Overheating Yanmar HELP!

[Gary]

1987 H28.5 / Yanmar 2GM20FMotored a solid 11 hours at 2800 rpms couple months ago without incident and put it in its slip where it remained till yesterday. Motored out of the harbor about 10 minutes and then sailed about 2-3 hours. Coming back into the harbor, started the engine and within about 2-3 minutes the high temp alarm sounded. Today, I found the coolant completely full, the raw water strainer slightly dirty, but not near enough to cause problem. The impeller and its bearing was replaced last week. I also scraped quite a nice family of barnicles off the prop and shaft. Then I started the little girl and.....for the life of me.....since the discharge is below the waterline, I can't tell if water is being discharged......or blowing air and the resulting splash from the big "bubble" makes it look as if water is coming out. I held my fingers over and in the outlet and just can't tell. Don't really know how much water is suppose to come out, but it doesn't feel like any. Any help appreciated!

 

[Greg W]

Impeller

I would start with the impeller as that is the only thing which changed since your last use.Greg W

 

[patrick]

I once had a problem with

eel grass plugging the thru hull. It would block the line there and never got to the strainer. My solution was to put a tee sideways on the thru hull with a cap on the top end which I could remove and quickly clean the inlet. This of course lets some water into the boat so be prepared for that if you do this. Have a wooden plug available and pick a good place and time if you can.The side of the tee went to the valve and hose feeding into the strainer in case you are wondering about that.

 

[Steve Dion]

Start with the raw water intake and follow it.......

Gary:Start with the raw water intake (thru hull). When you open the valve and the strainer cover is off you should have a good flow of water. Next you need to check the hoses to see if they may be collapsing.Remove the hose to the pump and be sure that you are getting water flow to the pump. Then be sure to check the impeller again. I could be the wrong one or it may also be defective. Sometimes these impellers have been known to spin on the brass center (the vulcanizing has given up).If all of the water is flowing to this point, you may need to clean the heat exchanger (rod it out).Last but now least you will need to r/r the mixing elbow.Once you check out the raw water side and trace it trough also. We really don't hear many problems on the fresh water side, but it can be a probelm too. Was anything done to the antifreeze since your last voyage? If so, there can be an air lock in the fresh water cooling side of the engine too.

 

[Jeff D]

Impeller

Don't know how your boat is slipped but the exhaust is only under the water if the boat is moving. If you can stand a few slips over you may be able to see the exhaust. The water coming out should feel warm. If there is no water the exhaust will sound kind of tinny. My first thought is that the impeller was put in backwards. The paddles need to be facing the right direction.Checking to see if there is a clog in your valve can be done by putting a clear cheap hose on the valve long enough to rise above the waterline. Open the valve and check for water flow.Hope there is a simple solution.