Thread Tools Search this Thread
Old 02 August 2011, 07:46   #1
Country: UK - England
Length: 4m +
Join Date: Aug 2011
Posts: 1
Mariner 40hp pumps water then stops.

I have a 40hp mariner, the yamaha based one. The engine starts and runs fine but after 3-4 mins the tale tale stops and engine gets hot!
The impeller is fine and pumps plently of water while the engine is cold. The engine seems to stop pumping water when it gets hot. I'm am confused.

Any ideas? Many thanks.

Bbturbo2 is offline   Reply With Quote
Old 02 August 2011, 08:16   #2
Country: UK - England
Town: worcester
Length: no boat
Join Date: Aug 2008
Posts: 40
Could the thermostat be faulty

Could the thermostat be faulty, think these are simple and cheap to replace

ben tye is offline   Reply With Quote
Old 02 August 2011, 08:20   #3
Country: UK - Scotland
Boat name: Wildheart
Make: Humber/Delta Seasafe
Length: 5m +
Engine: Merc 60 Clamshell
MMSI: 235068449
Join Date: Apr 2007
Posts: 4,538
More likely the impeller - when cold, the water is "bypassed" to allow the block to remain (theoretically) at a constant temp. When the 'stat opens, suddenly there is a lot more volume needing filled with water, and if the pump is half gubbed......

Any idea when it was last changed?
9D280 is offline   Reply With Quote
Old 02 August 2011, 15:25   #4
RIBnet admin team
Nos4r2's Avatar
Country: UK - England
Town: The wilds of Wiltshire
Boat name: WhiteNoise/Dominator
Make: Ballistic 7.8/SR5.4
Length: 7m +
Engine: Opti 225/Yam 85
MMSI: 235090687/235055163
Join Date: Jul 2005
Posts: 12,551
Does it choke up at the same time?
Need spares,consoles,consumables,hire,training or even a new boat?

Please click HERE and HERE and support our Trade Members.

Join up as a Trade member or Supporter HERE
Nos4r2 is offline   Reply With Quote
Old 02 August 2011, 16:22   #5
Country: UK - Scotland
Boat name: No name yet
Make: Avon
Length: 4m +
Engine: Honda BF30
Join Date: Jun 2010
Posts: 153
Had a Yam 2.5hp that did exactly the same. When cold it would pump away fine, but as soon as it got hot, the flow would stop. Had the thermostat out, tested and back in 3 times, even stuck a new one in eventually to no avail. After a lot of head scratching came up with the theory that exhaust pressure in the leg was forcing the water back down through the head via the rubber bypass hose on top of the thermostat housing. Proved it by crimping the bypass hose, replaced the impellar (which looked perfect,) problem solved. Obviously it was able to create enough pressure to force the water around when cold, but as soon as the thermostat opened and there was a little exhaust pressure from the other side, flow stopped.

Not saying that yours has the same system, but certainly sounds like the same symptoms.

free is offline   Reply With Quote

Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Our Communities

Our communities encompass many different hobbies and interests, but each one is built on friendly, intelligent membership.

» More about our Communities

Automotive Communities

Our Automotive communities encompass many different makes and models. From U.S. domestics to European Saloons.

» More about our Automotive Communities

Marine Communities

Our Marine websites focus on Cruising and Sailing Vessels, including forums and the largest cruising Wiki project on the web today.

» More about our Marine Communities

Copyright 2002-2015 Social Knowledge, LLC All Rights Reserved.

All times are GMT -5. The time now is 03:58.

Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2016, vBulletin Solutions, Inc.