If your raw water cooled, you're almost at the point of boiling the water in the block. Water will boil at 212 degrees. It won't boil until about 250-260* in a closed system that maintains a 15-16psi. This is why our cars have 15psi radiator caps. Keeping it under psi raises the boiling point.

Either way, its too hot. What engine do you have, and what is your oil temp??

I did not replace that hose. It was in good shape on both ends. Had great flow thru strainer last year. Not so great this year.

Not sure. What is the difference, and how do you tell them apart.

Thanks for the info. I have a 500EFI. Not sure what the oil temp is...No gauge for oil temp. Where would the sender go for oil temp?

the merc marine tstat will have 3 small holes drilled in it and 140 deg if i remember correctly,a automotive tstat does not have the holes drilled in it and opens closer to 190 deg,way to hot for marine use.

I believe the difference is temp. The automotives tend to have higher opening temps (180 auto vs 140 for marine). Those are approximates bit your thermo should have a temp stamped into it.

You should have a 140* thermostat in the 500EFI. Your way to hot.

http://www.cpperformance.com/p-23819...-807252t1.aspx

Does the engines temperature remain consistant or is it flucating? My initial thoughts are if its consistantly staying at those temps, irregardless of rpm and speed, i'd guess a Tstat issue.

500EFI's use a 140* Tstat and should run 150-160* on the guage.
I would also verify your water temp guage is reading correctly.
At 200-210* you would have quite a bit of steam coming out the exhaust. The high water temp alarm would also be going off.

Have you checked the p/s & oil coolers for any blockage? It doesn't take much to limit flow which can make it run hot. I fought that one a couple of yrs ago. Randy

Thanks Guys for all the ideas. Hopefully I'm going to get some time today or tomorrow to figure this out. Supposed to head to Powell for a few days on Wednesday.

Mike, thanks for the Tstat info one of the first things I'm going to check. Wouldn't doubt finding a auto stat. Been working thorough a few screwy issues since I got this boat last year and have seen stuff like that on it already.

Griff, good call, I didn't think about it at the time but the exhaust was putting out alot of steam so temp prolly was that hot. (gauge most likely correct or at least close).

Mild Thunder, Gauge pretty steady always has been. When you are running it's about 10 degrees warmer than idling.

Randy, Definitely going to back flush the coolers and everything else I can get at.

Thanks again everybody, after reading these thoughts I bet I find a high temp auto thermostat. It has always run warm.