4BY2 Overheating - can the thermostat be removed?

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Re: 4BY2 Overheating - can the thermostat be removed?

Postby knotflying on Fri May 25, 2018 4:36 pm

Don't know why it is there V in the water pump. To me it is an engineering reason not an emissions reason,
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Re: 4BY2 Overheating - can the thermostat be removed?

Postby captstu on Sat May 26, 2018 4:40 pm

Progress, but still leaking.

Removed the thermostat from the position near the exhaust manifold. Reassembled the engine with the thermostat on top of the head near the water pump - the other place it appears in the parts manual and the only place it appears in my service manual.

Well, the coolant in the heat exchanger now heats to 160 degrees - before it was room temperature - indicating (at least to me) that the water pump is working and the new thermostat in the head position is working.

The ran at normal temperature - just below 190 - for 20 minutes at 1600 RPM.

When I increased the speed t 3200 RPM the temperature rose rapidly to 235 degrees when the overheat alarm triggered.

At that point, I measured the zinc cap on the heat exchanger at 160 - seems about normal - and the raw water outlet at about 110, also seems normal. The domestic hot water inlet was 135 - low, but it had cooled.

I do not see the leak - and can not get the new 20 PSI cap off until it cools.

Question: Any idea where I should look for the leak?????

Question: After a run, what is the temperature at the heat exchanger zinc? Thank you
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Re: 4BY2 Overheating - can the thermostat be removed?

Postby knotflying on Sun May 27, 2018 7:00 am

Well, once you get the new cap on I would pressure the system to 20 PSI and see if it holds pressure. If it does, IMO, that would indicate a blockage rather than a leak. My next step to confirm that would be to remove the thermostat and reassemble without it and see what kind of temperature increase you get. When my thermostat dislodged I could not get more than 145 degrees on my temperature gauge. Keep in mind mine is a 180, so the temperature may be slightly higher.
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Re: 4BY2 Overheating - can the thermostat be removed?

Postby captstu on Sun May 27, 2018 10:45 am

The mechanics finished up - water is now circulating thru the heat exchanger when the engine is hot.

I took the boat for a test this morning - ran fine up to 2300 rpm than as I accelerated to 3900 rpm, the temperature suddenly went from 205 to 230 degrees - indicating to me there was a loss of coolant incident.

When I checked more carefully, the heat exchanger cap was only partially on, the overflow bottle was full, and water was everywhere where it had sprayed out of the overflow bottle.

I took off the cap (about 45 minutes), put 2 quarts of water in the heat exchanger and put the cap back on.

The engine ran OK but still over heated after 5 minutes or so.

This may be another loss of cooling incident or it may be air entrapped in the water lines.

The local Yanmar folks say I have to burp the engine by opening a burping valve?????????

How do I burp the Yanmar 4BY2 after low coolant is discovered?
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Re: 4BY2 Overheating - can the thermostat be removed?

Postby captstu on Wed Jun 27, 2018 6:10 pm

The saga continues - but the overheat continues also.

The mechanics removed the fitting between the exhaust manifold and the hot water return line. It is sealed with two "O" rings that appeared crushed. They replaced them.

On observation during the sea trial after the above "O" ring replacement, we observed the raw water flow thru the sea chest STOPED at about 3000 RPM. Wow. On careful inspection, the mechanic found still another busted hose clamp - the 4th we have found - this one on the hose from the sea chest to the wash down pump. The mechanic also found the "O" ring in the water wash-down pump inlet fitting was mis-seated.

We agreed there was no real reason to retain the wash-down pump until this overheat is fixed, so the mechanic moved the flush hose bib fitting from the "T" on the wash-down pump to the sea chest. When we tested after this change, the water no longer stopped flowing at 3000 RPM, but the overheat continued, although it took much longer to take place.

Next, I cleaned the inlet screen on the raw water inlet - it was partially clogged with growth even tough the bottom was painted and the screen cleaned in May.

The overheat continued - but took 10+ minutes to overheat.

Tomorrow morning, I will pry open the inlet screen and clean it more completely.

Each time, we find a new problem- correct the problem - and the overheat symptoms change slightly.

Now, the heat exchanger is rising to about 200 degrees when the overheat occurs - so it is unlikely the problem is in the coolant circuit.

I need a great idea.

A lesson learned again: If you have any original Ranger-supplied hose clamps inspect them carefully or change them for safer clamps. I have no way of knowing if Ranger installed a bad batch or mis-installed the clamps, or they were abused by a former owner . . . but, they don't seem to do their job any longer.
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Re: 4BY2 Overheating - can the thermostat be removed?

Postby Osprey on Sun Dec 23, 2018 11:26 pm

Some time back Mike (knotflying) posted detail information on thermostat servicing. In one of the posted images of the thermostat the BMW identification shows but only a small portion of the part number. Could Mike check his on-hand spare part and post the BMW, rather the Yanmar part number?
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Re: 4BY2 Overheating - can the thermostat be removed?

Postby knotflying on Mon Dec 24, 2018 9:32 am

The number on the Thermostat is 2248038. It is rated at 88 degrees centigrade. It will be interesting to see if you can purchase just the thermostat from BMW. It seems that BMW sells the whole assembly with the thermostat as a single unit. I purchased mine via Yanmar. Sometimes you might be better off biting the bullet and get the part from Yanmar. I can't recall the price, but I don't think it was excessively expensive.
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Re: 4BY2 Overheating - can the thermostat be removed?

Postby captstu on Mon Dec 24, 2018 10:18 am

There are two thermostat assemblies on the 2BY2 according to the prints. One is where you expect, near the coolant pump. The other is on the exhaust manifold. Only one of these seems to be used.

I bought the one on the head, about $75. Mine was on the exhaust manifold, surprise. I think the actual thermostat Disks are the same.

My 4BY2 was overheating and the heat exchanger was cool. When the thermostat was removed, it was jammed shut! Leave it out until the engine ran cool. Not so easy. After removal the heat exchanger got to 150+.

With the thermostat out it still overheated, just took longer.

Found air leaking into sea chest, capped off the wash down pump. Better, but still overheated at 3400 rpm.

Replaced impeller, slipping on shaft at high rpm. Better still but still ran at 220 degrees.

Replaced thru Hull, elbow and sea chest with straight, no turns, strainer and mushroom thruhull.

Engine now runs perfectly at 195 degrees at 3500 RPM with no thermostat.

I recommend removing the thermostat (a very hard task) and be sure your engine cools well before you put in a new one. I don’t see the need for a thermostat if you typically run and 3200 RPM or above.


Photos coming soon.



Stuart Bell
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Re: 4BY2 Overheating - can the thermostat be removed?

Postby knotflying on Tue Dec 25, 2018 10:25 am

captstu wrote:Engine now runs perfectly at 195 degrees at 3500 RPM with no thermostat.

I recommend removing the thermostat (a very hard task) and be sure your engine cools well before you put in a new one. I don’t see the need for a thermostat if you typically run and 3200 RPM or above.


Stu, I am not sure why your engine would run at 195 degrees without the thermostat. In my opinion that is hot without a thermostat. My experience when the thermostat was stuck open was 142 degrees at WOT. You may still have an issue somewhere and that is why you are getting acceptable temperatures with it out.
These engines are calibrated to run within specified temperature ranges so I would not normally recommend leaving out the thermostat.
The removal and replacement of the thermostat in a difficult and time consuming job. So I would check for leaks, clogged intake, collapsed hoses, bad pressure caps, air infiltration and do a heat exchanger flush before a thermostat inspection and removal was done. A bad thermostat is not a common issue. Once I removed the old thermostat I would check it out for operation and accuracy. You can do this by first inspecting it and ensure that it is in a closed position when cold. Then heat up some water to boiling (212 degrees at sea level) and then turn off the stove and let it cool to 190 degrees or a little higher. Drop the thermostat in the water and it should open fully. If it works properly put it back in. And make sure it is seated and locked in properly. If you know it is working now keep looking for the culprit. The only thing you may not have inspected at this point is the sensor. This requires removal of the exhaust manifold to get to it and to me, the last thing you would want to check.
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Re: 4BY2 Overheating - can the thermostat be removed?

Postby captstu on Tue Dec 25, 2018 10:49 am

Mike,

I agree that 195 is higher than the design temperature. It is also far better than it was before the old Seachest was removed and the old through Hull removed.

I’ve now put about $15,000 into this overheat problem and I’m ready to enjoy the boat without worrying about it further.

Later today I’ll photographs and a parts list of what I did post it on the Boat website.

In the meantime I can’t imagine where to look?

I’ve put the remote pressure overflow tank on with a new cat. There’s no longer any signs of a leak in the engine is no longer consuming water, so I must presume the last water loss problem I had was because of local boiling rather leaking in the usual sense.

I do not think there any problems in the coolant system any longer. My infrared thermometer shows the heat exchanger rising above 160°. This indicates to me that coolant heat is being transferred to Ocean water at of acceptable rate.

The result may not be ideal as the engineers originally thought but it is perfectly acceptable to run the engine and extended period of time at that temperature.

If it were easy to put the thermostat back in I would do that, however on my boat putting the thermostat involves the removal of the heat exchanger and several other components.

Removal of these components requires removal of about a half a dozen hoses. This is the rough equivalent of a heart transplant on an engine. I’m just not willing to take the risk of introducing additional leaks and additional problems to find a remaining small problem that does not seem to influence the operation of the engine in a negative way.

The boat makes adequate domestic hot water, in fact it makes shower water faster than I can use it. I still have a tempering valve on the hot water heater to keep the domestic hot water temperature manageable.
Stuart Bell (561) 352-1796
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Re: 4BY2 Overheating - can the thermostat be removed?

Postby captstu on Tue Dec 25, 2018 4:28 pm

I've written up a summary of the overheating problem on my 4BY2. It may be of interest to anyone with a Ranger fitted with a Yanmar engine - because of the strange decisions Yanmar made on the thermostat placement.

Anyone with a Ranger should consider the photo and problems I had with the thru hull. Since there is an elbow installed prior to the shared sea chest, the engine is vulnerable to overheat if marine growth gets thru the screen before the strainer.

The writeup is on the boat's web page:

http://www.shearwater-sailing.com/index.php/solving-the-shearwater-cooling-problem/

While you are looking for your overheat, note that Ranger and Yanmar use distinctly different types of hose clamps. While my boat's Yanmar clamps are all in good condition, several of the Ranger-supplied clamps have failed - check your boats clamps carefully.
Stuart Bell (561) 352-1796
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R-25 Shearwater IV
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