[vishy76]

Coolants and their types

This thread has been jointly compiled with bhpian Vigsom. Thanks to him for the expert inputs!

Coolant. A very simple yet crucial component in the era of modern (comparatively) high compression ratio engines. It’s a fluid that is second to only engine oil in an internal combustion engine, yet is ignored most of the times.

In the olden days, the word “coolant” simply implied “water”. Water with its high specific heat capacity (which basically means it needs a lot of heat in comparison to other liquids in order to raise its temperature by a specific amount) was perfect for car radiators in theory. The high specific heat capacity ensured it could transfer a large amount of heat easily from the engine block to the radiator. There were two downsides or shortcoming however:

- Firstly, water has a comparatively high freezing point of 0 degrees Celsius. This means it would freeze and block cooling system pipes and radiators in the winters.

- Secondly, water would react with the iron present in the engine block and form rust. This rust would eventually choke the radiator over time too. This would also impact the heat transfer (by forming oxides) and cause issues in both the radiator and engine block.

In order to overcome the former, alcohol was added to water and used as a coolant. Alcohol formed a mixture with water which would lead to a “depression” in freezing point, thereby preventing freezing. Unfortunately, the boiling point of alcohol was much lower than water, which would mean the resulting mixture would also boil very early (around 80 degrees Celsius), needing frequent top-ups.



Inorganic Acid Technology (Ethylene Glycol)

The writing was on the wall. There was a need for a liquid that would offer the depression in freezing point normal alcohol such as ethanol would, yet not boil over early like the former did when it formed a mixture with water. The answer to this predicament was (and still in many cases) is ethylene glycol. Ethylene glycol-based coolant is called “Inorganic Acid Technology based coolant” because it contains silicates and phosphates in order to comply with the metal parts in a cooling system.



An Ethylene Glycol and water mixture (in a 60:40 ratio) would freeze at - 45 degrees Celsius (thus beating even alcohol in this regard) and boil at well over 100 degrees Celsius. This means the fundamental issues of early freezing (due to inherent properties of water) and early boiling (due to properties of alcohol) stood solved. Ethylene Glycol however brought about two other minor headaches:

- Firstly, its chemical composition meant it would disintegrate and lose its properties, thus requiring a change every 2-3 years

- The more lethal property of Ethylene Glycol was that its disintegration would exponentially increase its electrical conductivity. An electrically conductive liquid when in contact with the iron present in the engine block would be the perfect recipe for rust formation

Thus, started the hunt for a liquid which would further last a lot longer. This is not to say that Ethylene Glycol isn’t used in today’s cooling systems. The green coolant used by many manufacturers even today is ethylene glycol. It does a better job of controlling rust formation in older engines with iron blocks and has additives in the form of silicates and phosphates.



Organic Acid Technology (OAT)

Organic Acid technology was the answer to the previous bottleneck. Organic Acid Technology ensured that the coolant itself was composed of non-degradable chemicals (thus addressing the fundamental issue that IAT brought to the table), while also being silicate, borate and nitrite free, further preventing any chances of increase in electric conductivity with ageing and the rusting that followed. The biggest ace up its sleeve however was the fact that OAT offered superior protection to aluminum under high temperatures, a property that would exhort many manufacturers to shift from IAT to OAT.



The G12 and G12+ coolants (pink coolant) used by Volkswagen are OAT coolants. Both are phosphate, amine and phosphorous free. The only issue with OAT, was that it was a step back in corrosion protection as compared to (perfectly functional) IAT.



Hybrid Organic Acid Technology (HOAT)

Simply mixing the two coolants (IAT and OAT) would not be the solution (as expected) and lead to an even more corrosive mixture. However, the final breakthrough in coolant technology was brought about by HOAT or Hybrid Organic Acid Technology. Theoretically, it is impossible to mix IAT and OAT (as mentioned before), but HOAT allows both to work in tandem, while offering excellent rust protection, very high B.P and low F.P and lasts beyond 5 years (up to 1.8L km in some cases).



HOAT is used by Volkswagen (G12++ and G13) and is also reverse compatible with OAT (G12 and G12++ that I mentioned before). Honda also uses HOAT (blue coolant).


Debunking common myths associated with coolant colours and grades

With all the types of coolants listed down, I will end this short post by shedding light on some common myths and trying to clear them.

- It is NOT advisable to mix two different coloured coolants unless you are sure that they are both OAT, IAT or HOAT. As I mentioned before, mixing different coolant types with each other might increase chances of corrosion and cause disaster. It is always thus advisable to put distilled water instead of mixing coolants having different colours

- Putting a coolant colour that hasn’t been recommended in your car can have many ill-effects in the long term.

Taking an example of a VW TDI here. VW recommends G12 OAT coolant be poured in. I pour in green coolant (IAT). The TDI sports an aluminium block. The IAT won’t offer the same protection to the aluminium block that the OAT is supposed to, which will lead to corrosion not only inside the coolant galleries in the engine block but also cause ancillaries such as the engine oil cooler to suffer. It is thus instrumental to pour the right coolant or pour distilled water as a stop-gap measure.


- If your car uses green coolant or any IAT based coolant, it is instrumental that you change coolant on or before time. As mentioned before, IAT becomes a bane as it ages and degrades, eventually assuming a corrosive state and encouraging rust in the coolant galleries and supporting ancillaries.



- For a layman, the easiest way to distinguish a conventional coolant from a long-life coolant is that conventional coolant concentrate would look green and opaque, while long life coolant would be clear and most importantly, oily to touch

- Toyota’s coolant has an initial drain interval of 1.6L km and every 80K km thereafter

- BMW uses an HOAT coolant that is both nitrite and phosphate free to prevent aluminium corrosion in its engines. It is blue in colour:


- The last point but what is probably the most important one, the colour of the coolant (red, blue, orange, pink) does NOT define its chemical composition (HOAT, IAT or OAT). The same coolant colour across manufacturers may have variations in chemical composition. Always read what is written on the coolant bottle, consult manufacturer recommendations and then decide what is best for your engine (credits to bhpians Vigsom and Porsche_guy for both these images):





Here’s a short video by Scotty Kilmer that sums this entire post up:

https://www.youtube.com/watch?v=qYX4kRaOvTM

[Aditya]

Thread moved out from the Assembly Line. Thanks for sharing!

[VKumar]

Originally Posted by vishy76

This thread has been jointly compiled with bhpian Vigsom. Thanks to him for the expert inputs!

Awesome post Vishy, thanks to you and Vigsom for bringing this one up. Short, crisp, and precise. Just what the doctor ordered.

Even I belong to the same older category which always knew only this about coolant:

• Hara (Green) coolant
• Gulabi (Pink) coolant
• Neela (Blue) coolant

Going to a store to get the coolant (Just once in life though), I just carried this perception that it has to be of same color. And if it's different color, then I have to change it asap to the same older color.

Now, I will read further and see if I can upgrade to a better one in my cars, just for the sake of trying it out - but only after properly studying it all.

[vigsom]

Thanks for the good info on coolants, @Vishy76. The first time I seriously started looking at coolant grades was in 2010 when I got my first Corolla, and was astonished to see the replacement schedule of the factory coolant viz. first change after 1,60,000km against the 20,000km for the conventional green stuff. A few recommendations:

1. always ensure that the coolant system is completely flushed and even residual coolant is removed. Even a simple de-mineralized (DM) water flush will suffice. Some cars have the thermostat on the water pump suction line and that arrangement leaves about 25% of the system volume in the system even if one were to drain out the coolant via the lowest point (typically the radiator drain OR the lower hose).

No service workshop has the patience to do the flush until clear water is seen, but this step is non-negotiable for those who want to keep cars for long.

2. The difference in pricing between

a. ready to use coolant and coolant concentrate, or
b. conventional coolant and long life "oily" coolant

is of the order of just 50-70 bucks a litre. I would always go with a superior long life coolant, preferably in a 50:50 mix. Just see what I'm holding onto even now. Approx 1L left after using (or losing some of it) in an Etios in 2016, and in the Pajero Sport in 2019.


3. It is extremely important to use DM water as the diluent. Most of the "distilled" water available in the market is suspect. Exide DM water is available at some places. If that isn't available, one should trust DM water from standard manufacturers eg. Diet Aqua in Chennai, but nothing like filling some DM water direct from a water treatment plant.

[aaggoswami]

Excellent thread !
My employer offers coolant of various varieties. From what I know, HOAT are of three types :

1. HOAT with Silicate and Organic Acid
2. HOAT that is Phosphate free and
3. HOAT with Phosphates and Organic Acid

Moreover, there is something called Si-OAT which is Silicates and Organic Acid, also sometimes referred as Silicated HOAT.
Not sure how HOAT is different from Si-OAT. Can anybody please elaborate on this ?

[Sran]

I have learned from my 2 decades + of driving, if your car needs water it has to be satiated only with distilled water unless it is a 60 year old Willy's jeep or ambassador which can also run on sweat. Concentrate coolant is superior to the pre mix one and for the love of your vehicle open the bonnet at least once every week.

[Jeroen]

Originally Posted by Sran

. Concentrate coolant is superior to the pre mix one

Why would that be? Mixing yourself can lead to incorrect ratio/dillution and you’re DM is unlikely to be as good as what is factory used for the pre-mix.

I must confess I havent used concentrate coolant for decades. Not sure if it is available across the different types of coolants these days.

Jeroen

[Kosfactor]

I prefer to go to the nearest OEM spare parts shop or dealer to get a bottle of premixed coolant if needed.

Wrong coolant or wrong dilution is one way to damage the water pump / seals around it prematurely.

[hserus]

If they say 1:3 dilution it is simple enough to do this.

There are also multi technology coolants (oat and hoat specifically mentioned in some cases like Valvoline while others like Amsoil say “poly organic acid” while still others just declare “suitable for all vehicles”

Take these on advisement - but if you change your coolant every 30-40k km and three years there should be little negative impact if you’re using any of these generics. In tropical conditions trusting to super long life for any coolant is a bit of a risk.

[abhi9044]

Thanks, Vishy76 and Vigsom for this useful post. What I have learnt from my experience is, no matter what fluid it is, it's best to replace it at or before the manufacturer specified intervals.

Else this is what happens:-





This is my friend's 2008 Suzuki Alto which has done about 75k on the odometer. I'm pretty sure the coolant wasn't replaced for 6-7 years which led to this condition. In fact, it was so bad, that the hoses had rust flakes sticking to them.

On the other hand, this is how a coolant looks like after 2 years in my 2015 WagonR.



As you can see, although the car was only used for 5000 km during these 2 years, there is still some amount of oily residue and some little flakes in this too. This indicates, that no matter what, or how less your car is driven, coolant, like engine oil, also breaks down with time.

[motorotor]

This is seriously useful info! Thanks for sharing.

[coolmel]

Many thanks for this thread. I have been using the Amsoil Dominator Coolant Boost in my 7 year old Etios Liva for the past few years. Can someone also shed some light on coolant additives like this please?

[ike]

So the ultra long life coolants (the one I have come across is yellow from Amsoil) is OAT or HOAT? It says it is suitable for all vehicles however my car usually takes in IAT (green) coolant. Is it safe to use OAT/HOAT in an engine where manufacturer recommends IAT coolant? I have so far stuck to the recommended grade (color rather) and change it as per schedule. One problem I have had with MASS is that their coolant comes out of random bottles and cans. I have seen them using coolant from a sealed bottle only once. So I usually get that replaced at a Shell fuel station after every service.

[SN88]

Hi All

Following on my previous post that Honda asked me to change the coolant for my Honda city 2008 MT to blue coolant from green, I searched a couple of shops and all of them said Honda city 2008 used green not blue!!

I am confused what is the correct one. Should I change or let it be green? The coolant is relatively new as I had changed approx 10 kms prior.

[vigsom]

Originally Posted by coolmel

I have been using the Amsoil Dominator Coolant Boost in my 7 year old Etios Liva for the past few years.

@coolmel, the coolant boost was just not necessary in an Etios, which already runs on Toyota Super Long Life coolant. I have no technical info on the product so can't comment.

Originally Posted by ike

So the ultra long life coolants (the one I have come across is yellow from Amsoil) is OAT or HOAT? It says it is suitable for all vehicles

@ike, If you're anyways scrupulously replacing coolant as per schedule, you have nothing to worry even with IAT. However, should you wish to switch, please have all the IAT coolant removed, system flushed with pure DM water, and then switchover to HOAT or OAT. The AMSOil Antifreeze and Coolant Long Life Formulation( the can would be black in colour with a yellow cap) is an OAT coolant 50:50 premix as per info that I have. Its specs meet the Toyota super long life coolant formulation.

Originally Posted by SN88

searched a couple of shops and all of them said Honda city 2008 used green not blue!! Should I change or let it be green?

@SN88, Where did you get the green stuff added in your 2008 Honda City? At an FNG?

I've known Honda to have a blue long life coolant only. I'd recommend a replacement right away, only because you don't want to see the wrong coolant in. IAT to OAT is an upgrade, but the reverse is a downgrade.