Kart Radiators: Right Temperatures, Sizes and the New-Line Range
Updated: 3 days ago
The radiator is not a passive accessory: it decides the temperature at which the engine works, and on a two-stroke kart engine this changes power, reliability and the life of internal components. Yet it remains one of the least understood components, often chosen by looking only at the kart brand and not at the season, the class or the engine.
At TKS RaceLab we distribute the New-Line Racing range, one of the reference brands in radiators for racing karts. This guide explains how liquid cooling works, the right temperatures for each class and how to choose the correct radiator size.
In short The radiator is chosen according to class and temperatures: for OK, KZ and other water-cooled engines the reference is 48-52 °C in summer and 50-55 °C in winter, while the Rotax works between 55 and 60 °C. Only water is used as coolant, and the fins must be kept clean.
How kart liquid cooling works
A two-stroke engine generates heat at every combustion: part becomes motion, part stays in the engine components and must be dissipated to avoid overheating and seizure. In the highest-performing karts this heat is removed by a liquid circuit: a centrifugal pump, driven by the axle (on Rotax engines it is driven by the engine itself), pushes water into the cylinder and head, where it absorbs heat; the hot water flows out into the radiator, a core of finned tubes that gives the heat to the air; from there the cooled water returns to the pump and the cycle starts again.
In karting only water is used as coolant: mixtures such as ethylene glycol, common in cars, are not allowed, because in the event of a leak they would make the track extremely slippery and dangerous for all drivers. During operation the water heats up, expands and goes slightly under pressure, up to about 0.9 bar: this raises the boiling point by a few degrees and avoids cavitation, the formation of vapour bubbles that would reduce the efficiency of the system and could damage internal parts.
Why the radiator core is made of finned tubes
The core of a kart radiator is not a simple tank: it is built from a series of thin tubes linked by very closely spaced metal fins. The reason is purely thermodynamic: the amount of heat a body can give off to the air depends on the available contact surface, not only on the amount of water flowing inside. The fins multiply that exchange surface in a compact space, allowing the radiator to give off much more heat than a smooth tube of the same external size. It is the same principle by which a larger core cools more: not because it contains more water, but because it exposes more finned surface to the airflow.
This is why bent fins or fins clogged with debris are a real problem: even a small blockage of airflow between the fins reduces the effective exchange surface, and therefore the cooling capacity of the radiator, even if the core is nominally the right one for the class. Regular cleaning of the core with compressed air, as well as internal cleaning against limescale, is part of the maintenance that keeps the water temperature in the correct window.
Why the right temperature matters more than the lowest possible temperature
A common mistake, especially among beginners, is to think that a colder engine is always better. It is not. An engine that is too cold does not deliver its power, struggles to carburate correctly and wears abnormally. An engine that is too hot, on the other hand, expands its components more than it should and risks seizure, the most expensive and sudden damage that can happen on track.
The right temperature is therefore a window, not a minimum to chase, and it should be kept there as much as possible, whatever the outside temperature.
Reference temperatures by class
OK Junior, OK, KZ and other liquid-cooled engines: in the liquid-cooled engines of these classes, the reference is water between 48 °C and 52 °C in summer. In winter it is advisable not to go below 50-55 °C, to stop the engine running too cold.
Rotax: the Rotax engine runs hotter: the reference is between 55 and 60 °C in all seasons. We cover this in detail in the dedicated guide below.
→ Read also (in Italian): The Rotax engine radiator: the right temperature and how to manage it
How to choose the right kart radiator size
The basic principle is simple: the larger the radiating core (or if the radiator has a double circuit), the more heat it can dissipate, and that is the right choice when outside temperatures are high. With ambient temperatures above 35 °C, even on direct drive engines it is worth moving to larger models, normally associated with gearbox classes: in the New-Line Racing range we are talking about models such as Double, Big and Corsa.
In spring and autumn, when the ambient temperature is more moderate, a radiator with a smaller core is generally enough and easier to manage. For winter there are specific, smaller models designed for direct drive engines: some come with a radiator blind fitted as standard, the most effective accessory for reducing the impact of the air on the core when temperatures drop sharply.
A radiator oversized for the season struggles to keep the engine up to temperature in the cold, while an undersized one cannot dissipate enough heat in the heat: in both cases you risk chasing the right temperature even with all the right accessories fitted.
Blind: managing the cold without changing radiator
When the temperature drops and the radiator cools too much, you do not always need to fit a different radiator: the blind is a panel that covers part of the core and reduces the effect of the air, bringing the water back into the correct temperature window. It is the most practical and most used tool in the cold months, together with the angle of the radiator itself: more upright and exposed to the air to cool more, more tilted to keep the temperature up.
→ Read also: Kart radiator blind and deflector: how and when to use them · The Rotax engine radiator (in Italian)
The New-Line range in the TKS RaceLab shop
In our shop you will find the complete range of New-Line Racing radiators, from models designed for the hottest conditions to compact winter versions, plus radiator blinds for every model, brackets, deflectors and maintenance accessories such as internal cleaning fluid, useful against the limescale deposits that over time reduce heat exchange.
Frequently asked questions
What is the right water temperature in a kart?
It depends on the engine: for OK, OK Junior, KZ and other liquid-cooled engines the reference is 48-52 °C in summer and 50-55 °C in winter. The Rotax runs hotter: stay between 55 and 60 °C in all seasons.
Does a colder engine always run better?
No. An engine that is too cold does not deliver its power and wears abnormally, just like one that is too hot. The right temperature is a window to stay in, not a minimum to chase.
Which radiator do you need in very hot weather?
With temperatures above 35 °C a larger radiating core is advisable, even on direct drive engines: in the New-Line range this means models such as Double, Big and Corsa, normally also used on gearbox classes.
Which coolant is used in a kart radiator?
Only water: mixtures such as ethylene glycol are not allowed, because in the event of a leak they would make the track slippery and dangerous.
How do you reduce cooling in very cold weather without changing radiator?
With a radiator blind, which covers part of the core and reduces the effect of the airflow, or by tilting the radiator further so it is less exposed to the airflow.
Not sure which radiator or blind you need for your class and the current season? Message us on WhatsApp and we will help you choose the right one.
👉 You will find the New-Line range in our shop: Corsa MAX radiator complete, Big MAX radiator complete, RS MAX radiator complete and radiator internal cleaning fluid.
Conclusion
The right radiator is not the biggest or the smallest in absolute terms, but the one sized for the class, the engine and the season you race in. Understanding the correct temperature window, choosing the right core and knowing when to use a radiator blind is one of the simplest and most useful skills to learn for the track, in terms of both performance and reliability.
Technical data: Rotax MAX Challenge 2026 technical regulations.
Questions about this topic?
Message us on WhatsApp: we answer personally, with the experience of people who live at the track. And if you want to drive a real racing kart, with Arrive & Drive you get into one of ours, ready on track. The right spare part? You will find it in the shop.
Arrive & Drive Pro by TKS RaceLab: 2026 karts with Rotax Senior MAX and DD2 engines, Alfano 7 telemetry and trackside technical support at Lonato, Franciacorta, Cremona and Ala. Message us on WhatsApp for information and availability.
TKS RaceLab | Performance Engineering Karting | tksracelab.com
Read also: Kart radiator blind and deflector: how and when to use them → · XPS range: gear oil, chain lube and kart maintenance → · Maranello chassis range: classes and how to choose →
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🛒 In our shop: New-Line Racing radiators → · EM Technology radiators →
Author: Sergio, TKS RaceLab | Published: 17 August 2026 | Updated: 8 October 2026
TKS RaceLab is the Italian online store dedicated to karting: spare parts, accessories and everything you need to get on track. With Arrive & Drive you arrive at South Garda Karting (Lonato), Franciacorta, Cremona or Ala and find your kart ready to go. No hassle, just driving.
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