I thought I'd update on the coolant pressure performance. It's on the brain now that my radiator started leaking. Turns out Subaru still sells radiators for my GL. How grateful I am for that.

From a cold start by the time the RPM's have fully dropped it'll be steady around 10-12 PSI. When driving it'll fluctuate anywhere between 4-12 PSI. I think I should have tapped into the thermostat rather than the heater core inlet, that way I could see if the thermostat has opened or closed. 

There is a correlation between RPM and pressure, however the temperature of the engine does play a factor. I'm not informed enough to say how much is head pressure and how much is the pressure buildup from heat, but it's cool to see them all interact by watching the gauges. 

I live in an area with lots of rolling hills and vastly different temperatures between summer and winter. I actually have to keep the revs above 3k in order to keep the engine warm enough in winter. I don't cover my grille, I've found that prolonged highway driving with it covered can cause the engine to get a bit too toasty for my liking. About 1/2 way up on the temperature gauge.

 

Only cover half the grille. That’s what I do in winter - but I do it over half the radiator behind the grille on my EA81 brumby to help it get to operating temp quicker and hold it there during our winter weather. It’s only a piece of cardboard so it’s easy to remove when needed if there’s a warm day. Sometimes I run to work with the cardboard in place, then in the arvo I need to remove it otherwise the engine runs on the hot side enough to trigger the thermo fans. 

I did cover my grille for a week or two. I actually had my license plate covering the driver side of the grille since when I replaced my bumper it didn't come with the license plate mount so I had to get creative.

I think it'd be cool to have a vacuum solenoid and actuator hooked up to the thermo fan relay. That way I could have some sort of active louvre that opened with the thermo fan in cold temperature. Of course I'd need to 3D print a custom grille but I think it'd be a fun project.