Two stroke oils - corrosion resistance

[Gerry45]

A while ago I did some comparison tests on the corrosion resisting ability of some popular 2 stroke oils. The winner, Castrol TTS, was quite unexpected. It is a high performance fully synthetic (PAO) type, and when designed, building in corrosion protection would have been well down on the list of 'priorities'. It's quite low viscosity at 'storage' temperatures so this wouldn't have helped to keep a thick protective film on the test brgs as long as with some of the other oils.

This result has puzzled me for some time. Does anyone have any good ideas as to why the TTS may have come out tops ?

Gerry

 

[25362]

Highly refined mineral oils or even PAOs have very little, or no, inherent anti-wear performance. A successful EP and antiwear additives' formulation may be the answer to TTS favourable results.

Let's start by saying I don't know the formulation characteristics of Castrol's TTS. However, when one says fully synthetic, one not necessarily means PAOs.

Synthetics could also be PIB fluids (polyisobutylenes) which are more tacky than mineral oil, forming a tough lubricating film under severe conditions. They are used, among others, for two-stroke engines in that they alleviate problems associated with deposits, such as port blocking and smoke formation, whilst providing excellent protection against wear and scuffing.

There are other synthetics such as esters that offer a number of advantages over mineral oils as the lubricant component of two-stroke engines. Their use shows less engine fouling due to their clean-burning characteristics, with much lower ring sticking and lower levels of dirt build-up on ring grooves. Plug life and ignition performance are also improved. Secondly, their polar nature enables them to stand larger dilutions of up to 150:1, while mineral oils have oil:fuel dilution ratios of 50:1. This fact results in lower oil emissions, good for the environment. Esters have also been mentioned as factors to reduce emissions of (carcinogenic) PAH and smoke.

 

[Xtrema]

What corrosion test did you perform?

 

[Gerry45]

Good ole British Winter outdoor tests, ie. high humidity atmosphere! I was trying to simulate the effect of leaving small two-stroke engines idle over a winter of non-use where the crank bearings are at risk of corrosion.

I did immerse some oiled brgs in some water too. The Castrol TTS was best in this situation too.