2003 Mercury 25 intermittent water flow

matt2002

Petty Officer 2nd Class
Joined
Apr 26, 2007
Messages
165
I just got a used 2003 25 HP long shaft Mercury outboard that will take a few minutes for water to start coming out of the water pump indicator.It is then intermittent and when it starts to flow again after a 45-60 second pause its very hot water coming out.This cycle constantly repeats.Water pump ? a blockage ? I have no idea when the impeller was replaced and I don't think its ever been replaced because the motor is pretty new and was in storage for a while.
Thanks in advance !
 

btorear1

Recruit
Joined
Apr 23, 2007
Messages
4
Re: 2003 Mercury 25 intermittent water flow

If it has been in storage the impeller may have dry rott. My mariner 115 did something similar. Then I replaced the impeller and it solved my problem
 

jimlad

Chief Petty Officer
Joined
Feb 4, 2007
Messages
569
Re: 2003 Mercury 25 intermittent water flow

Mat2002 Welcome To Iboats I Would Change Impeller For Piece Of Mind :)
 

matt2002

Petty Officer 2nd Class
Joined
Apr 26, 2007
Messages
165
Re: 2003 Mercury 25 intermittent water flow

Thanks for the replys.What do you think of Sierra parts as compared to Mercury parts.I'm in East Quogue , Long Island , NY , USA.
 

jimlad

Chief Petty Officer
Joined
Feb 4, 2007
Messages
569
Re: 2003 Mercury 25 intermittent water flow

IMHO i would get merc parts try dougrussell.com for parts and prices cheaper parts are not always better :)
 

matt2002

Petty Officer 2nd Class
Joined
Apr 26, 2007
Messages
165
Re: 2003 Mercury 25 intermittent water flow

Got the water pump kit from a local dealer.The old impeller was fine.I put in the new one with the other parts that came with the kit and guess what ?
Still have the same problem. Any other ideas ? Thermostat ?
 

Harker

Chief Petty Officer
Joined
Sep 21, 2003
Messages
452
Re: 2003 Mercury 25 intermittent water flow

My 98 25 Mariner does the same thing..it trickles a bit inbetween the thermostat opening and closing though. The water is pretty hot but it's not boiling hot and I can hold my hand in it. Check your head temp by seeing if you can hold your hand on it for a while when it's running.
 

10 FOOT INVADER

Petty Officer 3rd Class
Joined
Apr 29, 2007
Messages
94
Re: 2003 Mercury 25 intermittent water flow

I have a 03 mercury tracker 25 hp long shaft. When first started it will take a couple of minutes before water starts to flow out of the tale tale spout. This is normal, the thermastat is cycling. You can pull out one of the pressure tap plugs in the cylinder head and hook up a cheap temp gauge to monitor temp. On your engine at wot what rpm are you getting? The reason I ask is that since new, my engine would only hit 4200 rpm. Pushes my 10 foot invader around 21-25mph. Mercury only makes 1 prop for this motor. If I rev it out of the water it will rev way past the 4200 mark.
 

Harker

Chief Petty Officer
Joined
Sep 21, 2003
Messages
452
Re: 2003 Mercury 25 intermittent water flow

I get 26mph with mine on a 1750 modV jonboat. I have four props for mine..one is a comp prop that is 15 pitch, the stock 13 pitch,a merc 12 pitch and a 9 1/2 pitch that I use when the boat is loaded to the gills for ducks. I use the comp prop 99% of the time cause it is the smoothest running of the four. Sounds like you need to lower your pitch to get the rpms up a bit.
 

matt2002

Petty Officer 2nd Class
Joined
Apr 26, 2007
Messages
165
Re: 2003 Mercury 25 intermittent water flow

It was the thermostat.
 

bermuda8

Cadet
Joined
Jun 17, 2007
Messages
28
Re: 2003 Mercury 25 intermittent water flow

I'm having the same issue - was the thermostat clogged? Were you able to replace it yourself? if so, how hard was it to replace?

Thanks
 

jmburock

Petty Officer 2nd Class
Joined
Aug 25, 2005
Messages
174
Re: 2003 Mercury 25 intermittent water flow

The thermostats on these motors get clogged with sand pretty easily. Very easy to replace but you will need the kit with the new gasket. They also sell stainless steel replacement thermstats. That's what I plan to put in next time around as the brass ones seem to corrode. Also check your poppit valve if you have one (usually next to the thermostat). The rubber on mine deteriorated and also needed replacement.
 

bermuda8

Cadet
Joined
Jun 17, 2007
Messages
28
Re: 2003 Mercury 25 intermittent water flow

I've read a number of posts and some guys say the changing stream out of the tell tale and hot water are normal. How do I tell if it is the thermostat. I just had a new impeller put on.

thanks
 

jmburock

Petty Officer 2nd Class
Joined
Aug 25, 2005
Messages
174
Re: 2003 Mercury 25 intermittent water flow

The water from the tell-tale should be luke warm- 80F or so depending on the ocean water temp. It should never be steaming. You need to open up the thermostat panel to check if it the thermostat is clogged/ broken. You can take out the thermostat, put it in a pot of water on the stove and it should open up at the thermostat temp (mine is 143 F).
 
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