How did Sinclair Oil put "liquid nickel" into gasoline, and what were the chemical mechanism(s) by which it was supposed to reduce engine wear?

Question

The April 22, 2022 Veritasium video The Man Who Accidentally Killed The Most People In History is worth a watch, and was the basis for the question Why would tellurium + sodium hydroxide have worked as a good anti-knock gasoline additive (if it wasn't so smelly)?

But today I've come across a different heavy metal additive to gasoline!

I fondly remember the Sinclair Oil dinosaur statues and the free green dinosaur soap we sometimes got with a fill-up. But this circa 1964-1965 (from the reference to the 1964 World's Fair at the bottom) advertisement mentions a new "liquid nickel" additive to gasoline that "reduces engine wear as much as 29%".

Question: How did Sinclair Oil put "liquid nickel" into gasoline, and what were the chemical mechanism(s) by which it was supposed to reduce engine wear?

I've proactively added the organometallic-compounds tag; if lead was introduced in its tetraethyl form, maybe nickel was made soluble with organics as well (not sure about that tellurium in the linked question though).

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From the advertisement:

Liquid Nickel in Sinclair Gasolines is an exclusive Sinclair discovery that:

• Reduces engine wear as much as 29%
• Combats harmful engine deposits
• Restores lost power in old cars
• Keeps new cars at peak performance
• Sinclair and only Sinclair has Liquid Nickel

Source: US National Park Service's Tourism and Dinosaurs

Answer 1

In a 1965 paper [1], researchers from Sinclair described the properties of the gasoline additive nickel isodecylorthophosphate. In their words

The outstanding performance features of this nickel additive can be summarized as follows:

1 . Reduces abnormal deposit-induced ignition phenomena, such as rumble and wild ping, both in the presence and absence of other deposit modifiers.

2 . Reduces equilibrium octane requirements.

3 . Modifies combustion chamber deposits without adding to the total amount of deposit accumulation.

4 . Reduces engine wear.

5 . Prolongs exhaust valve life.

6 . Functions as an effective carburetor deicer.

7 . Functions as a good rust inhibitor.

They don't describe the mechanism by which the deposit modification occurs, though they do attribute the carburetor deicing and rust inhibition effects to the surfactant properties of the additive, and they speculate that the extension of exhaust valve life is to due to the nickel compound "softening" depositions on the valves so that they come off more easily and do not build up.

The introduction to the paper also describes the fortuitous discovery of the effects of alkyl metal salts as resulting from addition of amine alkylphosphate surfactants for deicing and rust inhibition. It was observed that the surfactants reacted with galvanized surfaces in the presence of water and produced a gelatinous precipitate, which was identified as comprised of alkyl zinc compounds that were soluble in gasoline. Concerned that these compounds might have a detrimental effect on engine performance, Sinclair researchers added them to gasoline and found, to their surprise, that there were actually benefits. This prompted a screening of gasoline-soluble metal compounds, from which nickel isodecylorthophosphate emerged as the best candidate for commercialization.

[1]Schoen, W. and Pontious, R., "New Gasoline Additive Improves Engine Performance, and Durability," SAE Technical Paper 650941, 1965, https://doi.org/10.4271/650941.

Answer 2

Another newspaper advertisement tells us the US Patent Number 2,937,992.

The patent tells us that the nickel compound is an oil-soluble nickel dithiophosphate:

A particularly suitable nickel dithiophosphate which can be employed with advantage is that prepared from a di-2-ethylhexyl dithiophosphate obtained by reacting a technical mixture of 2-ethylhexanol with phosphorus pen tasulfide. The nickel dithiophosphate is employed in my improved lubricating compositions in a small or minor amount sufficient to inhibit oxidation and bearing corrosion and in most instances the amount used provides about 0.03 to 0.2% by weight of phosphorus on the basis of mineral oil in which it is incorporated.

The preparation of the nickel di-2-ethylhexyl dithiophosphate base is included:

Basic nickel carbonate (2585 g.) was added portion wise to 13,375 g. of dry di-2-ethylhexyl dithiophosphoric acid at 80 to 132 F. over a period of 3 hours. The solution was dehydrated under vacuum (20-30 mm.) at 185 to 200 F. to give, after filtration, 12,230 g. product, pH 6.8, and acid number (D-974) 20.9.

The patent also presents laboratory engine tests.