HAVE 99 28 SONIC, NEW TO ME THIS YEAR. REPLACED IMPELLARS IN THE SMALL BLOCK TWINS OVER THE WINTER. I NOTICED THAT RUNNING ON THE HOSE ,ONE OF MY ENGINES HAS A MANIFOLD THAT GETS WARM WHILE THE OTHER STAYS COOL AT IDLE. i HAVE NOT HAD THIS BOAT IN THE WATER YET. IT HAS CORSA QUICK AND QUIET. I ALSO NOTICED THAT THE MANIFOLD THAT GETS WARM HAS LITTLE TO NO WATER COMING OUT THE EXHAUST FLAPPER. THE MANIFOLDS LOOK LIKE THEY WERE JUST REPLACED AND LOOK NEW ON THIS MOTOR, I SEE NEW GASKETS AT THE RISER ALSO. I DO NOT KNOW MUCH PRIOR HISTORY OF THIS BOAT. ANY IDEAS ON WHERE TO START? MY OTHER MOTOR BOTH MANIFOLDS STAY COOL AND EVEN AMOUNT OF WATER FROM FLAPPERS. THANKS FOR YOUR IMPUT.

pull the plugs out the bottom of the manifolds and see if water comes out, or sand or sediment...........

On a lot of the larger big blocks one side flows a little better due to plumbing. When the water hits the y, some of it goes one way and some goes the other. Both boats I've owned recently did this because of the plumbing it favors one side a little.

Still make sure you check for junk as mentioned. Also, sometimes guys install new gaskets cause of a leak and then do a paint job to make it look better for sale. Parts are not always new as they appear. Just check it out thoroughly. I've seen that they typically are about 20-30 degrees different from one side to the other. Port side being the hotter one. That evens out once the boat is on plane if all else is as supposed to be.

Pull the block drains and see what comes out.....I had to coat hanger mine a few times to get some sand etc. out. BTW...My boat runs hotter on the hose. Perhaps try testing in the water.

Thats a good idea. Ill check that first since its free and easy. Is this a common problem? What threw me for a loop was how the Port engines manifolds stay the same temp on the same hose while my other motor is different.

When i winterize mine at the end of the year, i get sand and junk from the plugs. If low water flow comes out of those or no water, use the coat hanger or a pick or something like stated.

Also check and make sure they used to correct gaskets? I had a guy put on the wrong ones on some crusader manifolds and had same problem

I'll put in my $.02
If the boat previously blew an impeller, the broken chunks of rubber always seem to get caught in the hoses. Disconnect the hoses, and make sure there are no rubber pieces in them.

i put new manafolds risers and impellers on my small blocks .and running on the hose one inbord manafold port side ran 20 degrees hotter than the other according to the heat gun. out bord on the starboard was the same the merc dealer said it does that on the hose but not in the water he was right both the same in the water. buy the touch it seemed hotter than 20 degrees but the gun proved differn't.

Update.......Pulled plug from bottom of manifold, it was so full of crap I could not jam a coat hanger or screw driver in there. I ran the motor with the plug pulled and only a tad bit of water. Manifold has to go. I pulled the spark plugs to see if there was any detectable damage and all looked good, nice and light tan. Compression test yielded 160-170 on cylinders 8,6,4,2. of starboard engine. I guess if there is a bright spot that is it. I keep you posted.