Mercedes-AMG servicing and repair in Sharjah

These are two separate faults on one engine and they are the two that decide whether a 6.2 is worth buying. The head bolts of the early production run corrode where they pass through the coolant jacket, lose clamp, and let coolant seep at the head face — which is why the smell arrives before the puddle, and why it is often noticed after a hard drive rather than in a car park. Separately, the camshaft lobes and the rockers riding on them wear on engines that have not had oil changed often enough, and that wear is progressive rather than sudden. So the work is to look, not to guess: a pressure test on the cooling system held long enough to find a seep rather than a leak, the bolt heads and the head face inspected directly, and the valvetrain listened to cold and then looked at through the oil filler and the cam covers. We say which of the two we have found, because they are not the same repair and they are not the same decision for an owner.

A supercharged engine has a failure the turbocharged ones do not: it is driven by a belt through a coupling, and that coupling wears. When it does, the blower turns a little less than the engine thinks it does, and the car simply feels ordinary — no warning light, no stored fault, nothing a scan tool has any opinion about. That is why an owner is so often told nothing is wrong. The second item is the small electric pump that circulates coolant through the air-to-water intercooler, and here the symptom is the giveaway: a car that pulls properly for the first minute and then loses its edge is a car whose charge air is no longer being cooled, and in this climate that is the condition it will spend its life in. We measure rather than infer — intake air temperature after the intercooler read as live data on the road, boost pressure against what is being requested under load, and the coupling inspected with the belt off.

This engine puts its two turbochargers in the vee between the cylinder banks rather than outboard of them. It is a good design and it makes the car respond the way it does, but it means the oil feed and return lines run through the single hottest volume on the engine — and the moment that matters is not while driving, it is the minute after the key comes out, when the coolant stops moving and the heat that was being carried away sits in the vee instead. That is what the car’s after-run pump exists to deal with, and it is why an after-run circuit that has quietly stopped working is a more serious fault on this engine than the same failure would be on a conventional one. So we check that the after-run actually runs before we look at anything else, then read the oil condition and the turbocharger shaft play directly. The advice that goes with it costs nothing and is worth more than most repairs: give the car the half minute at idle before switching it off after a hard drive.

This is the single most misdiagnosed item on an AMG, because the gearbox is described as an automatic and is then treated as one. It is not: AMG removed the torque converter and put a multi-plate clutch running in oil in its place, which is what gives the car its response from rest and what makes the fluid in it a working part rather than a lubricant. A converter absorbs a shunt at take-up; a clutch pack transmits it, so the same wear that a conventional automatic hides, this gearbox reports to the driver’s seat. The right first move is therefore to read the clutch adaptation values and the gearbox oil temperature under load, not to quote a rebuild. A great many of these gearboxes are one fluid service and one relearn away from behaving properly, and the ones that are not will say so in the adaptation figures before anybody opens anything.

A large-capacity V8 at idle produces a pulse that a rubber mount alone will pass straight into the cabin, so these cars use mounts filled with fluid and, on some of them, mounts the car actively changes the stiffness of. When the fluid leaks out, the mount does not fail in any way that stops the car — it simply becomes a rubber mount, and the owner is left with a vibration that everybody can feel and nobody can find, usually after being told it is an engine problem. It is diagnosed by looking at the right thing: the mounts inspected from underneath for the fluid that has left them, the engine’s movement watched under load against the brakes, and, where the car has the active type, the mount’s own control checked for whether it is being commanded at all. It is a cheap answer to an alarming symptom, which is the best kind of finding to be able to give somebody.

This is the highest specific output of any four-cylinder engine sold in numbers, and it gets there by pushing a great deal of air through a small engine — which makes the temperature of that air the limiting factor rather than an incidental. On a European ambient the charge cooler has margin. At 45°C standing in traffic it does not, and the engine protects itself by pulling timing and reducing boost, exactly as it was designed to. So the first question is whether the car is faulty or is doing its job, and that is answered with data rather than opinion: intake temperature after the cooler, requested against actual boost, and any timing correction, all read on the road at the moment the owner says the power disappears. Where the answer is heat, the honest advice is about the cooling circuit and the driving, not a part. Where it is the turbocharger itself, the shaft is checked directly — a roller-bearing turbo gives a different and much earlier warning than a plain bearing one, and it is worth catching at that stage.