timmfive
New member
Keywords / Title:
Yanmar 3GM30 raw water cooled (RWC) Johnson pump raw water pump failing to reprime, causing engine to overheat.
We had this intermittent problem for almost 1 year.
What follows is my trials and errors, and ultimately a solution to this issue.
I am hoping this will help others out there as there seem to be alot of threads outlining the same/similar issue... but no solution found.
Problem:
- Engine overheating in rough seas, confused seas, and sometimes with steep following seas.
- Due to above circumstances, the engine would often overheat when approaching land, or when the wind died completely but left some sea state behind. Either scenario is the worst time to not have your engine!
- Explained the circumstances that caused the overheating to previous owner. He never had the issue in 13 years of running the engine.
- Also, we didn't have the issue during the first 6 months of having the boat.
- So issue must be new, or I must have introduced it during maintenance in some way.
- Quickest way to resolve issue was to undo supply hose on the intake side of the pump, let air/water drain out into bilge until solid column of water, reattach, start engine, let cool. Continue for another 15-20 minutes or so... hope...
Engine / pump specs:
- Yanmar 3GM30 raw water cooled. 13 years old. (Would estimate ~4000 hours?)
- Pump is a Johnson Pump F4B-902, 10-24509-02. Impeller Johnson 810B.
Actions taken:
1) Rebuilt pump completely. Same issue.
2) Threw a few new impellers at it: same issue.
3) Systematically ruled out backplate, paper gasket, intake filter, hoses, air leaks, back pressure, exhaust manifold/gooseneck etc.
4) This year, we replaced black intake hose with clear one to observe water/air flow.
Naturally on heel angles above 20 degrees, air would accumulate quickly and pump wouldn't reprime.
However, even on on 5-10 degree angles but with steep seas, small bubbles from the breaking seas would slowly accumulate. Eventually they would reach a stage where the pump would fail to reprime.
So with the clear hose I was able to observe the issue... why was it happening? Why can't the pump reprime? Why doesn't it just suck through the air bubbles as it goes along?
5) Experimented with different routes of the intake hose: far below waterline as possible, "S" shapes, loops, etc.
Regardless of intake hose position, air would accumulate.
6) Tried replacing the 3/4" (19mm) intake hose to 1/2" (~12mm). Idea was the thinner hose would introduce more suction. No joy.
(Interestingly, both diameters would empty a bucket of water in exactly the same amount of time!)
Even putting finger on end of intake hose... just doesn't seem to be enough suction in my opinion...
Solution:
- Went to Yanmar distributor with old pump in hand and a pair of calibers to measure inner chamber diameter, as well as Cam size.
- Didn't need calipers to see the cam size on new pump was 2 to 3 times thicker than original pump!
- Yanmar agent insisted the pump I had was the one for the fresh water (3GM30F) model and that the 3GM30 raw water pump is a smaller one he showed me.
- However, smaller Yanmar branded pump was ~€500. And exact "like for like" replacement of my bigger Johnson pump was "only" ~€220.
- So a bit of a surprise/confusion, but was reluctant to pay twice as much for a smaller pump.
- Was more logical to get the same pump that had worked fine for 13 years.
- The main thing was seeing the Cam size in the new pump. I will attach pictures.
- Note: the cam in both pumps are not replaceable... (else I would have fixed this last year!!!)
New Johnson pump specs compared to old pump:
- Yanmar p/n 128397-42500
Old Pump: Johnson Pump F4B-902, 10-24509-02. Impeller Johnson 810B.
New Pump: Johnson Pump F4B-903, 10-24509-01. Impeller Johnson 810B-1. (no paper gasket)
Old pump Inner chamber diameter: 50.2 mm. Diameter to cam: 48.25 mm.
New pump Inner chamber diameter: 50.0 mm. Diameter to cam: 46.00 mm.
Old pump moved ~180L/h at 1000 rpm.
New pump moved ~420L/h at 1000 rpm.
New pump moved ~630L/h at 2000 rpm.
(Yanmar manual says it should move ~700L/h.. but doesn't state rpm... and i'm not sure if this is in reference to the smaller Yanmar pump that I "should have", or the one that I Do Have...).
New pump had a noticable, considerable more amount of suction when putting finger on end of intake hose.
So much suction, that I was almost afraid my finger would get stuck on end of hose and I would have to kill engine.
Whereas, with the old pump, the suction was feeble and there was easy to plug hose and unplug hose with finger/palm.
Another test, was with intake hose full with a column of water, holding the intake hose vertically:
Old pump the water would be seen to work its way down thru the pump a slow, but considerable pace.
New pump the water would still work its way down... but very very slowly in comparison.
And *ULTIMATELY*... the new pump would prime anything...
ie: take a dry hose, dip it into a bucket of water, and it would suck the water thru the length of hose.
You could introduce air, etc, at anytime, and it would quickly fly thru the hose, thru the pump and thru the system.
No problems since and we've been in some rough seas, steep seas confused seas, etc. (Aegean Meltemi)
All conditions where before we would wince and wait for the untimely <<bbeeeeeeeppp>> of the engine overheat alarm.
It has take awhile for us to gain trust in the engine in such conditions, but now we have regained confidence.
Any bubbles from breaking seas just get sucked thru. The water coming out of the exhaust is noticably more in volume and power.
I have read that the max heel angle to run the Yanmar is ~15 degrees.
We don't motor when sailing on a steep heel angle.
Just motor when we need to get into a port, or if the wind dies.
Root cause:
- Previous owner took the boat up to the UK thru the French Canals. Had no problems.
- We had no problems in UK, English Channel, North France, etc.
- We took the boat back down to the Med thru the French Canals. Had no problems until once were in the Med.
- (In hindsight!) Reason why the pump cam was worn so much, so quickly:
a) 13 years old...
b) the silty, sandy water in the canals increased wear on cam.
(If the pump is rotating at ~2500 rpm, multiplied by 6 impeller vanes hitting the cam = ~15000 laps of the cam a
minute = 250 laps / second. introducing sandy/silty water makes a quick job of sanding down the cam with rubber vanes)
- - -
Conclusions...
Researched this problem for a solution on the internet.
(Google "yanmar 3gm30 johnson pump" for example.)
Found over 30 threads on dozens of sites that highlighted similar/same issue, but no solutions posted! The original poster would disappear, or get sick of people telling them to change the impeller.
I will try and go back to all the threads I found over the past year and point them to this post in case it helps anyone out there.
Least I can do. It was a very frustrating issue as it was so intermittent and hard to repeat.
The conditions that caused the issue weren't condusive to troubleshooting... it was more.. get it working, get to port safe, etc.
Sounds simple now in hindsight... but at the time was hard to pinpoint. The clear hose really helped me understand the issue. Very cheap step in the troubleshooting process. Some of the forums did hint and replacing the pump, but quoted the pump at being €500. The reason I didn't do this sooner was that €500 was a very big expense for us, especially as a troubleshooting step, with no guarantee of resolve.
In conclusion... the pump is easy to take off and take to Yanmar and do a comparison with new pump. Shame the cam isn't replacable as on some pumps. Hopefully the measurements above will help someone out there too.
(See attachment of old + new pump side by side... the picture is worth 1000 words).
Yanmar 3GM30 raw water cooled (RWC) Johnson pump raw water pump failing to reprime, causing engine to overheat.
We had this intermittent problem for almost 1 year.
What follows is my trials and errors, and ultimately a solution to this issue.
I am hoping this will help others out there as there seem to be alot of threads outlining the same/similar issue... but no solution found.
Problem:
- Engine overheating in rough seas, confused seas, and sometimes with steep following seas.
- Due to above circumstances, the engine would often overheat when approaching land, or when the wind died completely but left some sea state behind. Either scenario is the worst time to not have your engine!
- Explained the circumstances that caused the overheating to previous owner. He never had the issue in 13 years of running the engine.
- Also, we didn't have the issue during the first 6 months of having the boat.
- So issue must be new, or I must have introduced it during maintenance in some way.
- Quickest way to resolve issue was to undo supply hose on the intake side of the pump, let air/water drain out into bilge until solid column of water, reattach, start engine, let cool. Continue for another 15-20 minutes or so... hope...
Engine / pump specs:
- Yanmar 3GM30 raw water cooled. 13 years old. (Would estimate ~4000 hours?)
- Pump is a Johnson Pump F4B-902, 10-24509-02. Impeller Johnson 810B.
Actions taken:
1) Rebuilt pump completely. Same issue.
2) Threw a few new impellers at it: same issue.
3) Systematically ruled out backplate, paper gasket, intake filter, hoses, air leaks, back pressure, exhaust manifold/gooseneck etc.
4) This year, we replaced black intake hose with clear one to observe water/air flow.
Naturally on heel angles above 20 degrees, air would accumulate quickly and pump wouldn't reprime.
However, even on on 5-10 degree angles but with steep seas, small bubbles from the breaking seas would slowly accumulate. Eventually they would reach a stage where the pump would fail to reprime.
So with the clear hose I was able to observe the issue... why was it happening? Why can't the pump reprime? Why doesn't it just suck through the air bubbles as it goes along?
5) Experimented with different routes of the intake hose: far below waterline as possible, "S" shapes, loops, etc.
Regardless of intake hose position, air would accumulate.
6) Tried replacing the 3/4" (19mm) intake hose to 1/2" (~12mm). Idea was the thinner hose would introduce more suction. No joy.
(Interestingly, both diameters would empty a bucket of water in exactly the same amount of time!)
Even putting finger on end of intake hose... just doesn't seem to be enough suction in my opinion...
Solution:
- Went to Yanmar distributor with old pump in hand and a pair of calibers to measure inner chamber diameter, as well as Cam size.
- Didn't need calipers to see the cam size on new pump was 2 to 3 times thicker than original pump!
- Yanmar agent insisted the pump I had was the one for the fresh water (3GM30F) model and that the 3GM30 raw water pump is a smaller one he showed me.
- However, smaller Yanmar branded pump was ~€500. And exact "like for like" replacement of my bigger Johnson pump was "only" ~€220.
- So a bit of a surprise/confusion, but was reluctant to pay twice as much for a smaller pump.
- Was more logical to get the same pump that had worked fine for 13 years.
- The main thing was seeing the Cam size in the new pump. I will attach pictures.
- Note: the cam in both pumps are not replaceable... (else I would have fixed this last year!!!)
New Johnson pump specs compared to old pump:
- Yanmar p/n 128397-42500
Old Pump: Johnson Pump F4B-902, 10-24509-02. Impeller Johnson 810B.
New Pump: Johnson Pump F4B-903, 10-24509-01. Impeller Johnson 810B-1. (no paper gasket)
Old pump Inner chamber diameter: 50.2 mm. Diameter to cam: 48.25 mm.
New pump Inner chamber diameter: 50.0 mm. Diameter to cam: 46.00 mm.
Old pump moved ~180L/h at 1000 rpm.
New pump moved ~420L/h at 1000 rpm.
New pump moved ~630L/h at 2000 rpm.
(Yanmar manual says it should move ~700L/h.. but doesn't state rpm... and i'm not sure if this is in reference to the smaller Yanmar pump that I "should have", or the one that I Do Have...).
New pump had a noticable, considerable more amount of suction when putting finger on end of intake hose.
So much suction, that I was almost afraid my finger would get stuck on end of hose and I would have to kill engine.
Whereas, with the old pump, the suction was feeble and there was easy to plug hose and unplug hose with finger/palm.
Another test, was with intake hose full with a column of water, holding the intake hose vertically:
Old pump the water would be seen to work its way down thru the pump a slow, but considerable pace.
New pump the water would still work its way down... but very very slowly in comparison.
And *ULTIMATELY*... the new pump would prime anything...
ie: take a dry hose, dip it into a bucket of water, and it would suck the water thru the length of hose.
You could introduce air, etc, at anytime, and it would quickly fly thru the hose, thru the pump and thru the system.
No problems since and we've been in some rough seas, steep seas confused seas, etc. (Aegean Meltemi)
All conditions where before we would wince and wait for the untimely <<bbeeeeeeeppp>> of the engine overheat alarm.
It has take awhile for us to gain trust in the engine in such conditions, but now we have regained confidence.
Any bubbles from breaking seas just get sucked thru. The water coming out of the exhaust is noticably more in volume and power.
I have read that the max heel angle to run the Yanmar is ~15 degrees.
We don't motor when sailing on a steep heel angle.
Just motor when we need to get into a port, or if the wind dies.
Root cause:
- Previous owner took the boat up to the UK thru the French Canals. Had no problems.
- We had no problems in UK, English Channel, North France, etc.
- We took the boat back down to the Med thru the French Canals. Had no problems until once were in the Med.
- (In hindsight!) Reason why the pump cam was worn so much, so quickly:
a) 13 years old...
b) the silty, sandy water in the canals increased wear on cam.
(If the pump is rotating at ~2500 rpm, multiplied by 6 impeller vanes hitting the cam = ~15000 laps of the cam a
minute = 250 laps / second. introducing sandy/silty water makes a quick job of sanding down the cam with rubber vanes)
- - -
Conclusions...
Researched this problem for a solution on the internet.
(Google "yanmar 3gm30 johnson pump" for example.)
Found over 30 threads on dozens of sites that highlighted similar/same issue, but no solutions posted!
The original poster would disappear, or get sick of people telling them to change the impeller. I will try and go back to all the threads I found over the past year and point them to this post in case it helps anyone out there.
Least I can do. It was a very frustrating issue as it was so intermittent and hard to repeat.
The conditions that caused the issue weren't condusive to troubleshooting... it was more.. get it working, get to port safe, etc.
Sounds simple now in hindsight... but at the time was hard to pinpoint. The clear hose really helped me understand the issue. Very cheap step in the troubleshooting process. Some of the forums did hint and replacing the pump, but quoted the pump at being €500. The reason I didn't do this sooner was that €500 was a very big expense for us, especially as a troubleshooting step, with no guarantee of resolve.
In conclusion... the pump is easy to take off and take to Yanmar and do a comparison with new pump. Shame the cam isn't replacable as on some pumps. Hopefully the measurements above will help someone out there too.
(See attachment of old + new pump side by side... the picture is worth 1000 words).
