Ask the Mechanic

WHICH OF THE COROLLA SPACIO IS FUEL EFFICIENT?

Hello Paul, I am torn between the 1.8cc and 1.5cc Corolla Spacio. Which has better fuel economy and why?

Vincent

Hello Vincent, the 2001-2007 Toyota 1.8 Litre 1ZZFE and 1.5 Litre 1NZFE Corolla Spacio engines deliver approximately the same fuel economy of 15km per litre because of weight body engine ratio and the fact that the smaller 1.5 litre engine delivers 109Hp at 6,000 rpm (higher engine revolutions) while the 1.8 litre delivers more power 120Hp at 5,600 rpm (lower engine revolutions).

Common sense would suggest that the smaller 1.5 litre engine carrying the Spacio should be consuming less fuel than the bigger 1.8 litre engine carrying the same car. However, the smaller engine works harder (6,000 rpm) to deliver peak power and consumes as much fuel as the bigger 1.8 litre engine, which works less (5,600rpm) to deliver more peak power and, therefore, better efficiency (combination of power and fuel economy). This is easier to understand by appreciating the car body weight to engine size ratio.

The smaller 1.5 litre engine works harder than the bigger 1.8 litre engine to carry the same car. The more revolutions a car engine runs, the more fuel it tends to consume. However, there are other factors that affect fuel economy such as the quality of fuel efficiency enhancing additives, engine maintenance standard, tyre condition and driving style. The bigger 1.8 engine makes acceleration on the highway easier while the smaller 1.5 litre engine is sluggish. On the flipside, the 1.5 litre engine is easier and cheaper to maintain and tends to have less severe engine repairs.

MY CAR ENGINE RATTLES WHEN I ACCELERATE

Hello Paul, my Corolla Spacio 2004 model makes a rattling sound when you accelerate. However, this sound disappears gradually on acceleration. What is the likely cause?

Jordan Ssekitto

Hello Jordan, your car may be experiencing the infamous engine rattle. This is a metal to metal clicking or scrapping sound that is continuous or intermittent during acceleration. The engine rattle usually comes with reduced engine performance or engine stalling in extreme cases when driving uphill. The engine rattle is usually caused by one of these factors; worn out spark plugs, engine timing fault, damaged catalytic convertor or fuelling with the wrong octane number, causing excessive cylinder knock. 

Worn out spark plugs will reduce engine power and this will be felt more as you drive uphill or attempt to overtake. A faulty engine timing either advanced or retarded will affect ignition and combustion efficiency. This will reduce engine performance and cause an engine rattle.

A catalytic convertor is an exhaust pipe fitted honey comb shaped ceramic filter which chemically renders exhaust smoke less harmful to the environment as it passes through. When the catalytic convertor is damaged, it will block the exhaust pipe causing exhaust back pressure. This situation will reduce performance and cause a rattle. Occasionally, a faulty engine positive crank case ventilation system or vacuum system can also reduce engine performance. Have the car inspected by a qualified technician and run computer diagnostics for precision.

SHOULD I DOWN SIZE MY TOYOTA HARRIER RIMS?

Hello Paul, I drive the Harrier 2005 model with net weight of 1,730kgs and of 2,994 cc. The recommended tyre size in the logbook is 225/65R17. I recently discovered that the previous owner had 235 instead of the recommended 225 tyres. Should I remove them?

Ahmed

Hello Kassim, your 2005 Toyota Harrier has two applicable tyre and rim sizes as recommended by Toyota in the user manual. The narrower but higher profile tyre size 225/65 R17 comes with rim size 6.5JJx17 ET35 and the wider but slightly lower profile tyre size is 235/55 R18, which comes with rim size 7JJx18 ET35.

Before you swap your tyres, understand that downsizing from the wider 235/55 R18 tyre to the narrower 225/65 R17 tyre will require replacement of both tyres and rims. Also, tyre performance will be altered as the wider lower tyres tend to provide better high speed stability, road holding and grip. The narrower but higher tyres you want to downsize to might improve your fuel economy and ground clearance a little bit.

However, other factors such as your Harrier engine size (3.0 litre), driving style and maintenance condition may erode the perceived tyre downsize gains. Bottom line; the compromise of road stability and the cost of replacement rims and tyres may not make financial or practical sense.

WHY DOES MY CAR EMIT WHITE SMOKE?

When I start my Toyota Hilux 3.0 D-4-D, the engine emits white smoke. My mechanic has suggested changing engine oil, which I have not done yet. Is this the right course of action?

Gary

Hello Gary, it would be good to know if the white smoke is emitted from your Hilux D4D Diesel engine after cold starts or persists as you drive the vehicle. Either way, the common cause of white exhaust smoke is engine coolant leaking into the engine combustion chamber due to a faulty head gasket or damaged cylinder head. This is usually a result of prolonged or severe over heating episodes.

Common symptoms are unexplained loss of coolant or contamination of engine oil by the coolant. However, there are other causes of white smoke from a Hilux D4D engine. In unique situations, raw unburnt diesel emitted out of the exhaust due to damaged and faulty fuel injectors or rarely incorrect injection timing can cause white smoke during a cold start up.

Ordinarily, excessive fuel in the combustion chamber will cause black smoke. This causes delivery of unregulated amounts of diesel, which reduces fuel economy and performance. Intrusion of engine oil in the combustion chambers due to worn out piston rings will cause blue smoke. A compression test with the right tools would confirm this. Either way, get a second opinion from another mechanic who should examine the car carefully to confirm or rule out any of the above.

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