I was also thinking cavitation.
Nissan changed the design for the SR water pump because of high rpm cavitation, so it may be an issue with some Subaru's.

Are you sure the Mishimoto has better flow? It may look bigger and better but internally it may be restricting coolant flow.

 

i considered cavitation, but one weekend i decided to shift at 5k rpm (usually do around 6k) and it still had the problem. pretty damn sure there is no air in the system, ive opened the cap and refilled quite a few times and also done the squeezing the pipes thing.

thermostat has 6 small holes drilled in it to let fluid by in case it is stuck, but not so much that it flows too quickly.

update from today is that i saw the temps go up a little while sitting in traffic... i was sitting outside a restaurant with the car on and i smelled a little burnt coolant. also when i got back popped the hood and saw the fluid level in the tank (the main one, not the reservoir by the turbo) has risen quite a bit since this weekend with no added fluids.

 

Are you running a 50/50 mix of coolant?

 

Coolant resovoirs filling up are generally a symptom of a blown HG.

 

someone mentioned one of the hydrocarbon test strips, sounds like a good Idea to me. If it is the gaskets, make sure you get them done by someone familiar with Subaru... If the Bolt torquing sequence is not followed exactly it can cause future issues. and it's about the most confusing one I've ever done..

oh here it is (for the old cars, don't know if it's changed)
i know it's no good without the pictures but just for refrence

Cylinder Head Installation
1. Apply a coat of engine oil to washers and bolt threads.
2. Tighten all bolts in sequence as shown in Figure 2 below to 22 ft. lbs (29 Nm or 3.0 kg-m).
3. Then, tighten all bolts in sequence to 51 ft. lbs (69 Nm or 7.0 kg-m).
4. Back off all bolts by 180° in sequence first; and then back them off by 180° again.
5. Tighten bolts 1 & 2 to 25 ft. lbs (34 Nm or 3.5 kg-m).
6. Tighten bolts (3), (4), (5) and (6) to 11 ft. lbs (15 Nm or 1.5 kg-m).
7. Tighten all bolts an additional 80-90°in sequence.
8. CAUTION: Do not tighten bolts more than 90° at this time.
9. Further tighten all bolts by 80-90°in sequence again.
10. CAUTION: Ensure that the total re-tightening angle [in steps 7 and 9] do not exceed a total of 180° rotation

You get that ?

 

What. The. Fuck.

 

if i ever need work done to the car that i cant do myself, i take it to mike over at S&R performance. he is very knowledgeable about subarus, and they have consistently done top notch work on my car


i dont think the headgasket is the problem, i see no signs of leakage anywhere on the engine. most likely will end up replacing the thermostat, getting a crawford water pump, external oil cooler, and replacing a section of the bottom radiator hose with solid pipe (dont know if i posted it before, but a subaru race team found their water pump cavitating under high load and collapsing the hose. fixed it by replacing a 3" section in the bottom hose with solid metal piping).

 

That's cool, but since subaru head gaskets don't leak externally, before I spent a penny on any parts I'd do some testing, it's cheap insurance. it'll be a bummer if you pay a ton of money and not fix the problem. I'm glad to hear you have a good scooby tech, they are hard to find! I had to hire a part time dealer mechanic back in the day and he tought me a TON about these unique beasts. like the shop rate clutch change when we were rallying, not a lot was known about the EJ engine in America when stressed.. since, until 1998 no one REALLY raced them here.

 

I think you're way ahead of yourself here, with the possible exception of replacing the thermostat.

You have a problem with the existing cooling system, not simply a wall you are hitting on track with a functioning OEM system. You can't even do 3 laps you said. Something's wrong, not just "not up to the track demand".

What the other Jeff said above.

 

well im putting my money on the cavitating water pump and collapsing bottom radiator hose seeing as a suby race team had that problem. instead of just replacing the hose though, i would like to replace the water pump as well just in case that has also gone bad. and because my thermostat is drilled I would like to replace that as well. Also, an external oil cooler can't hurt. For the way I beat on the car on the track, it is definitely a safety precaution.