6
5.6 Vehicle Diagnostics
CCaarreesshhoouullddbbeettaakkeennwwhheennwwoorrkkiinnggoonnvveehhiicclleess,,aasstthheeuusseerrmmaayyffiinndd
tthheemmsseellvveesswwoorrkkiinnggiinncclloosseepprrooxxiimmiittyyttoovveerryyhhoottccoommppoonneennttss,,ssuucchh
aassrraaddiiaattoorrssaannddeexxhhaauussttmmaanniiffoollddss..
AAiirrCCoonnddiittiioonniinngg::With the air conditioning set to maximum cooling, the output air
temperature should be in excess of 15°C colder than the ambient temperature
outside the vehicle. To avoid the instrument being affected by thermal shock, the
thermometer should be focused on the air duct rather than directly into the cold
air stream. Temperature differentials of less than 15°C indicate that the air
conditioning system may need to be checked.
HHeeaatteerr::To test the heater it should be turned on, while the air conditioning
should be off. With the engine running at the usual operating temperature, the
user should take a reading from the heater inlet and outlet hoses. It would be
expected that the outlet would be approximately 10°C cooler than the inlet hose.
Any significant difference in the two figures indicates restricted through flow,
which should be investigated.
RRaaddiiaattoorr::With the engine running at the normal operating temperature, the user
should check the temperature drop on the inlet and outlet. The drop in
temperature should be fairly even. Scan the radiator surface (see Fig. 4) for any
cold spots, which are symptomatic of a blockage.
TThheerrmmoossttaatt::To check that a vehicles thermostat is performing as expected, it is
necessary to monitor the temperature of the hose adjacent to the thermostat
housing. If the thermostat is working properly, it will open as the vehicle reaches
its normal operating temperature (85-105°C). This is apparent, as there is a
temperature surge in the hose. If the hose temperature increases gradually, but
never reaches operating temperature, the thermostat is faulty or is missing. In
the event of no rise in temperature, this indicates that the thermostat is stuck in
the closed position, or other parts, such as the pump have failed.
Fluctuating temperature readings are indicative of a failed spring in the
thermostat, or air in the system.
CCyylliinnddeerrMMiissffiirriinngg::Injector and manifold gasket problems can be detected by
taking temperature readings from the separate branches of the exhaust
manifold. If one of the branches is much cooler than the others, then a misfiring
cylinder is indicated. In this case, the difference in temperature will be more
pronounced before the engine is at normal operating temperature. If an exhaust
branch is hotter than others, it is likely that a weak mixture is reaching that
cylinder.
