I am soon going to be changing the coolant on my 05 WRX. It will be the first time that I have attempted to do this myself and I have done a search of the forum and found some very helpful info which is great. The coolant hasnt been changed for 2yrs and the car has probably only done 10-15,000Ks max in that time. The car itself has only done 45,000Ks. I will be using genuine coolant and I have a 5ltr container.

I just have some questions about flushing the radiator/ engine etc.

1: Do I need to completely flush the whloe sytem, just the radiator, or is it not that important.
2: If I flush do I need to use a flushing agent or just run a hose from the tap or better still pour in distilled water instead of using tap water.
3: Do I have enough coolant if I do a complete flush??
4: Do I need to add a Subaru Conditioner to the coolant. I ask this because I have seen on some sites and on You Tube that some people recommend adding a condioner to to it. It was mainly American sites and videos so I am guessing it may be just something they have to do over there for whatever reason???

Thanks for any helpful comments in advance.

Flushing the whole system would be best but seen that you havn't done that many kms i would assume the vehicle has had genuine coolant its whole life and so it would NOT BE ESSENTIAL to flush entire system!

To flush i simply use a garden hose, undo top and bottom hose and let the coolant drain. Then simply turn on the hose and place it in the top hose going through the radiator until it runs clear and then through the block!

Do you have enough for an entire flush? I don't think so as from memory i use about 6.5-7L but keep in mind this was on a GC8 so I COULD BE WRONG!

You will need at least 7L to replace the coolant, I doubt you will need to flush the system as long as the service schedule has been followed, eg, coolant replaced every 2 years and genuine coolant has been used. Just remove the rad cap on the header tank above the turbo, undo the drain plug on the bottom of the rad, undo the thermostat housing, remove the thermostat, so you will need a new gasket for that, and let it drain.
Genuine coolant is already mixed and ready to go, no need to add anything.

When you reinstall the thermostat, make sure the jiggle valve is at the top.
You need to make sure the system is bled properly when you refill, probably the hardest part of the job, you need to make sure that the thermo fan's kick in, that way you know the thermostat is open and all the air is out.

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F.B. Racing
01 WRX (STI badged)
2010 XR5 Focus
06 Impreza Hatch 2.0i

When I take out the thermostat do I just need to replace the gasket or is there any other seals that need to be replaced. I think I remember reading someone mentioning some sort of O ring seal on the thermostat before. I could be mistaken.

The o Ring seal is the gasket.... sits around the thermostat

Personally I wouldn't replace the thermostat unless it needs replacing...

Take lid off header tank
Undo bottom hose, wait for radiator to empty
Take coolant line off turbo (not the one coming from the header tank, the other one)
Stick a garden hose into this line, and it will flush through the motor etc. Give it a few mins.
Stick the garden hose into the header tank, this will flush the radiator
Put bottom hose back on
Stick a funnel into the turbo line you flushed through
Pour coolant into funnel until visible in header tank
Take out funnel & put turbo coolant line back on
Top up header tank

I've found this way works best in getting all air out of the system and doing a proper flush. Reason why I take off the bottom hose and flush the motor and radiator separately, is so there is less chance of crap coming out the engine etc into the radiator.

Pretty sure I learnt this method from someone else on the forum...

Thanks for your comments guys.

Jezza I wasnt looking at replacing the thermostat I was going to remove it to do the flush as suggested in one of the replies, your flushing suggestion though sounds good and if I dont have to remove the thermostat then that can only be good. My main concern is getting all the air out off the system when refilling.

I guess I am going to need more than the one 5ltr container of coolant that I have to do this properly.

Just leave it running with cap off until the bottom and top hose are hot, ensure heater is on. Once hot turn car off bang cap on start car and run till fan kicks on then off. Test drive to ensure it dosent over heat, then bobs your uncle your done. SIMPLE.

don't need to turn heater on, there is no tap in the system

__________________
Its just the internet dude, its not real.
F.B. Racing
01 WRX (STI badged)
2010 XR5 Focus
06 Impreza Hatch 2.0i

peace of mind i always turn the heater to hot, regardless if it has a tap or not. unles its been bypass.