Mazda BT-50 Engine Problems

The fact that the fuel economy average seems to be creeping up can have a lot to do with the fact that you’re becoming more familiar with the vehicle and using more throttle as a result. But remember, too, that until you reset the average on the trip computer, what you’re seeing is the full history of your consumption from when the trip computer was last zeroed, not just the most recent trip you’ve done.

It's true that engines often start to use a little less fuel as they 'bed in’ after a few thousand kilometres. And for a modern turbo-diesel like yours, I reckon 10,000km or even 15,000km might be the magic number. However, don’t be too disappointed if it doesn’t come down a whole lot. I reckon for that vehicle, driven the way you’ve described, 10 or 11 litres per 100km isn’t a bad average to aim for.

Other factors play a big part, too. Does the vehicle have a bull-bar or roof racks? Both these add weight and aerodynamic drag respectively, and can easily make the car consume more fuel. A roof rack at 100km/h can be worth an extra litre per 100km.

There are many reasons for a vehicle to enter limp-home mode. One of them, of course is transmission temperature, but there are lots of things being monitored, from the temperature of the engine oil, coolant temperature, oil level and even the operating temperature of the EGR valve (which is often water-cooled in vehicles like the Mazda).

The point being that even though the transmission entered limp-home mode, the actual problem may have been elsewhere, but the vehicle’s computer believed that shutting down much of the transmission’s functions would preserve and protect the rest of the driveline. Don’t forget, either, that there are many things – a failed solenoid, low fluid level, even a faulty wiring connection or earth – that can cause a transmission limp-home event beyond actual overheating.

There’s a very simple check you can do to see whether the battery or the charging system (alternator, regulator and wiring) is at fault here. With the engine running, place the probes of a multi-meter (switched to measure voltage) on the relevant battery terminals. If you see a figure of anywhere between 13.2 and 14.7 volts, the charging system is doing its job. You might need to rev the engine slightly off idle to see these numbers, but the voltage going into the battery should be in that range.

At this point, the battery becomes the main suspect, and a worn out battery will often neither hold a charge nor accept one.

An open circuit on a fuel injector is usually caused by either a broken wire to the injector, a loose terminal somewhere in the electrical circuit that drives the injector or a burned-out coil in the injector itself.

Changing the suspect injector will tell you if the coil is the problem, but if that doesn’t fix it, you’ve got to work backwards from the injector until you find the fault. Bear in mind that if the injector itself is at fault, the other three injectors might be ready to go out in sympathy. Modern common-rail engines can be hard on injectors and they sometimes need replacing before they’ve done 100,000km.

This is a really common problem with this model (and the Ford Ranger with which it shared its mechanicals). Many buyers avoid this model for this very reason. Even though many fixes have been tried it seems that this car, shown a hill and a hot day, will often overheat.

Several theories exist including that the EGR valve is the problem, as it fails and allows coolant to escape (usually into the engine cylinders). But even when the EGR valve is working properly, this engine is prone to running too hot. Some other theories hold that the thermal management of the engine itself was just underdone and there’s no real fix for it. That’s borne out by the number of people who have tried different radiators, thermostats and cooling fans and still have a vehicle that overheats.

But you could try reverse flushing the radiator and making sure than every part of the cooling system is working efficiently and properly. That will maximise your chances of not having the engine overheat but, in this case, there are no promises.

Rather than the steering completely locking up, it’s more likely you’re feeling steering that has lost is power-assistance. It can make the wheel extremely heavy and could feel as though the car won’t steer at all. This is linked to the engine stalling, because the power-steering on this vehicle is driven by a belt from the engine. No engine means no power-assistance.

The other questions, of course, are why is the engine stalling and why only on left-hand turns. There are plenty of things that can cause a modern engine to stall from a dirty fuel filter to a blocked injector or an electronic fault. And about a million things in between. An electronic scan of the vehicle might throw up a fault code that will help a mechanic unravel what’s going on.

We have heard some reports of Ranger and BT-50 (they're the same vehicle mechanically) suffering oil pump failures with fairly terminal results for the rest of the engine. The other quirk with this engine is that you can't drain the engine of oil and leave it for any more than a few minutes without the pump running dry and needing to be primed before the engine is started.

Not all mechanics know this and many a Ranger or BT-50 engine has been destroyed when the oil has been dropped from the sump and the mechanic has gone to make a cup of tea or do some paperwork. They return half an hour later, replace the sump plug, fill the engine with oil and start it up. But because the pump hasn't primed, there's effectively no oil pressure and the engine is reduced to scrap in a few short seconds.

The problem is partly to do with the different design of the pump and there are even companies that have engineered more conventional oil pumps to replace the standard units on these engines.

This sounds like another one of pesky electrical problems which occur but don't really create havoc beyond making you wonder why it's happening. In many cases, this sort of problem can be caused by a poor earth somewhere on the car or even a chafed wire that is short-circuiting and turning random lights on and off.

But it could also be a symptom of something more serious with the car's electrical systems, so an electronic scan of the vehicle should be your next move. That will rule out a lot of things and also possibly pin-point the problem.

The clue here might be in the fact that this problem occurs when you drive slowly for an extended distance. This could suggest that something (engine or transmission perhaps) is becoming hot and the vehicle is switching to limp-home mode to avoid damaging any components. Also, it could be a dodgy sensor which is simply making the vehicle 'think' it's getting hot.

It sounds counter-intuitive, but driving slowly can lead to overheating as there's less air flowing over the radiator and/or oil coolers to whisk temperature away. When you stop the car and re-start it, the on-board computer goes back to its default settings and away you go again until the sensors detect more heat build-up.

With that in mind, I'd be checking the radiators and oil coolers for a build up of dust, mud, leaves and other rubbish which could be blocking airflow. But before you start replacing sensors and other components, have the car scanned (by a mechanic) to see if any fault codes make themselves apparent.

The rule of thumb states that if the engine fires on starting fluid sprayed down the intake, but won't run on the fuel in its tank, the first thing to check is the fuel pump. Just because there was some fuel present when you cracked the seal on the fuel injector, does not necessarily mean that there's enough of it or the fuel pressure is sufficient to start the engine.

Modern common-rail diesel engines use very sophisticated fuel systems which use super-high pressure. Without a pump to build up to this pressure, the injector won't deliver the right amount of fuel for successful running. But you should also check the operation of the glow-plugs as well as the condition of the fuel filters. An electronic scan is also a good idea at this point, before you start replacing expensive bits and pieces.

Be extra careful fiddling with engines like this one, especially if you're messing about with the injectors and fuel system. The inherent pressures are so high, that a leak can act like a water-jet cutter; sufficiently powerful to remove a finger.