overheating very quikly

[mercrude]

1983 mercruiser 485 (6066778) 185 hp IO<br />this boat had a carborater problem I fixed that took boat on lake and within five minutes the temp guage went to 240 f shut off motor let cool took it home changed thermastat, bellow tube(had a hole in it ) and rebuilt impeller with kit started boat with muffs let idle temp went up to 220 f antifreeze boiling out from under resivoir cap please help

 

[hondon]

Re: overheating very quikly

When you did the carb did you think it would be ok to fire this thing off for a minute without water to the lower? How did that impeller look when you changed it,and where is the rest of it?

 

[oldboat1]

Re: overheating very quikly

The motor would also have a water circulating pump on the front if it's fresh-water cooled, as well as the impeller in the I/O unit (latter pumps in raw water to cool the exhaust manifolds and risers, or just the risers -- depending on the cooling system you have.) Both have to be working. Is the thermostat correctly installed and working?<br /><br />another thought -- possible you have an air bubble in the closed system. You might try operating the engine without the cap on the heat exchanger. If after a bit you see some water movement going on, you will know that the thermostat opened and that the water circulating pump is working -- in addition to (hopefully) getting the air out.

 

[mercrude]

Re: overheating very quikly

after I put the carb on I hooked up muffs and ran it in drivewaysemmed to be ok<br />when I changed the impeller in lower unit the impeller was very trashed it was fried rebuilt impeller pump cleaned out what pieces I seen

 

[mercrude]

Re: overheating very quikly

this unit has a closed cooling system, the thermastat would only go in one way,

 

[oldboat1]

Re: overheating very quikly

could be pieces of the old impeller blocking water coming up from the impeller, as indicated in one of the posts above, or could be the new impeller is spinning on the shaft (shaft key not engaged). It's possible too that there is an air leak in the impeller housing, possibly at the wear plate. You may have to break it down again, check it and reassemble if you can't confirm that the impeller is pumping water up from the lower unit.

 

[mercrude]

Re: overheating very quikly

when I start the motor with muffs on I am getting water out of proppeller and jet holes nice and strong unlike before I put new impeller in

 

[bjenkinsnc]

Re: overheating very quikly

Does heat exchanger get warm to touch when running? You can also feel the hose going into heat exchanger from manifold to see if it is pressurized, indicating that engine coolant is flowing into heat exchanger. Maybe the new thermostat is stuck open, not allowing engine coolant to flow thru exchanger. Possibly a new bad thermostat.

 

[mercrude]

Re: overheating very quikly

I started boat thismorning felt heat exchanger warm but not hot I felt the exhaust manifold it was very hot only ran motor for about four minuites should the exhaust manifold get hot?

 

[bjenkinsnc]

Re: overheating very quikly

I don't think so, if system is performing properly. Did you use a mercruiser t-stat?<br />It really sounds like t-stat not working or engine coolant pump problem. Again, does engine inlet on heat exchanger feel pressirized?

 

[crazy charlie]

Re: overheating very quikly

How old are the manifolds/risers.Open one of the small brass drains on the riser while running to check your flow.It should shoot out pretty far if the flow is good. charlie