Blown head gasket with SC.
 

I've probably blown my headgasket or cracked a head. Under boost the exhaust gases escape into the coolant passages causing the reservoir to overflow. The car runs fine so I don't think is a major failure yet, hopefully caught the problem in time.

I still have to disassemble the engine for specific details, but I was wondering how common is this issue.
Engine is on stock internals, rotrex supercharger running 10-12 psi at rev limiter (300 crank hp). The car was boosted for 20/25k miles now, used almost as a daily and seeing a fair amount of track time (15/20h).

Did you monitor your temps?

Yes, everything was ok until not.

Coolant temp started rising during a hot track event (>86F), I've stopped and found coolant all over the engine bay. Oil temp was ok (230F max) but coolant spiked to 240.
I've refilled the radiator (once to car cooled down), and still used it for like a couple of weeks as a daily with no problems. I've tought that was a combination of the hot day, and coolant not in best shape.

A couple of days ago, I've used the car for a "canyon drive" driving hard and I had the same issues, so there is absolutely a problem :bonk:

The exhaust gas pushes all the coolant out of the radiator and the car starts overheating, at least that is what I think.

No contamination on coolant or oil by the way.

You need to stop driving it until you get it fixed. You're not only getting contamination in your cooling system, you're probably also getting coolant in your oil.

Yes absolutely. After the other day the car was towed home to avoid any risk even if it's "drivable".

Did an oil change just to check how things are and no contamination, really weird... that is why I'm wondering if it's common on this engines.

did you change the pcv valve to a stiffer one like the wrx sti one?

Compared to previous model Subaru engines, the FA20 engine has had very little issues with blown head gaskets, especially in their naturally aspirated state. Installing a blower or turbo increases that risk, but you knew that when you installed it. I think Toyota may have shared some of their technology with Subaru on head gasket design and manufacturing when they partnered, because Toyota and Lexus don't seem to have head gasket issues with engines that they build in their factories.

I've read that around 600whp, lifting the head becomes more common. Definitely not from something under 300whp though. The cylinder walls are pretty thick on this engine from the factory compared to the EJ

What super charger sys, sorry i may have missed it , I seen the rotrex version ...


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I've got the dual radium catch can since day one (it was still na). I think it's the usual subaru failure, head gaskets and rod bearings are a classic on this engines.

Nice to know I'm the only one untill now lol. Probably spa and the nurburgring are more hard on the engines than other tracks and it's a matter of time for similar builds.

I'll have more info once the engine is out of the car, I need to ship my car from belgium to germany but with the whole covid situation I think will take me a couple of weeks.

Good to know.
Yes of course I knew the risks but I was expecting bottom end problems and not at this power levels.
I will let you know the root cause, I thought maybe someone had similiar issues, but apparently not. I think gasket or head lifting due to assembly low quality of this car, but are all suppositions.
For example on the ej series you can find almost everything online, but to be fair those engines are around since the cars were invented and they are used more in racing applications.

Thanks for the inputs!

This is really interesting. So your oil looked fine when you drained it? Maybe you could just retorque the heads?

That wasn’t answering his question. A catch can won’t change the fact that the PCV valve needs upgrading so you don’t pressurize the crankcase. Unless you ran the system open/ventilated to atmosphere, you will be pressurizing the crankcase when on boost.

The head bolts are suppose to be single use. They are torque to yield. This is not good advice.