To AllDODGE, BUP, ZONE 5, AND OTHERS. Thank you guys for providing a world of helpful info in general on this site. Concerning oil temps, here’s my experience, and just my 2 cents worth on oil temps. Post is a little long but hope the info helps some folks that are worried about oil temps that are a little high. My opinion is that most boaters are running with too low oil temperatures to remove the moisture.

My 502MPI's with 2x12 coolers, still had all the old deteriorating original oil cooler hoses and restrictive fittings, and remote mount. So instead of replacing the hoses, I decided to just remove everything and try it. NOTHING but the oil filter left. Motor should get more oil flow than before without all the restrictions, and there’s less potential leakpoints.

The reason I removed the coolers was to get rid of more moisture in the oil. The oil used to be brownish instead of black like an automobile, it smelled more acidic, and inside of the valves covers and the underside of the intake was some milky sludge. There were no water leaks anywhere. I know much of this collection of moisture was due to reversion issues in the exhaust. A lot of boats have that and are unaware that’s what causes moisture in the oil, as well as corrosion of the exhaust valves. I have corrected the reversion, but the low oil temps were just not burning enough moisture off to keep the oil dry.



OIL TEMPS: Readings taken on the front of the oil pan below oil level.

WITH COOLERS 150 to 190 slow to fast CRUISING, 225 but only at WOT for several minutes. These are summer temps. Winter, fall spring was colder oil. The oil pressure used to be 20 at idle, 65 at WOT .

WITHOUT THE OIL COOLER, and summertime 95 deg outside air, Slow cruising at 35-40mph the oil is now 240/250 degrees, faster cruising(4000rpm) it’s 265 deg,

After cruising and then running close to WOT for another 5 minutes it is at 300. The oil pressure now runs 13-14psi at 600 rpm idle right after a WOT run, but climbs a bit as the oil cools a little. It now runs 57psi after running at WOT, 5100, for a few minutes and everythings been heated up.



The oil looks much much cleaner, and doesn’t smell as acidic as it did before with moisture in it. Running it this way so far this summer (about 30 hours on the oil) everything looks good. As other people on OSO website have mentioned seeing this, and I have also, seen a single SBChevy on a small cruiser boat that is run near WOT most of the time for years with no cooler, about the same oil temps as mine, and not having any issues whatsoever.

I also know other people running w/o coolers on BBC motors with no issues. However, none of us run literally at WOT for 30 min or more in the hot summer. That could be an issue in summer with a built motor though. If we’re cruising hard on a long run somewhere, I always back off 300 to 500 rpm even when I had the oil coolers. Fast enough, but easier on motors.

JOURNAL BEARINGS(ALUM). I have read up on it, but I have no experience with knowing if at what point any degrading of the alum journal bearings could be an issue. A couple articles indicated a max of around 300 deg oil going into the alum bearings would not be an issue. Any input anybody has on this would be appreciated.

Mine are stock motors except for advanced timing over stock, Eddie Marine exhaust, and a little cleanup on the ports.

Also I spotted a bulletin for a Mercruiser 1075 , https://www.scribd.com/doc/101451908...-Owners-Manual, it states on page 33 the max allowable oil temp is 284, so that makes me a little more comfortable seeing 300 only at WOT in very hot weather.

300* would scare the crap out of me, I shut it down at 260*
also more heat = more chance of detonation.

While that small block may be running wide open, it’s probably spinning 4200 rpm max if that. You’re spinning your 502 another 1k rom over that. I’m not sure I’d want to take the gamble. I’m with Dan, I’d be shutting her down if oil temp started creeping toward 300.

Do you plan to pull it to check bearing wear at some point?

Have you cut a filter open yet?

At 300°F I'd be concerned about the viscosity of the oil being enough to support the load of combustion. And at 300°F seals, detonation the process window just gets too small. No room for error. 300°F never. Shoot I don't like over 220°F, but that's how I built my engines 180°F oil stats and 120°F water stats.

The oil permanently changes at a molecular level when it gets that hot and does not regain the same lubricating properties it had, even once it cools down. I'd not be happy seeing anything over 260, ever.

Until I put the larger cooler on mine, my oil turned black after a few short cruses. It now stays about the same original color, but I also have a high volume oil pump 80 psi cold idle,

what size/brand oil coolers are people running on mid-hp 750 hp engines.im about to put better ones on mine because of the same problem