Thinking of buying a second hand car and are not sure if you should choose a petrol or diesel car, find problems that commonly occur and make an educated buying decision.

For many years, I have been driving both petrol and diesel engine cars. This is my advice, and when I go looking for my next car, these are the things I’ll be looking out for. But before I get into the list of checkpoints, here is some general information about diesel engines:

Diesel engines made stronger than petrol engines as the forces within the motor are really high, almost double that of their petrol counterparts. The compression inside the cylinders is really high because diesel does not use spark plugs to ignite the fuel. Diesel is compressed until it ignites. Glow plugs are used to warm the initial fuel mixture and aid the starting process, that’s why you don’t just turn the key as you would with a petrol engine. You need to heat the glow plugs first before you swing the engine.

A diesel engine is therefore highly stressed and as a result, it has a stronger engine block casting, much stronger cylinder head and stronger parts all round. All these things add weight, and as the engine is heavier, the engine mounts need to be stronger and heavier too same with the front shock absorbers it’s a knock on effect of trying to ignite relatively stable diesel fuel using high compression. So in short, diesels are heavier as they are built stronger.

The benefits of course are that diesel offers very good economy (I think the VW 1.9 Tdi is about as efficient as a Toyota Prius) and this is further improved when you add a Turbocharger. And this is where some of the problems begin when considering a used diesel engine car if you do not service them regularly, you stand the chance of over stressing a motor that is already quite stressed. By not changing the air filter when dirty, will make for an engine that runs hot and the item that takes the strain most is the turbocharger.

I’m not saying you should avoid used diesels, it’s just that they are not exactly like petrol. In return for the economy, make sure they are well looked after and keep them serviced regularly.

NOTE: It’s worthwhile noting that this information is for USED diesel engines, but following this advice will definitely prolong the life of any engine.

Benefits of Diesel:

Fuel Efficiency: Diesel fuel has about 14 percent more energy in it than petrol fuel, so it’s going to be hard for petrol to beat diesels economy. When driving long distances at a constant speed, diesel’s economy is unbeatable.

Pulling Power: Diesel delivers raw torque right from the bottom end. When towing a boat or a trailer you sometimes need to check that it’s still with you!

Well made Engines: As diesel engines are built stronger, they tend to last longer too. Make sure they have been serviced as required.

Be aware of the following things:

• Worn glow plugs: Diesels tend to start first time, every time. If you need to let the glow plugs go again, or if the glow plug indicator light is lit for a period of more than 5 seconds, it could mean that they have seen better days and they are expensive, much more than a set of petrol spark plugs!
• Oil and Sweating: Because of the high compression experienced with diesel, make sure that there is no sweating from around the head gasket or sump.
• Turbo: A worn turbo and inter-cooler that are covered in oil or show signs of leaking are to be avoided as repairs to them are costly and usually require replacing. Turbos that are worn show signs of oil use, smoking engine and/or lack of power.
• Injectors: If you put your foot down or accelerate aggressively, and the car leaves a plume of smoke behind, then it’s reasonable to assume the injectors are worn (if the car did not smoke with normal use). This can be costly as the whole injection system needs recalibrating when they are replaced.

You should feel quite at home in a diesel powered car, it’s not really all that different from a petrol car. You should note improved economy, and a lower revving engine.

I’d be delighted if you found this article useful and that you find a better car for your needs.