4BY2 Overheating - can the thermostat be removed?

[Osprey]

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?

 

[knotflying]

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.

 

[captstu]

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
Ranger 25: Shearwater
(561) 352-1796

 

[knotflying]

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.

 

[captstu]

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.

 

[captstu]

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.