high coolant temp when idling at uneven surface.

strange, i parked my 1999 expedition on an uneven surface (banked 20 degrees left) and after a while of idling the temperature went up close to H and oil temp hot lamp went on.

didn't panic as i know the ford expedition is smart enough to do cylinder deactivation to cool engine in case of cooling system failure.

i moved to an even surface and shutoff engine. opened hood, coolant in reservoir was slowly boiling.

waited five minutes, restarted and temp was back normal.

continued journey with temp in normal range. no power loss, no knocking.

my theory is hot coolant in the reservoir touched the cap (because of bank angle) and might have caused cap to expand a bit and let air in or out hence the boilover.

coolant levels were normal last i checked, will check again in the morning.

Error

Air bubble in the cooling system? When you banked, the bubble went to the high side cylinder head?

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error sounds right.

just checked coolant level after engine cooled down. it is at normal levels and is clean and clear.

ahhh just another fun day of truckin'

something about being parked on a left bank is affecting the coolant system.

happened again today, less than 8 degree left bank, parked idling and coolant went up to 112 deg C (via bluedriver live data).

normal coolant idle temp is 99 to 103 and this truck idles for 20 to 30 mins regularly on our multiple stop trips with no issue, as long as it's a flat surface.



intake air temp at 55 deg C. Ambient 31 deg C.

still baffled, current theory i have is hot coolant touching coolant cap somehow allows some air to get in but there should be positive pressure so even that's still kinda iffy.

coolant levels normal and it's clean.

Air bubble in system, radiator core blocked internally on one side, pump belt slipping, hose pinching .

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Air


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Is it the original radiator in the Expy ? If it is I'd be looking at getting a new radiator.

original from 1999.

air, that would explain it.

doesn't it self vent any air as coolant circulates though?

will a coolant drain/refill remove the air?

When you say “banked left”, are you saying that the driver side is high?

i too think it’s air but can’t explain why.

And coolant change could solve the problem- as long as you properly burp the system.