Tuesday, January 21, 2014

Emergency Engine Starting

I recommend learning how to hot-wire-start marine engines. Our old monohull, a WestWind38, we briefly had a bad starter button and I had to learn how to start the engine without it. Diesels are easier to start than gasoline engines because all they need are compression, fuel, and air while gasoline engines also need high voltage spark to the spark plugs. I'll focus on diesel engines in this post because that's what is normally used in modern auxiliary sailboats.

You will need a good starting battery to turn over the motor to get it started, but electricity is not needed for the engine to run (unless it has a shutoff solenoid that needs power to allow the engine to run). To turn over the motor, you need to power the starter motor. The starter motor will normally have a big solenoid mounted on its side ('Solenoid' in the photo). There will be a big red wire from the battery connected to a bolt on the solenoid ('Battery Wire' in the photo). There will sometimes be another big wire connected to the solenoid, which provides the connection to the starter motor ('Starter Wire' in the photo). In other cases, this connection is an internal connection between the solenoid and the starter motor. There is a third, smaller wire that is the connection from the ignition for activating the solenoid ('Activation Wire' that's yellow/brown in the photo). There is a second photo from 2carpros.com that shows a clear view of the back of the solenoid.

Volvo MD2040D Engine Starter and Solenoid Components

Starter Solenoid, courtesy of carpros.com
The ignition switch at the helm supplies 12v on the Activation Wire (Starter Trigger Terminal in the photo to the right), causing the solenoid to be activated. Contacts internal to the solenoid close, connecting the battery wire to the starter wire, and causing the starter motor to turn.

Of course, the diesel has to have the engine stop disengaged, because that stops the flow of fuel. The Volvo MD2040 engines on LUX use a mechanical stop cable that causes the high pressure pump to stop injecting fuel into the cylinders, causing the engine to stop. Newer engines that don't have stop knobs will typically use a stop solenoid that is electrically activated.  If your engine uses one of these solenoids, you will need to hot-wire it to allow the engine to run. Learn whether your solenoid is activated to allow the engine to run or if it is activated to stop the engine. In the first case, you'll need to hot-wire the solenoid to allow the engine to run. In the second case, you'll need to hot-wire it to stop the engine. Or you may be able to pull the stop lever by hand - it depends on how the stop solenoid operates.

There are two approaches you can use to starting an engine when the starting system at the helm doesn't work. In both approaches, you must have a good starting battery. Make sure that the stop cable or solenoid is not engaged. Make sure that the engine is not in gear and the throttle is at idle setting.


When you hot-start an engine as I'm about to describe, you and your various body parts and clothing are very close to machinery that will soon be rotating. Getting a T-shirt caught in the alternator or water pump belt can yank you into the engine compartment and cause serious injury. Keep all body parts and clothing away from the engine. And watch out for the wire you're using to jumper the starter.

When you start the engine, your head is going to be close by a suddenly very noisy engine. Be prepared for the noise and don't react in a way that imperils you.

Method 1

If the starter solenoid is good, all you need to do is jumper from the Battery Wire to the Activation Wire on the solenoid. I use a good quality (16 gauge wire or greater) alligator clip jumper wire. Clip to the Battery Wire and touch it to the Activation Wire terminal on the starter solenoid. Make sure that you're clear of all rotating parts because the engine will turn over and should start. You'll also get a few sparks as you make contact. Note that the ignition does not have to be 'on' for the engine to start and run. This is like a lawn mower that can start unexpectedly when the blade is turned by hand. On LUX, the Activation Wire is an insulated terminal, so I have to remove it from the solenoid to gain access to the solenoid Activation Terminal.

Method 2

In some cases, you may have a dead solenoid. Either the coil in the solenoid has broken or the contactors are worn out and not passing the battery's power to the starter motor. In this case, you use a short, fat cable (#2 or larger) to jumper from the Battery wire to the Starter Wire. You're using the wire as a replacement for the big copper contactor that's in the solenoid. You may need two hands to properly hold the cable and make a firm contact between the two connectors on the solenoid. You'll get more sparks with this method, because there is a lot more current involved.

With both methods, don't leave the jumper wire connected for long. It should only be used long enough to get the engine started. The alternator should be charging if it wasn't damaged in whatever caused the starter solenoid to fail.

If you have an engine that has a compression release lever, and there is little battery power left, you can activate the compression release, start the engine turning over with the battery power you have, then release the compression release to get the engine started. This procedure would be useful where the alternators are also damaged and are not able to charge the batteries.

By learning how to hot-start an engine, you are a safer mariner, able to make landfall with engine power even if something like lightning takes out most of the electrical system.



Anonymous said...

I've had to use Method 1 and while it works, the sparking made me nervous. I've added a remote starter switch (typically used by auto mechanics) to my toolkit. The link to the one I bought is below.

Chuck Collins, Leopard 44


Terry said...

The sparks can indeed make one nervous, especially with Method 2 where more current is involved. The remote starter switch is a good idea, but requires that you have your toolkit handy. Knowing how to jumper a diesel motor is useful when on other people's boats. Be aware that the more modern diesel engines that have a traditional on-off ignition switch typically have a stop solenoid that must be activated to allow fuel to flow.