94 4runner 3vze 5 speed.....So I've had a water leak for a while now. I spent a good while chasing down a CEL for the EGR Valve. Fixed that, and now I'm moving on. So I found the leak on the upper idler pulley and when removing the drain plug to fix the leak I noticed yet another leak at the thermostat housing. Soooo, I did what anybody else would do, I took that off also. To my surprise, I have no thermostat. lets go back a couple of months. Its hot here in Texas in August so I had a couple of hot highway driving days, AC on going the speed limit. Turned on the heater, temp rushed back to normal, no problem. Maybe a bad thermostat (i thought), maybe a bad radiator, maybe 110 degree days. Either way, it didn't overheat very often and when it did it was damn hot outside and the AC was on. Well since its cooled down out here it hasn't overheated, keeps normal temp, no problems. Here's my question, and maybe I have my answer already. Since it has no thermostat could the PO have done that because of the overheating? Could the radiator be clogged up and need replacing? When I drained the radiator the coolant was clean nothing chunky or brown. I'm obviously going to replace the thermostat (with a jiggle valve of course). Any ideas?

 

Same thing happened to me, I walked into a can of worms.. redid the whole top end, PO had no Tstat too, all water galleys were clogged and needed new everything from radiator to waterpump to pulleys 2000 later.. runs fine

 

Its got flow through the block, it even goes through the throttle body valve (had to pull that off once before also). Also, this runner runs great, starts up every time. I've spent a lot of time wrenching on it and its getting decent mileage 17-18mpg, better than my Jeep and ten years older than my Jeep too.

 

While your down there you might consider replacing WP also. How's the timing belt look?

 

Thermostat is a restriction in the coolant flow for a reason; to help the engine warm up by keeping the coolant flow out of the radiator. It is open at operating temps but is still a restiction in order to keep the coolant in the radiator long enough for thermal transfer. No thermostat and the coolant circulates too quickly for an efficient thermal transfer.
Install the correct thermostat, new radiator cap and flush the cooling system. Pressure check the coolant system to ensure there are no leaks.

 

I'm with Sensei.

Sometimes it's hot as balls outside and the coolant doesn't keep up. But flushing the system and getting the right coolant could help.