Just as a side note, the 5TD-6TD series diesel engines are just plain fuel hungry, especially in a counter-insurgency role where the tank primarily either sits in idle or perform limited tactical maneuvers.
The nature of them being opposed two-stroke-cycle engines, with very short stroke distance, large piston diameter, and high RPM means they can cram a lot of peak power output in tight (especially flat) spaces, with the unfortunate downside being low torque at low RPM (poor acceleration), short time between overhaul (high RPM = high wear), and bad fuel economy (fuel-rich combustion at low RPM). They really are more intended for the soviet armour spearhead, long-distance breakthrough, not for rat-blasting.
Although in the near future, engines like 6TD could see a resurgence. A very interesting development recently have been electric transmission in tanks and AFVs reaching operational maturity, which benefits engines like 6TD immensely, since it means the diesel engine only have to operate at ideal RPM condition where its advantage in high energy density can be used in full, while its disadvantage in bad low RPM performance can be perfectly ameliorated by the natural feature of electric motors.