07navi
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You can borrow a pressure tester a O'reilys for the cap but I would just throw a new cap and stat in there for starters.
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Cooling is a simple equation. All that is needed is coolant flow, and air flow.
Stop one, or both, and you will experience overheating.
Your truck uses a closed cooling system. As the coolant heats, it expands, and
travels to the overflow bottle. When it cools, it reverses flow via a siphon back to the radiator. Outside air does not enter the 'closed' system. If it does, no siphon will occur, and the coolant level will keep getting lower.
How air enters the cooling system.....deformed cap gasket, loose/damaged connections, any unit failure/break in the system.
As mentioned, a properly working t-stat is important. A t-stat that only opens
partially, or not at all, will cause overheating. To check a t-stat, remove it, and
place it in boiling water to determine if it opens, or not.
Of course, the coolant must always be at the 'full' level. If continued filling is required, you need to check for leaks. A simple pressure test using a pump connected to the rad cap opening will detect any leaks. To check the block, the
t-stat must be removed.
Ensure the fans activate at the proper temps, check a maintenance manual for fan activation temps (I didn't see any temp numbers in my Owners Manual).
Nice explanation, and photos, Joe. My '04 only has 19K miles on it, so I am not familiar with the engine compartment. I don't recognize a t-stat housing in the photos. I see the 'bulge' you reference, but I can't tell you what it is.
From your explanation: "driving the truck around the block, I was sitting in it typing this response. The temp gauge was dang-near on red". It would seem that the water pump could be your problem. Overheating in such a short drive indicates a lack of coolant flow. Fumes coming from the engine bay confirm that the temp gage is not the culprit.
The following is a link to diagnose a faulty water pump: https://www.yourmechanic.com/article/how-to-diagnose-a-faulty-water-pump-by-rocco-lovetere#:~:text=There are several safe ways to inspect if,for leaks. Step 6: Inspect the coolant reservoir.
That is just the shape of the gasket. Thermostats are critical on these modular engines, there is a top and bottom valve and they have to function well. The bottom part closes off another passage and needs to function right. I highly recommend you take it out and put a Motorcraft one in. I will see if I can find some diagrams on that.
I’d say either water pump and/or air in the system.
Have you verified both fans are operating and not just one?
Thank you! I’ll read that soon. I wonder if replacing the water pump is something I can do in my own driveway.
Please excuse my explanation or description, I was using that nub as a reference point for the particular “gasket.” It looks like the steam or vapor was coming from that location.
As for the Ford OEM thermostat, I figured as much. I will try to get my hands on one and hopefully I can return the “premium” brand thermostat.
Thank you all again for your help! I’d be stoked if I can fix this myself!