Lexus IS Radiator: Specs, Fitment & Common Faults

A genuinely useful piece of context: if you own the IS300h hybrid specifically, it has a separate inverter coolant system, and if it detects overheating, the car likely won't let you continue driving at all.

Illustration for editorial purposes

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OEM Part Number: 1640031870 (as quoted in catalogue listings — confirm via VIN) — aftermarket radiators Nissens 646948 / Denso DRM51021

Accuracy note: Covers the Lexus IS (2013-) as listed in the UK aftermarket catalogues. Radiators are sold by engine, gearbox and air-conditioning fitment, and one model usually has two or three different cores — a thicker core for diesels and automatics, a thinner one for small petrols — with different hose positions, so a radiator for the wrong engine will not connect up. The references below are UK aftermarket listings whose fitment lists name this generation, labelled by brand with the core size in mm; genuine numbers are those quoted against the listing. Check your engine code and whether the car has air conditioning against your VIN, and replace the coolant and bleed the system after fitting.

Radiators (aftermarket)	Nissens 646948 (400 x 708 x 16 mm, soldered aluminium core, plastic tanks, fits IS 250 2.5 V6 4GR-FSE 208 PS); NRF 550147. Nissens 606547 (400 x 722 x 27 mm, soldered aluminium core, plastic tanks, fits IS 200t and IS 300 2.0 turbo 8AR-FTS 245 PS); Denso DRM51021; NRF 550171.
Core sizes & variants	The IS 250 takes a slim 16 mm core and the 2.0 turbo a 27 mm core, both with 38 mm connections.
Genuine (OE) numbers quoted	1640031870 (IS 250); 1640036130 (IS 200t/300)
Fitment notes	The IS 250 unit is often on back order.

Accuracy note: genuinely worth knowing: whether a IS has air conditioning or a larger optional engine can change radiator sizing on some variants — fitment guides that only ask for model and year can still get this wrong, so cross-check the engine code where possible.

Lexus IS Radiator: The Part That Keeps Everything Else From Cooking

Unglamorous as it is, the Lexus IS's cooling system sits behind nearly every serious engine failure that isn't just ordinary wear — and one that went unaddressed for too long. Noticing early warning signs here is a small cost against a potentially very large one.

Before you buy: radiator size and design vary significantly by engine size, transmission type, and whether your car has air conditioning. Always confirm against your VIN before ordering.

Lexus IS Radiator: What It Does

On the Lexus IS, engine coolant sheds its heat into the passing air via the radiator, which is what keeps engine temperature in a safe working range. On automatics, it frequently pulls double duty cooling the transmission fluid through its own internal circuit — a detail that makes getting the exact part number right especially important.

Lexus IS Radiator: Watch: Replacing It

🎬 Watch: Radiator replacement 2006-2013 RWD Lexus Vehicles!!! (older gen)

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2IS (2006-2013); no 3IS radiator swap found, only a cooling upgrade vlog on an IS350.

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A Genuinely Useful Piece of Context Worth Knowing — Lexus IS Radiator

If you own the IS300h hybrid variant specifically, this is genuinely important: it has a genuinely separate inverter coolant system, distinct from the normal engine cooling system, specifically to keep the power electronics at a safe temperature. It's also genuinely important to know that if the hybrid system detects an overheat, it will likely not allow you to continue driving at all, as a protective measure — the car may genuinely need to be towed rather than driven even a short distance. This doesn't apply to the conventionally-engined IS variants.

A genuinely useful, emergency-only tip worth knowing on the hybrid variant: if the inverter coolant level is found low in a genuine emergency, temporarily topping it off with plain water rather than proper coolant can get you safely to your destination, with a proper inspection and refill to follow once there.

It's also genuinely worth knowing that diagnosing the exact cause of an overheat warning is genuinely difficult without a proper scan tool, and it's worth always properly diluting coolant concentrate with distilled water per the bottle's instructions, since undiluted coolant can itself cause overheating.

Lexus IS Radiator: Faults, DIY Difficulty & Aftermarket Advice

These are the same regardless of make or model — see our full Radiator Guide for the three common failure modes, confirming fitment against your VIN, and OEM vs aftermarket guidance.

More Lexus Radiator

The same part, covered across other Lexus models.