Im on my second new Quicksilver 140 degree thermostat and no luck. They were both stamped 140
My engine will run around 155-160 then cycle up to 180 with these, first one only up to 170. Running it without a thermostat it holds 110
I even tested them in a pan of boiling water with a thermometer and they both just start to crack in the 150's
Should the stat be fully open at 140? or just cracking at 140
Not sure what I should do now.

ttt
No one?

Going out on a limb here, are you using a crossover?

Yes I am running a crossover with a bypass

OK, now do you still have your old thermostat, or did you toss it? Did you put your old stat in, or was it there when you bought the boat?

Did your old one have 3 - 1/8" holes drilled in it??? Mine always did when I had crossovers and stats.....(540's making 675hp) NA

Just a thought!

Had the same issues ... Found the port side of the crossover hot to the touch and the starboard cold . I think the water was taking the path of least resistance ( by-passing to the exhaust).Tossed the t-stats and now working with restrictors in place of the t-stat ... getting closer ... but still not where I would like to be .Running a 11/16 th hole want to try a 9/16 th .Should know after friday.Cross-overs are a pain in the ass ... just have no other option with superchargers.

Yep, that's what I was getting at. I replaced mine with new ones and had the same oscillating temps. If he still has his old one he can take a look and check to see it it has the holes.

Do a search, there are several good threads discussing this. Check in the technical forum.

Guess thats my next step is the old thermostat back in the motor.
In the pan my old one starts to crack sooner then the new ones. Quite a difference in opening from old to new with the pan tempature in the 150 range. Old is definately open more. Maybe because the spring is more worn out, not sure.
I had the motor rebuilt so I was putting a new one in. Trying to keep the temp around 140
Last year with the old one in it would run in the 150-160 temp range.

I did have 3 holes drilled in the old one. First new one I did drill 3 smaller size holes in it.
Still not making sense watching them in a pan not opening up till way past 140