Needing 'Dr. House', but for Fords. Cooling system mystery

[Chance02]

Early 2002 Sport (radiator is 01 model - discovered when I decided to replace the cap today), 120K.

Cooling system was flushed, filled, new thermostat in May. Last week, a spike on temp gauge had me look at coolant level, woah - ultimately needed five quarts - in seven months! No smoke, no milky look to oil, no performance issues, no visible residue, no puddles, and only recent (and short-lived) spiking. Where was coolant?

I was thinking intake gasket, head gasket, lower thermostat, but I did a pressure check first - I took it to the shop that did the FNF - pressure was fine. So presumably no leaks.

Their thought (the shop) for the 'loss' of fluid was an air bubble in the heat exchanger that finally 'burst' and the system sucked up whatever was in the degas until truly filled. (I filled the degas twice before filling the radiator directly)

The gauge still spikes (once warm, spikes for ~20 secs, then normal again), but I see from this forum that that is not uncommon and the shop is willing to swap out the thermostat for free (warranteed) if it continues.

So, I'm not inclined to go looking for trouble with a truck that excepting a slightly rough idle is running fine. But the whole thing seems like *too* happy an ending. With pressure holding in the system, I'm thinking it was 'just one of those things' that I'll keep a closer eye on now.

Or is there a question I should still be asking? Does their explanation seem plausible to any of you?

 

[XLT99]

The shops explanation does seem plausible, since sometimes air does get trapped in the cooling system, and when it finally gets purged, the coolant level appears to drop. I cant think of any other reason to explain the loss since you said it doesnt appear to be leaking, burning it, and the system is holding pressure.
After i smashed my radiator a while back and replaced it, air in the system made my temp gauge spike several times until everything was purged. Since it seems like there is air in you coolant system, that could explain your gauge spiking too

 

[koda2000]

Weird... I wouldn't think it could possibly take that long to burp. I think I'd be checking the coolant fluid level daily, for at least the next month, if I were you. After replacing my lower radiator hose, my '01 4.0 SOHC XLT wouldn't burp, but spiked once within the first 1/2 mile of driving, overflowed the coolant reservoir and then required 2 more qts of antifreeze and never did it again.

 

[wood1]

I've had to slightly remove heater hoses and allow air to escape with the engine running to "burp" stubborn air out of a cooling system. It is plausible but I would watch my coolant level like a hawk.

Should add that you do not do it to a warm engine, cold only!

 

[Chance02]

Good news. Thanks all!

 

[FIND]

Read the title and thought... so he wants us to insult him and then run a dozen expensive tests before randomly having an epiphany.


It's not lupus.

 

[Chance02]

FIND:

Actually I wanted a British comedian seeking a dramatic role using an expert American accent to tell me that it isn't lupus. ;-)

 

[Chance02]

Not a happy ending in this episode.

A very difficult to detect cracked block. No symptoms except for the disappearing coolant.

It was an interesting experiment but its off to a charity auction. Hopefully a DIYer can replace the engine or keep it going a few more years with an additive.

Chance out.

 

[corkey]

first off, some sanity here,, a cracked block and there would be a milkshake in the oil,
a coolant leak, and there would be a smell,
a head gasket, milkshake again,,

it is a long drawn out affair to burp the coolant properly , and most shops don't do it right anyways,, the temporary pegging of the temp gauge is steam in the neck above the thermostat, it is only there for a couple of seconds as the air passes, that is the why it does it,,
make sure the rad is full and the overflow tank is at the proper level , and the hose to the overflow is not blocked, and it will resolve itself,
you said the temp comes back down, and it runs okay,,

i would say change the plugs, and drive it ,,