Intermittent Overheating

[Blvdst]

My 05 4.0L is intermittently overheating. Radiator has been flushed and new coolant added. New thermostat and gasket. Radiator fins are clean. No signs of a leak. Pressure test was good. New belt and fan clutch. Everthing is fine until it is driven in the city with stop and go traffic for more than 30 minutes. Today it reached the hot level but not at the overheat mark to trip the overheat light. Once the air flows through the radiator at 30 or more mph the gauge will drop to the normal level which is one tick below the midway pont. I'm thinking it needs a water pump since it will cool down if air gets to the radiator. If you have had a similar problem with yours I'd like to hear how you resolved it?

 

[BrooklynBay]

Are you sure that it's over heating, and it doesn't have a faulty temperature sending unit? Check the temperature with an IR gun or a thermometer.

 

[03Explo20]

My 03 was doing this and I found a slight leak behind the plastic piece where the top radiator hose goes. When I ordered a new part, it came with the sending unit also. After the install I rarely see any movement. Make sure you use Motorcraft parts (thermostat) when you replace things. I tried a Fail Safe in there and it was a real POS!

Is the water pump leaking anywhere? I think they tend to sprout a leak somewhere when bad??

 

[Tech By Trade]

If you don't have low fluid, a leak, or an air bubble in the system, you may be right about the water pump as the plastic fins on the impeller do "wear away". Is your fan clutch wired up right? Also, you may want to test that thermostat with some water on the stove and a thermometer. I have gotten a bad one out of the box before.

 

[07gtman]

Any luck with that .I would be looking at the fan first,If you can spin it super easy,the clutch is not right.It should have a little tension when you try and spin it.
Tech By Trade made a very good point about an air bubble, Run it with the radiator cap off for at least 15 mins. keep an eye on the fluid level while doing it.