The cooling system is composed of a timing belt driven water pump, a 87 °C thermostat in the engine block itself. The thermostat receives coolant from the engine block and from a bypass running from the engine head. This system allows a very accurate opening and closing operation, avoiding thermal shocks and big coolant temperatures amplitude.
The D24 was fitted in the Volkswagen LT range from Volkswagen Commercial Vehicles, with factory production from August 1978 to December 1995. Specific dates of the variants - CP: 08/78-11/82, DW: 12/82-07/92, 1S: 08/88-07/92, ACT: 08/92-12/95.
The D24 was also found in a number of Volvo Cars - specifically the 240, 740, and 940 and was coupled to Volvo ZF, Automatic Aisin Warner AW55, Automatic Borg Warner BW55, M45, M46 (overdrive) or M47, m47 II and m90 transmissions.
In service, the unit proved to be a somewhat mixed bag; some owners reported excellent reliability and long engine lives, others complained of overheating, frequent blowing of head gaskets, cylinder head cracks (cracks between the valve seals are common and do not represent danger if the cracks do not exceed specifications, premature wear of the bottom and top end bearings, low oil pressure etc.
A poorly maintained cooling system could also lead to overheating and, especially with the higher stressed turbo engines, head gasket problems. The head gasket problem has been treated with the adoption of a multi-layer steel head gasket which replaces the fiber one.
The camshaftdrive belt also required changing at the recommended intervals, which was a pretty involved job, not least because of poor access in the under-floor engined LT vans, and the necessity of special (and expensive) locking tools to carry out the replacement, which have always been scarce and are becoming increasingly difficult to obtain.
The top end also featured adjustable tappets using the bucket and shim arrangement, and required checking every 25,000 miles (40,000 km), although later (1990–) models had self-adjusting hydraulic tappets.
In many cases however, engines that have been looked after properly and treated with mechanical sympathy (this engine is particularly sensitive to being thrashed from cold, it is important to go gently until warmed up, and to avoid short journeys which will exacerbate rapid engine wear) have been known to clock up 500 000 - 600 000 miles