I just bought this boat with about 200 hours on it. Impeller was replaced before i bought it and i just put a thermostat in. Normally runs between 150-180 but sometimes will hit 220! I am planning on replacing impeller and backflushing the lines. Any other suggestions?

Drill three or four 1/8" holes in the stat.

It should run between 160 and 180* all the time. It definately should not get to 220*. At 200* or so, the alarm should be going off. If its not, then its a bad gauge.

If your boat is equipped with sea strainers, have a look at them to make sure they are not clogged

Also look to see if the circ water pump is leaking or not, That would make it run hot. Do you think the warning horn is working? it should beep at key up to let you know it works some times.

The alarm is def not going off. I will check to see if it beeps with the key. The boat does not have a strainer so im afraid i sucked up something.

When people talk about overheating and can't find the cause, I wonder
why no one ever mentions cleaning out the oil cooler? In fact, cleaning
out the seawater section of the oil cooler is shown as a yearly maintenance item in my 575SCi owners manual (it's the same cooler that is used on the 500EFI). You have to take them off and rod out the water section. Get all
the little tiny stones and various clogs out.

Several times over the years I've sucked sufficient sand to clog them enough to have high temps. And these are stone sizes that can make it
past many sea strainers.

Pesky Varmint

The oil cooler is moounted on the back of the engine right? Looks like it will be fun getting it off, having to work around the sport tubes and all

you can remove the end caps ( one bolt on either end ) and use compressed air to blow out any debris in the cooler.

Sweet. Thnx every1 for the help!