4BY2 Overheating - air in sea chest at high RPM

C

captstu

Well-known member
Joined
Nov 10, 2014
Messages
862
Fluid Motion Model
C-248 C
Vessel Name
Shearwater IV (SOLD)
We had kind of a breakthrough on finding and fixing the over heat problems with my 4BY2.

So far, the heat exchanger has been rebuilt, the exhaust manifold thermostat has been removed and found to be frozen shut, the “O” rings in the fitting that join the exhaust manifold to the water return line have been replaced - we have found a number of warn gaskets. Temporarily there is no thermostat on the boat.

The lines to the hot water heater and cabin have been removed and plugged.

Today, for the first time, we had two people on board so we could look for the suspect leak at 3000+ RPM.

The observer noted that as the RPM rose, the water flowing thru the sea chest STOPPED suddenly. We believe this indicates an air leak into the raw water inlet or a failed raw water pump - the impeller is new since the problem started and the old one had only a small portion of a single blade missing. I back flushed both the transmission oil cooler and the air exchange cooler to remove any potential impeller parts.

So, we went looking at the line from the sea chest to the wash down pump and flush fitting. The mechanic found a failed hose clamp - the 4th we have found since I owned the boat - and also found the inlet fitting to the wash down pump was partially pulled out of the pump. Clearly either of these could have caused the air leak we were seeing.

So, the mechanic removed the hose from the sea chest to the wash down pump. He also removed the flush fitting from that hose and connected the hose bib fitting directly to the sea chest. Tomorrow, I will remove the hose bib from the sea chest and replace it with a bronze plug - just to be sure.

The overheat problem did not go away.

The boat was bottom painted in May and the problem started 2 weeks later. After the problem started, I replaced the raw water impeller — but did not replace the raw water pump impeller gasket - a new one is now on order.

There is some minimal bottom growth that I will scrub off tomorrow.

Any idea where else I can look for the air leak?
 
If the through-hull opening was partially blocked as a result of the bottom painting, or if you sucked something into it while underway, the engine may be trying to suck more water than the sea strainer is getting. I would try clearing the through-hull and see if that helps.
 
I'm with Brad that the sea strainer opening could be obstructed with paint or old/new growth. Is there a scoop on the hull opening? There should be one. Are the openings inside the scoop clear? When I have my boat out of the water I scrape the inside of the scoop with a thin screwdriver, there is always growth up there.
Sometime ago there was a thread on here about an R27 overheating. The marina in New Bedford, MA didn't care for the original sea strainer size and water flow. They pulled the boat and installed a larger sea strainer and thru hull, solved the problem.
Lack of water flow has to be the root cause of the issue.
I would think the impeller would be leaking if the gasket failed, mine has an O-ring

There is a pump assembly on Ebay for a 6BY if you need one, confirm the part number is the same for the 4BY
https://www.ebay.com/itm/Yanmar-6BY-Mar ... Sw4shX-6M8
 
I am with the rest, Check the intake strainer at the bottom of the hull. Also, the vertical pipe with the elbow could be somewhat blocked. If it were me I would remove the elbow and valve so you have a direct shot down the inlet pipe. Make sure it is pristine. At this juncture, short of installing a larger inlet assembly I would install a tee instead of the elbow and put a plug at the top of the tee for future clean out and inspection.
 
I tried clearing the sea strainer and will do more today. I agree it is the likely problem.

I also just found out they pulled the raw pump cover to inspect the new impeller. It was ok.

I do not know if they also replaced the impeller ‘O’ ring. I’ll order an ‘O’ ring today.

There were at least 2 problems originally. The exhaust manifold thermostat was not opening so no coolant was flowing thru the heat exchanger. This may have masked the water pump problem.

While the bottom has some growth now - enough to expose the problem of the cracked hose clamp or wash down pump, when the boat first went back in the water, the thru Hull was clean.

It is likely the raw water pump is leaking due, in part, to growth on the thru Hull.

Thanks


Stuart Bell
Ranger 25: Shearwater
(561) 352-1796
 
On reflection, I don’t see how an air leak in the raw water pump could be causing my problem.

If the raw water pump was leaking air, I understand with the pump. But, I can’t see how that Lee would cause they’re the flow back up hill into the Seachest.

Today in addition to cleaning the through hole elbow and valve more thoroughly, I plan to disassemble the Seachest. I think that was an early coming in through the washdown pump, but I’m beginning to believe now that leak is fixed that there is an additional leaks in the Seachest self but, I can’t see how that Lee would cause they’re the flow back up hill into the Seachest.

Today in addition to cleaning the through hole elbow and valve more thoroughly, I plan to disassemble the Seachest. I think that was an early coming in through the washdown pump, but I’m beginning to believe now that leak is fixed that there is an additional leaks in the Seachest itself?

I plan to inspect or replace the gaskets at the top of the Seachest that go through the dog to see if they could possibly be leaking.
 
While you're in the water cleaning the bottom, check the grates on the through hull. They should be facing forward. Not all of the early boats were assembled properly.
 
If you are sure it is a water supply issue causing the over heat thru a process of elimination you should be able to find the problem. Have you always had an over heat issue? If yes look at design,If no don't change design. You had the bottom painted this year and had no issues after the paint job ( yes,No) If yes look there, If no its not plugged up from paint. Did the problem start at one time. If yes you picked up debris and it is restricting flow between thru hull pickup and sea water pump. Or small leak has occurred causing air to be pulled in reducing water flow. ( along with the over heat you should be experiencing elevated exhaust temps.) Has the over heat been a gradual issue and finally became a major issue If yes start from the sea water pump and move to the thru hull pickup. Remove and inspect each hose fitting, clamp, and don't rule out a hose. I have seen hoses deteriorate from the inside delaminating and causing a restriction of flow. Sea-chest, lid cracked gasket deterioration, a chunk of debris stuck in inlet or outlet of housing or at hose. Its something simple just hard to find. Start looking where the water comes in and finish where the water goes out. If it is a air leak or restriction in the raw water cooling side thru a process of elimination you will find it .

It could be has simple has something like this. We had the boat for a season and I noticed at high speed cruise or WOT the temp was slowing going higher and higher. Because of the type of Sea-chest installed debris can get past the screen and the next place it can build up is the Reverse gear cooler. When I inspected it I found the hose was installed glue was applied to the hose instead of the cooler flange.( factory install) This resulted in small chunks of glue plugging 25% of bottom portion of the cooler tubes and the inlet had a build up of glue causing a partial restriction in flow. ( there was also debris caught up in there too. It was a simple fix but nothing that I expected to see.


Keep going you will find it.
 
The boat ran very well for nearly the 5 years since I adopted her. The problem started 2 weeks after I had the bottom pressure washed, cleaned, and painted. At that time, the thru hulls were lubricated and now turn easily.

We believe, now, that the sea chest is leaking air into the system at high RPM.

I intend to change the thru hull to a proper (my opinion) fitting where the shut off valve is integral to the sea chest and there are no intervening elbows or other plumbing.

Once this is changed, I intend to replace the sea chest with one having an inlet on the bottom - connected directly to the thru hull, and ONE outlet on the side. I will connect the sea chest to the raw water pump with no intervening fittings - so at least this problem will not recur. I also intend to remove the inlet screen on the thru hull so I can more clean and inspect the thru hull.

WHAT SIZE TUBING CONNECTS THE EXISTING THRU HULL WITH THE ENGINE RAW WATER PUMP? Looks like 1 1/4" but I want to check before the boat is pulled.

What is the brand/part number of the existing sea chest?

Thanks for all the help. Hope is eternal. /Stu
 
I disassembled the sea chest and found a cracked ‘O’ ring on the stem. I also put in the new gaskets supplied by Ranger. The kit contained two thick washers, one replaced an identical washer at the top of the bowl.

I can’t figure where the second 4” diameter washer goes??

Replacing the O ring and removing the wash down hoses got rid of the air leak in the sea chest.

But, the engine still overheats above 2400 rpm after a few minutes.

Coolant seems to no longer be leaking into the bilge.

Ideas?


Stuart Bell
Ranger 25: Shearwater
(561) 352-1796
 
I am not familiar with a sea chest design on a ranger - I thought we all had scoops --> seacock --> Pipework to strainer --> pipework to engine and head. (unless your sea chest definition is the sea strainer?)

you mention in you post that the seacocks were lubribicated: could this have introduced any foreign object blocking flow?


If you do have a sea chest like these: https://www.google.com/search?rlz=1...i8i7i30k1.0.RfU_1cnTKMs#imgrc=NZDR_ZVzO81L0M:

Then is there anything with the attitude of the boat at speed (above 2400RPM) that could be causing the issue? perhaps the water level in the chest is dipping below the intakes with a high bow up angle?

If the water in the sea chest is at an acceptable level with no air; then my deduction is the issue is up from the sea chest.

Got any photos you can post?
 
My sea strainer is:

https://www.go2marine.com/product/20704 ... JrEALw_wcB

I think it is a chest rather than a strainer because there are 3 outlets.

We found that at high rpm, the chest/strainer filled with air. We were sure this was ‘the’ problem. The builder had connected the wash down pump to the strainer/chest and we found a broken hose clamp on the line to the wash down pump.

We also found a damaged inlet fitting on the pump and a bad seal on the strainer/chest.

Plugged the opening and removed the wash down pump. We also replaced the seals on the strainer (only 1 outlet so it is no longer technically a chest).

At rpm there is no air visible in the strainer any longer.

But she still overheats.

The mechanic opened the raw water pump to inspect the impeller and did not replace the O ring. Any idea of this could leak air at high rpm and cause the raw water pump to under Deliver?

How do I test the flow of raw water?

What should the flow be?

Thanks for helping. Sorry about the chest/strainer confusion.


Btw, the engine is no longer losing coolant?


Stuart Bell
Ranger 25: Shearwater
(561) 352-1796
 
You seem to have troubleshooted a lot here. You have found many small issues that have contributed to your over heat problem. I have never performed a high rpm flow test.I would test pump and flow efficiency at the manufactures flow rate at idle. With a cold engine it is best to test. I would disconnect the end of the line (Raw water connection) and install a hose extension so I could measure using a 5 Gallon bucket. I believe this would be the hose connection at your exhaust riser. The spec for the sea water pump on my engine 220hp D3 Volvo is 1cuft per minute 7.48 gallons a minute. I would assume your pump spec is very close to this. When testing flow I would want the 5 gallon bucket to fill in less then a minute at idle. A flow meter is the true way to measure, I have never had to get that technical in trouble shooting an over heat. If it failed the test there is a restriction on suction side of pump, pressure side of pump, air leak, of a poor output of pump. Some times having a good impeller does not always mean you have a good pump. Pump housings wear out. The more wear the less efficient they are. Pumps can develop seal leaks that leak in not out. The o-ring could be an issue, normally the o-ring would cause a leak outward. Has your sea pump ever been replaced ? Some boats go hundreds or thousand hours without replacing some do not because of the water they run in. Deep clean seawater is less abrasive to the pump components. Warm shallow water has more particulate in it because the bottom is stirred up, running aground is very abrasive too. I have seen Bravo stern drive housings destroyed with in 100 hours and the impeller still looks good ( polished vane ends but fully intact). Sounds like your narrowing it down the issue. Good luck
 
Brian,

The pump is working sufficiently to keep the exit raw water from the heat exchanger to between 105 and 115 degrees up to 2000 RPM. During our first 2-person test, we found NO water entering the raw water pump above about 2000 RPM.

We found the cause to be one of three breaks:

1. There was a bad hose clamp on the line between the strainer and the raw water wash down pump. When I was learning about engines, I was taught the engine raw water must enter thru a dedicated line. This raw water connection for the wash down pump should never have been tapped into the raw water inlet line that feeds the engine.

2. We found the inlet fitting from the raw water line to the wash down pump was mis-seated in the wash down pump and was likely leaking air into the circuit at high RPM.

3. Finally, I found a damaged small 'O' ring at the top of the strainer where it opens for clean out. This ring shows signs of erosion and was likely leaking air into the strainer.

I don't know which of these three was causing our major air leak, but there is no longer any air in the inlet strainer (Sea chest) at any RPM.

Clearly, at high RPMs, the air load would have exceeded the ability of the raw water pump to purge itself - and we observed the pump no longer pumped any observable water at about 2500 RPM and above. Dropping back to below 1500 caused the raw water pump to re-prime.

At the same time I was repairing the problems we just found, I went in the water (best part), scrubbed the bottom, and removed the silly fins on the ocean side of the thru hull. Then I took a coat hanger and cleaned - as best I could - the inside of the fin retainer (external strainer) and well up into the thru hull until I reached the equally silly elbow where I leaned best I could. I had previously cleaned the other side of the elbow by reaching in from the strainer with a long plastic scraper and cleaning it out.

Silly inlet strainer: http://www.discountmarinesupplies.com/S ... YgQAvD_BwE

Neither cleaning resulted in significant debris removal.

The net result:

I STARTED THE ENGINE AND GOT REPEATED CHECK ENGINE ALARMS. Complete with horn, buzzer and blinking "Must Reboot" on the Yanmar engine display.

I checked for water in the fuel filter - a known cause of CHECK ENGINE - and it was nearly clean.

Just because I wanted to see how much progress I had made on the overheat, I took the engine to 3700 RPM for a few minutes - the CHECK ENGINE stopped - only to return again when I slowed down - and the temperature did not heat enough to trigger the overheat alarm.

Clearly, I'm making progress on the over temperature problem - although I still have to change the water pump gasket that was not replaced the last time the mechanic helping me opened it up to see the just replaced impeller.

Now, if only I can fix the CHECK ENGINE so I can go back to working on the overheat.
 
You did not mention if you removed and inspected the hose that comes off the sea chest to the raw water pump or checked the hose from the raw water pump to the heat exchanger, two possibilities of restrictions.
 
There was air leaking in to the sea chest/strainer.

I checked the hose from the strainer to the washdown pump and found a broken hose clamp. I checked further and found the inlet fitting from that hose to the washdown pump had a crack.

Rather than repair both of these problems, I disconnected the flash fitting from the washdown assembling and connected the flash hose bib directly to the strainer with a 2 inch piece of hose and two new hose clamps.

It was still air leaking in to the strainer so I disassembled it and clean it completely inside and out. In the process I found a small O-ring on the top of the rod in the middle of the strainer that had a crack in it and was probably leaking air.

I replace that O-ring, the top seal gasket, and the dome ring gasket with new gaskets.

Then I tested the engine. There is no more air coming in to the water inlet up to at least the sea strainer.

I was able to take the engine up over 3500 RPM for a few minutes without overheating, although it is still not cooling as well as it did before the problem started.

During the test run the engine raised “ check engine quote about every 10 seconds. I operated the display to read out the other codes and there were no recorded codes.

The last time this happened it turned out to be a couple of teaspoons of water in the Racore filter was tripping the water detector on the bottom of the filter. I drain the filter there was nearly no water present. The check engine problem Recurred.

I disconnected the electrical sitting to the Racore filter hoping the check engine light problem would go away. It did not.

When I took the boat up above 2500 RPM the check engine problem disappeared, only to return when I went back to idle.

Since there is still a small overheat problem I plan to change the O-ring on the raw water pump this morning. The mechanics open the pump and reuse the O-ring so this is a just in case change.

I am clueless about what to do with the check engine so I plan to face east now towards the sun and murmur a continuous tone hoping for the best.

Thanks for the help. Every idea triggers another idea.

Know anyone that wants a goodbye and a great boat?


Stuart Bell
Ranger 25: Shearwater
(561) 352-1796
 
Well, I do not think you answered my question. Did you remove the hose from the "Sea Chest" (I call it the sea strainer) to the raw water pump and the hose from the raw water pump to the heat exchanger and make sure there are no obstructions. Also check the elbow that goes between the hose from the sea chest to the next hose going to the water pump. While you are at is check that hose as well.
 
Sorry,

I did not remove the hose from the sea chest/strainer to the elbow - but I did probe the hose with a plastic pipe and was easily able to reach into the elbow several times with no obstruction.

I did not remove the hose from the sea chest/strainer to the raw water pump at the strainer end. But, I did back flush the transmission oil cooler and the air charge cooler by removing the impeller and removing the top of the strainer. There was unobstructed flow there.

I did not remove the pipe between the elbow and the sea chest/strainer. But, I did cut all the interfering fins off the thru-hull inlet screen. They were, as expected, somewhat clogged with growth since cleaning 2 months ago. They are gone. I was able to probe up from the thru hull to the elbow with a snake and able to feel the elbow clearly. I did remove a very small amount of growth from these parts.

I also removed all connection between the sea chest (then operating as a sea chest) and the wash down pump after we determined significant air was leaking into the sea chest at high RPM. Rather than fix the two leaks we found, we just removed the wash plumbing and capped the sea chest. I will not be replacing the wash down pump since the idea of a destructive air leak into the raw water cooling system is worse than the thought of another thru hull dedicated to the wash down pump.

The engine cooled about normally on the test run. 10 minutes at 3500 RPM resulted in just under 220 - and I have since found a crushed "O" ring that could the cost of this last leak. (hopefully).

Thank you and everyone for all the help.
 
Yes. It ran 208 at wot before this happened.

I removed the crushed “O” ring from the raw water pump and saw a slight water leak with engine off. One of several problems.

Once the Check Engine problem is solved and the O ring I ordered is in, I’ll test some more.

Hoping to sell her as is. So many verifiable problems takes away any trust.

I have no real idea where to look now, check engine, no error codes and the desolation MUST REBOOT cycle every few minutes.

$7500 in parts and labor to replace parts I can’t reach with no end in sight.

Mechanic wants to pull boat and replace thru Hull, sea strainer, hoses and valves next. Just Monet, no idea.

Frustrated.

Thanks for the help, your ideas give me hope.


Stuart Bell
Ranger 25: Shearwater
(561) 352-1796
 
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