I am attempting to change the antifreeze in my 2003 496 mag ho engines. I can't find any plugs in the block. I have drained about 75% of the antifreeze by removing one of the lower hoses, but can't figure out how to drain the bolck. Any suggestions would be appreciated.

Question, why are you draining the antifreeze??

Best Regards,
Ray @ Raylar

They're 18mm hex plugs that have an allen pattern also in the head. They're obvioulsy black and hard to see.

The starboard one is almost but not quite behind the oil dipstick tube and blends in very well....

The port one is slightly above where the old generation KoolFuel would rest. They're not easy to get to. I made another post about using the Snap-On Socket, FSUM18A as an easier means of getting them out and back in..

Thanks for the help. The reason I am changing the antifreeze is Mercruiser recommends it be done every 5 years. I spoke to one of Mercruiser reps at a boat show & asked him why, & he told me it looses it lubrication properties & also forms a gummy substance that can block the passageways. For the price of 5 gallons of antifreeze, I figured it was cheap insurance. Thanks, again, SDFever.

Raylar, do you think changing antifreeze is unnecessary??? Ed

It is 100% necessary. It will silt up after 5-7 seasons; and not flow or cool as well. If your antifreeze bright pink, it's probably still fine. But if it starts to turn silver/metallic--it's time to change it.