Need help with radiator problem and near overheating

[Stick4503]

2004 Explorer with a 4.0 sohc 4x4 with stock suspension. Engine is completely rebuilt and has 4000 miles on it.

Problem started a few weeks ago. Temp gauge reads just under half most of the time, but when under strain the gauge runs up to around 3/4 or a little higher. Turning heat on will usually quickly lower the heat reading. No coolant leak or loss. No steam or smell of typically overheating but seems as if the engine is hotter than normal. Top radiator hose is very very warm (can only touch for a few seconds) , top of radiator is cool (can leave your hand on the fins for a long time) bottom of radiator is as hot as the top hose, bottom radiator hose is warm as well.

Thermostat is new, housing is new. Water pump is old but has no visible damage, rust or otherwise messed up fins inside.

Radiator is old, aka not replaced with the engine. Do I have a blocked radiator, bad temp sensor, bad pump, bad fan clutch. I don't want to change them all if they are not needed. Fan can be turned by hand and stops quick when engine is turned off. Or am I looking at a transmission problem. Gas mileage with new engine is still piss poor 13.5 -14 around town, not city. new fuel pump, I know these things don't get great mileage but I was looking for a little better than this with a new engine.

 

[IPcamper]

It sounds like, to me, that you are not getting good flow through the radiator. Did you flush the radiator? It might be be partially clogged. Also wash the outside of the radiator, remove bugs, dirt, etc that might block airflow. Check for bent fins. Are you sure the thermostat is good? D you have air trapped in the top of the radiator?

Check to be sure the fan clutch is working. If it is not engaging the fan when it is hot, it will not pull air through to cool.

 

[apenland01]

If you have rear heater, make sure it gets hot too. Thermostat put in the right direction? Weak fan clutch?

 

[Stick4503]

Flushed yes , No bug build up, fins are good. First thermostat was brand new second one was good but used, same results. Not sure of trapped air in radiator, could be I guess but it ran 3 plus thousand miles just fine before this started.

No factory rear heat. Heater works fine.

What is odd to me is that the radiator has such a difference in temperature. Top being cold and bottom being hot. I thought hot water came in the top and cooler water left the bottom.

 

[Stick4503]

I have not got used to this new format. How do I get this to show up under the new post page like it used to?

 

[apenland01]

Silly question, but are you touching the fins on the radiator and not the A/C condenser? If the radiator is cool to the touch, but the top hose is hot, then I would think you must have a blocked radiator right at the top. You have an interesting situation, if it is indeed overheating and not just a bad or disconnected sensor.

 

[Stick4503]

So this problem is solved. The initial sometimes near overheating was cause by a brand new Dorman thermostat only opening part ways the headgaskets were totally destroyed by the replacement brand new Dorman thermostat failing to open at all after just 3 weeks. DO NOT BUY A DORMAN THERMOSTAT IT COST ME NEARLY A THOUSAND DOLLARS AND MAY HAVE CAUSED WEAR TO MY BRAND NEW REBUILT ENGINE. I have lower compression to my number 6 cylinder now.

 

[Number Twelve]

I had that happen in 1984. One Stop Auto Parts. Total rebuild of the engine. The new thermostat never opened. Coolant was blowing out the radiator cap within 2 miles on the maiden voyage.

These things happen.
You would think all new thermostats were tested before they were shipped out of the factory, but apparently they aren't.