Cooling system
I bought a 94 4Runner a couple months ago for my son to learn on and eventually drive. Part of my plan is also to get him working on vehicles a bit (he's 15).
So we've been fixing some of the more obvious problems with this vehicle and getting to know it. I noticed some odd shifting behavior and reading indicated that it won't shift into 4th until it's up to temp. We noticed it's been slow to get to temp and just recently drove it far enough to see that ours is losing temperature on long, straight, level areas and then downshifts into third. So I suspected thermostat.
We dug into that yesterday and discovered that the cooling system was filled with water. I should have checked this sooner. Turns out it had no thermostat in it. So we flushed it out with tap water, replaced the thermostat with a 180 degree unit, replaced upper and lower hoses, cleaned and sealed the upper opening, and filled it with fresh 50/50 mix. That made a huge difference. It shifts nice and smooth, oil pressure isn't high at temp now, and power is improved. Next weekend we're planning to do the valve covers.