Haven't been as active as usual in this forum, but have been meaning to post a question about an issue we experienced towards the end of last year.

Basically, the engine at startup would not circulate water through the cooling system.  Nothing appears out of the ordinary.  I have a small inline filter installed just before the muffler that I installed at least 5 years ago.  Right now our solution to the problem is to unscrew the cap of the inline filter which somehow gets the water flowing and then we screw it back on.  I cannot find any blockages in the system.  I also tried tightening all the hose clamps (all connections are double clamped).

Anyone have any thoughts as to the culprit?  

For now I'm running the engine with the filter housing in place but without the screen inside it.  May replace with a filter with a slightly coarser mesh screen.  As long as the screen catches debris 1/4" or larger (the ID of the manifold inlet barb) thats sufficient.

Writing this from a 6 year old memory......When I first purchased my Laser, I had a rust obstruction in the metal connection point where the small rubber hose connects to the thermostat on the starboard side of the motor.  I was getting partial water flow (didn't realize that at the time) and a consistent, slow rise to overheating.  I pulled the hose off, stuck my marlin spike in the connection point and water with rust debris poured out instantly. Cant remember which end was clogged so try both.   Never had a problem again.  I don't think water was flowing freely through the thermostat, which likely led to it not opening in a timely manner.  Worth checking...Two hose clamps and a little wrestling match in a tight space if I recall correctly.

  Ron

Hi Ron yes thats a spot worth checking, as well as the water inlet pipe on starboard side below the air intake. See my May 21, 2016 post in this at:   http://laser28.org/forum/forum_posts.asp?TID=546&KW=&PID=3310&title=preventative-maintenance-tip-for-cooling-system#3310" rel="nofollow - http://laser28.org/forum/forum_posts.asp?TID=546&KW=&PID=3310&title=preventative-maintenance-tip-for-cooling-system#3310

So I quickly removed the hose from where it connects to the muffler and voila, water instantly began flowing.

Thanks for everyone's comments so far.  Most seem to suggest some sort of blockage of debris is the problem but I'm not so sure.  If it was a blockage, I don't know how simply detaching the hose from the manifold momentarily and reattaching it would be sufficient to get the water flowing.  I suspect some sort of air blockage in the line that I'm effectively "burping" from the line when I remove the hose.

I could also try unscrewing the cap in the intake strainer by the fuel tank to see if that burps the line as effectively as well.

I'm open to other suggestions.  Last time I had a water flow problem I ended up replacing all the hoses and the problem disappeared but I never figured out the cause.