Two years ago the hose connection separated from the coolant bottle, draining all the coolant on my 2003 S-type 4.2 with my wife driving it. Since the coolant was drained there was no overheat warning. Since we had had a very slow coolant leak waiting to be repaired, she ignored the low coolant warning. Engine ran a few miles with no coolant and stopped. From that point on it could never build compression again and it needed major head repair. I ended up replacing the engine with a salvage unit.

If there is supposed to be a failsafe, it certainly did not work for me. Perhaps it is based on coolant temperature, therefore failed to work since there was no coolant.

 

That may have been the culprit. Couldn't get a coolant temp reading (at least one off the charts) - did it even show that it got hot?

Wow that's a shame...

I assume the check coolant level was already engaged bc of your slow leak - on an S-Type it takes no more than a pint or two of missing coolant to get to low coolant warnings.

If the car had no clue it was getting hot i'm sure it cooked the head and dropped the valve seats, maybe even warped the head.

On a car that knows what the coolant temp is, the computer will shut down the party before it gets to that point. Mine did and I thought I had hurt the motor while inspecting the car. Let it cool off for an hour fire it back up, no white smoke, no milky oil no drama, just got hot again quick. (bc thermostat never opened).

Take care,

George

 

Yup, that is why I always advise not to let a slow leak lull you into complacency. You never know when slightly low coolant might one day mean empty!