As I'm sure the more enthusiastic PC builders out there are aware, there has been a lot of discussion on many PC forums about the cons of Feser 1. Not going to rehash the arguments but would like to share my personal experience.

Finally got bored enough to upgrade my system after 2.5 years (the old one is still in my sig). This is the longest time I’ve gone between upgrades ever. Didn’t really need to upgrade but couldn’t resist the urge.

So, Feser 1…

I had quite negative expectations of what my water cooling loops (separate ones for GPU and CPU) would look like after 2.5 years of running coloured Feser 1 without ever draining the loops (just periodic top ups of 10-20ml). Probably not even a good idea to go that long with distilled + silver coil. After all the negative press on the Net I was expecting a nightmare of cleaning last night.

Drained the GPU loop that was using red Feser 1 and found:

- Some staining on the tubes and reservoir as expected, now a pink tinge but zero clouding which was surprising.
- Poured the old Feser out in the sink and the colour was still a deep red and quite uniform looking.
- No gunk that I could see anywhere in the Feser or the loop. Could be all stuck in the rad’s for all I know but seems unlikely.
- There was some notable staining (veins) between the copper base and plexi on the GPU block though. Several small pockets at various places but no corrosion.

Staining can’t be avoided when you use dyes of any kind in the loop so overall not too bad.

Onto draining the CPU loop:

- As per the GPU loop there was some staining in all parts of the loop but there was also heavy clouding in all the tubes this time. - Not sure if it’s due to different components or the purple versus red Feser?
- The big test, what did the EK Supreme HF (copper + plexi) look like?
- Very surprisingly, quite clean given the 2.5 years of running. There was a small amount of gunk, like soggy pocket lint on the top of the fins.
- It probably covered less than 5% of the surface area of the fins and there were no other deposits.
- Was easily all cleaned off buy squirting distilled water onto the fins with a squirty bottle and my finger.
- Brushed a few bits between the fins away with an old toothbrush and more distilled.
- No solvents, tomato ketchup, or solvents required.
- Block looked pristine at the end with just the above.

Admittedly I was planning to replace the Feser 1 on both loops with distilled + kill coils but after what I saw last night I’ll save that for the next rebuild I think. I have plenty of purple and red Feser left and reusing everything except there’s a new EK GPU block (new card so…). It’s already stained and after 2.5 years without any notable gunk I can’t say Feser is performing badly for me.

Not saying it’s a better solution than distilled + water, that’s still my preferred approach for my next major loop rebuild but for now, can’t fault Feser to be honest. Thought I’d just share my personal experience with Feser given all the negative testimonials surrounding it. Not trying to peddle to promote it in any way, just that it may not be as bad as some make out so don’t drain your loop if you’re happy with how it’s running now. Suspect that the exact conditions and component combination has a bigger factor on gunk build up. There have been reports of some oxidation issues with distilled + kill coil or PTNuke, again only under certain conditions.