bertram31.com

I read AndreF's reply in the "Diesel Fuel in oil pan" post regarding leaving a 6BTA at idle for too long with great interest. Andre put this up from his engine manual:

"Caution; Do not idle the engine for excessively long periods. Long periods of idling (more than 10 minutes) can damage an engine because combustion chamber temps drop so low the fuel will not burn completely. This will cause carbon to clog the injector spray holes and piston rings, and can cause the valves to stick. If the engine coolant temp becomes too low (60 C (140 F)), raw fuel will wash the lube oil off the cyl walls and dilute the crankcase oil; therefore, all moving parts of the engine will not receive the correct amt of lubrication."

We do a lot of salmon fishing here in Northern California where trolling at 1.5-3 knots is the norm - in other words, trolling at idle speed. With 454's, I actually shut one engine down and trolled at idle speed on the other to keep below 3 knots. With the repower, I am planning on transmissions with trolling valves to ensure that I can keep Shambala below 3 knots with bigger wheels. I've fished on a friend of mine's Blackfin 32 with Yanmar 4LH's and trolling valves and they worked great at keeping us in the 1.5-3.0 knot range.

However, after reading Andre's posts I am now wondering if/how I will be able to keep the cylinder temps up high enough at what is usually idle speed trolling. All the trolling I"ve ever done on boats with trolling valves has been at idle speed

Would changing the thermostats on a 6BTA to keep the cooling system temp warmer at idle prevent potential damage from the loss of lubrication mentioned in Andre's manual?

Is there a different injector size that I should be inquiring about from Cummins that would prevent the lubrication issue at idle?

Thanks in advance.

John Vietor

John,

I have Cummins 6BTA's (370's) in my boat as well and have asked the same question for the same reason. I have a few, somewhat random, thoughts on this. (full disclosure: I'm a diesel newb but reading / learning/ living it)

First if you have not joined up over at http://www.boatdiesel.com" onclick="window.open(this.href);return false; I can tell you it is worth every penny. The Cummins "B Series" forum is super helpful. There is so much good info there it is amazing. Tony Athens, who owns Sea Board Marine (http://www.SBMAR.com" onclick="window.open(this.href);return false;), moderates the Cummins forum and is very knowledgeable. He addresses this very question here: http://www.sbmar.com/articles/low_speed ... e_diesels/" onclick="window.open(this.href);return false; Poke around on his website and in the Cummins forum and you'll find additional information on this and many other subjects. Don't want to appear to be a "fanboy" here but Tony has been very helpful to me and, yes, he sells all sorts of stuff for these engines and installs them / sells them etc.

Running these diesels at the dock in neutral is not good for them at all. As long as you are in gear you get reasonable heat in the cylinders and don't have issues. I start and go as soon as possible then I have about a 1.5 mile idle through a no-wake area anyway. I get a slight amount of smoke that disappears as soon as I put the motors in gear. Why? Well, same RPM but a little more fuel to hold RPM with a load that results in higher combustion chamber heat. At least that's my theory. In an otherwise healthy engine, smoke at no or very light load is un-burned fuel.

My motors run 180 to ~ 185F under all conditions / loads when in gear. If I go to neutral they cool down to about 170 to 175 using stock thermostats. If you get similar numbers and are thinking about changing these to run hotter, think really hard. Overheats are the kiss of death for these motors (and for other high speed / high output diesels in particular) and can happen really fast at speed. I think you'll be fine if you idle with a load, meaning in gear, not idling at the dock.

OK, now I'll let the real experts chime in here....

Hope this helps!

JD

JD,

Thanks for that. Yes, I am a member at boatdiesel.com and I did post the same question over there hoping Tony might chime in. He has been a great resource regarding the 6BTA's for me on the West Coast and I am expecting to put his water pumps and crankcase breather on my 6BTA's right out of the box.

I always start here because of the boat specific knowledge.

I think my biggest concern about the trolling valves had more to do with how much of the load was released by the trannies slipping when the trolling valves are engaged. Is there still enough load to keep the cylinders at an optimal operating temp.

Thanks for the response. I appreciate it.

John Vietor

John,
If this was a real serious issue, truckers would never get half million to a million miles out of their engines because half the run time is at a truck stop, loading/unloading.

I drove over the road for two years in the 70's and I never shut the engine off even when fueling.

Dive boats, trolling are all done mostly while idling.

I wouldn't be worrying unless one plans on running in water that has ice flows.

Beautiful. That's all I needed to hear!

Thanks Bruce!!!