing bolts, actually two are stud and nut, and these can be reached from up top, in fact I found them easier to undo from up top with a ring spanner and flexible handled ratchet but I guess it depends on what tools you have available to you as to what you find easiest.


Now it’s time to undo the exhaust and earth straps underneath. There are three 14mm nuts on each exhaust flange and if your vehicle has it I suggest undoing the exhaust mount that is not far back from the firewall.

This will give you some movement with the exhaust if you need it when lifting the engine out. Our vehicle had a 17mm bolt in this mount. The two earth straps are undone with the 10mm bolts on either end.


Next up the 14mm nuts can come off the engine mounts –


And finally before it’s time to lift the engine out, the gearbox to body mount needs to be undone and lifted out of the way. At the body end it can just be loosened but the nut and bolt at the gearbox end will need to be removed. Leaving this in place won’t allow you to lift the engine enough to clear the engine mounts and exhaust.


With the mount out of the way you can put your lifting gear in place and a jack under the gearbox and lift the engine enough to clear the mounts and a few good wiggles and you should be able to seperate the two and lift the engine out.

With the auto it’s a good idea to refit the transmission to body mount rather than just letting it sit on the crossmember. If you look carefully sitting it on the crossmember actually puts pressure on the torque converter which can lead to seal failure or possible pump failure which you don’t want. Refitting the mount will hold the transmission up enough to keep the converter off the crossmember.



I think we’ll leave this part there and tackle the cylinder head removal in Part Two and engine reinstall in Part Three.

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