I recently had to replace the coolant in my Mk1 1.6 1991 Eunos (Blown rad hose!), and used Comma Xstream Green coolant as reccomended on their website for MX5s. However looking at the bottle this contains silicates and apparently they shouldn’t be used in a Japanese engine?
I’ve seen conflicting information as to whether this is an issue, some say this is just due to Japanese water being softer and they find Phosphates better suited and Silicates work better in Europe, so there is no issue. Others say that it’s a complete no-no. I’m not sure why this would be the case if the engines are otherwise identical, especially as I’m mixing it with distilled water anyway.
Having discovered the small crack in the after replacing the hose I need to drain the system again, so do I stick with the Comma, or should I be using something else, if so what’s best?
Help me MX5OC, you’re my only hope! 
I am under the impression that the MX5 (and most Jap engines) need silicate free antifreeze.
I put my car details into the Comma website and it recommended the XStream G30 Silicate free, OAT concentrate :
http://www.commaoil.com/productsguide/view/6/351
We don’t need anti freeze where I live, so we use a corrosion inhibitor. For the UK I seem to remember that Roadster Robbie OC tech guru recommends some stuff sold by Mazda, a pre mix, can’t recall the name.
PS I found this in the tech files
I dithered over this last week when buying antifreeze in Halfords. One was for pre 1998 engines (containing silicates), and the other was for post 1998 engine (without silicates). I chose the silicate free in the end.
Maybe the MkIs can use silicate based coolant then? - as both Halfords and Comma would seem to suggest…
Seems odd as I thought the engines were basically the same across MkI-2.5.
OK. I’ve been reading up on silicates in antifreeze, and there are two main points to consider:
- In a cooling system, silicates offer metal parts ( especially aluminum ) a high level of fast acting protection against corrosion and pitting.
2. Over time ( after two years) silicate drop out occurs and the inhibitors drop out of solution. Silicates are blamed for deposit build up in radiators and heaters, causing engine overheating, poor heater performance and wear in the waterpump and seals.
Although I just bought silicate free antifreeze, I don’t think I’d be too worried if I had the alternative - just make sure it’s changed every two years.
Iddy