I cleaned out the idle air control valve and replaced the gasket.
Another friend told me the 07+ Silverados are plumbed the same my brother described.
I got a two quart expansion tank and some bungs welded in the radiator. Cut and capped off the old lower water neck and made a new, longer one that better clears the valve cover.
Put a bung in the top of the other side of the tank too in case we want to put a bigger fitting there.
So I ran a 1/4" hose from the top of the hot side of the radiator to the top of the expansion tank. Ran a 1/2" hose from the bottom of the expansion tank to the bottom of the cold side of the radiator. Ran a 1/4" hose from the overflow fitting of the expansion tank to the bottom of the overflow tank.
Once it's warmed up at idle there isn't any coolant flowing into the expansion tank, but if you rev it up there's a little stream. The level in the expansion tank never seemed to change. When I take off the cap, even if the engine is hot and running, there is no sound or spray. When I have the cap on the expansion tank and the overflow hose from the expansion tank hooked up to the bottom of the overflow, the overflow tank does get some bubbles in it, but it still has no coolant in it. One indication of cooling system effectiveness I've noticed is that when everything is working right (minimal air in the radiator), the fans only run for about 30 seconds and the engine is cooled back off. If it does have air, the fans will run for minutes or continuously. Now they just run for 30 seconds or so. So I think it's working. Drove for about an hour on the highway. Only 70F outside. Temps were 176F at 65mph, 181-183 at 80mph. Once at the start and once at the end of the trip, after getting up to speed it went over 190F briefly but then came back down around 180. Never did that with the AC on. This is with no skidpans/shields on, they may actually make it run cooler. Expansion tank had about the same amount of coolant as I started when I got back. Let it idle for a few minutes until the fans kicked on, they only ran for 30 seconds and shut off. No noticeable pressure in the expansion tank when I took the cap off, did see one bubble in the overflow tank while it was idling, but that's still basically dry.
Also, intake air temps with the old cooling setup were 110-120F, but it was about 90F outside. Today it was about 70F outside and intake temp was about 90F. Thinking about making some kind of hood scoop or making the stock one ducted over there.
We mounted the expansion tank and overflow tank, ran it until it got hot enough to run the fans, coolant level seemed not to change, so hopefully it's good now. Going to drive it around this week.
We did some other little things on the Outback like getting the rear hatch power lock working and worked on mounts for the recovery ramps. My friend noticed the short vertical vacuum hose in front of the throttle body was cracked so we swapped it out with the one from the old engine.
The Impreza has been handling funny for the last couple weeks, I've looked at it a few times and finally noticed one of the tires is about to blow.
At least one wheel is bent so we went through those. I have at least four steel wheels that are pretty straight (.030-.040") and a bunch that are bent .1"-.2", so I have to get a couple tires and do some wheel/tire swapping. While I was trying to get one of the wheels off I noticed the LR strut was moving around at the top. The top hat is broken. With weight on it, not a big deal, but when it droops out it can wave around and wind up elsewhere. The other side is cracked about 3/4 of the way around. So I need to replace those.