Ask the Mechanic: How does an oil leak affect the engine?

Hello Paul, I have a 1999 Rav4 which I imported in 2014. However, on the first day driving it, I noticed oil leaking around the engine. At the garage, a mechanic said the gasket was faulty and tried fixing it with some kind of glue called silicon. However, a month later, it started leaking again. What are the dangers of such leakage on the engine and general performance of the car and what must I do to completely fix it?


Hello Kenneth, thank goodness you have paid attention to a maintenance issue and bothered to find out how to deal with it. Like human beings, vehicles require regular maintenance to avoid serious damage. The leakage around the top of your engine is caused by a worn out engine top cover gasket kit which usually gets warped due to exposure to engine heat. This kit also comes with spark plug oil seals, which should all be inspected or replaced at the 100,000 kilometres service (when wear and tear occurs).

Use of silicone paste is an emergency but temporary measure, which often fails sooner rather than later. Initially, the worn out engine valve cover gasket and spark plug oil seals will leak small negligible amounts of oil with the leakage increasing overtime. Any loss of engine oil is not good as it reduces engine oil pressure and causes gradual damage to fast moving engine components. Also, oil leaking in the spark plug tube will damage the spark plugs as well as affect engine performance.

Oil leaks around the engine tend to trap dust, which forms a paste or grime. This not only makes your engine dirty but also damages vacuum hoses where it tends to stick. Please go to Toyota Uganda or the nearest dealer in genuine Toyota spare parts and buy an engine valve cover gasket kit and spark plug seals.

It is also prudent to check your mileage just in case your car has covered 100,000 kilometres at which mandatory timing belt and fuel filter replacement should be carried out. Toyota will have the genuine replacement parts for you and you can find a good mechanic to carry out the replacement procedure. Let me know if you need any further clarification or assistance in this regard.


Hello Paul, I own Toyota Progress which I have been driving for the last two years. However, I lost its key and to replace it, I was also told the car needs to be taken for programming. How safe is this programming and how much would it cost? I have also noticed a leakage around the timing case. What could be the problem and how can it be fixed.


Hello Rashid, the ignition key for your Toyota progress is designed to work with the car security system to prevent unauthorised entry and start up. The security system is composed of an immobiliser control module and key reader which recognise a specially encoded transponder chip incorporated in the key. When you use the correct key, it will be recognised by the immobiliser control module which will then authorise the engine control module to supply spark and fuel to start the car. A breakdown of any of the components or loss of the key will prevent starting.

Getting another key requires buying it from an authorised Toyota dealer and it must be programmed to the immobiliser control module to be recognised. Attempts to bypass this system can be futile or very costly.

The leakage around the timing case area suggests that your car may be due for the 100,000 kilometre mandatory valve top cover gasket renewal. This is done together with the camshaft and timing case oil seals (which you see leaking).

I would go further to confirm the mileage of your car and if it has reached 100,000 kilometres, replace the engine timing belt, timing belt tensioner and roller.

It is also time to replace the long life fuel filter fitted in your fuel tank. These procedures should be carried out by a qualified mechanic using parts from genuine parts dealers.


Hello Paul, I have a Jaguar Xtype which gives that pocking sound as you start it in idling mode. What could it be?


Hello Charles, what you called a ‘poking’ sound in your engine as it runs during idling could be one of a couple of factors. The first is a possible breakdown of the engine plumbing or cooling system. When coolant is not moving freely due to water pump failure or buildup of vacuum pockets in the coolant lines, you can experience that sort of noise. Discuss with your mechanic and suggest that an inspection of the water pump is done to confirm that the pulley is running unilaterally and it does not leak.

Feeling the coolant rubber hoses can help detect whether coolant is flowing through them.  To avoid car engine cooling system damage, renew all the radiator coolant every two years. This will keep the corrosion inhibitors and lubricant additives in tip top protective condition.

Also, check all pulleys and other accessories and belt rollers in case you have a damaged bearing.

While you are at it, check the timing chain and chain guides, under the timing case, for wear and chain slackness. They usually need to be replaced around 100,000kms.

Email your comments and questions to: [email protected]