Losing my coolant??

can anyone help?<br />i just put new risers on my engine(mercruiser-350.260hp)3weeks ago,and it's been running great.two days ago i took my son out for a day of fluke fishing,and on the way back in to the dock, she started running a little hot. by the time we made itin she over heated to the temp of240deg.ifilled the exchanger back up and ran the engine at a high idle for about 20minutes and everything was ok. next day went for a short cruise of about 1hour,cruising at about 3grand,at15mph.and by the time we got back, she was out of water again.there was no water in the bildge,i found no leaking hoses, and i checked my oil for water contamination,buy it was nice and clean.i'm pretty lucky there,i guess!!but now i'm at a loss.anyone unlucky enough to have had this problem and is willing to advise me,it would really be appriciated as i am stumpped.

Re: Losing my coolant??

Hi,<br /><br />Last year I had I/O merc and the same thing happened to me. It turned out that I hit a GRASS patch and the INTAKES were cloged. The boat overheated. I didn't know it at the time, but I couldn't figure out why after it cooled down, i was fine when I got back to the dock. (its because the grass drifted away while I was waiting for the engine to cool down)<br /><br />As for loosing coolant,<br /><br />My 470 merc was loosing coolant every 2-3 days.<br />It turned out to be the manifold. The coolant was leaking into the exhaust. Once I changed it, the boat was fine.<br /><br />Hope this helped,<br />Lou

Re: Losing my coolant??

Those symptoms sound like a bad riser still... if the coolant isn't in the bilge and it's not in the crankcase it's gone out the exhaust. Since it's an easy job I'd pull the risers and check for coolant in the manifolds a.s.a.p. Maybe one of the gaskets failed... did you use a sealer?

Re: Losing my coolant??

Pressure test your heat exchanger just like<br />you would on a car radiator. You will hear<br />where leak is.<br />You can buy such a tool at any auto store for<br />about $25.

Re: Losing my coolant??

2nd reply - Also pull your valve cover fill<br />caps and while running engine watch for steam<br />or discolored oil.<br />Also check all spark plugs - any electrode <br />look different than the others ?

Re: Losing my coolant??

i want to thank everyone who responded tomy cry for help.as of late yeaterday afternoon,the problem has been solved.it could have been avoided had i followed the directions that came with the new risers i installed.i'm not sure who said it but you were right the coolant was going out the exaust via.my riser gasgets.didn't bother to read instructions because i figured i knew it all, how hard can two gasgets,andrisers be?there are only 8 nutsto tighten down.but what about that loose nut on the other end of the wrench?after i found the directions and read them,i now know that after the first day or so of running the new risers, i was supposed to go back and tighten the riser nuts again.well now i know, and i'll never forget.i guess thats what happens when your in a rush to get back on the water 5 more minutes at the end of the day could have saved me two days of good fluke fishin,had i took 30 seconds to look at the directions THANKS EVERYONE again,for the feedback.i'll be watching this sight to see if i m ight be able to help out when i can.