Old Junker Toyota Pickup Overheating

I'd check to make sure the thermostat isn't broken before doing anything else. I'd also look in to make sure the whole radiator isn't clogged with scale. Then I'd check to make sure the water pump was happy.

I would not be surprised if all three of these were issues.

Note that an acid flush to clean all the scale out may cause the radiator to start leaking if it's already in bad shape and marginal. But it's not a bad idea if you're intending on keeping the thing running for a while, and if the water pump is good.

Maybe the fluid isn't circulating at all. (Water pump?)

Maybe the flow regulation isn't working, and so the coolant isn't getting to the engine block. (Thermostat?)

Also, maybe there is inadequate pressure in the system due to a leak somewhere. (Radiator cap?)

A car engine's coolant, which is largely water, has to heat far above

Without the pressure, your coolant would boil off quickly.

But too much pressure is, of course, undesireable. That's why, just like a pressure cooker, there is a way to relieve pressure. This is typically in the radiator cap, which is spring loaded so that its seal can lift under pressure.

That popping sound you hear, could it be your radiator cap bleeding off pressure prematurely?

That would explain why you are losing coolant, and why the engine is overheating.

If the liquid boils inside the engine block due to inadequate pressure, the resulting vapor can't do a useful job of keeping the engine cool, you see. Water vapor has very little heat capacity compared to liquid water! Once the coolant passages in the engine block are full of nothing but vapor, you are going to overheat.

So, first thing, try replacing the radiator cap.

Maybe the fluid isn't circulating at all. (Water pump?)

Maybe the flow regulation isn't working. (Thermostat?)

Also, maybe there is inadequate pressure in the system due to a leak somewhere. (Radiator cap?)

A car engine's coolant, which is largely water, has to heat far above

Without the pressure, your coolant would boil off quickly.

But too much pressure is, of course, undesireable. That's why, just like a pressure cooker, there is a way to relieve pressure. This is typically in the radiator cap, which is spring loaded so that its seal can lift under pressure.

That popping sound you hear, could it be your radiator cap bleeding off pressure prematurely?

That would explain why you are losing coolant, and why the engine is overheating.

If the liquid boils inside the engine block due to inadequate pressure, the resulting vapor can't do a useful job of keeping the engine cool, you see. Water vapor has very little heat capacity compared to liquid water! Once the coolant passages in the engine block are full of nothing but vapor, you are going to overheat.

So, first thing, try replacing the radiator cap.

Where does the coolant go when bled off by the cap? Either just into the atmosphere, or into a reservoir from which it can be sucked back when the pressure drops, creating a vacuum (which the cap is also designed to relieve). It depends on whether you have an open or closed type pressure relief system.

Among everything people have mentioned here, check the oil as well.... you say the fluid keeps getting low, but none on the ground.... is it leaking into the crankcase?? If so, it may not such an easy fix...

Good luck..

Fwed

Say, would that be the 3.0 V6 in your truck? (not a bad idea to add important info like that, ya know)

If so, your headgaskets are blown at cylinders 1 and 6. Call the Toyota dealer and see if your truck still qualifies for the headgasket recall.

The 22RE also can blow it's headgasket and cause similar results, but it isn't nearly as common a problem nor is it covered by a recall campaign.

Toyota MDT in MO

I am not a mechanic but the local junkyards in my area scrap out the radiators from toyota trucks as they are almost always clogged.

Just my 2 cents, Good Luck, Chris