Im more paranoid as one day towards the end of this season I sucked in some mud coming off the sandbar and started overheating at cruise. The oil temp alarm came on at 260, I shut down and the motors were dieseling and steaming. Started up and idled for awhile, the motors cooled down, did some slow cruising and the muck cleared out of the engine and everything went back to normal. But through that entire episode the oil temp gauge never went over 265 so I was really wondering about that upper limit. I suppose temps in the heads vs oil temps may be what's confusing me here, but I didnt expect that to happen when reading oil temps barely higher than normal.

Putting on aluminum heads on now so I would prefer running a little further away from the upper limit, or thats my thinking anyway.

Got it. Hopefully we'll get that dialed in on a warm day later this month and see how that affects oil temps.

Wouldn't a non-bypass with a pressure relief valve dumping to my manifolds accomplish the same thing?
My mechanic bud is pushing towards crossover, no bypass, and no stats. KISS principle and says running cold will be fine.

Oil temp not a concern in that situation, metal warping (head and block) snd gaskets (head) blowing would be the concern….to start with. My goodness, never let am engine run that wsy again. :(

To be fair, im pretty sure im not the only person on these boards who sucked in some mud and started overheating. Backed off and had engines shut off within 10 seconds of the buzzer going off. I wasn't going to keep running around like that lol. About the oil temps im surprised (not not understanding why) they would be reading just 5-10 degrees over normal cruising temp when the engine was obviously starting to overheat.

You may have to put a new impeller in the sea pump. It does not take much to ruin them.

What's your water pressure?

Agreed, but this isnt the cause of it as I've replaced them several times as regular maintenance since putting these motors in.

I don't get accurate readings since having moved the sender to the thermostat housing awhile back. Am putting on new intake manifolds that have a rear water port so will be relocating them there. Hated having them in the bottom of the block as they were a PITA to remove for winterization and they kept fouling with debris. IIRC when they were in the block I was getting 25 psi with the stats in and around 5 with them out.

When you use a crossover with out a by pass hose the only water to your exhaust will be from the holes in the thermostat when it is closed. This will also cause high water pressure at that point.

https://cimg8.ibsrv.net/gimg/www.off...2299615249.jpg
https://cimg6.ibsrv.net/gimg/www.off...e7e29c0132.jpg
This is what I run and my temps where I expect them to be. Now my oil cooler is a little small and my oil runs 280 just as it comes out of the oil pump, when running hammer down. I don't check it after the cooler so it goes back in much cooler than that. I run Amsoil 15w50 racing oil and their tech support told me that oil is good to run at 300. At the end of the season my oil is really clean and still hard to see on the dip stick. I have checked all points on the heads and engine with an IR temp gun and my temps are super close everywhere so no hot spots. I do have a Stewart 160 thermostat and I have never seen water temps over 165, even after running wide open for over 10 miles.

Yes I understand. What I proposed is to either run relief lines from the rear water port of the intake to my exhaust manifolds, or to put a pressure relief valve prior to water hitting the crossover, dumping to the exhaust. Just asking in case anyone has done it before and it worked for them.