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Several reasons for odd behavior of head gasket leaks. Expansion and contraction from heat and cooling changes the volume of the leak. Carbon deposits can break loose inside the cylinder and plug the leak into the cooling system until the carbon is burned and then pushed through the leak. Trapped air bubbles around the water pump vanes causing it to not move the coolant, and air around the thermostat causing it to not open. The coolant flow powered by the water pump, with a closed thermostat, is engine and heater core going past the thermostats coil end, with part of the coolant tapped off to go through the Throttle Body and Idle Air Control Valve. Air tends to collect there and in the heater core and when that system is full of air the pump does not have water to pump. If and When the thermostat opens the radiator is added to the inlet of the water pump. On a side note: most people (even videos on YouTube) think the car thermostat spring is bimetal and moves when heated or cooled. Wrong. At the center of the thermostat coil is a sealed copper colored cylinder with a piston inside that is fastened to a rod that goes through the valve and connects to the peak of the thermostat. The cylinder is connected to the valve. The inside of the cylinder is filled with wax. When heated the wax liquefies and expands rapidly and pushes the cylinder away from the piston and rod and pulls the valve open. As it cools the wax shrinks and the spring pushes the valve closed. Originally, Bees Wax was used.

They overheat when the combustion gas bubbles collect on the thermostat and cause the thermostat to close. Varying throttle conditions and driving angles means this happens differently. And the amount of coolant that's in the system has an effect also. It is generally expelled into the overflow bottle with combustion gasses when the system pressure rises above the cap's pressure rating - venting gasses and coolant - eventually leading to cavitation in the water pump. It's all academic though - you definitely have a bad head gasket. The mechanic is correct. If you want to fix it permanently you need to install 251 pistons and STI 770 gaskets. GD

Looks like you’ve got the most common issues covered. I’d start with the vacuum modulator, but really my gut feeling is that the auto might be toast - with that said I have very little experience with autos so cover all bases if you can before calling it quits on it. Someone in the know will tell you more though. And this is the forum to be on for this sort of help! Cheers Bennie

Correct - the thermostat is a form of wax motor. It is surprising how many people do not understand the basic operation of components like this. Then they go and make themselves look really dumb on YouTube. GD

Very unlikely that an old Subaru is going to be an "investment". Even the most valuable old Subaru's - typically the pristine low mileage Brat's, etc - only fetch about $10k. Not very impressive in the scheme of automotive investments. I expect my 1984 GMC Jimmy (K5 Blazer) will be worth $25k+ within the next 10 years. Being I have $5k into it - that's likely a 500% ROI. An old Subaru is likely to have cost more than it's worth by several times over during it's lifetime. The net profit will be negative after you consider the purchase price and all repairs over it's lifetime. It will not be an investment at all. Especially the most common of Subaru's - the station wagon. They are not what people are looking for - sure some people are, and some have fond memories of their parents EA82 they grew up in, etc. But those people will be few and far between compared to more popular and memorable vehicles like sports cars, lifted trucks and SUV's (4x4's), etc. The relative numbers that are available (they are still common), and the lack of demand means there's a surplus of supply - driving down the values. And when people look into owning one they find they can't get parts and service for them - further reducing their viability for collecting - vehicles in this category aren't collected for their rarity or their performance, etc. They are only collected to be used. The types of vehicles that attain great value are pretty easy to recognize - they are rare, or sporty, or unique, or iconic. Trust me no one is really looking for a Chevy Citation, an 80's S10 truck, a Ford Granada, a Celebrity Station Wagon, or an endless number of other vehicles that are just forgotten history. Why? Because they weren't special. The Subaru EA82 station wagon is not special. And will never be worth anything with the exception of a handful still out there that are basically unused with just a handful of miles on them. Anything with more than 50k miles will be essentially worthless. GD

It might help again if you can identify the wiring your gifted friend shorted out. Where it is located, more importantly the colours, main and trace Someone may recognise it.

Check your pitch stopper rod and ensure it’s still bolted in firmly. Also check for broken engine or gearbox mounts. Cheers Bennie