You gotta love diesel engines.
When they run the way they should, they purr like a kitty.
But when things go wrong, they can be a real pain.
Here are some troubleshooting tips that can help you get your diesel truck back on the
Cold weather vs warm weather.
As you probably know, diesel engines can act very differently in cold weather. They can
be cranky, hard to start, and temperamental.
When temperatures drop, there's a whole line up of problems that plague diesel
Oil thickens which requires more battery power to turn the engine.
Available cranking power in the battery decreases.
Colder engines are harder to start because diesel engines rely on heat from
compression instead of a hot spark from a spark plug.
Water from condensation can accumulate in the fuel system.
Diesel fuel thickens and will sometimes form wax deposits.
Troubleshooting Starting Problems
Does the engine turn over? If yes, does it turn over fast enough?
If the answer is no to either of these two questions, check the battery cables and connections, clean if needed, then try
starting your truck again. If it still won't start, try jump starting your vehicle.
If your vehicle starts by jump starting, allow it to run for 10 to 15 minutes. While it is running test the alternator output
with a meter by placing the leads across the battery posts on the DC 20 volt setting. The voltage reading should be 13.5
to 14.5 volts while running. If the reading is less than 12.8 to 13 volts the alternator is either not working correctly or there
is a wiring problem.
If the alternator voltage tests normal, test the battery(ies) as follows:
1. Shut off the engine if it's running. Make sure the engine has been running long enough to charge the battery(ies)
2. Turn on the headlights for two minutes, then turn off.
3. Measure battery voltage. Voltage should read 12.4 to 12.6 volts.
4. You will need assistance for this step. Measure the voltage while someone cranks the starter. You should see the
12.4 to 12.6 volts before starting the vehicle.
10 to 11 volts while the starter is cranking
13.5 to 14.5 volts after the vehicle starts (if it starts)
If the voltage drops below 10 volts while cranking, the battery is probably on its way out. A voltage of 5 to 8 volts while
cranking means the battery (or batteries) is definitely in trouble.
If your vehicle has two or more batteries connected in parallel, batteries can be tested individually by removing them
from the vehicle and running the voltage test by placing the battery in another vehicle (preferably a gas vehicle) and
measuring the voltage as described. Be sure to mark cables before disconnecting.
(This is for a light duty diesel truck. This will work for a big rig if the batteries are not too large to fit in the battery
Alternate method for testing big rig batteries:
Mark the wires and cables and take a picture of the batteries and connecting cables for later reference if needed.
Then disconnect the cables so that no two batteries are connected, and the batteries can be tested individually. Test
each battery with a battery tester. No load voltage should be 12.2 to 12.6 volts. Test the voltage under load. Most battery
testers have color coded voltage scales that will tell you if the battery is good.
If engine turns over slowly and the battery voltage checks out, check the viscosity of the oil. Engine oil may be too thick.
Engine oil for diesels should be changed to a lighter weight in cold weather.
If the battery tests good and the engine will not turn over, you will need to check all your wiring connections. There may
be a bad ignition switch, loose connection, broken wire, or starter problem. Corroded battery posts are sometimes the
If the engine turns over properly but won't start, you can make a few quick checks as follows:
OK, so this sounds stupid, but everyone has done it. See if you have fuel in the fuel tank.
Do a quick check on the air filter. Replace if dirty.
Check the water separator. Drain if needed.
Use winter diesel fuel if you haven't already.
Check the fuel filter. Replace if needed.
Fuel pressure from the tank to the injector pump can be safely tested. Testing fuel injector pressure can be very
Testing injection pump output pressure by someone other than a qualified diesel mechanic is not recommended.
THIS IS A RISKY TEST. DO NOT DO THIS IF YOU ARE NOT QUALIFIED. INJURY OR DEATH IS A DEFINITE RISK
If your diesel engine is equipped with glow plugs, check the condition of the glow plugs. Glow plug may be tested while
still in the engine, or it may be tested out of the engine.
1. Remove the glow plug cap (if testing while still in engine). Use a multi-meter on the lowest resistance setting to test
the glow plug resistance.
2. Place the negative lead of the meter on the outside part of the glow plug and the positive lead on the top part. The
meter should read 1 ohm or less for a working glow plug. If it reads much higher than that, the glow plug is probably bad
and needs to be replaced.
Keep in mind that the majority of starting problems, around 90%, are caused by contaminated diesel fuel. Water in the
fuel, dirt, or other contaminants sometimes appear in diesel fuel. Some diesel fuel dealers have been known to add
dirty engine oil to fuel tanks as a way to make a few extra bucks. You can imagine how that would affect the fuel system
For problems starting in warm weather, if the battery is fully charged, the problem is usually fuel-related .
Check air filter, water separator, and fuel filter.
Faulty glow plugs can also be a problem, even in warm weather.
Black smoke is caused by too much fuel entering one or more cylinders. The cause is usually a faulty fuel injector or
injectors, faulty injector pump, or clogged air filter.
White smoke is caused by insufficient combustion. This happens frequently when the engine is first started. If it
continues after the engine is warm, it probably indicates the injector pump timing is off or engine compression is low in
one or more cylinders. It can even be caused by water in the fuel.
Blue smoke is never a good sign. This is an indication that one or more cylinders are burning oil. Worn piston rings, bad
valves, or worn/scored cylinder walls are the culprit. If you have to add engine oil frequently that is a sign the engine is
either burning oil or leaking somewhere.
Overheating can be disastrous to a diesel engine so it must be avoided as much as possible.
Check coolant level with cool engine. Check condition of coolant. If coolant is low look inside the radiator. (Not all
radiators allow you to do this). Look at the condition of the cooling tubes. They should be clean and free of sludge and
chemical deposits. Have radiator serviced if necessary.
Check condition of hoses and all connections. You can usually smell antifreeze if there is a leak.
Check oil level
Check radiator cooling fins for bugs or other debris and clean if needed
Some trucks use electric cooling fans instead of belt-driven fans. You may be able to hear the fans run (with your
window down) if engine idles for very long. Check electric fans and belt-driven fan if so equipped.
Check belt tension and condition. If you find a broken belt, do not start your truck. Irreversible damage may occur.
Check tire pressures
Check to make sure no brakes are dragging
Gear down in hot weather and turn off the AC if engine starts to get too warm
Spokane Diesel Truck Repair
23514 N Austin Rd
Colbert, WA 99005