Need a water pump too? Now is a good time. This will be written up shortly too.
Many of us have Subaru's with around 100k or more miles, and the original radiator. You may notice your temperature gauge is riding up a little higher than it used to. Radiators are quite easily replaced on a Subaru, heres how.
Subaru's with automatic transmissions will have additional lines on the drivers side of the radiator with ATF in them. This procedure is primarily written for vehicles with manual transmission but you can figure out the minor missing pieces of the procedure pretty easy. Pinch off the lines to the tranny and reinstall them when you are finished pretty much sums it up.
Allow motor to cool.
Inspect all of your hoses in the cooling system. There are 2 going from the firewall towards the motor. These are your heater hoses and quite possibly need replacing.
Financial tip: I have found hoses to be nearly twice as expensive at Napa Auto Parts as the ones at Autozone. There are premium quality hoses available as well and I like Napa for many parts but have found them to be extremely overpriced on rubber hoses.
Obtain parts prior to attempting replacement. You'll need:
Radiator. Obtain a cap that fits the new radiator as well. 13psi is the factory rating for the cap on most models.
Upper and lower radiator hoses. 4 large Tridon type clamps. (Junk those old crudded out Subaru clamps!)
On some EA82 models you will want to obtain an o ring for the coolant tube going into the water pump.
Thermostat might be a good idea, up to you. Get a gasket for its housing as well. Its advisable not to use any RTV/gasket sealant as the gasket will seal just fine.
Coolant. Typically you should use the same type of coolant as is in the system. If your coolant is green or red obtain the same kind. Some are red/orange. These are Dexcool and similar hi efficiency coolants. These are great but I have found they should never be mixed with std green coolant (even though the jug says you can). The mixing of the hi tech and std coolants creates a glycol mixture that is more corrosive than either type by itself. The newer coolants can be used if you completely flush the system. It may be advisable to top off your system and drive it to a shop to have the entire cooling system flushed, or use a Prestone Flush and fill kit, available at Parts/discount stores. This back flushes the system and cleans out stuff that might be lingering in the heater core.
1. Drain coolant. The "petcock" is your radiator's drain plug. It is usually located on the passengers side of the radiator, on the edge about 6" from the bottom of the radiator. It is plastic and can be brittle at times so a gentle breaking loose of it may be difficult. Be sure to contain any coolant that drips out into a good drain pan as it will splash in many directions.
Remove/loosen clamps to the hoses you would like to replace. Then twist the hose at each end to break it free from what it is attached to and pull it off. Cut your new hoses to the same length as the old ones.
Unplug the wire from the passenger side of the radiator, should be a single yellow wire.
Unplug the cooling fans from their plugs and maneuver the wires so the radiator will be able to be pulled up and out. Remember a radiator fin can be sharp so you might want to exercise caution or wear gloves. You may have fan that is on the end of the motor that turns all the time. In this case you will possibly have to remove a protective shield
Remove the two bolts at the top and place them in a safe place. Push the radiator toward the rear of the vehicle about 1/2 inch. You may have to use a screwdriver to pull the vehicle metal away from the radiator.
Pull the radiator up and out out of the vehicle. Some coolant may come out of the drain as you remove it so be somewhat careful.
Lay the old radiator on the ground and compare it to your new one. Remove any components on the radiator that are on the old one and not on the new one such as sensors, fans, etc. You might want to clean the threads well on the sensors too.
You might want to rinse out any debris that have collected over the years. Amazing what gets up in there!
Gently place the radiator back in its spot. note the two rubber or metal/plastic stops on the bottom and be sure they go where they should.
Attach any hoses, make sure you put the coolant drain plug back in, and fill with 50-50 antifreeze mixture. Top off the reservoir if necessary.
After everything is back in you or a friend should start the car with the radiator cap off. Allow the coolant to circulate and you will probably find the coolant is low in the radiator. Filling it while the motor is running is probably a good idea, use caution.
Put the cap back on and watch for any leaks. Test drive the vehicle and make sure the gauge is coming up to operating temperature. It is a smart idea to bring along some 50-50 mix of antifreeze for the test drive in case you spring a leak or find the system isn't working in some manner.