The Best Triumph HD4X Hybrid OAT Coolant Alternatives — Analysed in Detail

Whenever you’re servicing a Triumph motorcycle, you might come across the section that says you have to replace the coolant every 4 years (regardless of mileage done) with “HD4X”.

But HD4X Hybrid OAT Coolant isn’t always available, depending on where you are in the world and how you buy (from dealers, stores, or online). So it’s good to know a Triumph HD4X Hybrid OAT alternative.

If you ask people on forums, you’ll get a wide range of recommendations, including

• “Just use HD4X from a Triumph dealer” (fine, but may not be convenient)
• “Any coolant is good” (there’s some truth to this, but it helps to be close to spec),
• “Engine Ice/Evan’s” (Evans is good for storage, Engine Ice is expensive), or even
• “Just use water” (don’t do this unless you have a race bike, distilled water, and have some corrosion inhibitors handy)

Trying to sift through the noise, we’ve checked the data sheets for HD4X coolant and tried to find the best alternative.

Summary: The three best Triumph HD4X Hybrid OAT Alternatives

You can read the below in detail at your leisure. Don’t blindly trust us, check the facts!

But the three best Triumph HD4x alternatives are below.

In summary, like Triumph HD4X, both of these are hybrid OAT coolants that contain silicates, and manufacturers suggest you shouldn’t swap from a silicate-enhanced to a silicate-free coolant.

What is Triumph HD4X coolant? The Data Sheet

Here’s what Triumph says about HD4X coolant in the manuals.

• “HD4X Hybrid OAT coolant contains corrosion inhibitors and antifreeze suitable for aluminium engines and radiators.” (Triumph Tiger 900 manual)
• It’s a “year-round, Hybrid Organic Acid Technology (known as Hybrid OAT or HOAT) coolant” with a “50% solution of ethylene glycol-based antifreeze” (Triumph Speed Triple 2011 manual)

For more technical information, the data sheet for HD4X from Finol says that Triumph HD4X

• Based on monoethylene glycol
• Free of amines, nitrites or phosphates

This info sheet mentions it’s free of nitrites, which contradicts with the info below. This info sheet for Triumph HD4X Hybrid Oat says that it is

• “An ethylene glycol-based engine coolant formulated for optimum performance in heavy-duty diesel engine applications but equally suitable for light duty use.
• It uses “established [corrosion] inhibitor technology and is phosphate and amine-free. The inhibitors in HD4X include organic acids in combination with borate, silicate, and nitrite which are well known for their ability to provide excellent protection in heavy-duty applications particularly where there is potential for cavitation erosion-corrosion to occur.
• “HD4X uses sophisticated stabilisation technology to eliminate the potential for formation of silicate gel (often observed with inferior products). Other additives ensure good compatibility with hard water.”

Note on nitrites in HD4X — a helpful reader wrote to Finol Oils to clarify the issue above (their name obscured for privacy reasons).

According to Ken Cummins of their Technical Department, “The inhibitors in HD4x include organic additives in combination with borate, silicate, and nitrite.”

So based on this we know that Triumph HD4X

• Is based on ethylene glycol (like most coolants), in a 50-50 mix
• Is phosphate and amine-free
• has silicates, borates, and nitrite (inorganic corrosion inhibitors)

What is an OAT and HOAT coolant?

The purpose of a coolant is to cool your engine. The best easily available coolant is water. It conducts heat well.

Unfortunately, water (even if it’s distilled) has a few drawbacks. Primarily, it will eventually cause your engine to rust. Secondarily, if you live somewhere cold, it can freeze and crack your engine. Finally, if there’s a leak in your system and it boils, you’ll get worse heat conduction and of course lose all your coolant to steam.

So motorcycle (and car, and truck) coolants have two things in them to make them better than water for general use:

1. Antifreeze/antiboil (the former is more important), and
2. Corrosion inhibitors.

Ingredient 1: Antifreeze (Ethylene Glycol)

By far, the most common form of antifreeze, and the one that all manufacturers recommend, is ethylene glycol, also technically known as monoethylene glycol.

Alone, ethylene glycol isn’t nearly as good a coolant as water. But when mixed with water, it performs well as a coolant.

The main problem with ethylene glycol is that it’s toxic to animals (and humans), so you can’t dump it as easily.

The second most popular type of coolant that’s a common aftermarket coolant is propylene glycol. It doesn’t carry heat as well, but it’s non-toxic. That’s what Evan’s Waterless Coolant is made of.

Nonetheless, every motorcycle manufacturer whose manual we’ve analysed has recommended an ethylene glycol-based coolant. This includes Triumph HD4X.

Ingredient 2: Corrosion inhibitors

So that’s the coolant part — what about corrosion inhibitors?

There are two kinds of corrosion inhibitors:

• Inorganic acid salts: Silicates, phosphates, borates, nitrites, and amines. These are all various compounds that stop rust from forming on the inside of your cooling system. These are good at preventing corrosion, but don’t last long (2-3 years).
• Organic acid salts: proprietary compounds that are unique to each manufacturer, but which are NOT the above. These generally aren’t as effective as preventing corrosion, but last longer (5-10 years).

There are also Hybrid OAT (HOAT) coolants. They’re “mostly organic, but with some inorganic acid coolants”. These are sometimes referred to as Si-OAT or P-OAT, referring to the fact that they’re OAT coolants, other than the silicates or phosphates they have.

Triumph HD4X is a HOAT coolant, and specifically a Si-Oat coolant.

The reason HOAT coolants exist is because of trade-offs. The OAT coolants last a long time, but adding some silicates or phosphates adds a lot more anti-corrosion ability, at the trade-off of having to replace the coolant every now and then.

So in summary — Triumph HD4X is an OAT coolant with some inorganic acid salts in it — borates, silicates, and nitrites, but free of phosphates and amines — making it a HOAT coolant, or also a Si-OAT coolant.

What are some equivalents to Triumph HD4X coolant?

Scouring Amazon and the internet, and reading through spec sheets, there are three primary candidates that are alternatives for Triumph HD4X. The classic and best candidate is Zerex G-05, which is high-quality and easy to obtain.

There are also two other alternatives that will work, though they lack nitrites.

These below are Si-OAT / HOAT coolants that are based on ethylene glycol.

Coolant	Ethylene Glycol-based	Silicates	Nitrites	Borates	Phosphates	Amines
Triumph HD4X (baseline)	✓	✓	✓	✓	✕	✕
Zerex G-05 (best candidate)	✓	✓	✓	✓	✕	✕
Peak OET European Vehicles Blue (Alternative one)	✓	✓	✕	✓	✕	✕
Motorex Coolant M5.0 (Alternative 2)	✓	✓	✕	✓	✕	✕

The most important thing to bear in mind is that you can’t go from a Si-HOAT to an OAT or HOAT without silicon in it — or vice versa — without draining the coolant.

Zerex G-05

(Updated to add this in mid-2022, based on the new information above about nitrites. Before clarification from Finol that HD4X contains nitrites, I wasn’t sure that Zerex G-05 would be an appropriate candidate.)

One commonly recommended alternative for Triumph HD4X is Zerex G-05, which is also written G05. Like HD4X, Zerex G-05 is a Si-HOAT formulation.

Valvoline says that G-05 is a HOAT coolant that’s low in silicates (which it does contain) and is phosphate-free. Valvoline also says that Zerex G05 does “contain nitrites designed to protect engine cylinder liners from cavitation”.

However, digging into spec sheets confirms that Valvoline Zerex G-05 also contain borates. Per the SDS, it has disodium tetraborate (a.k.a. sodium borate).

Therefore, as an ethylene glycol-based coolant that contains silicates, nitrites, and borates, but which is free of phosphates and amines, Zerex G-05 is a great candidate to replace HD4X in Triumph motorcycles.

Peak OET European Vehicles Blue

PEAK Lubricants is an American lubricant brand owned by Old World Industries. They make a range of coolant formulations for different kinds of vehicles, and PEAK OET European Vehicles Blue is a great candidate to replace Triumph HD4X.

(“OET” stands for “original Equipment Technology”, and is just branding.)

Per the fact sheet available on the website, Peak OET European Vehicles Blue coolant:

“… is an ethylene glycol-based antifreeze/coolant specifically developed for use in any European vehicle requiring a Blue silicate-enhanced hybrid organic acid technology (Si-HOAT) formula. It contains high-quality organic and inorganic corrosion inhibitors and is free of nitrite, phosphate and amines chemicals.”

Reference (contact us if that link goes down).

Peak calls this a “Si-HOAT” formula, which is just another way of saying it’s mostly an OAT but it does contain silicates — just as we want for our Triumph motorcycles.

Even though Peak doesn’t mention it contains borate, they specifically mention other coolants are borate-free, (e.g. Peak Asian Blue).

Even though Peak is free of nitrites, the fact that it is a Si-HOAT formula makes it a good candidate.

Motorex Coolant M5.0

Another common alternative to HD4X is Motorex Coolant M5.0. It’s a lot more expensive, though.

Like Triumph HD4X, Motorex M5.0 is a hybrid OAT (HOAT) coolant that contains silicates. It’s a lot more expensive than the other alternative, but it’s also a more premium brand.

Motorex is a big brand of Swiss-made coolants and oils. They are the recommended manufacturer for all KTM bikes. KTM is a premium bike manufacturer, so even though those companies have a partnership, at least KTM working with them is a vote of confidence.

Per the website for Motorex Coolant M5.0, it is “… based on ethylene glycol” and is “nitrite-, phosphate- and amine-free.”

Motorex M5.0 contains silicates. In fact, this is the specific reason that Motorex says you shouldn’t change from Motorex M5.0 to Motorex M3.0 (which doesn’t contain silicates”, as “the protective silicate layer may solve which could have a negative impact on the flow in the cooling system”. (see archive copy of reference doc here).

While Motorex M5.0 doesn’t have nitrites, it does have most of the important ingredients of Triumph HD4X, and so makes a good candidate as an alternative.