2004, XLT Adrenalin, 120k miles

Very odd problem just started yesterday.

Wife drove it in the afternoon ... came back home talking about it being "HOT" and having the "Check Gauges" warning come on.

Took it out for a test drive and sure enough it was running HOT ... not all the way in the red, but very VERY high up the gauge.

Just had the radiator and upper hose replaced last summer and it's ran fine since then.

Here's what I did today to test:

- From cold engine (left overnight)
- Remove Rad Cap ... check fluid reservoir ... filled to "Cold" level

Rad Cap OFF
- Started engine, let run for 10 minutes .. temp was fine
- Turned on heater full blast ... (front a back) ... ran 10 more minutes ... temp was fine

Rad Cap ON
- Heater still running full blast ... 10 more minutes ... temp was fine
- Turned off heater ... 10 more minutes ... temp went very high (where it was yesterday)
- Turned heater back on full blast ... temp returned to normal

- Turned engine off.

That's it ... no signs of leaks or anything .. the fluid reservoir was full when I finished ... thought that was strange.

Also very odd gurgling noise coming from upper radiator hose ... almost a sloshing sound like the fluid was pulsing back through.

I replaced Thermostat a few years back (let's say 5) along with that black housing. Water pump has never been replaced.

Thoughts?

 

Quick Update ...

Let it sit for about 20 minutes and checked it again ... all the fluid (from the filled reservoir) had been pulled back into the radiator.

 

Another quick update....

Let it sit a few more minutes and tested again with Rad Cap OFF... lots and lots of gurgling, burping fluid ... replaced the Rad Cap and there was A LOT of churning going on in there...