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Coolant G13 G12 G11


New member
Well I bought the G13 as the bottle says it is backward compatible. I took that as half truth. I drained the systems, flushed the systems and added G13. I run three B5's - A4TQavant, A4TQsed, RS4.
Ouch. Within a month the rear head coolant seal was leaking and when replaced, the seal had swollen to double its diameter and was jelly.
The water pump on the RS4 spilled the coolant on a run back from up north. Both A4 thermostats failed within a week of each other.

OK there is lots of stuff about HOAT and OAT and IAT. but that doesn't help. Coolant bottles and owner manuals don't always have HOAT/OAT/IAT on them. So lets do some research.

Some sites gave stories of needing the phosphates/silicates for water hardness and calcium content but if you use distilled water then there wouldnt be an issue??

In a previous job I shipped equipment OS, so a check on Material safety data sheets (MSDS) found the G13 and G12 and G11 products.

G13 has Ethylene glycol, Sodium 2-ethylhexanoate and references to silicates
from the jag forum is a note -the silicates swell the rubber seals so not to use unless newer than 2005.
also the Sodium 2-ethylhexanoate attacks copper/brass joints due to their use in soldering flux.

G12 is similar but no silicates - Ethylene glycol, Sodium 2-ethylhexanoate

G11 contains - Ethanediol, Disodium Tetraborate Pentahydrate, Borax Pentahydrate, Denatonium benzoate

So a check of the coolant system
- radiators were copper pre 1996,
- water pump seals are rubber before 2005,
- cylinder head gaskets copper till 2005 maybe
- thermostats still look copper/brass colour
- interior heater core is either copper or polyethylene/polypropylene not sure what chemical reaction occurs here but a guess would be Sodium 2-ethylhexanoate eats the polyethylene/polypropylene based on the number of interior heater core failures

So a check of what chemical is in your coolant is always advised and a comparison to what components are in your coolant system. Carboxylic and Sebacic acid are in the same group as Sodium 2-ethylhexanoate
So the G11 is looking good, Toyota and Subaru run a red coolant that looks very similar to the G11 if you what to retain the red colour.
Expensive lesson but I guess i'm learning, hope this gives others a heads up.
Thanks for posting this. Same situation as you with an all B5 garage so easy to find yourself without any vehicles on the road. Not a pretty thought.