Following engine damage on a strimmer, is there a safe and simple diy
test to check that the tank contains a petrol and oil mixture to rule
out the use of petrol only as a cause of the damage.

Hello mowerman, when I read your question I thought of a way to do a
simple test and just went and tried it out. I stuck my finger into a
50:1 gas/oil mixture that I use for my 2-stroke boat motor and string
trimmer. I blew on my finger to accelerate the evaporation of the
gasoline (petrol) and after the gas was gone I can feel the oily
residue when I rub my fingers together. If you do this with straight
gas, you will notice no oily feel. Also, I am sure you have looked at
50:1 mixtures before. A proper mix using normal 50:1 additives turns
the gas a nice blue or green color. At least it does with the
additives available here in the USA. While neither of these
observations will prove that there was enough oil in the gas, either
would show that a significant amount was present. I would say that
normally when a 2-stroke engine is ruined due to lack of oiling it is
because that someone failed to add any oil to the gas. Usually a
person that knows they must add oil will add the proper mix. The
person who doesn't know adds none and goes on their merry way running
the engine to destruction.

Let me know if this works for you, Redhoss

I do not fancy the 'finger' method, but I put some fuel from the
strimmer tank in a jam jar and compared it with 'straight' petrol. It
was a different colour as you say. The chap using the strimmer when it
broke down is in the clear, thanks Perry-ga.

Hey, that is great!  Real " 'hoss sense", and I thought researchers
were just web wizzes (not really, all of you seem to have an
unbelievable fund of knowledge).
Myoarin