I have a 1993 ford f150 with the 4.9 straight six. Earlier in the summer I put a 180 thermostat in it because it was running hot sometimes. This seemed to do the truck. Now when driving the truck will run at the N of the normal on the gauge, but when left sitting and idling, the gauge starts to creep up. What could I do to fix this?

 

I would start with the basics. Im assuming your coolant level is full. I vote give your cooling system a flush.

 

Ditto. Sounds like a few possible things. Either radiator is plugged, missing your fan shroud?

Pull radiator and have shop test it. They can tell you the condition and if plugged they might be able to flush it. If not, just replace.

 

How much would a new radiator run me? And now that I looked at it I noticed my fan shroud is loose and the bottom has a chunk missing

 

Radiator | AutoZone.com

$120~

As long as most of the shroud is there, it likely is better then none. Does the truck ever overheat if it idles too much? Or just get warmer then normal?

You could pull the radiator, drain it and then flush it backwards(water in the bottom and let it run out the top) and see how much crud comes out. Likely the bottom gets full of sediment and plugs up the core. Might be too solid to flush out with hose? Might help some?

While it's apart, might want to back flush your heater core. Same issues there.

 

It gets warmer than normal but I have never lat it idle lOng enough to over heat but I have a feeling it might

 

Is the fan clutch in good shape? The fact that it runs cool while driving but heats up while standing still tells me that you may not be pulling enough air through the radiator. I have read that the fan moves about the same amount of air as if you were driving about 30-35mph. Check the clutch and the belt and tensioner to be sute you are moving enough air sitting still. Good luck.

 

Ya, could be clutch. Once warm, it still should have drag when you try to spin the fan. If it just freewheels like nothing then might be clutch.