Used Mercedes-Benz GL420

What to know before buying: Mercedes-Benz GL420

From 1 forum thread and 3 press tests · updated 12/10/2026

What the reviews say

• The cabin is exceptionally spacious, comfortable and practical, with seven seats and substantial cargo capacity when the rear seats are folded.[2][3][4]GL-Class
• The adaptive suspension delivers a very comfortable ride over cobbles and uneven roads, with Normal, Sport and Comfort modes available.[2]one sourceGL-Class
• The GL 420 CDI's 4.0-litre V8 diesel produces 306bhp and 700Nm; reviewers found it muscular and well isolated from the cabin.[2][3][4]GL-Class
• Its huge dimensions make urban manoeuvring difficult, although good visibility and bumper sensors help the driver judge its size.[2][3]GL-Class
• Fuel use is high and strongly driving-dependent: tests reported 8–9km/l, while brisk urban driving could consume 20–30l/100km.[2][4]GL-Class

Typical faults

• One GL 420 CDI expelled coolant from the expansion tank after warming up despite showing about 90°C; a failed head gasket was subsequently confirmed.[1]one source

  GL 420 CDI 4.0 V8 diesel

• The tested car's third-row seat mountings squeaked while driving, though the reviewer noted this might have been limited to that demonstrator.[2]one sourceGL-Class

Which engine and version to take

• Choose the GL 420 CDI's 4.0-litre V8 diesel for performance: 306bhp, 700Nm and 0–100km/h in 7.6 seconds, but expect heavy fuel use.[2][3][4]GL-Class

What to check at the inspection

• Once fully warm, check whether coolant is forced from the expansion tank. In the reported case it happened after roughly 1km and was traced to the head gasket.[1]one source
• During the test drive, listen for squeaks from the third-row seat mountings and check the powered folding operation.[2]one sourceGL-Class
• Obtain a vehicle-history check; Parkers specifically recommends this for every used GL-Class purchase.[3]one sourceGL-Class
• Confirm you can manoeuvre it confidently and that the front and rear parking sensors operate, because the GL's size makes tight manoeuvres difficult.[2][3][4]GL-Class

Verdict

Sources

1. [1]forum.autobazar.eu — Mercedes GL 420 cdi - vyviera voda - Auto-moto fórum · forum
2. [2]tvnet.lv — TVNET tests: "Mercedes-Benz GL 420 CDI" · press
3. [3]parkers.co.uk — Used Mercedes-Benz GL-Class Estate (2006 - 2012) Review · press
4. [4]motorsiden.dk — Mercedes-Benz GL 420 CDI test · press

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