Overheating a little

C

chazaroo

New Member
Dec 4, 2006
415
Florida
Boat Info
1996 Sundancer 250
Engines
single 5.7 w Bravo III
Got the boat back after replacing manifolds and risers. Tried WOT today for about a mile and temp went to about 190. Dropped sped to 5 knots and temp dropped to 170. I'm thinking the 190 is too high and I noticed a white powdery substance around the thermostat housing and I'm wondering if this is the problem. Anybody want to hazzard a guess? Motor is 5.7, fresh water cooled.
 
Was the powder there before the run? All else aside, I'm guessing that your thermostat needs to be replaced. It may be old, crusty, and not opening all of the way to allow adequate water flow at WOT.

Another guess would be that the heat exchanger needs to be taken out and cleaned in acid like a radiator.
 
Hampton,
Not sure if the powder was there before. I don't think so. It looks like the thermostat is the cheap solution. And it looks like something even I could do. As for the heat exchanger, is that something I should have the marina do?
 
chazaroo said:
Hampton,
Not sure if the powder was there before. I don't think so. It looks like the thermostat is the cheap solution. And it looks like something even I could do. As for the heat exchanger, is that something I should have the marina do?
Click to expand...

You can definately do the thermostat. As for the heat exchanger, I haven't done one, but I plan to do mine at some point down the road. In your boat, it may be pretty tight to get at. I'm guessing that there are four hoses and some mounting brackets. You might get expert advice here about cleaning it, but I think they use muriatic acid which I just bought at my pool store for $3/gallon. It's vicious stuff, but I'm sure with some caution and good advice you can do the whole job yourself.
 
Check the raw water pump. At high speeds the pump doesn't flow enough water if the fins are broken.

Doug
 
Hampton,
Thanks for the input. Think I'll do thee thermostat and if that doesn't solve the problem, I'll have the marina do the heat exchanger. BTW, any idea how often the heat eschanger should be cleaned?

Doug,
Might be fins but that was done 2 months ago.
 
On my last boat, I had the same problem and it was an impeller...


Barry
 
The thermo is a good start, but what the other guys are saying about the impeller is true as well. The easiest, and by far the cheapest fix would be the thermostat. After that, I'd probably go to the impeller. They need to be replaced periodically anyway, at least every three years. Heat exchangers are extremely variable based on environment and useage. If it's never been cleaned, it probably needs it, but if your impeller hasn't been kept up in the last couple of years, it definately needs it.
 
Impeller was done at the last annual service. That was just before Thanksgiving so it shouldn't be the problem. No idea when or if the thermostat was ever done so that's the first check. Then I guess the impeller (just to be safe) and then on to the heat exchanger...no idea if that has ever been done. Had a diver over today to do the bottom and he said there was some growth in the raw water intake but not enough to cause a problem and he removed it. I'm hoping the thermostat solves my problem. Always nice to hope for the cheap fix.
 
Well, if you've just done the impeller, I have to waffle back to the heat exchanger, after the thermo. If there's any chance you've toasted the impeller, I'd waffle back to that. On account of it only occuring at WOT, and there was "some" growth, I just try it again since the growth has been removed.
 
Hate to say the impeller again, but just because it was replaced a short time ago, if anything was snagged-a plastic bag, let alone hit something or got grounded and kicked up some sand etc, the impeller will be the first to go...When I had my 25' I had just replaced the impeller with normal service, and a few weeks later the prop got caught by a grocery store plastic bag, and the engine overheated slightly. It would run fine going slow cruising the intracoastal; and then even for a little while opening it up running out to sea, but after a little while it would overheat and the engine would go into slow mode. I could shut down for a while and do the same thing over. When I pulled it out, the impeller blades were in pieces.

Barry
 
What's cheaper to have checked the impeller or the heat exchanger? I figure start with the cheapest possibility and work my way up.
 
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