Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 16-11-2015, 11:31   #16
Senior Cruiser
 
colemj's Avatar

Cruisers Forum Supporter

Join Date: Oct 2005
Location: Presently on US East Coast
Boat: Manta 40 "Reach"
Posts: 10,049
Images: 12
Re: Fresh Water Pump Overheating on Yanmar 3HM35

Quote:
Originally Posted by a64pilot View Post
If it's the bypass clogged, removing the thermostat will eliminate the overheat and will be a trouble shooting step.
Not on all engines. Some will block circulation completely if the thermostat is removed (ours is this way).

I don't know about the OP's Yanmar.

Mark
__________________

__________________
www.svreach.com

You do not need a parachute to skydive. You only need a parachute to skydive twice.
colemj is offline   Reply With Quote
Old 16-11-2015, 11:52   #17
Moderator
 
a64pilot's Avatar

Cruisers Forum Supporter

Join Date: Oct 2013
Location: Albany Ga.
Boat: Island Packet 38
Posts: 17,056
Re: Fresh Water Pump Overheating on Yanmar 3HM35

Not arguing, but failing to understand, how does removing the thermostat, prevent flow?

My Miata would do what he is describing, and I drilled about a #30 hole in the flange thinking somehow it was air getting trapped and the pump cavitating causing the problem.
The hole solved the problem but later I found what looked like a piece of metal from a drilled hole blocking the bypass and figured it out.
Of course what was going on was since there was no water bypassing the thermostat, it never "saw" hot water and didn't open, you have to have some flow for the thermostat to get hot and open up, hence the bypass.
__________________

__________________
a64pilot is offline   Reply With Quote
Old 16-11-2015, 12:23   #18
Senior Cruiser
 
colemj's Avatar

Cruisers Forum Supporter

Join Date: Oct 2005
Location: Presently on US East Coast
Boat: Manta 40 "Reach"
Posts: 10,049
Images: 12
Re: Fresh Water Pump Overheating on Yanmar 3HM35

In some engine designs, the opening thermostat blocks the bypass channel (which is behind the thermostat). Removing the thermostat leaves the bypass as the route of least resistance for coolant circulation and little coolant circulates through the engine.

Mark
__________________
www.svreach.com

You do not need a parachute to skydive. You only need a parachute to skydive twice.
colemj is offline   Reply With Quote
Old 16-11-2015, 16:51   #19
Registered User
 
LeaseOnLife's Avatar

Join Date: Apr 2008
Location: out cruising again
Boat: Sailboat
Posts: 1,046
Re: Fresh Water Pump Overheating on Yanmar 3HM35

Mark is correct and some (all?) Yanmars use this style:

While opening the circuit through the heat exchanger (top portion), the short circuit (bypass) is being choked (bottom plunger).

Dirk

Edit: removing the thermostat will cause most of the flow take the bypass, the flow through the heat exchanger has higher resistance
Attached Thumbnails
Click image for larger version

Name:	121750-49800%20-500x500.JPG
Views:	53
Size:	41.1 KB
ID:	113187  
__________________
LeaseOnLife is offline   Reply With Quote
Old 16-11-2015, 19:04   #20
Senior Cruiser
 
Ocean Girl's Avatar

Cruisers Forum Supporter

Join Date: Jun 2009
Location: In transit ( Texas to wherever the wind blows us)
Boat: Pacific Seacraft a Crealock 34
Posts: 4,115
Images: 2
Re: Fresh Water Pump Overheating on Yanmar 3HM35

So a blocked flow of coolant will cause the pump to cavitate, and this will cause excess heat on the pump bearings? This sounds consistent with what I am seeing.
__________________
Mrs. Rain Dog~Ocean Girl
https://raindogps34.wordpress.com
Ocean Girl is offline   Reply With Quote
Old 16-11-2015, 21:36   #21
Registered User

Join Date: Oct 2009
Location: australia
Posts: 467
Re: Fresh Water Pump Overheating on Yanmar 3HM35

Your motor's coolant circulation system is what is known as a Pump assisted thermo cycle type, the pump used is a low efficiency centrifugal one not a Positive displacement one, thus the loads are not Great. If the pump body is full of coolant it should be able to run many minutes possibly an hour or so without generating the kind of temps you have indicated.
Have a look at post # 4 it has been asked for a reason that may help find the trouble.
__________________
shakey doug is online now   Reply With Quote
Old 18-11-2015, 09:12   #22
Registered User
 
RainDog's Avatar

Join Date: Jun 2009
Location: Varies
Boat: Pacific Seacraft 34 #142
Posts: 1,183
Re: Fresh Water Pump Overheating on Yanmar 3HM35

Sorry for the delay in responding. Indeed the problem was cavitation in the pump. Bleeding the coolant while the engine was running fixed the issue. The mechanic said these Yanmar are notoriously difficult to bleed.
RainDog is offline   Reply With Quote
Old 18-11-2015, 09:34   #23
Moderator
 
a64pilot's Avatar

Cruisers Forum Supporter

Join Date: Oct 2013
Location: Albany Ga.
Boat: Island Packet 38
Posts: 17,056
Re: Fresh Water Pump Overheating on Yanmar 3HM35

Quote:
Originally Posted by RainDog View Post
Sorry for the delay in responding. Indeed the problem was cavitation in the pump. Bleeding the coolant while the engine was running fixed the issue. The mechanic said these Yanmar are notoriously difficult to bleed.
So you had an air bubble, that became a real problem when engines started "reverse flow cooling"
The history is back in the day engines were cooled by thermal siphon, cool water in the bottom, heat rises out to the top and into the radiator, only flow was due to thermal siphon. Power increased and a pump was added to assist the thermal siphon. I'm pretty sure at least all our older boat motors are pump assisted thermal siphon.
Then some racer who understood things and knew the head was the hottest part of the motor, that it should get the coolest water started pumping the coolant in reverse, I believe the Chevy LT1 motor was the first mass produced motor to do so. Problems soon arose as these reverse flow motors had to be bled of trapped air when the coolant was changed, and old mechanics didn't know to do that.

I'm going out on a limb here, but I'd bet it's the water heater hose that is the cause of the trapped air in our boat motors, and we have to bleed our cooling systems just like they were reverse flow.
How did you bleed it? Reverse flow engines usually have a bleeder screw on the thermostat neck that makes bleeding easy
__________________
a64pilot is offline   Reply With Quote
Old 18-11-2015, 11:39   #24
Registered User

Join Date: May 2012
Posts: 466
Re: Fresh Water Pump Overheating on Yanmar 3HM35

One thing I would like to add here is if you have a water heater that is heated by the engine, the problem ( air lock ) will be much worse! Any time the coolant side of the cooling system is drained you must be very careful to remove all the air! the amount of air it takes is very small I might add, just enough to keep the sensing part of the thermostat from getting coolant on it. If a bleeder has not been installed at the high point in the system, my method of removing the air is to fill the system with coolant remove the highest hose to the water heater put a funnel in the hose ,put a short piece of hose on the outlet and route it to a container, hold funnel above highest part of the cooling system pour coolant in until coolant comes out the outlet hose, that coolant can then be poured into funnel continue doing this until no air is coming out ,connect the hose start engine rev several times and monitor engine temp carefully REMEMBER if the air lock is big enough the temp sensor will not show an overheat even if it is overheating!!! If problem persists try again. Note. yanmars are the worst
__________________
sartorst is offline   Reply With Quote
Old 18-11-2015, 11:49   #25
Moderator
 
a64pilot's Avatar

Cruisers Forum Supporter

Join Date: Oct 2013
Location: Albany Ga.
Boat: Island Packet 38
Posts: 17,056
Re: Fresh Water Pump Overheating on Yanmar 3HM35

You guys have about talked me into tapping and installing one of these in the thermostat neck
List: Coolant Bleeder Screw - 2005 Chevrolet Impala | O'Reilly Auto Parts
__________________
a64pilot is offline   Reply With Quote
Old 18-11-2015, 13:01   #26
Registered User
 
RainDog's Avatar

Join Date: Jun 2009
Location: Varies
Boat: Pacific Seacraft 34 #142
Posts: 1,183
Re: Fresh Water Pump Overheating on Yanmar 3HM35

Quote:
Originally Posted by a64pilot View Post
How did you bleed it? Reverse flow engines usually have a bleeder screw on the thermostat neck that makes bleeding easy
Bled it at the water heater port.
RainDog is offline   Reply With Quote
Old 18-11-2015, 15:18   #27
Registered User

Join Date: May 2012
Posts: 466
Re: Fresh Water Pump Overheating on Yanmar 3HM35

Quote:
Originally Posted by a64pilot View Post
You guys have about talked me into tapping and installing one of these in the thermostat neck
List: Coolant Bleeder Screw - 2005 Chevrolet Impala | O'Reilly Auto Parts
The problem with that is that the air lock is on the other side of the thermostat
__________________
sartorst is offline   Reply With Quote
Old 18-11-2015, 15:28   #28
Registered User

Join Date: May 2012
Posts: 466
Re: Fresh Water Pump Overheating on Yanmar 3HM35

https://encrypted-tbn3.gstatic.com/i...R75denAnmqVndO
something like this in the heater hose going to the water heater at a high point
__________________
sartorst is offline   Reply With Quote
Old 18-11-2015, 15:52   #29
Senior Cruiser

Cruisers Forum Supporter

Join Date: May 2013
Location: Oregon to Alaska
Boat: Wheeler Shipyard 83' ex USCG
Posts: 1,708
Re: Fresh Water Pump Overheating on Yanmar 3HM35

I'm 67 and have been around marine engines since I was little. Pop was a chief engineer. The tiny hole in the thermostat has worked for me since my dad taught me. A 1/16" is plenty.
Many small engines don't have a bypass circuit or they have one that still allows an air pocket to form, keeping rising hot coolant from touching the thermostat and transferring the heat needed to open it.
The tiny hole is enough for air to pass without slowing the heating process of a cold engine. I use it on almost all marine and auto engines. With the upper and lower disks the hole goes in the big one. My diesel truck has a similar thermostat. Sometimes thermostats come with the hole. For me, looking for or drilling the hole is automatic. Having the hole can't hurt.
__________________

__________________
Lepke is offline   Reply With Quote
Reply

Tags
heating, overheating, water, yanmar

Thread Tools
Display Modes Rate This Thread
Rate This Thread:

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


Similar Threads
Thread Thread Starter Forum Replies Last Post
Yanmar 3HM35 Bris4fun Engines and Propulsion Systems 17 17-08-2015 12:28
Yanmar 3HM35 F exhaust manifold wanted Allan M Engines and Propulsion Systems 2 15-05-2015 20:36
Yanmar 3HM35 Ocean Girl Engines and Propulsion Systems 33 29-12-2014 20:09
3HM35 Yanmar stalls under load. What next? Canibul Engines and Propulsion Systems 16 05-03-2014 11:46
Raw Water Pump vs Fresh Water Pump Cheechako Engines and Propulsion Systems 44 01-02-2012 15:31



Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 02:30.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.