Carver Owners Forum

I have twin 454s and they run fine at low RPMs. However, if I try to open the boat up at all, the starboard engine quickly gets too hot. 30 seconds or so and it is already at 200 degrees. I can back it back down and it will slowly cool off and be good to go again. I'm thinking it could be a thermostat or bad water pump. What do y'all think?

Sea water pump maybe - do you get good flow through the exhaust? Lots of steam or just water? If you get good flow out the exhaust and not a lot of steam, check the heat exchanger. The sea water pump is likely the culprit if the flow is limited and you are getting steam out the exhaust. I'm going to assume you have already checked the strainers to be sure they are not clogged...

It's not unusual to find gunk clogging the heat exchanger and that will limit flow for the cooling water and cause temps to rise with higher RPM. Sometimes the rubber gaskets on the heat exchanger also deform and can block cooling water flow. Thermostats don't fail very often, but when they do, they usually stick - so you will get cool temps sometimes and hotter temps at other times.

Hope this helps - good luck!

Hi there....could be quite a few things....this just happen??......if not check the easy stuff first, restricted water flow to and from engine ( hoses etc), pump impeller, is it close cooled (has heat exchanger) then need to check that as well as the thermostat.....after that engine circulation pump and engine timing ( too much total will heat an engine up)....dont know if this helps or not but its a start....hope you find it...looks like someone beat me to it but I will add this anyway...

Agreed there are several things that can cause this. Some more product info would help; engine make, closed or raw water cooled. I'm thinking Mercs but don't want to assume.

I would first physically confirm that there is indeed and actual overheat, don't assume that the gauge or sender are working properly. After you confirm there is indeed a cooling issue, my next thought would be when the last time the impellers were changed. If you don't know that, it's time to change them. While most folks get years of service out of them, chances of failures due to fatigue and wear and tear increase after the second year hence Merc's recommendation to replace every two years to minimize the chance of failure at the worst possible time.

All the above suggestions are good ones and possible causes. If it's a Crusader, the U oil coolers are known for causing this if not kept clear.

If it's an impeller failure and you find that parts of the impeller are missing, you must back-flush the system to get rid of the pieces that will be blocking cooling passages. Typically the oil coolers and heat exchangers will trap them and if not removed will continue to haunt you. When you back-flush and recover the missing pieces, put them back together on the related impeller like a puzzle, this will indicate whether you've gotten them all or not.

If closed cooling, what condition is the coolant in, and is it topped up where it should be? Several other things to consider but all the above are a good start.

Keep us posted.