What should I put in my radiator?

Topping up with water instead of coolant in the radiator dilutes the benefits . NET PHOTO

What you need to know:

Symptoms of a faulty vacuum system include uneven or erratic engine idling, engine surge or stalling at idle or premature detonation when you accelerate.

Thanks Paul for your advice which helped me fix my RAV4 with a manual transmission. The solution you recommended has worked miracles and my car is now okay. The engine performance is good and stable. I had to travel to Mbarara from Kabale to find a smart mechanic who could understand what you recommended.

You were also right my car is about to clock 100,000 kms. I have another question; is Toyota going to discontinue the manufacture of manual gearboxes in favour of automatic ones?

There is a rumour that the 2015 RAV4 will offer a six speed manual gearbox as an optional extra. What is the difference between the five speed and six speed gearboxes?
Joshua Mugisha, Kabale.

Joshua, it’s good to know that your car is running well, now you need to maintain it with good fuel and periodic service with recommended engine oil genuine parts. Don’t forget to replace the timing belt and roller bearing.

About your question, Toyota like many car makers now offers six speed manual transmissions alongside CVT (Continous Velocity Transmissions) and six speed automatic transmissions in their 2015 models.

The six speed manual gearbox offers more gears than the five speed manual gearbox. The extra gear on the six speed gearbox allows the engine to run at lower revolutions per minute which makes it more fuel efficient and economical while putting less strain on your engine.

Paul, thank you for the free car diagnosis. I have a Volkswagen Golf 4 and of late, it has developed unstable idling and frequent engine cut off (stopping) when idling.

When I accelerate, it has no power. I have replaced the spark plugs, air cleaner, fuel filter and even serviced the engine oil but this problem persists. My usual mechanic has run out of ideas and suggests that it might be the computer. What is your opinion?
J. Kibirige

Mr Kibirige, your VW Golf may have a leaking vacuum system. A faulty vacuum system can cause poor engine performance. Car engines are like one big vacuum pump. The intake stroke (when the piston goes down) creates vacuum which helps with suction of the air fuel mixture through the carburettor or throttle potentiometer.

Modern cars have a sophisticated fuel injection system which relies on engine vacuum to help the engine computer (ECM) determine how to calibrate the pulse and pressure of the fuel injectors.

Simply put, vacuum helps the computer to determine accurately the running condition of the engine and when to deliver the right amount of fuel. The ECM monitors engine vacuum through the Manifold Absolute Pressure (MAP) sensor.

The MAP sensor takes a barometric pressure reading before the engine starts, then it measures intake manifold vacuum. That vacuum, which is an indication of engine load, should be in line with throttle position, engine speed, and vehicle speed.

When the engine vacuum system fails, often due to a leak from a torn or broken vacuum pipe, the engine computer will assume a limp mode. In this mode, the computer will deliver either a rich or lean mixture of fuel.

This results in an increase of fuel consumption or a starvation of fuel supply which results in poor engine performance.

Symptoms of a faulty vacuum system include uneven or erratic engine idling, engine surge or stalling at idle or premature detonation when you accelerate.

A computer diagnosis can help to determine a faulty or leaking vacuum system via the MAP sensor. To locate an engine vacuum leak you need to look out for torn, broken or loose vacuum hoses which sometimes cause a hissing sound on the engine intake system.

Paul, I have just bought a used Range Rover Vogue 2003 from the UK with 12,000 miles on the clock. I see a check coolant warning light on my dashboard. Should I just top the radiator with water or coolant?
Mugisa.

Mr. Mugisa, your Range Rover has covered the equivalent of 200,000 kilometres. It is overdue for a major service inspection and check.

Find a good mechanic to inspect the cooling system and rule out corrosion damage, leaking gaskets, seals and coolant hoses. Once this is done, the mechanic should drain all the old coolant fluid from the radiator.

Replenish the coolant fluid and this should be done every two years.

A good choice of engine Coolant fluid should be composed of anti-corrosive agents for prevention of corrosion damage in the engine and critical moving components of the cooling system such as the water pump.

A good coolant should contain heat dampening chemicals as well as a lubricant called glycol to prevent friction damage of the water pump. A special priming procedure should be followed to ensure that there is no vacuum build up which prevents coolant flow. Topping up with water dilutes the benefits.