Ask the mechanic : Why does my roof leak?

Hi Paul, I am intending to buy a used car and the options I have in mind are either Toyota IST, Allex or RunX. Kindly avail me with technical information about the cost of general maintenance.
Thank You.
Diana.

Hello Diana, the Toyota RunX is the ‘Sprinter’ version of the Toyota Corolla Allex with a few more sporty design and interior additions.
Together with the Toyota IST, these three Toyota models are hatch-backs. The three models Allex, RunX and IST have impressive design and comfort features combined with sporty handling attributes suitable for town running, city parking and a quick dash out of town.
The trio are attractive because of their fuel efficient small but powerful 1.5 litre (Allex /RunX) and 1.3 Litre (IST) engines designed with 16 valve DOHC (Double Overhead Camshaft) drive trains with VVTi (Variable Valve Timing intelligent). Technically, what you need to bear in mind is the fact that on the used car market, you are likely to get a car with 80,000 - 100,000 kilometres on the clock.
You therefore need to plan and budget about Shs500,000 for the general service or renewal of the spark plugs, air cleaner, long life fuel filter, AC cabin filter, gear box (automatic transmission) and engine coolant. Use the Toyota recommended engine oil with viscosity grade 15W40 or the long life 5W30 fully synthetic oil. Preferably use engine oil with cleaning detergent additives which better protect the VVTi technology in your valve train.
Routine engine oil and filter service will cost you about Shs100,000 every three months. Depending on the condition and mileage of the car you buy, or the quality of roads you drive on, sooner or later you will need to replace front suspension components which will cost you between Shs200,000 and Shs400,000.
This is a one off expense probably not likely to happen again during your ownership of this vehicle if you buy genuine Toyota parts.
The Allex and RunX seem to have a better resale value Shs10m because of their more conventional Toyota looks and closer to saloon seating space. IST’s resale value of Shs7m could be because it has more aggressive sporty curves and internal layout which appeal to the smaller cross section of non-conservative drivers who enjoy driving a sporty hatch back.

Hi Paul, I drive a BMW X6. It once got a tyre puncture and even after I repaired it, the display shows a fault with the tyre indicator system. What should I do to rectify this fault?
Andrew.

Hello Andrew, your BMW X6, like many modern vehicles, has a Tyre Pressure Monitoring System (TPMS). BMW calls theirs the Tyre Pressure Control System (RDC), which means the same thing.
The TPMS/RDC uses sensors on all four wheels to electronically monitor tyre pressure. On different models with optional equipment such as run flat tyres, the TPMS relies on the Tyre Pressure indicator to relay real time information about your BMW’s tyre pressure. This system receives reliable information from tyre pressure sensors fitted in the pressure valves of each tyre. Once fitted, the sensors take a record of the balanced tyre pressure and will send a warning message to the driver once any of the tyres has a drop in tyre pressure due to a puncture or slow air leak. This sensor even helps to identify the particular tyre.
Once your tyres have been correctly inflated after a tyre repair or change, you must reset the tyre pressure indicator. This will restore normal function of the tyre pressure control. You can get the details of how to reset the Tyre Pressure indicator from your car’s user manual.Here are brief steps you can follow to reset the TPMS warning system:
Inflate and balance all tyres to pressure indicated on tire placard. If equipped with iDrive:
1. Turn ignition to ON position (engine off)
2. Select SETTINGS from iDrive menu.
3. Select VEHICLE
4. Select TPM
5. Select RESET

Hi Paul,
I enjoy reading your informative car repair advice every Thursday. My Toyota Land Cruiser roof leaks when it rains or during a car wash. I have taken it to the garage where it was confirmed that the sunroof does not leak. We cannot figure out where the water intrusion points are. What should I do?
Richard.

Hi Richard, all vehicle sunroof systems have water drainage channels on either side of the sunroof which allow rain or storm water to be channeled through special pipes to the bottom of the vehicle.
Overtime, the roof drainage system will get clogged by dust or leaves especially when the car is always parked on the road side.
To sort this out, you need an experienced body repair technician to dismantle the sunroof system and unblock the drainage system. This may involve removal of the interior roof lining.
This is a delicate area which calls for patience and expertise to avoid damaging the roof lining.

Hi Paul, I greatly appreciate the advice you give to different vehicle owners. I drive a Toyota RAV4 L 1996 model (2000cc). I realise it consumes a lot of fuel more especially while driving in town. It drives great. On average it consumes a litre of fuel every five km (town). While on a highway it makes 11 Litres. I have changed fuel sensors, plugs, the tyre pressure is always tuned to recommended level. What could be the problem?
Godfrey.

Hello Godfrey, your RAV4’s fuel consumption is on the high side especially during town running. A Toyota RAV4 with a 1.8 or 2.0 litre petrol engine should give you a fuel economy result of approximately nine to 11 km/ litre when driving in urban or city traffic or 14-16 km/ litre driving on the highway.
Of course these estimates are affected by the car tuning and maintenance condition as well as your driving style. In your situation, your mechanic needs to closely examine the ignition and emission systems of the RAV4.
Look beyond the spark plugs and examine the condition of the high tension leads in case they leak spark and do not fire the spark plugs adequately.
Your mechanic ought to examine carefully the engine throttle unit and establish whether the throttle valve opens and closes freely (without hindrance from accumulated soot). The throttle unit helps to charge the fuel delivered to the engine for the combustion process.
When the throttle unit fails, the fuel air ratios will most likely be rich (more fuel in the air fuel mixture) or lean (more air or less fuel in the mixture) causing the engine idling revolutions to idle at high revolutions above 1,000 rpm or surge erratically which causes poor fuel economy.
I hope you replaced the oxygen (O2) sensor with a new one, it helps to monitor the exhaust emission oxygen levels which helps to regulate the delivery of fuel by the engine computer.
The air filter ought to be in a good condition so as not to restrict air intake which leads to a lean fuel ratio. That should sort you out.

Hi Paul, thank you so very much for the great work you are doing. Could you kindly say more about the VVT-i engines? I thank you.
Ram William Lukwago.

‘VVTI’ means ‘Variable Valve Timing with Intelligence’. Variable valve timing systems allow air intake and exhaust valves to open earlier or later in the 4-stroke cycle.
This technology was developed by automakers in the 1960s in order to improve volumetric efficiency, decrease harmful emissions and reduce fuel pumping loses or improve fuel economy.
From the 1990s to date, the use of this technology by different car manufacturers has increased albeit in varying ways. Honda call it VTEC, Mitsubishi – MIVEC, BMW – VANOS and Toyota call it VVTi.
There are two main types of variable valve timing: cam changing and cam phasing. Camshaft changing is where the Engine Control Unit selects different cam profiles depending on the engine load and speed.
On the other hand camshaft phasing is where an actuator rotates the camshaft changing the phase angle.
Camshaft phasing advances or retards valve lift events by rotating the camshaft over a range of about 60 degrees relative to the crankshaft angle.
Retarding the camshaft’s timing, helps the engine to achieve better high RPM torque, while advancing the intake camshaft’s timing produces better power at low RPM.
To achieve this feat the VVTi system employs the engine computer (ECU) which uses sensors like the crankshaft position sensor and the camshaft position sensor to know how fast the engine is rotating by monitoring the position and location of the pistons and valves. The VVTi system employs the uses of a special oil control valve which acts as a hydraulic actuator which adjusts the camshaft via a rotating rotor.
This process is aided by other sensors such as the oil temperature sensor, coolant temperature sensor, mass air flow sensor which join the other sensors to give the ECU an all round status of the engine performance.
This informs the decision to vary timing in order to achieve better engine efficiency. It should be noted that timely and periodic engine maintenance with the manufacture recommended engine oil grade is crucial for the proper functioning of the oil driven actuator valve and indeed the whole valve train.

Ask the mechanic
By Paul Kaganzi
0772316145
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