overheating

[sunup]

Ihave a 16 ft trihull w/a 140 mercruiser 140 4cyl.<br />eng.(inboard)the problem I am having is when trolling the the water temp. goes from approx. 150 to about 200 in 20-30 min.,if I bring the rpm up to 1200-1500 (in gear) the water temp. will go back to 150 in 2-3 min.,and will climb to 200 again in another 20 mins.Any ideas on curing this?

 

[DHPMARINE]

Re: overheating

Plenty of ideas here on this board!<br /><br />My first idea is replace the water pump impeller in the outdrive.Now you know water is trying to get to the engine.<br /><br />DHP<br /><br />You don't list a year,but I'll guess it's also old enough to have a plugged manifold/elbow.But do the impeller first

 

[sunup]

Re: overheating

Sorry... its a '73 model with the motor being gone through 2 seasons ago..

 

[Don S]

Re: overheating

While the engine may have been gone through 2 seasons ago, how about the exhaust elbow. May also be the heat exchanger (if you have one). If it's covered with calcium deposits it won't transfer heat properly.

 

[waterone1@aol.com]

Re: overheating

As DHP And Don said, replace impeller first, check manifold and riser. If that doesn't do it, on a real long shot ( I saw this happen once) check the plugs for any sign of water, A leaking head gasket(or cracked head) can cause engine compression to displace the water untill higher rpms where the water pump provides more pressure.It's a real long shot, but it happened to me.

 

[Chris1956]

Re: overheating

Sunup, You do not say if you use the boat in salt water. If you do, check the water intake holes on the outdrive. Mine get full of barnacles near the end of the season. This restricts the water volume and causes exactly the symptoms you describe!