Coolant types

Updated 24 October 2026 · Independent, sourced reference

Coolant types are named after their corrosion-inhibitor package. This hub explains each family (IAT, OAT, HOAT, P-HOAT, Si-OAT and NOAT), where it is used, and links to the coolants in our directory that list it. The glycol base, ethylene or propylene, is a separate choice [1].

Disclaimer: General information only, not professional advice. Always use the coolant specified in your vehicle owner's manual. Using the wrong coolant can damage an engine.

Coolant types at a glance

Type	In our directory
IAT	10 products
OAT	42 products
HOAT	15 products
P-HOAT / P-OAT	9 products
Si-OAT	10 products
NOAT	None tagged yet

Counts come from what each maker publishes. 51 of the 139 products in the directory do not state a chemistry, and those are not counted. One product lists P-Si-OAT, a hybrid using both phosphate and silicate.

IAT (inorganic additive technology)

IAT is the original "conventional" coolant chemistry. Its inhibitors are minerals such as silicate, phosphate, borate, nitrite and nitrate, which form a protective blanket over the metal [1]. That film forms fast but is consumed as it works, so IAT coolants have the shortest service intervals [2][1]. IAT is being phased out in developed markets but is still common where price matters most [5].

Typically used in: Older vehicles whose manuals call for conventional coolant, and some low-cost markets.

Products in our directory whose makers list this chemistry:

OAT (organic acid technology)

OAT coolants rely on organic carboxylic acids and azoles and generally contain no silicate or borate [3]. Instead of coating every surface, the inhibitors adsorb where corrosion begins, so they deplete slowly and give extended life [1][2]. Typical extended-life ratings are around five years or 150,000 miles in light-duty service [5].

Typically used in: Many modern cars and light trucks whose makers specify an extended-life organic coolant.

Products in our directory whose makers list this chemistry:

HOAT (hybrid organic acid technology)

Hybrid coolants combine organic acids with a smaller dose of mineral inhibitors to get both fast and long-lasting protection [1]. The mineral part varies by region, which is why "HOAT" on its own is not specific enough to choose by [1]. Heavy-duty HOAT may need supplemental coolant additives to reach its rated life [5].

Typically used in: Vehicles specifying a hybrid coolant. Check which mineral inhibitor your spec expects.

Products in our directory whose makers list this chemistry:

P-HOAT / P-OAT (phosphated hybrid)

Phosphated hybrids pair organic acids with phosphate and avoid silicate. This is the typical Japanese and Korean approach [1]. Chiron groups P-OAT and Si-OAT as "lobrid" coolants: mostly organic, with low mineral levels [1].

Typically used in: Many Asian-brand cars. Follow the exact maker spec, since phosphate and silicate hybrids are not interchangeable.

Products in our directory whose makers list this chemistry:

Si-OAT (silicated OAT)

Si-OAT adds a little silicate to an organic base, the typical European hybrid [1]. Silicate gives quick protection for aluminium, which is why Si-OAT is favoured for high-output aluminium engines [5]. The Volkswagen Group G12++, G13 and G12evo family are examples of this direction. Audi publishes a mixing chart showing which generations are compatible [6].

Typically used in: Many European cars. See G11, G12, G13 and G48 explained.

Products in our directory whose makers list this chemistry:

NOAT (nitrited OAT)

NOAT is an OAT coolant with added nitrite, sometimes with molybdate, used in heavy-duty diesel engines to protect wet cylinder liners against cavitation [4][3]. Dober notes that these heavy-duty versions still belong to the OAT family [3]. Our directory does not yet tag any product as NOAT, so we show no examples rather than guess.

Typically used in: Heavy-duty trucks and equipment. See heavy-duty diesel coolant.

Why type matters more than colour

Two coolants of the same colour can belong to different families, and the same family is sold in many colours. MAHLE warns that colour cannot reliably identify a coolant [7]. The bottle's technology and OEM specification tell you what you need to know. See coolant colours explained.

Can you mix coolant types?

Mixing families dilutes each inhibitor package below its design level, so you can lose the long life you paid for. Even within one maker's own range, Audi rates some combinations as fine, some as reducing protection and some as not allowed [6]. The coolant mixing checker and can you mix coolant? walk through the rules.

How to find the right type for your car

Read the coolant specification in your owner's manual. Use the coolant the maker recommends, or one meeting its spec [8].
Look the spec up in Find my car coolant or on your make's page under coolant by car make.
Compare candidates with the compare tool, or browse coolants by brand.

New to the topic? Start with what is coolant or the head-to-head OAT vs HOAT vs IAT.

Sources

Frequently asked questions

What are the main types of coolant?

IAT (conventional), OAT (organic acid), and hybrids such as HOAT, P-HOAT and Si-OAT. Heavy-duty diesels may use nitrited OAT (NOAT).

Which coolant type lasts longest?

Organic acid (OAT) and low-mineral hybrid coolants generally have the longest intervals. Conventional IAT has the shortest.

Is HOAT the same as Si-OAT?

Not exactly. HOAT is a broad hybrid family. Si-OAT is a hybrid that uses silicate, and P-HOAT uses phosphate instead.

How do I know my coolant type?

Check the specification in your owner's manual and on the bottle. Colour is not a reliable guide.