<snip>instead, I'm using a premium transformer oil called Shell Diala, it is not great but does the job and is cheap. I'm using around 40L for this setup.
Please feel free to ask any more questions!
Good choice of fluid, we've used it for over 50 years as a coolant for industrial lasers. The main thing to be aware of is that Diala WILL very quickly cause all rubber and pvc parts to become very hard and brittle - esp the jackets of the cords & cables.
edit: Oh, regarding pumping Diala and similar oils...
As mentioned earlier the fluids attack most normally flexible materials. If your pump has shaft seals they WILL harden and along with that Diala has near-zero lubrication properties so the seals will wear faster. Put those together and the pump will start to leak in 2-3 years. You need to use a magnetic-coupled pump that has no shaft seals: The pump housing is sealed and spinning magnets on the motor shaft couple to ones inside the pump housing to drive the impeller.
Plus Diala is engineered to penetrate into materials and move through very very thin gaps. That means you need make sure all plumbing connections are well sealed using a paste-type of plumbing sealant or they will start to drip... Using Teflon tape just does not reliably work.
