Coolant Types

[Forrest]

Apologies, this is a coolant version of my recent battery thread.

I have read quite a lot recently about how modern coolant formulations are unsuitable for older cars. As I understand it there are three types of coolant available now.

IAT - Inorganic Additive Technology. This is the traditional (green/blue) ethylene glycol and silicate coolant which has to be changed every year or two because it becomes corrosive with age. Safe for use in older engines.

OAT - Organic Acid Technology. This is the modern (red/orange), phosphate-free, long-life coolant which can corrode components in the cooling systems of older cars from day one.

HOAT - Hybrid OAT. This seems to contain a mixture of organic corrosion inhibitors, ethylene glycol and in some cases silicates. Seemingly safe to use in older engines and lasts five years or more.

Now, as far as I can make out, Volvo blue/green coolant and Comma G48 which are both widely advocated for older Volvos and VWs respectively are both HOAT rather than IAT.

It seems a bit odd to me that the OAT can cause problems on its own but not when mixed in a hybrid solution. It seems especially odd that the classic community mantra seems to be to use IAT coolant when what a lot of people are actually buying appears to be HOAT. In some cases HOAT formulations appear to claim backwards compatibility with earlier (e.g. G11) standards.

Can someone please explain?

[360beast]

This is what use in my Volvos

https://www.opiecommercialoils.co.uk...ze-concentrate

[Laird Scooby]

The HOAT is a relatively new thing and i haven't done any digging to find anything out about it. I did however look quite deeply into OAT coolants and the short version is they are bad for anything older than 2000 and especially with cast iron blocks.

Additionally, if they are used in an engine that has previously had EG without a really thorough flushing, the acid in the OAT will cause the silicates in the EG to precipitate out and form a silicone gel that blcoks the coolant channels, resulting in HGF, blcoked heater matrices, radiators and so on.

Cars before 2000 generally didn't have gaskets or seals that would withstand the acid in the OAT coolant either so previously good components like water pumps, thermostat gaskets etc will suddenly spring leaks.

Personally i'd avoid the HOAT stuff until more is known about it, when the OAT stuff first appeared 20 ish years back, anyone and everyone and his dog were using it because it was hailed as the new big thing.
For aluminium engines built to use it, yes but even for aluminium engines that weren't built to use it (i.e. with gaskets that won't withstand the acid) it's definitely not something i'd even think about using.

For the record, both my engines are all aluminium and the Japanese spent nearly a decade developing the stuff to reduce corrosion in all aluminium engines caused by EG coolant. However, EG coolant causes less corrosion in all-aluminium engines than OAT does in cast iron/mixed-metal engines such as the red block.

As such, the safer bet is to use EG antifreeze, change it every two years (or soon after) and wait to see what happens with HOAT coolant - remember it's being tested on more modern engines than in the 7/9xx cars!

[griston64]

I've used Comma Super Coldmaster which is standard EG. Volvo's own and Comma G48 are also fine as they are standard EG with added corrosion inhibitors. Most people swear by the standard Volvo blue/green stuff for Redblocks

[Ian21401]

I’ve used Volvo’s own in my 1992 940 since I acquired it in 2005.

[Forrest]

I have only ever used Volvo coolant but it changed a few years back from a thick, gloopy dark blue/green concentrate (p/n 9437651, now discontinued) to a more watery paler green (p/n 31439721). I think they may both be HOAT, but I’m not sure. Hopefully someone more knowledgeable will confirm.

My understanding is that pretty much all antifreeze in the UK contains ethylene glycol as the freeze protection agent. The IAT, OAT or HOAT refers to the corrosion inhibitors.

I think Glysantin (BASF) produces coolant for Volvo. I think the older stuff was G48 and the newer is G64.

For the current Volvo approval of G64 see:

https://www.glysantin.de/en/zulassungslisten

Volvo coolant is advertised as the only coolant approved for use in Volvo car engines, so I’m guessing that must be it.

More details on the two products here:

https://www.glysantin.de/sites/defau...-08/g64_en.pdf

https://www.glysantin.de/sites/defau...-02/g48_en.pdf

Interestingly, G48 is still approved for Volvo trucks. It is also approved for older Volkswagens which is why I bought some Comma Xstream G48 recently. It struck me that it looked very much like the old Volvo coolant.

The G48 is advertised as “Silicate type hybrid technology” and its fact sheet says it includes “a blend of organic and inorganic inhibitors” whereas the G64 employs “robust organic acid technology fortified with silicate and phosphate”.

I’m not sure whether that makes the G48 HOAT. However the G64 appears to be what is called PSI-OAT.

So maybe Volvo has quietly moved us all to HOAT without really advertising the fact. If so, it puts some of those fierce red v green debates into perspective!

And it still leaves me a bit puzzled as to which is the best one to use.

[360beast]

Originally Posted by Forrest

I have only ever used Volvo coolant but it changed a few years back from a thick, gloopy dark blue/green concentrate (p/n 9437651, now discontinued) to a more watery paler green (p/n 31439721). I think they may both be HOAT, but I’m not sure. Hopefully someone more knowledgeable will confirm.

My understanding is that pretty much all antifreeze in the UK contains ethylene glycol as the freeze protection agent. The IAT, OAT or HOAT refers to the corrosion inhibitors.

I think Glysantin (BASF) produces coolant for Volvo. I think the older stuff was G48 and the newer is G64.

For the current Volvo approval of G64 see:

https://www.glysantin.de/en/zulassungslisten

Volvo coolant is advertised as the only coolant approved for use in Volvo car engines, so I’m guessing that must be it.

More details on the two products here:

https://www.glysantin.de/sites/defau...-08/g64_en.pdf

https://www.glysantin.de/sites/defau...-02/g48_en.pdf

Interestingly, G48 is still approved for Volvo trucks. It is also approved for older Volkswagens which is why I bought some Comma Xstream G48 recently. It struck me that it looked very much like the old Volvo coolant.

The G48 is advertised as “Silicate type hybrid technology” and its fact sheet says it includes “a blend of organic and inorganic inhibitors” whereas the G64 employs “robust organic acid technology fortified with silicate and phosphate”.

I’m not sure whether that makes the G48 HOAT. However the G64 appears to be what is called PSI-OAT.

So maybe Volvo has quietly moved us all to HOAT without really advertising the fact. If so, it puts some of those fierce red v green debates into perspective!

And it still leaves me a bit puzzled as to which is the best one to use.

It certainly sounds like the Volvo coolant isn't selling the right stuff to use. Take a look at the Castrol radicool in the link above, you can probably find it cheaper elsewhere. It was the only coolant we used on the older Rolls and Bentleys as they need ethylene glycol antifreeze too.

[Forrest]

I’ve found this, which gives a nice summary of the Glysantin coolant technology. Screenshot of relevant slide attached.

https://cdn.website-editor.net/61024...520Sector.pptx

If indeed pre-2018 Volvo coolant was G48 and newer is G64 then Volvo has actually been using organic inhibitors for a long time and enthusiasts have been believing that they are fine for older cars.

I guess this really boils down (pardon the pun) to whether the actual mix of inhibitors is sufficient to stop the ones best suited to the iron block destroying the aluminium head and vice versa. What concerns me more is that I think the original heater matrices are soldered brass and isn’t that what OAT has the greatest appetite for?

[Laird Scooby]

Originally Posted by Forrest

I’ve found this, which gives a nice summary of the Glysantin coolant technology. Screenshot of relevant slide attached.

https://cdn.website-editor.net/61024...520Sector.pptx

If indeed pre-2018 Volvo coolant was G48 and newer is G64 then Volvo has actually been using organic inhibitors for a long time and enthusiasts have been believing that they are fine for older cars.

I guess this really boils down (pardon the pun) to whether the actual mix of inhibitors is sufficient to stop the ones best suited to the iron block destroying the aluminium head and vice versa. What concerns me more is that I think the original heater matrices are soldered brass and isn’t that what OAT has the greatest appetite for?

I can't confirm any of that but wouldn't surprise me as manufacturers are always developing new fluids to replace old ones. Sadly althugh they often insist on them being backwards compatible, they're not. Honda faced a class action lawsuit in the USA over their ATF when they tried saying the new one was backwards compatible with the old one and suddenly owners were frying torque converters left, right and centre. As such i exercise extreme caution when a manufacturer (who is really only interested in selling new cars and using the new fluids) says something is backwards compatible.
There are other examples but i don't have them off the top of my head.

What you say about OAT having a voracious appetite for the soldered joints in brass radiators is correct though, most acids will attack solder rendering the original matrices a pile of brass scrap and gloopy one-time solder.

[wrinkles]

One word Blucol ideal for 7/900s used for years.