LOW OIL PRESSURE
I own an Alfa Romeo 147 which I bought as a town runabout four years ago. Eighteen months ago, after 98 000 km the water pump failed. This despite the service books showing a cambelt change at 49 000 km by an Alfa agent which should have included a water-pump replacement.
The failure of the water pump caused the cambelt to jump off its pulley and the pistons collided with valves; generally a messy event. The Alfa specialist to whom I entrust the car’s servicing reconditioned the cylinder head and the engine ran like new after the reasonably priced repair.
A few months later, the car started giving an intermittent low oil-pressure warning (a piercing beep) on pull-off. I went straight back to the service specialist who surmised the big-end bearings (apparently the usual suspects when oil pressure drops) were damaged when the pistons impacted the valves. He replaced the big-end bearings but the warning persisted.
I then asked him to do a manual oil-pressure test which produced perfect results. He replaced the oil-pressure sensor for good measure. Unfortunately, this did nothing for the problem. I’m now hoping you can cast more light on this dilemma. The low-pressure signal is not related to the oil level as it happens when the level is low or high.
I’ve also noticed oil smoke escaping from the dipstick-holder when I check the oil level and the oil on the dipstick is smoking hot. Could this indicate an issue with the oil-cooler?
Can you perhaps comment on whether the actions taken so far have been correct; whether the oil temperature could be an issue; and suggest other remedies? PETER GROBLER Cape Town
We covered oil-pressure-switch functionality in last month’s issue in this section. Basically, it is a spring-loaded switch activated by oil pressure (usually open circuit) when the pressure rises above the calibration threshold which correlates with the spring stiffness. It is quite a simple, mechanical device that tells the instrument cluster (and engine control unit) if the oil pressure is suf cient or not.
Electrical or sensor fault
The rst test would be to measure the actual oil pressure which your mechanic has done and found to be okay. It then points to a faulty switch, wiring short or open
circuit. As the sensor was changed, follow the electrical circuit to the instrument cluster to search for a loose connection or short circuit. It is possible a pulling-away action results in enough acceleration to cause an intermittent wiring issue.
Actual low oil pressure
Worn journal bearings can cause low oil pressure but this scenario would always be present, especially at idle (oil pressure generally rises with engine speed). Your mechanic has tested the oil pressure when the vehicle was stationary, so that rules out journal-bearing wear or a faulty oil pump. If possible, he should evaluate the oil pressure while you recreate the manoeuvre which sets off the low-oil-pressure alarm. If the oil pressure remains consistent, it is de nitely an electrical fault as described above. If the oil pressure dips momentarily, you have an oilpick problem rather than a journal bearing issue. It’s best to remove the sump to see if the oil pick-up piping is still in place and if the mesh lter is clear from debris. A low-oil-pressure dip is enough to cause terminal journal bearing damage because metal-to-metal contact is possible in that time.
Oil temperature
Oil temperature tends to hover around 100 °C when at full operational temperature. During extensive hard driving, for example on a racetrack, the oil temperature can crest 120 °C, requiring a highgrade, synthetic oil to provide optimum lubrication without chemically breaking down. In general, it is not advisable to run such high oil temperatures and many modern cars would go into limp-home/ engine-protection mode when either the engine or transmission oil exceeds a calibration threshold. Maybe you (or a mechanic) can install an oil-temperature gauge (if not standard tment) to monitor the oil temperature of the Alfa?