I don't think there's any reason to suspect a head gasket right off the bat like that. The first thing that comes to mind is the electric cooling fans. They are on the car specifically to keep it cool at slow speeds since you don't have natural air flow.
Get the car up to temperature, open the hood and wait for the fans to come on. If they come on you ...
If this were my vehicle, I would change the transmission fluid and filter. There is a baseless school of thought, more like an "old wives tale" that you will just cause damage by changing the fluid in an automatic transmission. But that is just a myth!
ATF is oil and oils break down over time, particles get into it from the mechanisms in the unit ...
It sounds like a failing throwout bearing. When the clutch pedal is depressed the part that actually moves the fingers or diaphragm of the clutch is the throwout bearing. While the clutch is disengaged the flywheel and pressure plate assembly are still spinning at engine speed. With the clutch the face of the bearing spins while the backside is stationary ...
NOTE: My original answer addressed only the cargo cover attachment point.
If you're trying to secure the tailgate strut attachment point:
I can't see any way to proceed that doesn't involve removing the plastic trim from this area. It isn't super difficult but it will be tedious to carefully remove the brittle plastic fasteners holding the trim in place ...
Too long for comment, but I suspect wastegate linkage or door not closing fully due to distortion from heat (it's really hot around there). You could try and get it hot enough to duplicate the problem, park, and attempt operate the wastegate manually with pliers or gloves... but it's tricky to get to without removing the turbo heatshield.
Also make sure ...
Cools at speed, but not at slow vehicle speed. Definitely an engine cooling fan issue.
It's either the fan itself or the sending units that tell the fan when to come on.
Best bet is to pick up a Multimeter and a manual that tells you the right signals from all the sending units involved (normally an engine temp sender.) I'd recommend either a Haynes or ...
Given that the issue vanishes "immediately" upon pressing the clutch, I would guess that the problem lies somewhere in the transmission or its linkages. The already mentioned throwout bearing is a possibility, especially with Subarus. Given everything you wrote here, and the well known throwout bearing issue, that seems the most likely candidate. Here is a ...
When you get your foot off the clutch, there is(or rather said there should be) a fixed connection between your engine and your wheels. If you see a rise in rpm without the car accelerating, there is no other possibility than that the connection has slippage somewhere. And while the clutch is the most plausible option, i also think it's the only possible ...
The cooling fan and water pump are usual suspects that you did not mention yet. A bad water pump will overheat an engine really quickly because there is insufficient coolant flow, a broken cooling fan usually only becomes a problem when a car is stationary or in slow traffic.
Assuming you're running a totally vanilla WRX it will have a 2 port boost solenoid.
For a 2004-06 car that is DENSO part # 16102AA360:
For those with an 02-03 car it's DENSO part # 16102AA160:
Which is basically the same but the electrical connector is on the other side.
Before replacing it might be worth giving it a clean (the genuine OEM ones aren't ...
Checking the pg. 28 of service manual suggests that you don't need to add any oil for replacing the dryer itself - just the 1ml for the replacing the hose:
Amount of oil replenishment
114 ml (3.9 US fl oz, 4.0 Imp fl oz)
7 ml (0.24 US fl oz, 0.25 Imp fl oz)
1 ml (0.03 US fl oz, 0.04 Imp fl oz)
PS: While the ...
I would guess you have a boost leak. Have the car smoke tested to check for leaks in the intake system (bring it to a shop that knows Subarus, there's a lot of nuance to look for). If it's been properly modded, it will have a tune for those mods, otherwise you'll risk damaging the engine in short order. Since the car's been running for years, it likely has a ...
The mirror glass is fixed by adhesive pads, which usually come with the replacement glass. Use a heat gun on the old mirror glass to soften the glue, and gently pull it out. Wear gloves, in case of shards.
Clean off any remaining old glue pad with alcohol, then put the new pads on the glass, and gently push into place.
It seems to me the system is running as it should. The only thing you could do is to have the tune changed to start the fans sooner (at a lower temp). As soon as the fans start, the temp goes down ... that sounds fairly normal to me. If it never overheats, and by overheats I mean blows its top, then I'd suggest the system is running as designed.
The thing ...
One of the bearings at the top of the struts may be worn. This could be causing the coil spring to rotate slightly under hard cornering. This could then cause a slight pulling in one direction, making the steering wheel be slightly out. Turning in the opposite direction may then correct the problem.
If your car has a map sensor and developed an air leak that would explain the rising RPMs. In a car with a map sensor the ECU will interpret the additional air flow from a vacuum leak as an increased load and will add fuel causing the car to rev faster.
Took the car in for service, and @SteveRacer was right. It was the air con - they did a full flush and recharge (it was the 120,000 mile service so it was about time anyway) and the problem has completely gone.
I would have sworn from where it sounded like the noise was coming from that it had to be gearbox. And I was embarrassingly wrong :-)
The coolant must be going somewhere. If you don't see any external leaks, the leak must be an internal leak. Head gasket would be the usual suspect here. Perhaps the leak is so small that you just don't see the water vapors? I.e. the coolant can still be going to the combustion chamber in small amounts that are invisible in the exhaust.
I would recommend ...
I've owned three different turbocharged Imprezas and can confirm that it's perfectly normal not to hear the turbo spooling up. In fact on a standard WRX if you can hear the turbo spooling that would normally indicate a problem!
If the Torque app is showing the right level of boost then you've got nothing to worry about.
Hm, I am thrown off by your mention of the clutch, throw-out bearing and deceleration notes, but I figure this is worth mentioning as it otherwise fits the bill.
There is a TSB/recall for 2015 Subarus with the 2.0L FA engine for pre-ignition causing the noise you otherwise seem to be experiencing.
Subaru Service Program WQW-5
Subaru has developed a ...
Re-pair your phone with your car
Goto your phone and delete your car as an audio device.
Goto your car stereo and delete your phone as a source device.
Re-pair your phone and your car and see what happens.
Seems to be an effective fix for me when I occasionally encounter this issue.
I'll start off by saying that this may not be an answer, but rather a methodology for diagnosis. On that Subaru, the turbo should be to the right hand side of the engine. You have oil pick up and return lines for the turbo. By design the serpentine belt can swing oil up onto the ceiling of the hood if they leak. The easiest way to troubleshoot this issue ...
Aside from the throwout bearing, the only thing else to check would be an accessory belt pulley/bearing going bad. If the bearing is just starting to deteriorate, the load on the engine as one accelerates can cause the bearing to whine and sound very similar to a dying throw-out bearing.
Very very likely to be the clutch release bearing(throwout). Clutch pedal operation will feel slightly differant slightly harsher if it is the bearing, but in some cases just the same as before any noise. In one or two instances I have found a noise which seemed to be a release bearing that turned out to be the transmission imput shaft bearing wearing. Is ...