Flushing a Subaru heater-core

[@metatechnologist]

"Top one goes into heater core bottom one comes out" I'm guessing it's going to be the same for all Subaru cars of this era. Also I wanted to do this in below freezing temps that's probably bad time do it in warmer weather!

[@loveleyday]

The overheating problem can also sometimes be traced to a tiny leak of air into the cooling system (head gasket problem usually), that allows a build up of air on the underside of the radiator thermostat (located at the bottom of the water pump). This artificially decreases the thermostat temperature, which in turn means it doesn't open, and the engine overheats. "Burping" the thermostat (search for it), or letting out the air, is all that is required to temporarily fix the issue, but longer term a head gasket is required.

[@SubieSpecs]

Don’t forget on world market and JDM, the thermostat is orientated like the turbos, facing forward. You can still get a bubble I’m sure, but it’ll always dissipate thanks to the jiggle pin hole being up top. Also don't forget the importance of the flow of coolant coming from the heater core to keep the thermostat open, it is of far greater importance than tiny bubbles on the cold side of the stat.

[@haac4825]

Great Info. Thanks

[@christianstockle7116]

Thanks for the video, very helpful. I have a 2005 2.0ltr non-turbo that I need to flush. Would you say it's pretty much the same process as your model year? Cheers!

[@SubieSpecs]

Basically. When bleeding, of you don’t have a bleed nipple, just crack the top hose off the rad a bit to let the air our.

[@christianstockle7116]

Thanks bro!

[@clintjeffrey3340]

What can you tell me about an over heating 2003 Forester, if I leave the Thermostat out the engine runs cool a bit below normal, if I fit the Thermostat (New) after 10 - 15 minutes Temp starts to rise, if I go for a drive it very quickly goes full scale. How much was the Heater Core too, mine is now blocked mainly due to the fact I poured some Nulon Gasket Blocker which completely stuffed the Core...

[@SubieSpecs]

So removing the thermostat can mask a head gasket fault, so if we want to figure out what’s at fault, we need to pop it back in. So what you need to do, is bypass the heater core by putting a loop on between the two heater core pipes out the back of the engine, and then put your new thermostat back in. Also, put the thermostat in a pot of water over 80c to make sure it opens, I have seen aftermarket and genuine both failed out of the box. Rare but can happen. Why put the thermostat in and bypass loop the heatercore? If you do this and the car runs mint, it’s a perfect confirmation that the fault was a blocked heater core, and replacing or getting it professionally reconditioned is the best course of action. If you still get overheats you can be sure the issue is not the heater core. Also make sure you use a genuine thermostat, none of the aftermarket ones I’ve seen come close to their quality. Lastly, doing the flush as in the video above can be good a stop gap to get you going. Let’s say you need a heater this winter, but can’t pull the dash just yet, then this will do. But I must stress it’s a less than ideal perma fix, as it will never work as well as a fresh core. The car in the vid here is still going with my flushed core and EJ20, but I’m dropping a 2.5 in this winter, and I know the half working core will give me issues, so replacing the core will be part of the engine swap.

[@clintjeffrey3340]

Hi Reuben...thanks for that, since my post I've had the car looked at with a mechanic friend of mine. We flushed and back flushed the radiator several times, some rubbish did come out, but it is a new radiator probably less than 12 months old. We flushed the Heater Core both ways, initially some dirty water was passed but we flushed it long enough for good pressure and clean water was passing, if the Heater was blocked it is clear now!...we then forced water through the Engine until we could see no more coolent. Reconnected hoses fitted the Thermostat topped up the Coolent. Test drove the car, before or this work, 15 minutes driving would be enough for the Temp gauge to go full scale, now the Gauge was holding at Normal but once you pulled up at a set of lights and idled the temp gauge would increase to about 70-80% but never went full scale. Once I was moving again the Temp would fall to normal. So something was still not quite right. The Head Gaskets were determined to be okay, pressure testing revealed no leaks, the Oil was clean the Coolent was clean, no apparent steam/water on the exhaust. We came to the conclusion that there must be minor blockage in the Engine water jacket just enough to cause overheating when the Thermostat is fitted. Solution - we drilled a hole in the Thermostat and that seems to have fixed the overheating and we still have enough heat to warm up the interior...hopefully that will be okay for a while...;)

[@SubieSpecs]

I can guarantee that you need a new heater core. It’s a dash out job. Back flushing can never fully unblock a heater core, it’s a temporary fix to get you functional, until you can afford to replace it. They are legit that important in a Subaru cooling system. Hope this helps.

[@SubieSpecs]

@2:16 - Preface BG having copper core, and facelift having alloy. This is JDM and world market I'm talking about. It you're in the US, the line between facelift and prefacelift is blurry AF, so this may not apply stateside/canada. To check what you have, pull a heater core hose off the firewall, and it it's dark-gold/brown looking - copper, if it's matte silver - alloy @3:00 - Make sure you don't have a split inner CV or steering rack boot when draining like this. If you do, drain first using the radiator drain cock, and put some plastic over the split boots before you start. @7:25 - I forgot to mention this is actually less than I got out of the first drain I did a year ago, this is mainly the last dregs I could get out - and it's still not enough for perfect operation. One difference is the crap here was all mushy, so the CLR had broken it down, on the first go a lot of it was solid scale, meaning the prestone hadn't actually touched it, must have just come out from the force of the water during the back flow. @11:41 - I should note there's some factors i've done to help. The nose is in the air, and the bleed funnel I use is fantastic. Without the funnel it takes twice as long.

[@dimitriruiz27]

I have a 95 Subaru L Wagon and this is the only video I've found that truly helps to the fullest. Also was wondering if you know of any websites that carry body kits and other performance parts

[@SubieSpecs]

Thanks! For body kits and stuff, it’s getting very hard these days to find em. All the good Japanese stuff is very rare now, but def keep an eye on croooober. Also join the 2nd gen legacy enthusiasts Facebook page if you’re not on there already!

[@dimitriruiz27]

@@SubieSpecs also where can I find that front oberlay badge? I've never seen one like that.

[@SubieSpecs]

It’s just the JDM badge. The Americans call it the “L7” badge.

[@cliftonlewis1420]

You said your first flush was brown and foamy. You have a bad head gasket. I've been working on cars for 30 years. I've owned five subarus. I've had more than my share of head gasket failures not just on Subaru either. It could be as simple as a small crack between a water jacket and a valve opening. Could even be a small area that the head gasket has just split inside of itself and you'll never be able to see it.

[@MarcGyverIt]

FYI, that CLR stuff, very bad for aluminum. Not a good choice.

[@SubieSpecs]

Good thing I mention which models have copper and which have alloy then eh!