lol i had the same thing happen to mine

Its 98 240 and had that upper plastic heater core coupler on the fire wall break while i was driving and had all the coolant leak out.
TEMP GAUGE DID NOT RISE ABOVE NORMAL
(I know the Temp Gauge is garbage)

Car drove fine but stumbled at idle and had what i thought was rod knock at low RPM's like when you first start off in gear but disappeard above 1500RPM's. Gently drove it home (20 MINS) since i though i had a spun rod bearing, parked it. Later went out to check it over when it cooled down, went to check the coolant level to find the rad was empty. I then looked at that coupler to find it broke.

So I figured the H/G popped but the strange thing was the car drove all the way home with out a problem.
replaced the coupler and filled up the rad..... fired right up

Idles fine bled the system, warmed it up to operating temp took it for a short drive,no smoke, no loss in power, no chocolate milk No more knock.

Ended up taking a 800 mile round trip with out a problem and still DDing it.