Loud Clank Underneath Engine...

[chaddeihl]

91 Nissan D21 4cyl...

When trying to turn the truck over, there is a single loud clank underneath the engine. Any clue what might cause that? Truck was starting just fine the other day.

Thanks

UPDATE: Just pulled the oil dipstick and the golden brown oil that was just above half full is now a milky white/brown color and is about 2 inches above the full mark. Did my piston(s) seize?

[audtatious]

Without the clank I would suggest the head gasket is blown because you have coolant mixing with your oil. With the clank it sounds much more catastrophic than that.

[WDRacing]

There should NEVER be metal on metal sounds. Best case, something is lose and banging against something else as the motor turns over, but with milky oil I'd say you're well beyond the best case scenario.

If the piston was seized the motor wouldn't turn over at all, unless the rod separated from the piston and is just in there banging around.

I'm 99% that you'll have to pull the motor for this diagnosis/fix.

[ImStricken06]

milky oil = engine coolant & oil mixing together.

clanking sound - could be many things... but it seems like you have a warped head, or a blown head gasket.