Yanmar 6BY 260 operating questions

What is the best balance of fuel burn, RPM's and engine load? What running temperatures do you expect at different rpm"s? A boat I am looking at has a 195 degree thermostat and a running temperature of 205 rising to 215 at high rpm's.

We have a 2011 rt 27 with the 4BY 180. It has a 195 Thermostat and when warmed up stays at 194 degrees. I would first at high RPM's put a heat gun on the exhaust just behind the engine, would see what the galley sink hot water temp is. Two things about diesels #1 heat is your friend because your heat igniting the fuel, and that water boils at higher temp when under pressure. Also check your coolant intake strainer, and know the condition of your Intake Impeller.

I have a 2013 R29 with Yanmar 260. I typically run 2900 to 3200 RPM's. Temps at 2900 typically 194-195. 3200 (12-14 knots depending on current) 199-201 temps. 3600 usually up to 205. I put a hose on the intake and blew it out reducing the temp so water flow is critical. I also ran barnacle buster overnight in the cooling system and it reduced temps by 2 degrees. Running at 2900 I typically see 1.4 gals/nautical mile and 1.2 to 1.4 per Nmile at 3200 depending upon current.

In our Yanmar 4BY2-150 we ran 185-190 degrees at normal crushing RPMs. At very high RPM it would go to 195-200 degrees.
Anything about 210 degrees is not normal. Above 215 degrees and you can start to damage the engine we were told by Yanmar.
Four things to check and act on in this order
1. Make sure the coolant is full right up to the fill cap. Doesn’t matter if you have coolant in the overflow container, the coolant needs to be right up to the fill cap on the engine.
2. As mentioned, clean the intake sea water strainer and make sure the hull intake grill is clear too.
3. Replace the impeller.
4. Run a batch of Barnicle Buster through the sea water intake system. See other posts on that for the process.

William Sanborn said:

We have a 2011 rt 27 with the 4BY 180. It has a 195 Thermostat and when warmed up stays at 194 degrees. I would first at high RPM's put a heat gun on the exhaust just behind the engine, would see what the galley sink hot water temp is. Two things about diesels #1 heat is your friend because your heat igniting the fuel, and that water boils at higher temp when under pressure. Also check your coolant intake strainer, and know the condition of your Intake Impeller.

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Thanks. That's helpful.

Captmike said:

I have a 2013 R29 with Yanmar 260. I typically run 2900 to 3200 RPM's. Temps at 2900 typically 194-195. 3200 (12-14 knots depending on current) 199-201 temps. 3600 usually up to 205. I put a hose on the intake and blew it out reducing the temp so water flow is critical. I also ran barnacle buster overnight in the cooling system and it reduced temps by 2 degrees. Running at 2900 I typically see 1.4 gals/nautical mile and 1.2 to 1.4 per Nmile at 3200 depending upon current.

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Good ideas!

I run exlusively at 2.5 gph at 2000 rpms, about 7kts depending on wind and currents. temps range from 189F in the winter to 192F in the summer. When doing multiple days in a row, I will run the boat up to 80 percent load for about 5-10 minutes to blow out the exhaust elbow about every 5 days or so.

fishheadbarandgrill said:

I run exlusively at 2.5 gph at 2000 rpms, about 7kts depending on wind and currents. temps range from 189F in the winter to 192F in the summer. When doing multiple days in a row, I will run the boat up to 80 percent load for about 5-10 minutes to blow out the exhaust elbow about every 5 days or so.

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Thanks for that information... When you run it up to 80% what temperatures do you see?

Thanks for that information... When you run it up to 80% what temperatures do you see?

Lee said:

Thanks for that information... When you run it up to 80% what temperatures do you see?

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203F in the winter and 205F-206F in the summer. The thermostat is fully open at 205F if I remember correctly. I have a post on that.

fishheadbarandgrill said:

203F in the winter and 205F-206F in the summer. The thermostat is fully open at 205F if I remember correctly. I have a post on that.

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Thanks!

Lee said:

What is the best balance of fuel burn, RPM's and engine load? What running temperatures do you expect at different rpm"s? A boat I am looking at has a 195 degree thermostat and a running temperature of 205 rising to 215 at high rpm's.

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You have a couple different question in you post. I will answer your first question (best balance of fuel burn, RPM and load) Diesel engine manufactures have a rating system. This gives a base line of how the engine is designed to operate. This rating does not predict longevity it basically limits the operator from premature destruction of the engine. I consider this engine failure with-in the warranty period. The common rating for most engines installed in a recreational vessel is (Rating 5- Pleasure Duty) or (M5 High output ) The recommendation of this rating is. ( Infrequent, light use (pleasure boats). Full power for brief periods (1Hr during a 12 hour period) under 300 hours/year. High RPMs will shorter lifespan.)
Another description with added recommendations
(This power rating is intended for infrequent use in variable load applications with a load factor of 10-30 percent. Full power is limited to one hour out of every eight hours of operation. Reduced power operation must be at or below 80 percent load.)

The inboard diesel engines that have been used by Fluid Motion Yanmar and Volvo Penta are rated has pleasure duty engines. IMO and the opinion of many marine servicing technicians fuel burn is the best indicator of how a Pleasure duty engine should be operated to maintain longevity. Fuel burn can be used in two ways. The rule of thumb is for every Liter of displacement the average fuel burn should be 2.5 gph per liter of displacement. The 6BY is 2.99L (3.0L x 2,5gph = 7.5 gph). This would in my opinion be the fuel burn rate that I would recommend operating the 6BY at. The load can be figured by max fuel burn rate. The 6BY properly propped should turn 4100 rpm and the max fuel burn should be 13.6 GPH. 260HP/13.6 gph = 19.1 horse power made from 1gph burned. If you set your max cruise range at 7.5 gph your 6BY will be making 143 hp. 143 hp is about 45% load. This should put the engine at just beyond max torque rating. What rpm is this? it will depend on the way the boat is loaded and propped. Most Ranger Tugs are over propped. Why? Because the factory props them for marketing not for best overall use. Most Tug owners use their boats for cruising. Full fuel, water, and gear. The added weight reduces the engine ability to make full rated max RPM which is essential for longevity. The best way to prevent reduced engine longevity is use fuel burn as your best cruising speed indicator not rpm. Bottom line keep your average max load below 50%.

What running temperature should you expect at different rpm. The bottom line is once the engine reaches engine operating temperature ( thermostat opening temperature ) the max differential should be -0/+5%. The thermostat opens at 190F this should be the operating temperature of the engine if all cooling system plumbing is installed correctly and in good operating condition. The thermostat purpose is to maintain a steady engine operating temperature. Opening and closing and throttling the coolant to achieve an even constant running temperature. The full open thermostat temperature is 205F. In a proper designed and installed vessel raw water cooling system the only time the engine should reach full open thermostat temperature is when the engine is under full load. The cooling system should be sized and installed to maintain the engine temperature with in the thermostat range. 190F to 205F. I use the 5% rule 190+ 5%=199.5, 200F is the highest I want to see at full 100% load engine making full rated RPM 4000 rpm + 100rpm. If I experience more than that it is caused from a poorly designed cooling system, causing restricted flow of cooling water. Or obstructions in the coolant system reducing coolant flow and reducing the coolings system to properly heat sync. The other cause which is common is an improperly propped engine that is operating over loaded causing excessive internal engine temperatures. If your engine is operating above 205F it is operating overloaded or has a compromised cooling system. At what point do you draw the line. IMO anything over 210F you have compromised cooling system that will reduce the engines longevity. At what point would I make changes to my cooling system? IMO if I have an engine that I can not push the sticks down and run WOT for 5 minutes and not maintain thermostat opening range in this case 190F to 205F I will make changes. I would not live with anything above 205F and would prefer 200F as max temperature with the average operating temperature running at 190F to 195F when operating at 50% load.

I don't know how to properly thank you for such an informed and detailed answer to my question. The time you have taken to address this issue is greatly appreciated! I have heard many opinions that the Renger Tug coolant water inlet may be undersized, and increasing the diameter of the through hull is advantageous. I wonder if anyone has established the optimal specs of the prop for the Ranger Tug 29 with the Yanmar.

Lee said:

I don't know how to properly thank you for such an informed and detailed answer to my question. The time you have taken to address this issue is greatly appreciated! I have heard many opinions that the Renger Tug coolant water inlet may be undersized, and increasing the diameter of the through hull is advantageous. I wonder if anyone has established the optimal specs of the prop for the Ranger Tug 29 with the Yanmar.

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In another lifetime, Brian Brown was a marine technician. Whatever he recommends, one can take to the boating bank.

That background was what I suspected from the articulate and knowledgeable posting...!