Noob with overheating problem

I am a first time inboard owner (1998 Air Tique) and i am having an overheating problem with the 351. Bought the boat last fall after a test ride. Helped the PO to winterize it and put in storage. PO said he put in a new impeller and thermostat. Took it out last week and launched. Idled at the dock while I parked the truck and then stated across the lake at moderate speed. Warning light came on and I shut down immediately. Limped back and retreved. Observations: 1. I could see some air bubbles going through the strainer; 2. After shutdown hose to starboard side riser was cool, the hose to port very hot. Brought it home and put it on the bucket and it ran hot at idle. 3. Bucket easily kept up with water intake.
Can you guys suggest a sequence for trouble shooting I should follow in trying to diagnose this problem. I am excited to finally own an inboard after many years of outboards. Thanks for your help.

Perhaps the PO reversed the direction of the RWP when he changed the impeller? Oftentimes people will remove the RWP to change the impeller and then forget how it was originally orientated and end up installing it backwards. Could the PO have installed the T-stat upside down?

Jim,
After the new impeller was installed, was the engine ever run without water hooked up? The rubber impeller in the RWP is water lubricated.

I am not a motor head, so I always state with some pride that I've had my 40 year old boat for 12 years and its never been to the shop. But a couple weeks ago it quit and I went through all the diagnostics and started throwing parts at it (hate to do that, but most were with some reason) Still couldn't get it. There are two boat shops near me, neither of which I am inclined to go to. A friend, working on it with me told me his auto shop was good, maybe they could take a look. They, a little bit reluctantly, agreed, so off it went. They were told its a boat, don't run it dry, don't run it in gear, reverse rotation, blah, blah, blah.   My cooling hose adaptor hose was attached and ready to go. So they got it going....(I don't want to get into it....I should have been able to do it) and we picked it up. Just on a hunch I thought, they probably thought they could run it a while without cooling, it wont hurt it, not thinking or knowing about the raw water pump. So before dropping it in the lake, I did a bucket run. Very little water coming out, next to no suction. So I open up the pump. Glad I had a spare handy.

Come on Larry, what did the shop find wrong?

quinner wrote: 8122pbrainard wrote: Come on Larry, what did the shop find wrong? Dipstick rotation was 180 deg off

Larry's or the engine's?

Thermostat opens at about 165 degrees. Installation question. Does the cone end go down into housing and round puck-like end face up or vice-versa.

Why not just test it in a pot of water with a candy or roasting thermometer.
A thermostat will not cause one manifold to go smoke and the other ok, you have a water flow issue.

Pics of the boat?

Thanks Keno. PO had it in upside down.

Hard to find a picture so I took one It's sideways, but you should get the point.