What are these on the left of the motor under the intake and why is one crusty, 74 inline 6 300

 

Looks like a core plug commonly referred to as freeze plugs. Engine coolant behind them, most auto part stores stock them just need to know size.

 

 

If one is crusty, you might have a slight leak. Antifreeze is on the other side of them, so if you decide to replace them be sure to drain your coolant.

 

X2 on commonly called a "freeze plug", or a "knock out plug" and yes they hold in what ever you are running in your radiator/block. So water, 50/50 antifreeze or straight antifreeze. That 1st one looks a little crusty, pic #2 looks great. Get a flat tip screwdriver and scrap around on the crusty one, if that is only VERY LIGHT outer surface corrosion you might be ok. But if you pick around and find some deep corrosion or worse case pop a hole in it...obviously time for a new one. No worries they are cheap.

The function of them is to "pop" out as a pressure relief point if your radiator and block contents freeze. To prevent the possibility of cracking your block.

If you have a real crusty one time to replace it, the 6 cyl should be easy to access. Drain radiator, tap/tip/flip/the bad one with a brass drift on one edge. Meaning spin it 180* like a coin spinning on its edge, on a table, then grab with vice grips and remove. Be careful you do not want to knock the complete thing IN the block.

To install a new one clean the hole, lay in place centered, use a socket that fits inside it nicely, and tap back in place. Make note of how far the old one is tapped in now. Have the socket and the new plug and centered as possible. And a 2 lb hammer works good, hit on it straight.

 

Thanks for all the good advice!!!

 

i always tap these plugs in so that they are slightly below flush in the holes. with some RTV sealer. these holes are where the casting sand was poured out of block when i was cast in the foundry.