General Diesel Vehicle Maintenance

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Changing fluids and filters


Greasecar conversion kitThough Diesel engines do not require regular tune ups like gasoline engines, they still require maintenance to optimize and maintain engine health. The most important things to service are filters and fluids. Your vehicles owners or service manual will lay out filter changing intervals. A dirty fuel or air filter can seriously hinder power and fuel economy. Lubrication oil should be changed regularly with oil specified for diesel vehicles and the coolant system should be flushed every year. There are also a number of diesel fuel additives that can be used to minimize injector tip fouling and fuel gelling.


Fuel additives

There are many diesel fuel additives available, each formulated to give specific results. Some are intended as anti gel and others for injector cleaning or cetane boosting. One commonly available additive is Diesel Purge, a concentrated injector and fuel system cleaner used on its own or as an additive.

Injector maintinence

Injectors can often foul over time, which affects proper spray pattern and can lead to increased emissions and carbon buildups as well as negatively affect power and efficiency. Injectors can be cleaned physically by removing and scraping off carbon and resin build up. Remember to always replace heat shields on pre-chamber engines. There are also a number of injector cleaning fluids such as "Diesel Purge" made by Lubromoly which run at 100% for strong cleaning without injector removal. If injectors are heavily cratered or pitted they will require rebuilding or replacement.

Pump tuning

Injection pump timing also plays an important role in performance and combustion. Always make sure that timing is reset properly after timing belt or injector pump replacement. Fine adjustments to pump timing can also eliminate problems with rough idle, knocking and power loss.

Winter tricks

A common solution to winter cold starting is to install a block heater. This will help keep the engine coolant warm for easier starting and quicker warm-up times. Cycling glow plugs several times before attempting to start the vehicle will often help smoother starting in cold weather. You should also make sure your fuel is winterized, diesel that is not winterized will cloud and gel at lower temperatures which may lead to breadown.

Old VW Tricks

Here are a few tricks to related to common problems with older VW diesels.

Busted return lines

The small braided return lines between the injectors of many older diesels have the tendency to become brittle or seep. It is always a good idea to replace them if they seem worn out. There are new synthetics such as Viton that will hold up to diesel fuel better than original rubber lines.

Filter basket

A common problem found in older VW diesels stems from a suction strainer in the diesel tank. When this strainer gets dirty it will create symptoms often confused with a faulty injection pump, plugged fuel filter or fuel line. This strainer can be serviced fairly easily by removing the fuel sender in the diesel tank and fishing the strainer out with a coat hanger. The strainer is a cylinder in the center of the tank with a loophole in the top that can be hooked onto. Replacing a strainer is a difficult task and most do not replace it, this means that you may have to replace your fuel filter soon after the strainer is removed.  It is, however, easier to replace the filter than clean the strainer.

Weak pump

(NOTE: This problem can also be confused with a dirty strainer)A common problem with older diesels is injection pump gasket failure. This generally happens when o-rings on the cold start or throttle shaft wear out. Rebuilding or replacing the injection pump is expensive and not an easy task. A cheap solution that can often be employed is to install an in-line electric assistance pump. The pump can be wired to the injection pump stop solenoid circuit and force prime the pump prior to starting and assist the pump once running. (This problem can also be confused with a dirty strainer)


Most issues related to the normal operation of a Greasecar system are related to fuel or coolant flow. Loose lines or fittings will cause air to trickle into the fuel system, causing stalling. Plugged fuel filters will create similar problems caused by several factors. Poor coolant circulation will result in inadequate fuel temperatures, which will lead to gelling in the fuel filter, or lines causing stalling and injection pump strain.

Air leaks

If you suspect and air leak, check all fuel related connections for traces of leakage. Loose fuel line clamps are the most common cause, but you'll also want to inspect the injection pump, injector return lines, copper washers on high pressure fuel fittings and any other threaded fittings in the fuel system, including the fuel filter. Clear braided vinyl or PVC line is often used in place of the black fuel line provided in the Greasecar conversion kit. This is generally done so that fuel and air can be observed in the lines; unfortunately these lines are prone to stretching and cracking and are often the source of air leaks. Translucent sections can be implemented in the fuel system using rigid tubing rated for diesel fuel use.


Bacteria contamination is a common problem related to need for frequent filter changes. If you suspect bacterial contamination the best solution is to drain and clean the fuel tank and replace the filter then use a biocide additive the next time you fill up. Bacterial contamination often relates back to the oil source and will continue to grow in the fuel tank after filtration. To avoid bacteria in the fuel system, potentially contaminated oil should not be prepared or used in the Greasecar system. To minimize risk when collecting from a questionable oil source a biocide can be added to the fuel prior to filtration.

Cold start

Colds starting problems can be caused by a number of factors, some of which are covered above. Factors related to the operation of the Greasecar system include: improper purge duration, blown purge valve fuse or incorrect fuel routing. Purge cycle will vary with vehicle and application but should be at least 15 sec for vehicles with high flow fuel systems to 1 minute in vehicles with low flow. (Excessive purge periods can result in vegetable oil tank overflow and depletion of diesel fuel). If you suspect a faulty purge valve, check for current at the valves power input. If no voltage is found inspect fuse and replace as necessary with a new fuse of proper amperage. Replace valve if power is available and the valve is not operating.

Too cold

Air locks in the coolant system are the most common cause for poor circulation, leading to inefficient fuel heating. First make sure that there are no kinks in the coolant lines or heat exchanger tubing. Inspect your coolant connections between the vegetable oil heating circuit and engine cooling system for proper plumbing. If this checks out, the next thing to look for is fuel blocking in the cooling system,usually caused by trapped air bubble at a high point. Position the vehicle so expansion tank is at the highest point, allowing air to float out of the coolant over flow line. It may be necessary to bleed air at several consecutive points in the cooling system, starting from the coolant out to the fuel filter and back up to the coolant return to the water pump. These symptoms can also be the result of a thermostat that is stuck open, refer to your vehicles service manual for testing procedure.

Too hot

Overheating of the engine can also result from improper coolant circulation, in which case all the same factors as above may apply. Also check for proper radiator fan operation and flush the coolant system as indicated in vehicles service manual.