Diesel injector cleaner: what a bottle can't fix

Injector cleaner won't fix what the EGR has already broken

A C5 that judders when leaving town and accelerating onto the motorway. Oil, air and fuel filters changed. And a bottle of injector cleaner in the tank as a last resort. That's the starting point of a discussion that isn't really about additives at all: it's about diagnosis. Because the most uncomfortable consensus running through the whole conversation is that pouring in cleaner once and hoping for a miracle is, in the words of one participant, throwing money away.

The product isn't the problem. The problem is what it's used for. Some people have been adding a splash at every fill-up for years and defend it as preventive maintenance for the fuel system. Others, without contradicting that, point out that a one-off treatment won't solve juddering that has been building up for a long time. The distinction between prevention and repair is the line separating the optimists from the sceptics.

What causes juddering in a diesel with a dirty EGR valve?

The usual suspect has a name: the EGR valve. In a car that does mostly city driving —start, stop, start— the exhaust gas recirculation ends up coked up, and the engine judders when it's suddenly pushed on the open road. The remedy doing the rounds isn't chemical: drive 5 to 10 kilometres on a dual carriageway at around 3,000 rpm to try to burn off some of that soot. The caveat gets repeated: try to. In the long run, a clogged EGR ends up causing problems anyway.

The other avenue being considered is the fuel itself. One participant points to the quality of diesel served at certain stations, with water, benzenes and varnishes in the mix, and recommends filling up at busy branded stations and not running the tank low. The counterargument comes quickly: diesel comes out of the same loading arm, and what differs is tank maintenance and additives. The debate over whether own-brand fuel is worse is left, at the very least, open.

Does giving the engine a good workout now and then help?

Here the agreement is broader than it seems. Climbing a mountain pass at full throttle or accelerating from a standstill to top estimulante ilegal is presented as a method for burning off deposits in the combustion chamber. One specific case: 3,000 euros saved on injectors on a second-hand car after putting it through that treatment. Against the antiestéticar of wrecking the turbo, the answer is that a healthy engine can take the beating, and that it's the ones driven at low revs that end up in the workshop, with the dual-mass flywheel and DPF suffering.

The technical nuance comes from someone who works with diesel engines every day: on overhauls of stationary engines with 24,000 hours —the equivalent of two million kilometres— the injectors had never been cleaned. No manufacturer includes that cleaning in the maintenance schedule. They're cleaned when there's a problem, not by the calendar.

From a bottle of injector cleaner to the diagnostic cable

The thread drifts into the back room: the Lidl ultrasonic machine for cleaning injectors, the ceramic additives from premium brands that do work but aren't cheap, and the old dream of plugging a cable into the car and asking it what's wrong. An unexpected case also comes up: juddering above 2,000 rpm caused by a loose battery terminal. Cheap diagnosis before expensive spare parts.

The prediction, with reservations: the bottle of cleaner isn't going to make that city-and-motorway juddering disappear. At best, it will keep clean what's already clean. What really moves the needle is knowing whether the problem is the EGR, an injector or a loose bolt. And no additive brand sells that.