mercury 20hp cooling

[30hpbob]

I am not sure I understand what should happen when I start my 1999 merc ob. Water does not immedeitly pee heavily out of the back of the ob, it is more of a spurt out (little water and air mix) . A few seconds after puting the motor in gear and moving the water begins peeing out with a nice heavy stream. I did notice that even while traveling fast the water flow would stop for a few seconds and then start back up with that nice flow of water peeing out. Is this normal or do I have something going on with the cooling system. Thanks for any help you may give.

 

[Maxz695]

Re: mercury 20hp cooling

Water should not stop unless the thermostat is closing off the flow but I don,t know first of all if your engine has a T stat. I would figure there should be a constant stream of water when under power and it suggests that you have something floating around in there blocking off water here and there. When was the last time you changed the waterpump impellor?

 

[30hpbob]

Re: mercury 20hp cooling

This OB does have a t stat and the water pump impeller was just replaced.

 

[Maxz695]

Re: mercury 20hp cooling

Where any fins missing on the old impellor? if so where they all found? also did you check the plate and the housing cup for wear? Someone with more knowledge of your engine will be of more help. Seems the T stat may be malfunctioning or the popit has an issue

 

[30hpbob]

Re: mercury 20hp cooling

No fins were missing,the impeller was still in pretty good shape but changed it anyway. The motor seems to run fine and the water temp that pees out is not unusally hot but I have never seen an ob that doesn't pee out water all the time when the engine is running.

 

[Delrod]

Re: mercury 20hp cooling

My 97 25hp will not pee until about 45secs after start-up. Then heavy to light pee depending on throttle. Totally normal its just the Tstat opening and closing. Been that way since new.

 

[30hpbob]

Re: mercury 20hp cooling

Thanks for the info. This 20 hp acts exactly the way yours does. About 45 seconds after it starts the water starts peeing out and while running at a higher throttle the water pees out heavey to very light. Every other ob that I have seen has the water peeing out all the time, even at an idle. Maybe I just have not payed that much attention to the cooling water. If the motor does heat up is there some kind of warning or does it just start running rough.

 

[Maxz695]

Re: mercury 20hp cooling

The thermostat is made to keep the engine at a proper tempature. If it is runing under the tempature nessecary the T stat wil temporarilly cose until running temp is achieved.and the stream will seem weak until it re opens. Keep your eye on it just in case the T stat has an issue. It should not totally stop though if it does then something is definitely wrong at that point.

 

[quicktach]

Re: mercury 20hp cooling

While you're thinking about it all, check your water inlet screens to make sure there's no restrictions. The way your engine's running doesn't sound abnormal. You may also notice a difference in flow in different water temperatures.