318 Chrysler marine engine overheats

[Slip356]

72 Century Resorter with Chrysler 318 marine engine all stock.
Replaced exhaust manifolds with good used that were pressure tested, not flow tested
With new 160 F thermostat engine runs at 150f which I consider good, however the exhaust manifolds run at 200 F on my IR gun, too hot in my opinion.
Removed the thermostat and the engine or the manifolds do not get over 110f that would tell me there is no blockage.
I’ve been advised a 140 F thermostat might be better but I can’t locate one. H2O pump just rebuilt with new impellers.
I’ve had the boat for 15 yrs, engine temp has always been at 150
Just recently started checking the exhhsust manifolds
Advice?

[Moderator]

Plugged risers or manifolds

[Moderator]

https://www.trojanboats.net/zencart/ind ... Path=85_90

[Slip356]

Moderator,
Please explain how the risers or manifolds could be plugged when as I stated, with the Thermostat removed, engine or manifolds didn’t get over 110F?
Tks,
Slip

[Moderator]

Sorry I missed you saying the manifolds ran cooler without the stat. BTW was the thermostat a marine thermostat? they are different style than automotive.
BTW is this raw water cooled or does it use coolant? I assume it's raw water.

[Slip356]

Still looking for professional advice. Is 200 F temp too hot on the exterior of the exhaust manifolds read with an IR gun. All engine details are in my previous posts.
Tks,
Slip

[Slip356]

Yes it’s raw water cooled from the lake. Thermostat is simple automotive 160f temp type. The 145F temp TS is priced anywhere for over $200 to the cheapest I’ve found on line is about $80. What makes them so expensive and will they likely improve cooling to the manifolds. The automotive type cost between $6-12.
As I’ve previously stated, engine has always run at 150f water temp over 15 yrs of ownership, so just recently using an IR gun to check manifold temps. Is 200F too hot?
Motor runs perfectly as it always has.

[prowlersfish]

The 318 marine and automotive thermostats are not the same Most of the marine ones close off the bypass when they open

marine thermostat.jpeg (34.52 KiB) Viewed 81 times

Do you have a photo of your housing?