351 running hot

"Ok trying to help out my mom

"Ok trying to help out my mom and her Boyfriend. They have a 27ft 1973 Sea Ray with a Ford 351 model 233 engine ( not the original engine replaced in late 1990's)

It was over heating at the end of last season and they just put it away for the winter to deal with this year.

Mech at yard changed out the water pump and tubes in the out drive
Changed cap (electronic ignition)
New wires
New Plugs MR43LTS

Still overheating 180-200 at low RPM

I get involved,
I put new ex manifolds and risers
New 143 degree stat
New circulating pump
Oil change and filter.

Take it out and these are the numbers
RPM TEMP
1000 140
2000 142
2500 145
2600 160
3000 165
3500 170-175

Now for the Questions (trying to get technical answers from these 2 can be a trip LOL So I dont know what the numbers used to be.)

Are these normal Temp ranges for this engine at these RPMS ??
What Oil would be recommended for this engine???

Would the spark plugs make a difference????
The Original Spec for the motor was a MR43T

Right now there is a MR43LTS by the mech.
Looking up the spark plug numbers the one in there now has a longer reach then the original.

Would the shorter reach one make the engine run any cooler???
Should the engine run any cooler???

Thanks to all in advance."

"It should run at around the 1

"It should run at around the 145 mark with that stat, regardless of RPM and load.
sounds like insufficient water flow for some reason.
I would do a flow test to see if you are pumping enough water.
You can disconnect the water inlet hose at the t'stat housing and run it into a bucket at 1000 RPM for a few seconds to check the flow.
It should pump about 5 GPM at 1000 RPM, so it should fill a plastic bucket in under 30 seconds.
If not, you have a restriction somewhere.
Don't run it long with the hose disconnected for obvious reasons.

Rod"

"Ask the mechanic that changed

"Ask the mechanic that changed the impeller in the outdrive it it was in one piece. If not, disconnect the water inlet on the inside of the transom and backflush from the T'stat inlet hose end. Then thru the OD. Remove the small plastic water inlet diverters on the lower OD and look for debris. If the plastic pieces are worn to where the edge is basically gone, replace them since the small edge diverts water into the leg at higher RPMs. I did mine along w/a new T'stat hsg. and feel it made a small difference. My engine stays at 143 F. no matter what RPM I am running."