Sizing a new oil cooler

Looking to replace my oil cooler with my repower project. I'm installing a fresh 454 with all stock Mercruier 340 components. The cooler I had was a stern drive unit with half of the body taken up as an unused power steering cooler. My tandem cooler now is about 4-5 inches on each side. My biggest concern is, can I go too big? I am looking at an 8 inch unit (5 inch body) as well as a 12 inch (9 inch body). Need I be concerned with too much cooling capacity by upgrading to the 12 inch unit?

 

Oil that runs too cold will build up sludge. It should get hot enough to boil moisture off.

 

Exactly... hence my concern. I have a feeling that some of my oil pressure issues at higher RPM's were due to the oil getting too hot. Unfortunately it's just a guess as I don't have an oil temp gauge. The old motor had so much blow by that it would blow the dipstick out of the tube at anything over 3600 RPM's. I am guessing that the excessive blow by was potentially contributing to the oil temp? then again, as I don't have an oil temp gauge it's all speculation.

 

Blow-by will heat up the crankcase. I assume the cooler doesn't have a thermostat.

 

no thermostat that I'm aware of unless it's in the remote filter adapter on the block. It's all factory Mercruiser components for a 1990 Bravo 454. I ended up ordering a factory spec 8 inch cooler. This cooler was OEM on the straight inboard 7.4 of that vintage. As my motor began life as a Bravo, then was transplanted as an inboard it still had the Bravo spec dual oil/power steering cooler. I was leary on going with the 12 inch cooler as I din't want to over cool the oil. Thanks as always! As soon as I get it in the water I'll report back.