The predecessor to the 3/4 tank rule was the “half-tank rule” introduced in 17 April 1989 by then Finance Minister Richard Hu
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to ensure that the use of petrol pricing to control the usage of roads in Singapore is not bypassed. Additionally, loss of duty on petrol is estimated at around $2 million a month...The primary reason is to allow Government to control car usage through petrol pricing and we cannot allow motorists to avoid this by merely nipping across to Johor...”
The half-tank rule did not deter motorists from visiting Johor. Post-Iraqi invasion led to petrol prices to jump from $1.12/l to hit $1.54/l in mid-Oct 1990, before stablising at $1.20/l. The difference of 48c per litre of petrol led to a surge in Singapore registered cars crossing to Johor to uplift the cheaper petrol there. The duty loss arising from this amounts to around $2 million per month, about the same level just before the introduction of the half-tank rule.
The availability of substantially cheaper petrol in Johor undermined the conversion to use of unleaded petrol in Singapore, made petrol taxes less effective in restraining car usage, and caused significant loss of revenue. Thus, the 3/4 tank rule, the present rule, was implemented.
So, Malaysia had no say to the 3/4 rule. She should not say anything because no fuel tank rule is best for her country.
<Singapore Parliamentary Debates, Official Report (7 April 1989) vol 54 cols 60–98>
<Singapore Parliamentary Debates, Official Report (15 January 1991) vol 56 cols 867–869>
https://www.todayonline.com/singapore/three-quarter-tank-rule-could-soon-include-diesel-vehicles