For farmers in particular, a simple, durable machine that can be fixed on the farm without expensive tools is invaluable. And most machines that fit that description are not new ones. Keeping your old machine working can save you money at least twice: the first time when you don’t have to buy a new machine, and the second time when you don’t have to pay the expensive mechanic at the dealership to fix it.

Let’s begin with starting problems in diesel machinery, because most of the reasons for starting difficulties are fixable by mechanically inclined people without a lot of special tools or training. This is low-hanging fruit for the do-it-yourselfer.

If you have a basic tool kit and mechanical skills (including how to use a voltmeter), you can troubleshoot most of the reasons a diesel might be difficult to start. Certainly there are starting problems that older diesel engines can have that are beyond the abilities of the normal “shade tree” mechanic, but often if you start by fixing the easy stuff, you will find that you have a good running machine on your hands again.

Diesel engines are so durable and simple that the majority of the problems they have are not actually problems with the engine at all. Instead, most of the problems are with external components, like wires and starters, or consumable items like glow plugs or filters.

The following advice can be applied to all diesel equipment, including cars, trucks, tractors and anything else, but is especially for those of you that own diesels made in the 20th century. As the models get closer to the new millennium, all of the following still applies, but there can be additional complications.

The first step in troubleshooting a starting problem is to decide if the problem has to do with fuel or electricity (or both). If nothing at all happens when you turn the key, you definitely have an electrical problem. It could be as simple as a safety switch or as complicated as a broken wire, but luckily we are talking about an old diesel engine, so its electrical system is not very complicated.

Think simple stuff first: Does the transmission need to be in a particular gear to start, or is there a safety switch on other components like the power takeoff (PTO) or even the seat? How about a “kill switch” or battery disconnect? Think for a minute before you declare it “broken.”

If the engine does turn over when you try to start it, you should start to see white vapor coming out of the exhaust pipe pretty quickly. It might look like smoke or steam to you, but it should smell like diesel fuel. If you don’t see the vapor, you probably have a fuel problem. Again, start with the easy stuff: Is there fuel in the tank? Is there a fuel shut-off valve?

Lots of old diesel machines are turned off by pulling a shut-off cable. If someone doesn’t remember to push it back in after shutting down, that can keep you from getting started. Clogged fuel filters usually cause other problems (like seriously reduced power) before they actually keep a machine from starting, but sometimes they can be the culprits, especially in very cold weather.

If your engine is not turning over vigorously when you try to start it, you probably need to look at electrical stuff, especially if you see fuel vapor and thus can rule out a fuel problem.

It can sometimes be hard to decide if the speed the engine is turning over is fast enough if you don’t know the machine well or just don’t have your ear tuned to the sound of starting diesels yet.

Luckily, there are some things you can check to get some clues.

First, before you do anything else, check your battery voltage with a voltmeter. I will assume we are talking about a 12-volt system here, but if you have a different voltage system you can just multiply my numbers by two for 24-volt systems or divide by two for 6-volt systems. If your system is anything other than 6, 12, or 24 volts, send me a picture because you have something pretty interesting on your hands!

The battery on your 12-volt system should show around 12.6 volts after the machine has been sitting overnight or longer; 12.7 volts is better, and anything under 12.6 means you should begin by charging the battery.

If battery voltage is a recurring problem, you should check the alternator. A rule of thumb for any age machine is that the battery voltage with the engine running should be at least 13.8 volts, and should be very steady, even with every electrical accessory turned on. Higher voltage is even better, up to about 14.5 (and steady).

Older machines used to be designed to charge at 13.8, but because of changes in battery technology most are designed to charge at over 14 volts now.

At 13.8 volts your battery will charge okay in the summer but that is really not enough to keep a battery fully charged in cold weather (it takes more voltage to charge a battery when it is cold), so if your charging system is set at 13.8 and you run a lot in the winter, you should consider trickle charging your battery when you are not using it to maintain it at full charge.

If your alternator is charging well, and you still have a weak battery in the morning, you should look for the possibility that something on the vehicle could be draining the battery when you are asleep. The easy way to identify this problem is to disconnect the battery overnight and see if it holds a charge. If it does, your tractor is a vampire and is sucking your battery dry at night.

If your battery is in good shape and fully charged, the next things to check are the big wires and connections from the battery. If they are dirty or corroded, that could be a place where you are losing power. If you aren’t sure, a really easy way to check is to try cranking the engine for a while (5 to 10 seconds) and immediately go feel the big wires with your hands.

Be careful, they could be hot (but they shouldn’t be)! Any warm spots are bad; they indicate a place that is resisting the flow of electricity. There are other more precise ways to test battery cables with a meter, but the heat test is easier. Small amounts of resistance might not heat up a cable enough to feel, especially on a cold day, but the big resistances will be easy to feel, and can even start to make smoke if you crank for a while.

Replace those cables; clean the battery connections and the connection at the starter. Don’t forget the ground cables and connections too. All electrical connections should be clean, shiny metal.

When it comes to battery cables, I am of the opinion that you can’t overdo it. I buy oversized cable (at least as large or larger than the original), I crimp (and sometimes solder) the connections on the end, and cover any exposed copper with heat shrink insulation (the fancy kind with the glue in it).

Some people disapprove of the amount of time and money I put into my overbuilt battery cables, but I feel that I’m just doing what they should have done at the factory in the first place; make battery cables to last! Battery cables don’t need to wear out as long as you protect them from corrosion and mechanical strain.

The cables I build will easily last as long as the machines I put them on, and I will never again have to wonder if the cables are the problem.

One more thing about troubleshooting slow-starting engines: People often think that if they can get a machine started with a jump, they must just have a weak battery. Unfortunately, this is not enough information by itself. Just because you can jump-start your machine with another running machine, you can’t assume the battery is the culprit.

The extra voltage supplied by a running engine (up to 14.5 volts, remember?) can push right past a bunch of resistance from bad cables and connections. Check for warm cables after jumping, and fix any you find. Treat the disease, not the symptom.

If you have checked all the above, but your diesel is still hard to start, don’t lose hope. There are still several more things you can check that are not expensive or fatal.

Glow plugs (if you have them), block heaters for cold weather and the kind of engine oil you use can all have a big impact on starting performance. More on those topics in a future article.  FG

Ron E. Wold is an ag instructor, musician, mechanic, welder and blacksmith in Vermont.