I am having this overheating problem, gauge acts like there is air in the system. Only i bleed the system for hours over and over again. I even installed one of those flushing tee's in the heater line to help with flushing/air removal. Runs in the correct temp usually for 10-20 miles and then will start going up, Heater is pumping out very hot all the time. Upper hose is always hot, bottom is always lukewarm/cool. Installed a new tstat and gasket (single stage) and fixed a leaky hose. Temp gauge will hop around between hot (not red) and normal.
Once or twice now the gauge has read fully warm as soon as i start the truck

Any ideas?

PS the blue wire that controls the heater valve is unhooked and i just pushed the valve to on full and unhooked the wire, is this going to be a problem,

 

What kind of thermostat are you using? I have had similar problems with the stainless steel type before.

 

Could have been stainless, Which ever single stage one the dealer sells.

 

why not get the dual stage? just a thought

 

I bought the t-stat before i knew that i should get duel. But does this sound like temp gauge overshoot? i thought that that was overheating just after startup. Mine overheats after 10 or 15 min. and drops to normal as soon as i shut off engine and restart.

 

When I swapped the 3.4L into my 4Runner it was overheating. I replaced the t-stat with a brand new one and was getting the same results. Then I simply removed the t-stat all together with great success until I read a post here one day about the geyser bleeding technique for the 3.4L.

So you may try removing the t-stat and see if it still overheats. This way it might eliminate the possibility of it being the t-stat. Just a thought.

 

I can't think of anything else it would be besides t-stat, unless if it's not flowing there could be some blockage maybe.....