Thread: Green coolant in my Defender TD5 confusion

Colour isn’t a real indicator of the type of coolant, a TD5 engine should have an OAT coolant which last I checked was available in red and green.

My Tdi had Nulon green which is not OAT. I assume (but can't be certain) that the green coolant in my TD5 is non-OAT green Nulon. The question still remains, if it has been there for a very very long time then what?

OAT and non-OAT both have corrosion inhibitors. TDi and TD5 are mixed metal. I have found nothing to say that a non-OAT does not protect as well as a OAT. BUT, there is info that the non-OAT is EU directive compliant pointing to toxicity or similar environmental reasons for cars in the EU switching to OAT coolants. My question was about potential damage and, if so, if it is wise to change and why.

Different silicate and nitrate contents in the fluids.

Very briefly (and loosely). One works by applying a coating to the surfaces which better protects from electrolytic reactions and is better suited to Aluminium rather than copper.

There are also benefits from cavitation perspective with regards to water pumps etc

Yes, but does it warrant a flush and change? And, since this green stuff has been in there for a long time am I inviting trouble by changing?

Not really. I know several running conventional coolant.

Up to you really

Ok that’s the end for me. To now 8 people have told me not to worry and just keep it as it is. My conclusion is this: it’s about EU regulations and both types provide protection. If a green coolant TDi can live a long and happy life then it’s good enough for a TD5.
Thanks folks!

Originally Posted by Parker

Ok that’s the end for me. To now 8 people have told me not to worry and just keep it as it is. My conclusion is this: it’s about EU regulations and both types provide protection. If a green coolant TDi can live a long and happy life then it’s good enough for a TD5.
Thanks folks!

remember coolant is cheap overall.

replace it once a year if it’s not technically correct and you shouldn’t have an issue.

thats what I was doing with my D2.


cheers 🍻 Chris

Originally Posted by Parker

My Tdi had Nulon green which is not OAT. I assume (but can't be certain) that the green coolant in my TD5 is non-OAT green Nulon. The question still remains, if it has been there for a very very long time then what?

OAT and non-OAT both have corrosion inhibitors. TDi and TD5 are mixed metal. I have found nothing to say that a non-OAT does not protect as well as a OAT. BUT, there is info that the non-OAT is EU directive compliant pointing to toxicity or similar environmental reasons for cars in the EU switching to OAT coolants. My question was about potential damage and, if so, if it is wise to change and why.

The main toxicity comes from the ethylene glycol which is in any anti-freeze, OAT, IAT, CAT, HOAT or otherwise.

OAT, CAT, IAT, HOAT all refer to the corrosion inhibitor type. Organic Additive Technology, Conventional Additive Technology, Inorganic Additive Technology, Hybrid Additive Technology plus I'm sure there are others.
As mentioned, colour mean nothing, it's just the dye they use. Would have been nice if there was a standard and the colours actually told you what type of corrosion inhibitor was used.

The main advantage of OAT corrosion inhibitors is their life, I think manufacturers changed to OAT to get longer life between changes.
The original anti-freeze used silicates and had a relatively short protection life (2-3 years).
Early OAT coolants were problematic with older vehicles (due to the materials used in the cooling system), now solved and the newer type is often referred to as OAT type 2.

I'm not sure how the different corrosion inhibitors react with each other so the best advice is to flush well before changing.
You need to mix at the correct ratio to get the best corrosion protection and the corrosion protection reduces with time hence the need to change at the manufacturers recommended intervals.

It's been pointed out to me that 'you don't need anti-freeze in Australia', correct but the ethylene glycol also raises the boiling point (as does the pressure in the system). I actually use a corrosion inhibitor in several vehicles that are not in regular use.

Back to the original question, as long as you flush out the old coolant you could use any type as long as it's mixed in the correct ratio and changed at the recommended interval.
As to the EU regs forcing the change to OAT? Never heard that one before.


Colin