Mercedes SL55 buying guide: powertrain

The SL55 AMG's 5.4-litre V8 may have been based on the SL500's, but very little of the less powerful, non-supercharged motor remains untouched. For starters, there's the belt-driven screw-style supercharger that sits in the vee of the engine block. With Teflon-coated aluminium screws, the supercharger can spin at up to 23,000rpm when the engine is at its limit. This rev limit for the engine is increased to 6,100rpm from the standard SL500's 5,600rpm ceiling.

To cope with this extra power and its associated stresses, AMG engineers adapted the crankcase to use special transverse screws. The engine also runs with a strengthened block, uprated bearings and pistons with greater resistance to heat and pressure. Also helping the motor to cope is an improved oil supply system with modified sump and higher capacity oil pump.

5.4 supercharged V8 lump gives over 500hp
5.4 supercharged V8 lump gives over 500hp
The SL55's engine bore remains the same as the SL500's, but stroke for the AMG was increased from 84.0mm to 92.0mm, giving the 5.4-litre capacity that is 473cc greater than the SL500's. Other changes made by AMG include cylinder heads with revised intake and exhaust ducts, higher-lift camshafts with longer opening durations and double springs for the valves.

Mercedes also used the SL55 to introduce fully computer-controlled engine mapping for the first time on its road cars. Along with the SL55's twin catalytic convertors, it managed carbon dioxide emissions of 340g/km, which were considered very reasonable in 2002.

Problems with the M113 V8 are very rare as it's a strong engine. Check the oil and coolant fluids are clean to the level, and make sure all of the visible pipework is in good condition as access around the engine is tight. The charge cooler for the supercharger sits in the engine's V and uses its own radiator, so have this checked for leaks or corrosion. A squeaky supercharger can be made quieter by squirting some graphite spray down the head of the supercharger. It's not a complete fix, but the supercharger is a strong unit and should give no problems, even with an uprated pulley fitted from established tuners such as Kleemann.

Much more of a worry is the five-speed automatic gearbox, which also came with paddle shifts mounted on the rear side of the steering wheel. On any test drive, check the gear lever slots from Park into Reverse, Neutral and Drive cleanly. If there's any hesitation, resistance or it needs to be given a shake to make it work, the plastic peg that prevents the lever inadvertently being knocked into Reverse without the driver's foot on the brake is about to break. It's a relatively easy part to replace and there are direct replacements made from aluminium available that cure the fault. A Mercedes dealer may elect to replace the entire unit, which can add up to £1,500 in components and labour rates. The gearbox also needs its fluid completely changed every five years, so early SL55s will need this addressed right about now.

The rest of the SL55's transmission is very tough, though watch out for cars that have been used on track as the AMG's weight will give every component a hard time. In normal mixed driving, the SL55 should go 12,000 miles between services.

Owner's view:
"The engine is generally bullet proof and there are owners out there with galactic miles on their cars."

Buying guide contents:

Rolling chassis
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