Q. I have a newer Scion and since I ride my bike to work as often as I can I only drive about 4,500 miles a year. Based on this information how often should I change the oil?

A. Even though Scion says to change the oil in your car every 5,000 miles, I would still change the oil twice per year. The crankcase of the engine can over time fill with contaminants such as water, coolant and gasoline. Under normal conditions, as the oil warms up it will “boil” off these contaminates. Driving short distance may never allow this to happen and could allow the engine to be lubricated with contaminated oil.

Mazda ‘fog horn’

Q. My wife and I own a 2000 Mazda MPV. For the last couple of years, when I’ve started the engine in the morning or when the engine is cold, the engine sometimes makes a very loud “fog horn” noise. It seems to occur in the winter and not when it is warm; the noise goes away and then comes back. A friend said he owned a Ford that made the same sound, and his problem was caused by an air intake valve. Have you come across this problem with other Mazda vehicles?

— Joe, Warwick A . The problem is with the idle air control valve. The repair is an updated and modified idle air control valve. If your repair shop has any questions have them reference Mazda technical service bulletin number 01-009/03.

Fan won’t go

Q. I was in an accident and rebuilt the front end of my Honda. The radiator, thermo sensor and wiring were checked but I can’t get the cooling fan to come on. I have replaced the coolant sensor and checked the fan and all seems OK, but the fan still won’t come on. Any suggestions?

A. Once you have determined the fan itself is good then you need to inspect the wiring, relays and power supply. You mentioned you replaced the cooling sensor. In this model Honda there are two: one for the computer and one for the cooling fan.

Leaking after repair

I have a 1994 Toyota Camry and just replaced the water pump. Now I have a leak at the front left side of the engine. Do you think I have another leak?

A. I would certainly go back to the shop that replaced the water pump. It could be a loose hose clamp or coolant that was spilled during the repair. Worse case, it may be a defective water pump or leaking radiator hose.

Check the distributor

Q. My aunt’s 1985 Cadillac Cimarron just stalled (she says it overheated), and now it cranks, but won’t start at all. A somewhat knowledgeable family member suggested the culprit might be a bad coolant temperature sensor. Do you agree? Do you have any other suggestions?

A. I would start with the basics and look for both fuel pressure and ignition. A faulty distributor cap and rotor could be the cause.

Ram’s faulty headlights

Q. I have a 1996 2500 Dodge Ram pickup and live in New England. When I start my truck, the running lights will work but not the headlights. The headlights will start working when the truck heats up (around 5 minutes). Any suggestions on why this is happening?

A common problem with these trucks has been a faulty headlight switch and the wiring to the switch. Inspect the wiring at the switch and look for signs of melting.

’96 Volvo stinks

Q. My 1996 Volvo 850 has a foul odor coming through the heat/air system. My local dealer doesn’t know what the cause is. A friend had a similar problem with her Volvo and had to sell the car. Do you have any idea what could be causing this problem and is there a solution?

A. I would start with a thorough cleaning of the air conditioning and heater ducts. In many cases this smell is due to mold and mildew buildup. It may help to spray a disinfectant such as Lysol into the ducts and air intake for the heater. If all this doesn’t work the air conditioning evaporator may need disassembly and cleaning.

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