outside water temperature

[oldboat1]

I'm curious about the effect of water temperatures on cooling systems. I boat in the Chesapeake and the Magothy River (a tributary), and the water temperature has been in the low 80s much of the summer, which is pretty normal. My old cruiser has a closed system, but when the incoming raw water is 80 degrees, I have to believe there is some diminished ability to transfer engine heat. With the air temp in the 80s and the water temp in the 80s, I run at about 180 degrees (20 min or so at 2500-3000 rpms). All things being equal -- a pretty big assumption with an old engine -- I think air and water temps are probably pushing engine temps up a little higher than I would like (maybe 10 to 15 degrees?). Anybody have some thoughts on this?

 

[crazy charlie]

Re: outside water temperature

There is no doubt that water temps and air temps will have an effect on engine temps,though 80 degrees should not make too much difference.If you are concerned you can look into an oil cooler.You can also consider a larger oil pan ,but that may be more of a job than it is worth. charlie

 

[flashback]

Re: outside water temperature

Oldboat1, 180 degrees on a closed system in salt is not a problem. You are correct in thinking that the temperature transfer is diminished, but all that should cause is the thermostat staying open a longer period of time in order to compensate, of course you will see a difference in engine temp on the gage because you have hotter water moving thru the engine.

 

[Bondo]

Re: outside water temperature

The Best my boat has Ever run was in 35* water....

 

[oldboat1]

Re: outside water temperature

Thanks to all -- interesting stuff. I'll be looking to see if it runs a little cooler this fall. I'm recalling that it was running cooler this spring, but I messed with the timing and replaced plugs since then, so I can't really say the water temp is the factor. I'll just wait and see -- keep settings at specs and wait for the water to cool down a little.<br /><br />I have the original Chris Craft owners manual ('77 Chevy 305 2bbl), and it refers to operating temperatures between 143 and 165 degrees -- thing is, it goes on in the next paragraph to describe the standard raw water cooling system, so that is the context. I would have been more comfortable if there was an asterisk saying temps are normally higher with the optional fresh-water cooling system (which is detailed later on in the manual, but without reference to operating temps.) I've also found that the engine temp remains a little lower (170-175)if I keep the rpms at about 1500 during my little fun runs, even with the 80 degree water temperatures. <br /><br />I'm losing a little coolant out the exhaust, I think (sometimes get a little whiff of antifreeze, and usually lose about a cup after running for maybe an hour or a little less). I assume it's getting into one or both of the risers, and I should probably fix that -- no other problems I'm aware of. I sort of hate to take off the risers because I might break a bolt or something, and I'll create more problems that way than I have now. I'm sure open to advice on that repair (potential leakage into risers), if anybody has suggestions. Maybe there is an easy fix.

 

[boat doc]

Re: outside water temperature

oldboat1<br /><br />a few other things to think about are a sticky thermostat, or a replaced thermostat. I notice a lot of people go down to the local auto store and buy thermostats for their boats (not a problem in closed cooling, if you get the right temp) Automobiles run hotter than boats, especially e.f.i. autos 200 plus. Another thing is an impeller getting weak, possably blocked water passages, just not getting enough water into your heat exchanger. Now the leak, usually what I see are heat echangers leaks. I do not know about your particular ablication, but most heat exchangers have a cap at each end. whith a cap comes a gasket, with a gaskets comes leaks. Also chevy circulating pumps a notorious for lasting about a year, and then leaking, not so much on closed cooling though.<br /><br />By the way, our test lake gets into the mid 90's in the heat of the day this time of year, and does not have that much of an effect on engine temp. maybe 5 degrees.

 

[oldboat1]

Re: outside water temperature

Boat Doc --<br /><br />I've had the boat a couple of years, and haven't replaced the t.stat or pumps -- so could be issues. The t.stat seems to open at about 145 at startup (i.e., rises to that temp and holds). If I let it idle it might rise to 150, but no higher. I'm thinking the thermostat probably begins to open at 140 and is fully open at 160(?), in keeping with the range the manual describes.<br /><br />I did in fact have a couple of leaks earlier this year in the exchanger, and had the unit reworked (incl pressure testing). I was assured that the tubing was also tested, but it could be leaking there and I wouldn't know it. (could be where the antifreeze leaks into the raw water, maybe?) So far, I haven't located any external leaks anywhere in the system.<br /><br />interesting note on your test lake. If you don't see an effect there, I shouldn't get one here. It could be, though, that testing doesn't include running for a half hour or so, and that the effect of the cooling water temp becomes more obvious after engine temp peaks and I continue running(?) <br /><br />If it were an outboard, I would probably drop the lower unit, replace the impeller, and clean out all the water jackets. I have never done that kind of thing with an inboard, and I think maybe I'm a little afraid of it.