Air heater – how long to operate

[Paul Berkshire]

Hi Tony,
I’m bypassing the ECM on my 6BTA 270 and wiring it with a switch and a light. My question is when and for how long should the air heater be engaged? Seems like pre-heating for too long could draw down cold batteries

Topic

[John]

After one of the contactors shorted out, I removed the ECM, all contactors, and wiring harness (that was fun). I could wire the heater grid in the JWAC, and control it with a switch, but I’ve not found the need for the heater. The boat is active from April to November in Rhode Island, and other than April and November, I’ve not had a problem with cold starts. I’m on a slip, plugged in, and the block immersion heater (Fleetguard #3825424) is on during the cool April/November months.

[Tony Athens]

Kevin,

You are pulling parts of the “circuit” out of context…

In what you just described, the engine OEM harness & all the ECM CRAP have been removed from the engine and now, you just have ONE solenoid operating the elements along with a coupling of wires vs. about 10 lbs worth. ..There are more wires on your engine to run the factory grid heater than to run the engine and the gauges at the helm..

Look & Study these two diagrams..

Cummins Marine Heater Grid Assembly Wiring Diagram

Simple Cummins Marine Grid Pre-Heater Control Setup

Tony

[firehoser75]

Kevin,
If I understand you correctly, that is how mine (following Tony’s tip) is wired. We only “cut in” to the low amperage part of the existing circuit and installed an on/off switch. We did not add a solenoid, but probably did add a low amperage fuse if I remember correctly.
Tom

[Kevin Carlson]

In Tony’s article he shows adding an auxiliary solenoid to power the heater elements. I don’t see why you couldn’t use the existing solenoids from the ECM and just hook up power to the low amperage connections. They are already hooked up to the heater elements.
Kevin

[firehoser75]

Clark,
In the application being discussed, if I were to forget to “turn the switch off”, all that would happen is what happens on the vast majority of engines with the air preheat system (very few have wired in a switch), and that is the preheat will cycle on and off until the engine reaches either a preset RPM or temperature.
Rob,
I have only started the engine without the preheat a couple of times so not a great “test”. However, without the preheat “its seems” to take a bit longer (more cranking) to start and with a bit more smoke. In this case, being as my engine starts easily and does not smoke much, a bit is maybe one or two seconds longer with a very small amount of additional smoke. So far (2 full seasons of use with about 90 days aboard each season), we have only forgotten to turn on the preheat once, and forgotten to turn it off (when we wanted it off) twice, and both times were early after the new install and we had not gotten our “routine” down yet. I know you can remove (disable) the whole system, but I thought having the option to still use it for starting while being able to manually control it seemed like a better idea. I just don’t want it (preheat) running while I am using the anchor windlass or thruster even though they have a dedicated battery.

[Rob Schepis]

firehoser Tom, do you actually see a difference when you use the grid heaters as to cold smoke or ease of cold start?

[Clark Leighs]

Different application but I use a MOM on, OFF sw. from COle Hersey.

For 10 or more years I used a standard on/off switch to control a small hydraulic motor. I used this thing often. Never a problem untill this last summer I forgot to shut it off. I got distracted. Burned the motor up and had to replace it.

I included in the repair the MOM on/OFF and now I don’t have to remember, just let go.

Sooner of later you will forget, It may take years like mine but it will happen.

[Tony Athens]

Reading this may show how simple & safe this could be.. The was on a 6BTA 260, but the setup is the same.

Simple Cummins Marine Grid Pre-Heater Control Setup

Tony

[Paul Berkshire]

Thanks. My problem is that the previous owner trashed the ECM so I don’t have the option of just interrupting the power supply to it. I either have to acquire a new ECM and the associated wiring or go with a completely manual system if I want an air heater

[firehoser75]

Paul,
My switch is not “straight” on or off. When the switch is “on”, the preheat will function as programmed by Cummins. That is, it preheats for about 10 seconds for starting, and then it will cycle on and off until you reach a preset engine temp (I think 140, but don’t quote me) or you increase RPM above a set figure (and you usually won’t be above the set point RPM until after warm up). The reason for this cycling is “pollution control”. When the switch is off (again the way mine is wired as per Tony), the preheat does not function. Because I turn it on prior to start and off right away after start, I don’t forget, as it has become habit.
My understanding is that when the preheat cycles on, after starting the engine, it draws a large amount of power, and is hard on the alternator especially if you are using another large draw at the same time (eg. windlass or thruster).
I am very happy with how mine works and can observe the results on the volt meter (voltage does not drop anymore like it did before the installation of the switch). Tony’s idea of a timer is another way to achieve the same result.

[Paul Berkshire]

Thanks Tony,
Is there any merit behind the “theory” the air heater is bad for your alternator when running? From what I’ve gathered the ECM cycled the air heater every few seconds versus a constant draw from a straight on/off switch

[Tony Athens]

Use an old fashion 5 minute twist timer– Usually 2 minutes is all you need–You’ll forget your switch.

Tony

[firehoser75]

Hi Paul,
I have the preheat wired with a switch on my boat. I only use the preheat for the first cold start each day. I turn on the preheat switch prior to turning the “power key”. As I turn the key on, I watch the voltage drop (quite drastically) indicating the preheat is “ON”. As soon as the voltage moves back up (usually about 10 seconds or so), that is when you start. For me, as soon as the engine starts, I turn off the preheat switch, as I only want the preheat to help with the start and to reduce or eliminate smoking at start up.
When at a dock with power, I use an oil pan heater. Keeps everything nice and warm.
Hope this helps,
Tom

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