check the condition of your hoses to make sure they are not collapsing.....my fisrt thought was that its mounted too high if you say they are not filling up all the way. If they are mounted too high and you keep getting air in the system i can see how this would be happening because the engine would be creating steam pockets every so often.

One other thing (and maybe i read this wrong) but is this going on while you are in the water or running it on a hose? If running on a hose...i wouldnt worry about it till you get out on the lake and this happens.....most if not all garden hoses dont have enough capcity to supply the engine with enough water. Drilling the holes will help get rid of the steam pockets too.

All my hoses are that heavy duty hose I cant even smash it with visegrips. Yes , it is only happening on the trailer with earmuffs, but why would one of my motors not do it and the other has temp to rise and fall? I will be on the river this weekend for the real test. On my thermostat housing my gasket that goes around the top plate has the 1/4 inch hole bypass in it so that is the same as drilling a hole in the thermostat (right)?
My seastrainers are below the water line.

Could you guys give me a bit more information on drilling holes in the thermostat. What do they do, how large and how many? Also, where are they and why don't they come that way OEM?

Thanks,
Bruce...

excursion, have you checked the thermostat itself? maybe its going bad? maybe the wrong one is in there? Not sure about what teh 1/4" hole you are talking about on the by-pass offhand. I would take it to the lake and do a fullon test there before starting to rip anything appart.

Outlawntexas, I have heard different things about drilling holes.....the most common reply to drilling holes i have heard you drill 3 holes all spaced evenly from each other and each one is a 1/8" drill bit. I personaly have done only two 1/8" holes and it worked out good for me in the past. :)

Wally,
What are they doing for you? :confused:

I had a similar problem with my boat. It turns out the gasket on the strainer wasn't sealing right, and it was sucking air and the temp guage would bounce around like it is on yours.

I would check all hoses and connections and any place that air can enter into the system, including the flushing connection.

i was getting the temp spike like whats going on here but while i was running....i never did find out what the real cause was. (my theory was the first builder put the wrong head gaskets on and it didnt have the right coolant flow through the engine) I drilled the two holes and it solved all the spiking problems for me anyway........ran at a steady 150 no matter how i was driving it :)

You might want to check the hose on the outside of the boat from the bellhousing to the transom. It should be tucked in the groove wrapping around the bellows area. I have heard of the hose getting pushed up and out of the groove and when you turn to port or trim out the hose kinks slightly. When the seapump starts pulling water it can collapse the hose. It's a bigger problem with standoff boxes because the hose is more susceptible to water pushing it up after big air and tailing in.

Gary