An interesting read on subaru cooling systems

I was cruzin the web trying to find solutions for my scoobies problems when i found this!

 

http://www.subaruoutback.org/forums/printthread.php?s=&threadid=17264

 

 

NO, Subarus don't have problems with their headgaskets!!!

I want to set the record straight. Subaru's don't have design faults/flaws with their head gaskets in any model/year. Blown head gaskets in subarus are almost always a symptom of of something else going wrong in your cooling system. In fact, the reason why so many subaru's have head gasket problems is due to the engine configuration they use (i.e Boxer) and the positioning of the thermostat.

 

I will attempt to explain the issue below:

 

All water cooled cooling systems (all makes of car) have a main flow of water through the engine. This main flow circulates the water through engine and radiator via two big hoses at the top and bottom of the engine. The engines temperature is regulated by a temperature controlled thermostat which restricts the main flow such that the water is regulated to a temperature of around 70 degC.

 

Almost all water cooled engines also have a secondary flow system that goes through your cars heater core to provide a nice warm heater for the interior of your car. The secondary flow also usually acts allows some movement of water even when the thermostat is closed. i.e. a circulartory path through the cars heater core.

 

The difference between subaru engines and almost all other engines is how the thermostat of the engine is controlled. In a conventional engine the thermostat opens when hot water inside the engine rises to the top and contact the active side of the thermostat. In a subaru engine the thermostat is located right at the bottom of the engine off the water pump. Thus the water on the active side of the thermostat stays much colder that a conventional engine. For the thermostat in a subaru to work correctly it uses the secondary flow system through the cars heater core. Hot water is taken from the top of the engine, were it flows through the heater core and back to the active side of the thermostat. Primarily, this is how the engines temperature is controlled in a subaru.

 

If the heater core becomes blocked or partially blocked heres what happens.

 

1.) The thermostat will open under the wrong engine temperature conditions.

2.) The engine will overheat under moderatly demanding conditions (i.e. a hill).

3.) The overheating will cause the water in the engine to expand and there will be a big spike in the pressure in the cooling system. This big increase in pressure coupled with the distortion of the cylinder heads will more than likely cause the head gasket to blow.

4.) The increase in pressure will override the spring in the radiator cap and the coolant will flow into the overflow bottle.

5.) When the demand on the engine reduces it will cool down. The reduced volume of water will cause the top radiator hose to suck in.

 

For you own sake if you have a blown head gasket and your car is overheating ( i.e. sooty water) try doing the following before you pull the car to pieces. You can either bypass the heater core or remove the thermostat. Both of these options should stop the car from overheating. Of course you would still need to have the head gaskets replaced and eventually replace the heater core but at least you would know what the heck was going on a why the head gaskets blew.

 

The reason why subaru dished out special treatment for the water in the cooling system was an attempt to stop the heater core from blocking and exposing Subaru engineer's for making such a thoughtlessly designed cooling system.

And a fix by an aviator for these engines

 

So here's the deal. All failures are caused by air in the cooling

system. No air, no problem. If you have air bubble AND you operate at

high throttle settings, the head will warp. It takes a long time to

show up. So if there was trapped air 6 months ago, then you might now

start to see discolored coolant, overheating. Or it might only occur

climbing a hill in hot weather. Only the 2.5 has this marginal

condition. All other Subaru's bullet proof.

 

My flying partner makes a living replacing gaskets on 2.5's these days.

Number one repair item. It appears that the 2.5 has an area at center

of block/head interface which doesn't have enough coolant flow. When a

bubble p***es by, it boils locally. This eventually causes head to

warp, gasket to give out. Subaru has tried 3 different style gaskets,

even adding coolant conditioner to improve heat transfer. Still a

problem. But absolutely all failures caused by trapped air in system.

All models of 2.5 liter the same.

 

The solution is very simple. Just drill and tap your coolant crossover

pipe and add a fitting that allows air to leave engine and rise to your

swirl pot. You will never have a problem. I operate my engine full

throttle for hours at a time. Fabulous engine.

Good information.

 

When a bubble p***es by? The software filtering needs to be modified a bit. P.a.s.s.e.s doesn't deserve to be filtered.

LOL, a very bored content filter I guess!

ok, so i started having a 'grugling' problem after a rain storm one day. it sounded like there was water gurgling from my dash. so i ignored it figuring it was just the drain reservoirs were clogged. well after this happened for a few days in a row, i realized my coolant res was bone dry. added some coolant, and went on with my life.

 

so i was driving and realized my AC was starting to get warm, looked down, sure enough my temp gauge was on the rise, pulled over, and got pissed. so i let it cool for a bit, drove down the road, boom, temp went down. this continued for the minimal times i drove the car before i got around to replacing the thermostat. took it to subaru, had them perform a flush and a thermostat change. on my way home, boom....overheating....

 

So i replace the radiator caps, both, on the radiator and the turbo res. still...same problem.

 

So i bought a internal combustion leak kit (you have a chemical that reacts to carbon dioxide)....nothing, test didnt change color. took a straw blew into the chemical, it turned bright yellow, after 8-10 minutes (when the test says it should happen in 2) there was a slight discoloration towards green....hardly something to be concerned with.

 

So i went up on a hill, and tried to remove any bubbles that may be in the system, so i reved up the engine, while slowly adding coolant into the upper turbo res, sealed it up as it was practically overflowing....BAM...Problem Solved!!! Its been 2mo since an over heating problem. Usually i could trigger it to over heat by having the AC on, and driving up a long steep hill...i can now run my car up a hill for forever, and i barely ever exceed the half mark.

 

well anyway, after this long rant, i can totally confirm that air was infact trapped in the system, and i feel like the subaru dealer i went to loves this because they get to charge 2400 (3800 as he was trying to have me replace my turbo as well) for a problem they caused by not properly adding the coolant into the system causing air pockets.

 

DO NOT HAVE THEM DO A HEADGASKET unless you are 10000% sure its not a clogged heater core or something as simple as an airpocket.

 

thanks for the info

this is some great info.

 

so really any subaru 2.5 will have problems. even a brand new sti?

 

everone should know this. not just in this section

I'll tell what, burping the system of a 2.2t is such a pain. No bleeder screw really doesnt help. Last time i flushed the system, it took me 3 seperate attempts before all the air was out.

Thanks for the info ydeardorff, I have been having a problem with my radiator for a while. I was having intermittant overheating problems, and since datrumole mentioned the overheating on a hill thing I've been realizing that most of the time it occured after an incline of some sort. Also I couldnt figure out why everytime I refilled my radiator all the coolant ended back up in the overflow tank. I was actually on the verge of posting the problem here today when I remembered the seach function. Big thing that had me scratching my noodle was the hose collapse thing, I knew it had to be something with air but I thought I had bled it out enough. Thanks for the great info, I just bought a new thermostat and radiator cap and will be replacing it this weekend, I'll make sure to post my results.

Ok, so here’s the back story:

I drive a 1990 legacy 2.2 5MT, it’s got 220,xxx miles on it, I live in Alaska so the morning are fairly cold right now with the day temps about 60-70. I have been experiencing the problem listed above, with most of the listed symptoms. The car would overheat sporadically, I would find my overflow tan overflowing after driving home from work, and the top hose would be collapsed when I would check it in the morning. Also, when it would overheat I would just refill the rad and it would be fine for however long until it wanted to throw a fit again and it would overheat. So after reading this post I replaced my thermostat and radiator cap, parked the car on a ramp, filled, ran, filled, ran, etc... After it couldn’t take anymore I idled it for about 20 minutes, temp never went over half, parked it on the ramp, idled more still no rise in temp. I then took it for a test drive to see how it handled, I made it about a mile before it started to overheat, so I started back to my house, as I was pulling in my driveway the top hose blew off the rad spewing coolant everywhere. I found I need to replace the rad now because the hose took about an inch of the pipe coming off the rad with it, but I rehooked the hose to the rad because there was still enough pipe to connect it securely and refilled the rad, see process above. then I let it idle again for about 20 min didn’t go above half, so I drove it to work the next day and it overheated about half the way there (approx 6-7 miles), I parked, let it sit for about 15 min and temp dropped below half and made it the rest of the way with the temp making it about 3/4 way to high. So after work I checked the level and everything was fine so I decided to drive home, made it there and the temp gauge never went above half. So I figure air bubble like mentioned above and it finally worked its way out that morning. So today I drive to work and it starts overheating again, same distance (I made it past the parking lot I pulled into the previous morning by about 200 ft) so I pull over let it sit for 15 min and start again but this time I don’t make it another mile before its overheating again so I throw it in neutral to coast to next parking lot and as I drop out of gear and the rpm's drop to about 600-700 the temp gauge starts to go down. so I pull into the next lot and I let it idle and watch the temp gauge go down to below half, so then I push the rpm's to about 2500 and hold it there for a few minutes, no change in temp, so I start heading to work again. I make it about 3 miles this time and it starts overheating again. I pull in the next lot, let it cool down a few minutes until its back below half and start off to work again. I make it about another mile, overheating again. so I pull off, let it cool again and as I am within a mile of my work I take off, I make it to the parking lot but as I'm pulling in a heal a squeal and the car drops temp down to about 65%. and my windshield gets a little spray on it. So after I park I pop the hood and the top hose had popped off again. Just as a note, every time it was overheating I was in a lot and about to turn off the car before it hit the red zone or it was only in the red zone for a few seconds before the car was off. Also, I recently replaced both the coolant temp sensor and the fan switch sensor about a month ago. There was no obvious damage to the hoses, no soft spots or bulges, no fraying of the ends or cracks at the bends. I use the import aluminum safe antifreeze/coolant.

So my questions:

What would make the car overheat while driving but cool it down when idling? Would the water pump be going bad? Do I need to replace my heater core as mentioned above? Would a professional rad flush be a better solution than doing it myself? I already know I need a new rad and its getting ordered.

Anything help anyone can provide would be greatly appreciated.

Any pictures ydeardorff? I'm interested in the type of fitting? A valve of sorts?

So then Porsche should also have problems with head gaskets. Is that true?

So then Porsche should also have problems with head gaskets. Is that true?

 

Porsche doesn't use Subaru engines they use Porsche engines, so why would a Subaru problem translate to a problem with Porsche. That is like saying because an american v8 has a known issue an Italian v8 will have the same issue. Because they are both V8s.

Porsche doesn't use Subaru engines they use Porsche engines, so why would a Subaru problem translate to a problem with Porsche. That is like saying because an american v8 has a known issue an Italian v8 will have the same issue. Because they are both V8s.

 

Ok then I'll quote some of the first post of this thread:

"In fact, the reason why so many subaru's have head gasket problems is due to the engine configuration they use (i.e Boxer) and the positioning of the thermostat."

So what does make the Porsche boxers be better then Subaru boxers as regards the HG problem?

dude.....I wish I had seen this thread earlier but luckily about 3 days ago my dad and I decided to take the thermostat out of my 94 Legacy and it fixed the overheating problem that I've been having for about 1.5 years now. its got a bad head or valve gasket for sure but it doesnt overheat because there is no thermostat.

 

 

about a week ago my heatercore sprung a leak while driving but luckily i was able to make it home. once home i disconected the heater core and routed it right back into the engine. it was still overheating after that so then we took out the thermostat and im pleased to say it fixed the problem.

Does anyone know what b temp thermostat should open at? We were told that the - reading of engine temperature is not accurate is only an estimate. You are advised to stick a thermometer in the radiator that cold temperature and watch heat up. We are concerned because the temperature inside the vehicle indicated car was at full no more running temperature. No it never moved from a certain point. But there was 142 degrees difference between when the car said it was hot or up to temp and when the thermostat actually opened.

 

Sent from my SCH-I545 using Tapatalk

 

The solution is very simple. Just drill and tap your coolant crossover

pipe and add a fitting that allows air to leave engine and rise to your

swirl pot. You will never have a problem. I operate my engine full

throttle for hours at a time. Fabulous engine.

 

i would love to see a picture of this contraption. the idea sounds pretty "cool". no pun intended. i know a picture would be pretty difficult so maybe the next time you have your intake manifold off for some reason.

that article is suspect.... the 2.5L with an open deck definitely DOES have issues. This is one of the major reasons they switched to the semi closed deck design.. to keep the piston bore from moving around when the engine expands and contracts.. Subaru, just like every other modern water cooled engine pulls the heat straight from the head (aka reverse flow) as it gives you heat much faster than the older cars did....

Originally Posted by ydeardorff http://legacygt.com/forums/skynetim/buttons/viewpost.gif

The solution is very simple. Just drill and tap your coolant crossover

pipe and add a fitting that allows air to leave engine and rise to your

swirl pot. You will never have a problem. I operate my engine full

throttle for hours at a time. Fabulous engine.

 

 

i would love to see a picture of this contraption. the idea sounds pretty "cool". no pun intended. i know a picture would be pretty difficult so maybe the next time you have your intake manifold off for some reason.

 

You guys means to drill a hole (and of course, to find a way to seal it) in this pipe?

http://s30.postimg.org/4tgr5c7f5/aaaa.jpg

is that the coolant crossover pipe?

Our Subaru Legacy 93, since when imported form USA back in 1996, never have had a thermostat...

i installed the thermostat today, and it runs little bit hotter than before, i heard it should hreach the temperature faster but not necessarily way hotter than before...

 

the temperature always have been half way, never under any circunstance, neither during prolonged (1 hours of hard climbing with 6 tall guys onboard and the cargo and roof full of cargo... and the temperature is half...

 

but the user manual says i should be worried ONLY if the temperature needle enter to the dotted aread and stays there... i have done 20km today testing the t-stat and the temperature is hotter but 5/8 way form the middle to the top, so the neddle is not in the dotted area. but....

 

since i had to drain the coolant for the t-stat install, i am sure there is air trapped... but while i investigate that ....

 

i have this question

 

what is this connector?

it is located (in subaru legacy 93) behind the passenger side headlamp

 

http://s13.postimg.org/444q351g7/y_este_conector_2.jpg

 

I have heard is something related with the temperature

 

in fact, when i connect them, the fan run faster

 

what is it?

Can anyone tell me what vaccine hose 23 on my 99 GT legacy is suppose to go?? The turbo acuator?

 

 

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You guys means to drill a hole (and of course, to find a way to seal it) in this pipe?

http://s30.postimg.org/4tgr5c7f5/aaaa.jpg

is that the coolant crossover pipe?

 

yes that is the one

Who makes this stuff up?

 

Of COURSE Subaru's have head gasket problems. It's more to do with the flaky(literally)lamination on the gasket as it does design. Replace with a non coated MLS of ANY brand and you'll not have an issue again. I've drained/filled all sorts of cars/trucks/tractors and have NEVER had an issue with needing to burp anything. Do it right the first time. It's much easier to do it right than to introduce air into the system in the first place. Do you think they "burp" anything from the factory? Of course not.

I have a 2000 outback, it has been overheating. Changed the thermostat, still overheating. Changed the water pump, still over heating. New radiator cap, still overheating. the reserve tank has fluid but doesnt go into the radiator when its needed. there is no water in the oil and none out the exhaust. the car runs really great other than the overheating. there is no leak anywhere that we can find. Please, any ideas?

what happens when its a oil leak on the headgaskets....