like mentioned..has to have a by pass with the stat, also use a merc 140 with about 4 1/8 holes drilled in it..ran the exact setup..ran 150 all the time...

You have something else going on.

For starters, I would not run the engines hard at 225* water temp. Thats pretty darn hot for a marine big block under tremendous load in a boat. Your oil temps must be very hot also if your water temps are that high.

You need a bypass hose, running from the crossover, to the thermostat housing. If you do not have this, you cannot run a thermostat. If you do have this, and the engine is still getting that hot, I would start looking for things like a lack of water flow. Such things as a clogged sea strainer, bad impeller, clogged oil cooler, collapsed hose, corroded water inlet at the transom if its a bravo, etc.

The reason your exhaust is probably steaming is its getting really hot, and the small amount of cold water they are getting is cooking in the manifolds and tails. I'd find the problem before you melt something.

There are a lot of myths about crossovers. Mine works perfect, to use a thermostat you must have the bypass hose. I used to use a standard thermostat and drilled two holes near the edge. I have more consistant temps now than with a water circulator. It also works better with a big oil cooler. This year I went with a high flow thermostat and drilled two holes in the center (looks like a cone) and they are even better now. I use a 160 degree thermostat and it runs about 160 deg at idle and about 150 running on plane. Good luck setting yours up, if you can post a pic or a link to one that would help.

x2

Thanks to everyone for your responses and help with the heating problem. My Crossover has the intake side naturally and one hose leading directly up to the matching thermostat housing. Then there are two other larger ports, one for each exhaust manifold. I was using a 160 degree thermostat with 4 small holes drilled into the outer parameters of the stat itself, this did not seem to change anything. I noticed yesterday that the water when on the Mercury pin flushette I have always used and works fine, that the water sort of surges, it'll pick up and then fall off, like a pump that looses it's prime. Therefore I am pulling the impeller today and checking everything for restrictions and impeller damage. I will post what I find later today.

Make sure u have the right thermostat gasket as well , if it has the square tip on the end your blocking water going to your risers

Problem solved!! after carefully checking everything, and replacing the impeller again, I found the cause, unbelievable but glad I found it. Restriction inside the oil cooler, some particles of plastic "not impeller material" got logged up and inside blocking the water flow. Cleaned it all out good and made damn sure it was clean, re-installed everything and now my good old 500 is running nice and very cool. About 120 degrees if that! Thanks to everyone whom responded and helped.

Glad you found the problem. Just noticed you are from Gulf Shores, went there last winter. Looked like a fun place to boat with the innercoastal waterway.