cooling issues on my 3.0...

chucks440

Cadet
Joined
Jun 7, 2011
Messages
22
Took the boat out today ( 1989 Maxum..3.0 Mercruiser w,Alpha ) and I ran into a overheating issue and after doing a little searching on the forums here I still have a question or 2. First,the boat had been out of the water for 2 yrs before putting it in this week.I had replaced the impeller prior to the last time the boat was run.When I launched it last week,it ran well with the temp hanging right at 160. Today it held right at 160 until the end of the day when I noticed it slowly rising over 200. Going faster or slower did seem to affect it briefly,but I still ended up shutting off a few times to cool it down.Temp ended up between 180-200 as I babied it back to the slip. I,m assuming I,m going to be replacing the impeller and the thermostat,but is there anything else to check also? and as far as the impeller...if I took the hose and thermostat housing off,fired the engine up,how much water should I see blowing out of there if the impeller is good? Is that a good way to test the impeller with the boat in the water? If the impeller is good and I dont have to take the boat out of the water,that would be a plus. But if not, I would rather have all the parts ahead of time and get this fixed in one shot. Thanks ahead of time!
ps...its an open cooling system and the boat had never been in salt water
 

dubs283

Vice Admiral
Joined
Jul 27, 2005
Messages
5,343
Re: cooling issues on my 3.0...

no need to pull the t-stat housing to test water pump output

simply remove the supply hose from the housing and at idle you should see a solid steady stream/flow of water - no air bubbles, just good water flow

there is a spec for number of gallons/minute at spec RPM for each engine in the manual

my guess is sitting for two years the impeller has a set to it and you are experiencing poor flow at all rpms
 

cr2k

Captain
Joined
Mar 19, 2009
Messages
3,730
Re: cooling issues on my 3.0...

++ on impeller.

They need to be replaced every 2 years running or sitting makes no difference.
 

chucks440

Cadet
Joined
Jun 7, 2011
Messages
22
Re: cooling issues on my 3.0...

Dubs,Cr...thank you for the replies. I had a feeling that the impeller was going to need to be replaced,but I figured its best to ask anyways! Thanks again!
 
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