R - 29 COOLING PROBLEM

[Thomwa]

6 cylinder Yanmar 150 hours, cooling expansion tank may be too small. I try to keep the expansion tank filled to low add line with the engine dead cool then run engine up to normal operating temp (low 200's). While the engine is at operating temp the expansion tank is full. If I fill any fuller than the low line it overflows and makes a mess around the bottle. Is this a common problem for the 6 cylinder, do I need a larger expansion tank? or is my engine running hotter than it should? I have looked for coolant leaks everywhere and also monitored the engine oil meticulously with no signs of coolant anywhere except around the expansion tank. Should I try changing my thermostat, my engine goes up to 212 degrees when held wide open 20 minutes. Andrew says that this is within limits. I will be interested in your comments and recommendations.

 

[SlackwaterJack]

The expansion tank should only have fluid in it up to the bottom of the "low" mark when the engine is cold, as the engine heats up, the expanded coolant will fill it to the "hot" mark. Then, as the engine cools, it should siphon the excess coolant back from the tank to the "low" mark when the engine is again cold. If the tank doesn't return back to the "low" line when cold there may be an air leak in the line from the tank to the heat exchanger. If the coolant isn't retuning to the "low" mark it can creat a "rachet effect" in that the fluid remains high in the tank and when next run the excess coolant will cause an overflow especially if more coolant is added to the heat exchanger.
During the course of operating coolant should only be added to the expansion tank just to the high mark with a hot engine, and not added to the heat exchanger when the engine is cold...same as your car. And also, like your car, the pressure cap on the heat exchanger (radiator) should only be opened when changing (draining and refilling) the coolant... and NEVER when the engine is hot. Never fill the expansion tank above the "hot" mark.

 

[SlackwaterJack]

Forgot to mention ...you should check that the tube that goes from the plastic snap-on expansion tank cap to the bottom of the expansion tank isn't missing or dropped off...that would prevent the coolant from being sucked back as the engine cools.

 

[Zuma]

Tugnut Search the terms "engine operating temp 6BY260" for quite a discussion on new 29's operating temperatures and issues from a year or so ago.

 

[JerryE]

The 4BY also seems to run hot. The manual says it should be 205º at WOT, but I'm running more like 210-212º which Andrew has also said is within specs. This may be why some or our engine hoses are straining under the pressure to keep the coolant from boiling. The (slightly) older engines liked to run around 175º so its hard to get used to these hot temperatures which, I guess, are needed for emission control. I suspect this is going to be true of all "common rail" engines which electronically (via the ECU) open the ejectors. This is supposed to represent a revolution in diesel engine technology, according to the suppliers of these systems to Cummins, Yanmar, etc.

Common rail systems require little or no heating up thus reducing noise and emissions. The most sophisticated systems can vary and produce up to 5 injections per stroke. For example, the ECU can inject a tiny amount of diesel (a pilot injection) just before the main injection reducing vibration and explosiveness. Varying the amount and timing of injections improves cold starting. The mechanical systems were cam driven and injected fuel in proportion to engine speed, only.

The system of having all the fuel injectors supplied by a common fuel (rail) source has been around for a while. Wikipedia reports they were used on submarine engines around 1916 and locomotives in the 1940s. After reading about the system, I'm beginning to have more confidence in the likelihood that the ECU knows what it is doing when it keeps the engine running at such high temperatures. It just seems scary...

 

[PhilR]

The 4BY2- 180 in my R-27 runs between 190 and 206 deg. I know from experience that the "hot engine" light and horn go off at about 228 deg. as I have had two hose failure incidents in the rearmost of the two portside coolant hoses. The second one I caught at 210 deg and shut down. That particular hose makes contact with engine parts in the vicinity of the oil dipstick which caused some abrasion and contributed to the first failure. We put a protective sleeve over a section of the hose when it was replaced.

Phil

 

[doke01]

Thomwa,

I have had the same issue with the 125HP Yanmar. I just did a coolant flush this year and I am hoping that helps. Let me know if you find out anything. I have found that keeping the expansion tank nearly empty when cool is the only thing that keeps the fluid from overflowing.

 

[SlackwaterJack]

The expansion tank should only have fluid in it up to the bottom of the "low" mark when the engine is cold, as the engine heats up, the expanded coolant will fill it to the "hot" mark. Then, as the engine cools, it should siphon the excess coolant back from the tank to the "low" mark when the engine is again cold.

the level in the expansion tank is supposed to be low when the engine is cool. It can even be below the "low" mark as long as the siphon tube isn't high and dry (sucking air into the system). When your engine is cold the tank is supposed to look "nearly empty".....
If you fill it when the engine is cold it would just be a "tank" not an "expansion tank".

New style diesel engines are designed to run "hotter" for better fuel burning (clean burn technology due to the new regulations)
The pressurized cooling systems now run at higher pressure than they used to (cars have been like that for years). The thing you don't want to happen is for your coolant to BOIL. Basic H2O boils at 212deg(sea level) and the coolant (it's not water anymore now that you've added anti-freeze) boils a bit higher. Then increase the pressure inside the system by 15-20 lbs and you won't boil until around 230 deg(ish). If you normally run at 210-220 deg you're well under where the coolant will boil and cause the engine to overheat. (boiling water adds air .. and air doesn't cool very well)