Diesel engines are serious misers in terms of sipping fuel. They’re also identified for their pulling power and rugged durability. Which is why diesels continue to be a popular choice in many pickup trucks these days. But diesels may also be known for their idle clatter, black smoke and cold-weather starting up complications.

When temperatures drop, numerous elements take place which can make a diesel hard to start. First, the oil within the crankcase thickens. Concurrently, battery output drops, lessening the volume of amps accessible to crank the engine. The 15W-40 multi-viscosity motor oil, a well-known warm weather selection with lots of diesel owners as of late, could grow to be too thick when temperatures go below freezing or plunge to zero or beneath. Straight 30- or 40-weight oils would surely be as well thick. The increased drag established by the cold oil can lessen cranking speed to the stage exactly where the engine might not make ample cranking compression and/or fuel strain to light the fire.

One of the 1st factors you ought to test when diagnosing a “hard to start” complaint, as a result, would be the dipstick. Should the oil is thick and globby, it might not be the proper viscosity for winter driving. Ask the customer what type of oil he’s been working with and when it was final adjusted. Switching to a lighter oil this kind of as being a 10W-30 (never ever anything at all lighter within a traditional oil!) may possibly be all which is required to enhance cold cranking. For genuinely cold weather, you could advocate a CG-4 rated synthetic motor oil.

The following issue that wants to become checked is minimum cranking speed. The rpm necessary to light the fire will fluctuate in keeping with the application, but Basic Motors says its 6.2L and 6.5L diesels with Stanadyne rotary injection pumps have to have at the very least 100 rpm when cold, and 180 rpm when hot.

Should the engine isn’t cranking speedy ample, test battery charge and problem, at the same time since the cable connections and also the starter’s amp draw. Difficulties in any of those areas can make any engine not easy to start. Should the battery is lower, recharge it and test the output from the charging system, as well.

GLOW PLUGS & DIESEL Starting up Complications

If slow cranking isn’t the problem, perhaps there’s something wrong with the glow plug system. Most passenger car and light truck diesels have glow plugs to assist cold starts. The glow plugs are powered by a relay and timer that routes voltage to your plugs for the prescribed quantity of seconds. When the timer runs out, the relay is supposed to turn off the voltage. But relays sometime stick and carry on to feed voltage for the glow plugs causing them to burn out.

One or two bad glow plugs on a V8 engine might not cause a noticeable beginning problem during warm weather, but it can when temperatures drop.

Glow plugs can be checked by measuring their resistance or continuity. Excessive resistance or a lack of continuity would tell you the plug is bad.

If one or more glow plugs have burned out, are heavily coated with carbon or are not receiving their usual dose of start-up voltage, the engine will develop into progressively harder to start as temperatures drop, and will idle roughly and produce white smoke during the exhaust for several minutes once it finally starts. If all the glow plugs are burned on the end, you’d better check out the injection timing because it is probably overadvanced.

To see when the glow plug module is providing power to your glow plugs, use a voltmeter to check each plug for the specified voltage when the ignition key is turned on. No voltage? Check out the glow plug control module connections, ground and wiring harness. The glow plugs themselves can be checked by measuring their resistance. Replace any plugs that read out of specifications.

Really hard beginning can sometimes be caused by a glow plug module that fails to turn the glow plugs on or doesn’t keep the plugs on long sufficient when the climate is cold. On GM 6.2/6.5L diesels, there have been reports of heat from a still-warm engine causing the 125-degree inhibit switch inside the controller to shut off making the engine tough to restart. The cure here is to relocate the control module away from the engine. On Ford 7.3L diesels, the control module can cut off early if there are two or more bad glow plugs. We have also heard of control modules that do not keep the glow plugs on long sufficient for easy cold weather starting up. The on-time is sufficient for warm weather, but not cold weather.


Unlike gasoline, diesel oil is adversely affected by cold temperatures. Diesel is made of heavier hydrocarbons that turn to wax when temperatures drop. The “cloud point” or stage at which wax starts to form for ordinary summer-grade No. 2 diesel fuel can range from 10 to 40 degrees. In the event the fuel tank contains summer grade fuel and temperatures drop, wax crystals can form in the water/fuel separator, causing a blockage.

The cure here is to pull the vehicle into a warm garage so it can thaw out, replace the water/fuel separator as wanted, then add an approved “fuel conditioner” additive on the tank (some manufacturers do not approve any additives or prohibit the use of specific ingredients such as alcohol that are found in some additives), or drain the tank and refill it with No. 1 diesel fuel. To prevent precisely the same point from happening again, you may advocate the installation of an aftermarket fuel heater.

Water in the fuel is another problem that may cause beginning and performance issues. Condensation that forms during cold weather could be the primary source of contamination. Water that gets into the fuel tank usually settles for the bottom because water and oil don’t mix. The water is sucked into the fuel line and goes for the filter or water/fuel separator (in the event the vehicle has one). Here it can freeze, causing a blockage that stops the flow of fuel to your engine. So if the filter or separator is iced up, the fuel tank requires to be drained to get rid of the water.


Another difference with diesel fuel is that it tastes good to certain microbes, especially if there’s water during the tank. Certain bacteria can actually thrive inside a diesel fuel tank, forming slime, acids and other creepy stuff that will gum up fuel lines, filters, injection pumps and injectors. Infected fuel often has a “rotten egg” odor, and leaves a black or green coating on the inside of fuel system components. The growth rate of most organisms increases with warmer temperatures, but some can thrive down to freezing temperatures.

To get rid of a bug infestation, the fuel tank desires to be drained and cleaned. A biocide approved for this type of use really should also be used to kill the organisms and to prevent their reappearance. The cleaning process really should be followed by a fresh tank of fuel treated with a preventative dose of biocide. In the event the fuel lines and injection pump have also been contaminated, they will also have to be cleaned.


To start and run properly, injector timing has to become accurate. A quick visual inspection will tell you if your timing marks are lined up. Refer on the vehicle manufacturer’s timing procedure if you suspect timing is off or the pump has been replaced recently. On newer diesels with electronic injection pumps or direct injection, you’ll will need a scan tool to make any changes.

Air in the fuel can also be a cause of tough starting up or a no start problem. Air could make the engine die after it starts, and make restarting difficult. Air can enter the system through any break during the fuel line or via a bleedback condition.

To determine if air would be the problem, install a clear return hose on the return side of the injection pump. Crank the engine and observe the line. Air bubbles in the fuel would tell you air is entering the inlet side with the pump. The injection pump itself is usually not the source of the air leak, so test the fuel lines and pump.

A worn or clogged pump can also make an engine not easy to start. In the event the affliction has been getting steadily worse accompanied by a loss of power, and also the engine has a lot of miles on it (more than 75,000), the underlying cause may possibly be a pump that requires to be replaced.

Before condemning the pump, though, check the fuel filters. Clogged filters can cause fuel restrictions that prevent the pump from doing its job properly. The primary water separator/fuel filter usually desires to be changed about every 30,000 to 40,000 miles, along with the secondary filter about every 20,000 to 30,000 miles. Newer fuel systems with a single filter usually require service about once a year. If the filter has been neglected, chances are it could be restricted or plugged.


A diesel engine that cranks normally but won’t start regardless of the outside temperature either has very low compression or a fuel delivery problem. If compression is okay, check the fuel gauge (out of fuel?). Then check out the fuel filters and lines for obstructions.

When the injection pump is not pushing fuel through the lines to your injectors, it may have a faulty solenoid. Listen for a “click” inside the pump when the ignition switch is turned on. No click means the solenoid and/or pump require to become replaced. If it clicks but there’s no fuel coming through the injector lines (as well as the filter and lines are not obstructed), the pump is probably bad and requires to become replaced.


Diesel injectors can suffer from exactly the same kinds of ailments as gasoline injectors, including varnish deposits, clogging, wear and leakage. Today’s lower sulfur diesel fuels are more likely to leave varnish and gum deposits on injectors, and also provide less lubrication so you may advise an additive to keep items flowing smoothly.

Diesel injectors operate at much higher pressures than gasoline injectors. Over time, their opening strain can drop. Up to 300 psi is considered acceptable on older mechanical injectors, but more than 300 psi means the injectors need to be replaced or reset back to their original operating specs. You will need some type of pop tester to examine the opening strain of your injectors if you suspect this kind of problem. On newer diesels, the opening stress on the injectors will depend on the injection system. On a Ford Powerstroke, for example, the minimum line pressure wanted to open the injectors is 500 psi. On a late model Dodge truck with a Cummins diesel and common rail fuel injection system, 5,000 psi is definitely the required opening pressure.

Dirty injectors will lean out the air/fuel mixture, causing a loss of power, rough idle and sometimes white smoke in the exhaust. Leaky injectors will richen the air/fuel mixture and cause black smoke.

There are a couple of ways to find a bad injector on a diesel engine. One is to use a digital pyrometer to test the operating temperature of each cylinder. A temperature reading that’s lower than the rest would indicate a weak cylinder. If compression is okay, the problem is restricted fuel delivery. Another quick check is to use an ohmmeter that reads tenths of ohms to measure the resistance in the glow plugs while the engine is running. The resistance in the plug goes up with temperature, so if one or two cylinders read reduced, you’ve found the problem. For example, if a glow plug normally reads 1.8 to 3.4 ohms on a hot, running engine, a reading of 1.2 to 1.3 ohms on a glow plug would tell you that cylinder isn’t producing any heat.


Black smoke is usually a signal that there’s also much fuel, not enough air or injector pump timing is off. One from the most common causes of this ailment is an air inlet restriction. The cause may perhaps be a dirty air filter, a collapsed intake hose or even an exhaust restriction. Diesels are unthrottled so there is no intake vacuum to measure.


White smoke usually occurs when there is not ample heat to burn the fuel. The unburned fuel particles go out the tailpipe and typically produce a rich fuel smell. It’s not unusual to see white smoke during the exhaust during cold climate until the engine warms up.

As mentioned earlier, bad glow plugs or a faulty glow plug control module can cause white smoke on engine start up. Low engine cranking speed may well also produce white smoke.

If white smoke is still visible after the engine has warmed up, the engine may possibly have one or more bad injectors, retarded injection timing or a worn injection pump. Reduced compression can also be a source of white smoke. Air within the fuel system can also cause white smoke.


If a diesel stalls when decelerating, it may indicate a lubrication problem in the injector pump. The first point that should be checked will be the idle speed. If low, it could prevent the pump governor from recovering quickly enough during deceleration to prevent the engine from stalling.

Water during the fuel can also cause stalling by making the metering valve or plungers inside the pump stick. Use of a lubricating additive may perhaps help cure this issue. If an additive doesn’t help, the pump may possibly have to become cleaned or replaced.