Ok this is a strange situation. I have a 1992 Toyota Pickup DLX V6 4wd.

I live in the midwest and since the temps have been climbing recently my truck overheated so I topped it off with some coolant (It tends to burn off some coolant). I noticed that this happened often when the temps are hotter so I looked into the issue and someone recommended replacing the thermostat. Easy right? Not really. I removed the thermostat housing and viola! Nothing! Someone had removed the thermostat all together. So I'm thinking, great now once I put the new one in everything will be fixed. Again, not so. After installing the new one, I took off down the road and 5 minutes later my truck was overheating into the red. Eventually I got it back to the house after some stop and go.

Now I am throughly confused. Obviously the previous owner had removed the thermostat for a reason. But why would adding the thermostat back in make my truck overheat?

 

adam-
A couple questions.....
still has the factory radiator shroud?
still the factory fan clutch and no fancy dancy electric fan?
Color of the rad fluid....red, green, clear, or brown?

Does it overheat while just idling....or does it have to go up a hill or be on the highway to overheat?

 

- Im not sure if it has the factory radiator shroud. The previous owner rebuilt the engine as it had a seized piston.
- Also, not sure if it has the factory fan clutch.
- Radiator fluid is green.
- It seems to be overheating even while idling.

I can take pictures of the radiator and fan clutch when I get home in a bit here.

 

When engine is at operating temp, fan clutch coupling is maximum. Fan speed will follow pulley speed most closely.

At operating temp, vehicle stopped and idling with no highway air blowing through fan clutch, as soon as you turn IGN off, the fan should stop turning after only a couple of seconds, like below (brand-new fan clutch)

If it keeps on turning for say 6-8 seconds, fan clutch must need replacement.

 

Using coolant overheating I have to wonder failed head gasket from a quicky rebuild

Time for a pressure test.

The 3.0 is not known for air pockets like the 22r series but if coolant is added on a regular basis

Blocked radiator

 

The fan shroud does nothing. Cooling wise. For a 3VZ-E. I've ran both ways. Winter/Spring/Summer/Fall. 15°F - 110°F. No difference whatsoever.

An engine idling is far more prone to overheating.

The question is...is it really overheating? Or is the gauge just saying it is? IOW is the gauge overheating or is the engine? It's in that stupid little prone to flow restricition add-on doodah way the hell back behind the hottest part of the engine. That's where I'd be looking first. The coolant leak is probably unrelated. Stupid intake manifold gasket design strikes again most likely. Fel-Pro fixes that BTW.
Severely oversimplified. To the point of deception.

That is NOT the way you determine if the fan clutch needs replaced. That's the way that you determine it's functioning properly actually. If it doesn't essentially spin freely "most" of the time it's seized(fully or partially), and must need replaced.

When cold, the clutch is engaged. When warm, or as you say "at operating temp", the clutch is disengaged. It only engages after the engine has warmed up when the temperature reaches the threshold requiring it to be temporarily engaged to provide higher fan speed for added cooling. After sufficient cooling is achieved, the clutch disengages until it heats up again(or until the engine has cooled below "operating temp"). IOW unless the engine has just been started, or it's starting to overheat, the fan cluch is disengaged. If you stop the engine and it spins for 6-8 seconds, that means the fan clutch is disengaged, and the engine temperature doesn't require it to be engaged. If it doesn't spin, it means the engine temperature is high, or it has not warmed up yet...or it's seized(fully or partially). Period.

That's just how they work in real life. I semi-see where you'd think that. But it just doesn't jive with reality. You think you know how/why they work. But that is NOT REALLY how/why they work. Close...but no cigar.

 

Sounds like the previous owner put band aid over the real problem. No telling what the problem is until you dig into it a little.

I have seen trucks overheat from idling but when driven they tend to cool down. My experience is when that happens the biggest reason is the radiator is clogged. The Preston kit will not clean it out. I take my radiators to a shop and they power flush them clean. In most cases it looks like mud coming out of the radiator when they do that.

I really don't know of a good way to flush the block and assume the Preston kit will help with that for getting out some loose particles. When cleaning the cooling system, don't forget to clean the heater core as well as you may just put some of the debris from it back into your system. I forward flush and back flush the heater core by itself.

I would start with cleaning the system and then test/check cap, fan, and thermostat.