I have had 2 people contact me about auto repair related things that they have come across here while searching for answers. I am writing up what I did this morning for that and because it seems that many of the folks that work on their Subies are younger and, for some reason, they don't document this sort of thing so it can be hard to find DIY's for repairs. I'm not used to that because the Jeep crowd will tell you what the symptoms were, what part numbers they used, provide photos of the repair along with an explanation and a final end result. It seems that many of the Subie forums are focused on wheel fitment and sticker bombs.
A while ago, I talked about the erratic overheating issues that I've been having. The first step was I wanted to rule out a faulty temp gauge, sensor or electrical issue. I installed a secondary temp gauge and...waited. Well yesterday the secondary temp gauge got up to 200 and then the stock gauge went up so I pulled over and found coolant near the lower corner of the radiator, drivers side. Now, the radiators on Subarus are aluminum with plastic ends and, quite often, the connection between the plastic and aluminum is where leaks occur. I opened up the overflow tank and it was...overflowing. So I was not sure if the coolant leaking was from the overflow or a faulty radiator. Typically, a leaking radiator doesn't cause an overheating issue. Just a mess. While it's possible that my radiator is blocked and, thus causing overheating, the next logical (cost efficient) thing to look at was the thermostat. It is not uncommon for a faulty thermostat to open randomly, or not open all the way. So I wanted to get everything cleaned up, install a new thermostat and, like before, wait to see what happens next. I suppose one could just order a new radiator but I like to know exactly what the problem is/was.
This repair is being done on a 2002 Impreza Outback Sport. It is very difficult to find DIY's on the OBS. Most things you find will be for the WRX which uses a slightly different radiator because of the turbo cooler. This is the motor after I got home yesterday and pulled the coolant overflow and the drivers side fan. Both are held in with 2 10mm bolts up top. Remove those and lift the tank out after disconnecting the hose form the filler neck. Disconnect the plug for the fan (located underneath) and wiggle that thing out of there. I did this because I really wanted to have a better look at the bottom of the rad. It did not appear that the leak was coming from there. This is good because finding a rad for the OBS was quite difficult yesterday. In fact, I never actually found one other than the stock unit which the dealer wanted $360 for. You can get all aluminum rads from Koyo or Mishimoto for about that price although Rally Sport Direct did not have ANY for the OBS. For the thermostat, most of the time I would never buy a thermostat from the dealer but you SHOULD in this case. I have read loads of threads about issues with non-OEM thermostats. Go to the dealer, bend over and get ready to pay about $40. I will say, it is a big thermostat. Much bigger than ones I've seen in V8 motors. It comes with the gasket.
Next, jack up your car and put it on stands. It's probably a good idea to unbolt the negative terminal on the battery so the fans don't come on. The t-stat is located under the car. Just follow the lower rad hose and you will see the t-stat housing. Remove the hose clamp, make sure you're drain bucket is under the housing and then pry the hose off. This may take some persuasion. Push the hose up out of the way and use a 12mm socket to remove the 2 bolts on the housing.
This is the thermostat. Notice where the coolant is leaking from. That hole is called a jiggle pin. The only real way you can screw up this simple repair is to not have that pin towards the front of the motor. It allows air bubbles to escape. Pry out the old t-stat.
Wipe off the surfaces with a clean rag. The t-stat housing is plastic so make sure there are no cracks in it. You will notice that the ears of the housing have metal sleeves. Don't get crazy tightening this back on or you will crack the plastic. Push the new t-stat into place. You will feel the gasket kind of seat in it's location. Put the housing back on and thread the bolts in. As you tighten it, you will feel the gasket compress and finally the bolts will come tight. Give it a bit more. Reconnect the rad hose.
At this point you are ready to fill up the rad. This car has a filler neck on the rad itself. The WRX does not so if you have a WRX, use the turbo cooler (it's the highest point in the system) to fill. Slowly fill it up. At this point, I cleaned the subframe of all the coolant that leaked the day before and then reinstalled the fan and overflow tank. You are pretty much ready to start it up now. One of the most important things about these cars is making sure to burp the system of any air. If there are air pockets in the system you will see those sporadic overheating issues. Motor gets hot temporarily when a bubble passes through and cools down once it leaves. A lot of people say to turn on the blower motor to 4 and set the heat for hot when you start the car up. The reason is to move coolant through the heater core and chase out any bubbles that may have entered during the draining/refilling process. I think the coolant always flows through the heater core in these cars but I'm not sure so it's good insurance. I leave the rad cap off while the car is running. You will start to see bubbles coming up the filler neck.
Be patient because this may take a while. The t-stat from Subaru is a 76 degree (C) one (172F). I let the car idle for as long as it takes to get to operating temp (although I do shut off the heat after about 10 minutes or the car takes forever to get up to temp). Eventually, my t-stat opened up (you'll know because that lower rad hose will get hot), and more bubbles came out as coolant moved through the block. Make sure you don't have anything in the way of the fans because that drivers once will come on. Put the cap back on, fill the overflow to the full mark. You are done.
I will drive it like this and see what happens. I am hoping to not have another overheat issue. If I do, then all that's left in the system is hoses, rad, and water pump. Doing a t-stat is easy, relatively cheap, and probably should be done more often because it can cause such a huge issue with warping the heads and/or leading to costly head gasket issues which I truly hope is not the case with this car because the motor only has 60,000 on it.