How do I tell that my engine needs overhauling?

A Toyota Premio car. 

What you need to know:

  • Overhaul may take two to three weeks, since it may take a lot of time to repair and restore parts (grinding, boring).

Hello Paul, my Toyota Premio 1998 model with 174,000kms is not able to gain speed easily. It shakes and cuts power when driving uphill and when I accelerate, it smokes. Although mechanics have changed the fuel filter, spark plugs and engine oil, the car is getting worse and now they say the engine needs overhauling. How can I be sure that they are correct? Monica.

Hello Monica, often, there are telltale signs that your engine might need rebuilding. Some problems might require replacing a few parts. Delay to repair may worsen the condition and warrant replacement of more engine parts and a more expensive job. A stitch in time saves nine. There are three major indicators of engine trouble; loss of engine power; loud engine noises and increasing exhaust smoke.

Loss of engine power can be detected when your car experiences delayed acceleration or trouble gaining speed or runs rough with erratic (unstable) idling. There are other factors that can cause loss of engine power such as aged spark plugs, dirty fuel or air filters. These can be ruled out during inspection by an experienced mechanic. 

An engine can lose power when it develops low engine compression. Engine compression is when the piston squeezes the fuel air mixture volume in the remaining space of a cylinder during engine running. The higher the compression of fuel air mixture, the higher the pressure before ignition and the more powerful the combustion from a given fuel charge. It is similar to how big a bang you get from how much you squeeze a balloon before deflation. The more you squeeze it, the bigger the bang. 

When the engine piston rings wear out due to poor lubrication or age (synonymous with high mileage) there is loss of compression which tends to leak like blowing a balloon with tiny holes. This causes loss of power as the reduced compression of fuel air mixture produces weaker combustion. 

A professional mechanic can determine low engine compression by carrying out a compression test using special tools. Loud engine noises such as banging, knocking and ticking can be indicators of a damaged engine with bad bearings or a damaged valve train. Fast moving engine parts can be damaged by failure of the lubrication system sometimes due to a poor oil service regime.

Excessive smoke from the exhaust pipe can be a sign of trouble, particularly if you see blue or white smoke. Blue smoke is a result of the engine burning oil which tends to seep past damaged piston rings into the combustion chamber where it is burnt. 

White smoke is a sign of the engine burning coolant which seeps into the combustion chamber due to a damaged cylinder head or gasket. The above conditions require immediate attention to avoid further damage and costlier repairs. Visit a professional mechanic as soon as you see these symptoms to assess the extent of damage and intervention required.

Is it safe to cut treads into a worn out used tyre?

Hello Paul, I have observed some people who cut treads with knives onto completely worn out truck tyres. Can such tyres work safely for cargo trucks? Birungi.

HelloBirungi, retreading worn out or bald tyres by cutting shallow treads into them with a knife is wrong and endangers the lives of people travelling in such vehicles and other motorists. One must appreciate the role of tyre treads to understand the gravity of this vice. 

Tyre treads are an important part of the outer vehicle tyre circumference designed in patterns according to the purpose of the tyre. Treads give the tyres better control on and off road, especially when it is wet or slippery and when you need to maneuver or stop the vehicle. 

Good tyre treads require depth in order to provide grip and control on slippery terrain or evacuate water to prevent aquaplaning (skidding on water patches) when driving over wet road sections. Deep tyre treads will allow cooling of the tyres to avoid overheating and damage of the inflated inner tyre sections as you drive along. 

Tyres have different layers of rubber (plies) which protect them as well as improve their performance.

The outer most layer is the one with the treads. Companies that correctly retread used tyres clean them up and replace the worn out outer layer with a new layer comprising effective and deep treads.

The process uses machines to bake or vulcanise the tyres and make sure the retreaded outer layer will not fail or peel off when driving. 

Why does my Highlander jolt or rumble at take off?

I have a Toyota Highlander but when I accelerate to between 40 and 60mph, I get this jolt/rumble feel. What causes that? Doreen Musoke.

Hello Doreen, a jolt or rumbling feedback when you accelerate is most likely a problem with a component in the vehicle drive system or final drive. These are components which transfer drive power from the transmission to the wheels. You could be looking at a loose or damaged propeller shaft, coupling and bearing. Get a mechanic to inspect the propeller shafts and other final drive components.

Why are my car’s plugs wet? 

The other day, my 1995 Ford F150 started for only three seconds and stopped. On checking, the plugs were covered with petrol. Can you please give me a hint of what is going on? Patrick

Hello Patrick, looks like your F150 ignition system is faulty. This system fires the spark plugs, which in turn ignite the fuel air mixture for combustion of the engine. The F150 ignition system comprises the ignition control module, coil, high tension leads and spark plugs. 

Each one of these should be inspected to determine if any of them has failed. A computer diagnosis can also help to establish this. Occasionally, a faulty crank shaft position sensor can cause that problem. A computer diagnosis will pick it up.

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