06 tacoma 4cly intermittent overheating

hey guys i need some input. ive read all forums and cant seem to find a definitive answer on this. 06 taco 4cyl (2trfe) 159k miles.
had the usual coolant bypass leak problem, slow leak of coolant for a while so like an idiot i kept putting tap water in to remedy this situation. ran with water/coolant for around 6-12 months (cant exactly remember) and then when it was leaking to the point of being undrivable i finally fixed the bypass line with a metal one and did coolant drain and fill using the coolant funnel kit with pink 50/50 coolant. when i drained the water/coolant it was rather clear.

so after about 5 months i am now having overheating problems. drove car for 1/2 hour on freeway and it started overheating. pulled over and overflow tank was empty and i believe steam coming out of it. allowed engine to cool down for 3-4 hours and put more water in the radiator and kept driving. on initial start the car warmed up and did started to get warm and overheat for about 1-2 mins as im going 60mph (almost pulled over again). then magically the temp gauge went back down and was steady in the middle for another 1/2 hour. then temps started to go back up to the top end if the range again. made it to my destination so did not try this a third time. so two consecutive overheats after 1/2 hour and overheating for 1-2 mins the second time on startup.

the next day i start it up in the morning and it starts getting in the top end of the range again. (drove about 1.5 miles). drove back home after work (0.3 miles) and then let it car idle. cant remember but it may have started to overheat on its own but i did pour more water into the radiator and overflow tnk as it was idling and after i did that vigorous bubbling coming out thru it.

next day after work i test the truck again. coolant looks brownish/orange ish and maybe a little pink. (hard to describe) pour more water in rad and let it idle and no overheating whatsoever. turned a/c on full blast works fine, then turn heater on full blast and works fine and no overheating at all. revved it up for a little bit and also nothing. took a vid of the radiator opening and small consistent bubbles coming up thru the brownish orange coolant and consistent white vapor coming out of the rad opening (was cold outside so not 100% sure if it was just steam or not) checked oil dipstick and oil appears to be fine and within top end of the range.

tested for overheating the next day, turned it on let it idle for 15 mins, checked hoses and top one is warm and bottom is not which is good. drove it for about 5-10 mins and 50ish mph and no overheating.

so at the end of the week i decided to not tow it and drive it 66 miles (1hr and 10min drive) to my destination. before i left i filled the rad up with tap water and i expected to start overheating after 1/2 hour like last time. however, this did not happen, drove the car for the whole 1hr and 10 mins at 60-70mph with the heater on full blast and no overheating at all. turned the heater off near the end of the drive to see if temp would change and it did not. let it idle for 15 minutes minimum and no overheating. then i block tested it for exhaust gases in coolant and tested negative and testing fluid stayed consistently blue.

next day i pulled spark plugs and all look to be ok and consistent. no major oil or coolant buildup on any of them. now i have rented a compression tester and will test it tomorow.

just stumped right now how it overheated consistently after 1/2 hour those two times and after i started it nd overheated for 1-2 mins and then went back down for another 1/2 hour. And after all that, putting more water in and driving it a full hour with heater on with no problems is what really gets me.

possible problems

1. air trapped in cooling system? not sure how well the coolant funnel kit but i went 5 months with no problems and now this. just think air trapped in their would not tke 5 months to happen. and if i did the drain and fill shouldnt my coolant be relatively good since there it is mostly new and only what was left in the block of my old tap water/coolant?

2. thermostat sticking closed sometimes? after 1/2 hour it started overheating those 2 times and if it is sticking closed then coolant is then blocked to the rad and eventually heats up in the block. wuld explain the coolant loss

3. dirty coolant clogging system somewhere? i did put mostly tap water in it before i did the bypass line so that may have something to do with it. but dont understand how i could then drive 1 hour at freeway speeds with no hiccups

4. head gasket? i did do the block test and it came back negative, but may have to redo again with a fresh coolant flush. the oil on the dipstick looks fine it is just the coolant that looks orange/brownish/pinkish.

hopefully the comp test is good tomorrow. if so i will most likely clean the coolant system multiple times with distilled water

will try to provide pictures if I can figure out how as this is my first post (sorry if it was so long)

 

Pressure test is easy and could reveal something.

Bad radiator cap or Tstat are certainly possible.

Make sure radiator fins arent clogged with mud or straw, especially between the condenser and radiator. Or the condenser itself.

 

Sounds like possibly a head gasket issue, since you have the plugs out I'd pressurize the cooling system and look for coolant leaking into the cylinders.

 

Yea I was looking for one at the oreilleys but didn't see any on the shelf, ended up renting the compression tester, should have just asked if they rentcoolant pressure testers also

 

Mityvac MV4560 is a relatively inexpensive pressure tester that should do what you need, unless it's a severely blown head gasket a compression test probably won't tell you much. The only other test that may reveal something is to put air pressure in each cylinder with it at TDC compression stroke and look for bubbles in the radiator.