Fixed

***Fixed: after flushing the system the truck is not overheating. Was likely material from the bad pump blocking flow through the cooling system.

 

It does sound like a stuck closed thermostat. I wouldn't trust the dash gauge to see if the temp sensor is working. Check actual values with a scan tool or remove it and check resistance values. I haven't seen a chart for the 3rz temp sensor before so a scan tool would be ideal

 

Well, I took the old thermostat out and tested it with a new thermostat in hot water today, they both work. I think it's the water pump. Only other thing it could be if water is boiling, gotta mean it's not moving, right? Thermostat open leaves water pump as the culprit... wasn't looking forward to this in my free time.

how can you tell if the water pump has failed altogether?

 

Leaking at the weep hole would tell you if the seals are bad. If it's the impeller then you need to check for good flow when the thermostat is open. Also check your radiator cap to make sure it's working and not stuck open or closed.

 

Thermostat is suspect but also..

 

This is a dumb question, but could I just open the radiator cap and look for pressure/fluid flowing out while the engine is idling and warm? I didn't grow up wrenching on anything but was guessing this might be a quick way to tell if the pump is at least pressurizing the system?

I have some fluoroscein stain (glows under blacklight) at my job, so might try putting some of this in the radiator fluid and using the blacklight to see if there is a leak also, assuming the pump is working at all.

 

You're not going to see anything down in the radiator neck except for the coolant level. The best indicator of flow would be comparing the temperatures of the upper and lower radiator hose. grab onto them, if one's cold and One's hot replacing the thermostat would be a good start.. If the radiator is doing it's job the air that is blowing on your hand when you stick it down by the fan (running) should be warm.

 

I just put a new thermostat in tonight, tested it in hot water before I put it in and it opened fine. Then I drove the truck for about 20 minutes and the top hose was hot, bottom hose mildly warm... heater does blow hot air, very hot...

What do ya think? Water pump going bad?

 

Do you have to top off the coolant level frequently? Is it low or slightly low every time you check?

 

have had to top it off a few times in the past month, maybe dropped an inch each week...

 

Do you habe any signs of coolant leaking anywhere (pink crust, green crust), like the bleed hole of the water pump? Or is is pretty dry on the outside of the engine..

 

trouble is I live on a dirt road, and it's rained about a foot in the past weeks, so can't get a clean look at the engine. I've used a flashlight to look while idling and don't see anything obvious. I'll have to check the bleed hole tomorrow. Haven't messed with the pump on anything before, gotta take a lot of stuff off to see it?

 

Get on the ground under the front, hopefully dry as possible and look up at the front of the engine with a flashlight. If it's leaking you'll see something..

If you don't have any external leaks and the coolant level is consistently dropping you may have a blown headgsket and/or cracked head.. The extra pressure from the cylinder compression can cause weird issues with circulation, you'll have hot and cold hoses, inconsistent heater core perf, and it can over heat with no erratic temp gauge

 

It sounds like it could be a clogged radiator. I had a 96 2.4 that had an overheating problem like that.

 

At this point I'm looking at changing the water pump and maybe the radiator too... I drove to work about 20 miles today and the water is boiling inside my top hose... whatever happens it's cheaper than paying a shop. No good shade-tree mechanics here to help me. Not gonna get bent over a barrel by a commercial shop.

 

Who is good to order parts from?

 

gotta do that. Thanks for the heads up. I may be parting this out soon if that's the case. Got no shop to work in and nobody I trust to help on a big repair.

 

(***Found solution)
I decided to replace the water pump, took the old one out and 5 out of the 6 fins on the pump had broken off... not sure when or how. This is why it was overheating but appeared to have flow... reduced flow due to broken fins...

No idea how much damage the overheat did to the engine but seems fine now with new water pump in terms of cooling.

 

Thanx for posting the solution. I've never heard of those fins breaking off.
If this happened to me, I'd install an OEM pump.