96 MC Prostar 190 overheating?

I was out this weekend and my temperature guage was readin 160-170, when pullin a boarder, but then drop to 150-160 when I came to idle. If I pulled out the shifter, and ran the motor to 2k RPM it quickly dropped to 140. It had an air leak in one of the hoses, but I replaced the hose. Thought that was the problem. Any ideas???

Adam,
the best thing to do is to replace your water impeller on your water pump. It's like $35, you probably have chewed up edges on it and don't even know it. I have a filter on my intake and it still gets chewed up

I've pulled off the cover of the water impeller, and it looked fine. I never pulled the impeller all the way out. Could it look fine and still be chewed up on the opposite side?

I just had an impeller go on my MC Saturday and yes it could look OK and still have chunks out of it - go ahead and pull it. Also, have you checked the hose to the transmission cooler? The screen can get clogged and restrict water flow.

Todd

How long since you replaced the impeller? Should do it every year, sounds like yours is worn and not pulling quite enough water. If you have the LT-1 engine, those Aluminum heads are about a $2000 repair if you overheat and warp one.
Make sure the oil cooler screen is clear, replace the impeller, and repl both thermostats if they are more than a couple years old. Less than $50 in parts.
You should be running at 160 deg, except at startup w/ hot engine, it'll go up to 200 or so (heat soak) then drop right down when water starts pumping through.

Mine doesn't run near that hot?? It normally ran around 140. At 180 is when the motor runs rough. I would think that if my motor go to 200 it would sieze.

Is it a TBI 350, or LT-1 350? TBI motor (truck motor) had iron block and heads, you'd have to be over 230 before worrying about the tmep ruining something (unless you're running at that temp for a long time).
LT-1 engine has aluminum heads and over 200 is dangerous. The LT-1 has a retard mode that kicks in around 180 (I think) and limits the engine to under 2000 rpms. Thats probably the running rough you feel when the motor is hotter than normal.
If you're normally at 140 operating temp, then you have the wrong top t stat.
When I said 200, that's the static temp of the hot engine sitting without cooling water circulating. That goes down immediately upon starting back up.
Check the Mastercraft website, www.tmcowners.com there is alot of info there and also on the old MC Forum (can access from the main MC Boat website under classifieds.

i replaced the impeller as well as cleaned all screens, hoses ect, and no change. I then replace the top thermostat, and it was right back down to 140-150. I put a 140 in there I guess i shoudl have put a 160. I know on e of them is a 140
I'm guessing its the other one. Where is that one located?

The upper t stat should be 160 and the bottom one 140 if you have the LT-1. Bottom one is located in the front of the engine behind the triangular cover, if memory serves. If you have the LT-1, the top stat needs to have a bleeder hole drilled in it (prevents cavitation and overheating or something like that on the reverse cooling LT-1s). Hole is a specific size and location, so get a stat from a dealer or get the correct info to drill it.

where is the upper t-stat located? I thought the upper t-stat was the one on top of the motor in the fron under the trianglular piece w/ the 4 hoses running out of it. That is the one I replaced. What type of caviation will you have if there is no bleeder hole? Will you be able to feel that? Mine did not have that hole when i pulled it out

The top stat is right on top of the intake manifold, where it is on a car. Take the air filter off, and its right under there. That one s/b 160 deg w/ the hole in it. Bottom on is behind the triangle plate. 140 deg, no hole. I don't think that you could hear the cavitation and I believe the boat will run ok w/o the update, but Indmar updated it for to help w/ overheating, more specifically, hot spots in the aluminum heads before the thermostats opened.
Remember, this info is for the LT-1 corvette motor. I still don't know if you have that or the standard TBI 350. That config may be different and I'm not familiar w/ them.
If you're still having problems, post your prob on www.tmcowners.com and plenty of people will help you out.