Letters to the editor

Copyright © 2001 FleetWatch magazine and FleetWatch On-Line.

No part of this publication may be reproduced without the prior written permission from the publishers. Views published are not necessarily those of the publishers.
Past Issues
April 2001

DIESEL
FUEL

FLEET
 USAGE
CHECKLIST

Fleet operators - big and small - are not in the habit of auditing fuel suppliers and storage facilities. This is despite the fact that laid down policy procedures and sample testing is essential in order to gain control over diesel fuel quality. Gaining such control is essential in South Africa's mix of First and Third World conditions where hi-tech equipment and weak supervision combines with fringe elements of fraud and corruption. Here is a suggested list of items that will give you, the transport operator, control over diesel fuel quality:
by David Scott

GAINING CONTROL OVER DIESEL QUALITY

Standard Quality Certificate

 The current specification benchmark is SABS 342. ISO 9000 certified companies supply all recognised fuel brands - a standard and quality certificate can be demanded for every bulk delivery. 
Check above-ground tanks



 Above ground tanks, such as bulk-to-farmer (BTF) tanks, experience much wider ambient ranges of temperature than do underground tanks. Daytime heat and cold evenings are the cause of water condensation in such tanks and water becomes a No1 problem. A rapid growth of microorganisms at the inter-face of diesel and water, where diesel fuel floats on top of water, causes blockage of filters. These bugs eat into steel storage tanks where diesel meets water - the astounding reason for a fuel tank bottom to leak or even drop off a complete structure. All above ground tanks should have bottom drain valves at their lowest point; check that these are fitted and use them to check for and drain off any water on a monthly basis
Tampering of fuel

Is fuel being tampered with in any way? It is worth conducting regular sample checks of stored fuel and diesel extracted from vehicle fuel tanks. Suppliers' laboratory analysis or an independent lab check could reveal some shocks - such as illegal blending with illuminating paraffin.
Checking for underground leaks

 Underground diesel fuel tanks also corrode but more commonly from the outside. Older single-skinned concealed tanks eventually leak due to external corrosion and pollute local underground water resources. All modern fuel suppliers claim to be 'environment-friendly' and should conduct regular pressure tests of underground fuel storage tanks to ensure the absence of any leaks.
Conduct regular checks of underground fuel tanks with water finding paste for water contamination. Remove the water and treat microorganism growth with a biocide. 
(See FleetWatch article May 200O - 'Water in Diesel')
Fuel tank breathers Ensure that fuel tank breathers are operating and not open to the elements in a rainstorm.
In-line water traps Make sure all diesel-powered trucks are fitted with an in-line water trap that also signals the presence of water.
Change fuel filters regularly Modern low emission diesel engines have ultra-high pressure injection systems that suffer from premature injector wear when subjected to 'dirty diesel'. Where a fuel filter is only filtering down to 10-micron, install a 3-micron fuel filter downstream of the 10-micron filter. Check and change fuel filters on a regular basis depending on operational conditions.
Read your Exhaust Smoke!
It usually indicates an inefficient use of fuel. The following will help you diagnose faults arising from exhaust smoke.
BLACK SMOKE
Black smoke is caused by large, visible, soot particles in the exhaust. This indicates that combustion is incomplete due to localised rich mixtures within a combustion chamber. Causes of black smoke are:
  • Incorrect injector pressures - generally too low.
  • Poor spray pattern.
  • Over-fuelling - wrong spill rate or governor setting.
  • Inadequate air supply - blocked air-filter or intercooler or worn turbocharger.
  • Incorrect injection timing.
  • Abnormally high cetane number.

Sooting of the crankcase oil causes thickening and can end up in gelling and bearing failures. It also accelerates ring sticking, carbon and sludge deposits as well as engine wear rates.

WHITE SMOKE
Commonly called white smoke, this is typically pale gray in colour and is caused by visible liquid fuel particles in the exhaust. This indicates that fuel is passing through the combustion chamber without vapourising or igniting. Causes are:
  • Low cetane number - check for IK (illuminating paraffin) usage.
  • Engine overcooling.
  • Misfire.
  • Burned valves.
  • Late injection timing.
  • Poor spray pattern - fuel impingement on cylinder walls.
  • Low compression.

Not all unburned fuel passes out of an engine. Some fuel condenses causing fuel dilution. White smoke will cause higher engine wear rates, particularly of the rings and liners.

BLUE SMOKE
Blue smoke is not fuel related but comes from burning of excessive amounts of crankcase oil in the combustion chamber. Typical causes are:
  • Worn rings.
  • Worn valve guides.
  • Incorrect honing pattern.