Temp gauge spiked, then normal?

Breaking my TRS cherry here, bare with me. Pardon the novella, but I'm trying to include as much detail to properly diagnose.

I have an '02 2.3 Duratec fleet truck with 173K on the clock that I bought about 500 miles ago. I know that the clutch, radiator, and timing belt were all done at various points in 2010, but other than that, I don't have too much history on the truck. It did sit for a while, long enough for the battery to go bad.

It ran fine all yesterday (~100 freeway miles) until last night when it did something wierd. I drove it from a cold start about 10 miles on the freeway to see my sister's play. It warmed up and behaved normally. It then sat for about 2 -2 1/2 hours. I then started it and hopped on the freeway again, but in less than five miles, the "check gauge" light came on and I noticed the coolant temp had spiked to red.

I immediately let off the gas and started coasting over to the side of the freeway. After half a minute or so, it rapidly dropped straight back down to normal operating temperature. (1/2 way on the gauge) I started looking for an exit to check it out and noticed the temperature slowly climing again to about 2/3s. I backed off again and limped off the freeway.

On surface streets, it returned to normal operating temperature and stayed there. I couldn't find a gas station so I got back on the freeway and found one a few exits down the road. I let it idle for a few minutes to see if it would heat soak and cause the gauge to spike again, but it did not. I then turned it off and checked the overflow tank and found that it was more or less empty with a little bit of coolant down by the bottom of the reservoir. I topped it off to the max fill line with water and hoped for the best.

The whole drive home (~100 miles) it was fine, no issues whatsoever.

When I parked it at home and shut it down, it started boiling coolant over the reservoir. I turned the car back on to check the gauges, but everthing was still reading normal temperatures.

So what gives? Did I have a air bubble or something in my system that caused the temperature to spike? Is my thermostat on it's way out? It only misbehaved the once. The truck runs and sounds totally fine, I drove it again this morning and it warmed up normally. I'd like to try and diagnose the issue before I hand it over to a mechanic who's gonna want to do a headgasket repair for $$$.

Any advice greatly appreciated, thanks all!

Steve

thermostat stuck then unstuck?
Idk really.. just watch it.

a stock temp gauge is really a glorified idiot light... if you really want to know what's happening, get aftermarket gauges. Personally this is my personal choice honestly, that way you can really know what's going on.

When I replaced the radiator on my ranger I topped off the fluid while it was running so the pump would circulate the coolant as i filled it. took it for a test drive and at first all seemed well, but then the temperatures started to steadily rise. After about 2/3 the way to high it rose very quickly at which point i made a very abrupt u turn and the temperature suddenly dropped to normal very quickly. when i got home i noticed the colant level was well below minimum (i had added coolant to the max level prior to test driving). i figured a large air pocket had displaced the volume of the coolant that was shown in the difference of before and after the test drive and when it shifted (pushed out of the engine and into the resovoir) the coolant level and engine temp reacted accordingly. it hasnt happened though since then however.

i had a friend whos honda had spiking temp and it turned out to be some sort of bypass hose that couldnt handle the pressure. there was coolant everywhere with no obvious source. it never leaked while idling.

those are my only 2 experiences on the matter.

You checked the overflow for fluid, but did you check the radiator? Start there, and tell us the condition of the antifreeze. It sounds to me like you may be low, but you really need to find out where it's going if so.

I would strongly urge addition of an aftermarket temp gauge.

You either have a problem getting ready to rear it's head?

Or the temp sender to your gauge and/or wiring to the gauge is shorting out to ground. I had a Cheby van do that. Heading down the highway at 60...and the temp gauge spiked....pulled over and it dropped to normal. Turned out the sender wire was grounding out against the engine.

S-