A couple months ago I replaced the water pump, thermostat, and coolant. My Toyota ran great and the temps and heater were running perfect. Well the last couple of nights we've had down to -20 deg F temps and my baby is acting really weird.
Monday AM the heater wouldn't come on for a really long time and the temp gauge kind of "hunted" back and forth in the middle. Then the heater came on and the temp slowly rose until it got up to the red. I pulled into a gas station and pulled the radiator cap and there wasn't any pressure (no spillover) but the water in there was circulating and hot (radiator was hot, hose was hot, etc). I let it idle for about 5 minutes and the temp dropped back to normal and I drove 50 minutes to work and everything was fine.
Yesterday I drove home from work and the heater wouldn't come on (in about 5 min of driving) so I parked it and let it idle and it still wouldn't come on but it started "hunting" again. This time I cracked the cap and it had pressure.
This morning the same sort thing... heater wouldn't come on after idling/warming up for about 15 minutes and then when I started to drive, bam, it came on and then the temps started to come up. I got to work (only about 10 minutes of driving) before it got up too high. I cracked the cap and again it had pressure and plenty of fluid (I checked it later after the temps went down to where it wouldn't spill over and the fluid level was full).
What's going on? The thermostat is apparently working (circulating water through the radiator after the water in the block warms up) but why would the heater not come on until after I started to drive? Does the heater have it's own thermostat? And why is the temp climbing and why the first time this happened did the temp drop back down to normal and run fine after I checked it?
Also, the water/antifreeze in the overflow bottle looks kind of "slushy" even though I have it mixed 50/50 (orange kind). It's not frozen solid but has ice crystals in it. The water I can see in the radiator is all liquid though. Could this have something to do with things?
Thanks folks, appreciate it!
Joa '90 3.0L 4Runner w/238K