Just finished my 525 project today fired for the first time , ran good just curious i put a 160 thermostat in it , but what did the 525s come with or what should be put in?

FActory spec book says 143 deg. Mine run 140 & 150 respectively so I'm sure that's what's in them.

They had a 140* tstat from the factory.

Griff would you have the part # for the 140 Degree thermostats? Also were would you recomend buying them? Thanks in advance

Any Merc dealer. The same one is used for all carbed Merc BBC engines. Make sure to use the factory gasket with NO sealer or your temp gauges will not work.

Griff your the man thanks for the tip.

What would you recommend for spark plugs in these engines?

I ran NGK UR5's( NGK stock #2771) in my 525SC stock and after bumping it up a little. They are the same heat range as the stock AC R41T's, but have a slightly extended tip to help the engine idle better and keep them fouling.