Radiators, expansion tanks and reservoirs
The Miata's plastic cooling parts age: the radiator's end tanks on the NA and NB, the expansion tank on the NC, the reservoir on the ND. This page lists who sells replacements and what they say. It is not a repair guide.
How to read it. Every claim is the seller's, as read on its own page on 1 October 2026 (the Go-Parts item is a retailer's article). This page carries no prices, which go stale; the seller's page has the current one, and whether it is in stock. Nothing here was bought or tested.
Radiators, NB (1999-2005)
| Seller | What it offers | Notes (as stated) |
|---|---|---|
| Moss Miata, radiator by CSF | plastic tanks on an aluminium core; includes the automatic transmission cooler connections; part 905-296 | CSF says each unit is leak tested at 150 per cent of operating pressure and passes a 10-foot drop test. Moss: 12-month warranty, not covering labor |
| Flyin' Miata | stock-style radiator made by Koyo, plastic end tanks, 5/8 in core, "built for automatics"; cap not included | calls it a "good budget replacement"; says plastic end tanks last "approximately a decade"; recommends its Crossflow radiators for track and turbo cars; says it may be a downgrade for a Mazdaspeed; 18-month warranty |
For the NA, I did not open a seller page: Mishimoto lists an aluminium radiator for the 1990-97 car (Mishimoto) and Good-Win Racing has a radiator category (behind its bot check). Both are from search results.
NC expansion tank (2006-2015)
On the NC the tank is part of the pressurised system, so a crack lets the pressure out.
| Seller | What it offers | Notes (as stated) |
|---|---|---|
| Moss Miata | genuine Mazda tank, 971-260, OE reference LFG1-15-350C | 2006-2015; 12-month warranty |
| Treasure Coast Miata | new OEM tank, LFG1-15-350C | says the plastic tanks "are prone to cracking as they age, potentially causing engine overheating", and calls the OEM tank "an economical solution to expensive aftermarket aluminum tanks" |
| Moss Miata, expansion tank by I.L. Motorsport | an aluminium tank to replace the plastic one, which it says is prone to leaks and cracks; it says it mounts on the OEM points with the hose connections in the OEM positions | 2006-2015 |
| Moss Miata, expansion tank by DaveFab | a TIG-welded aluminium tank, pressure tested, using the factory mounting points and hose, with instructions, hardware and a glass sight gauge for checking the coolant level | 2006-2015 |
| Moroso | coolant expansion tank for the 2006-2015 Miata | the page I could read gave no material or claims; search results call it aluminium |
ND reservoir (2016 on)
The ND's reservoir is plastic too. A retailer's article says it is a known weak point that cracks as the plastic gets brittle from engine heat, and that a yellow or brown tank is a warning sign. The same article tells buyers to get part number P51B15351 and not the older P51B15350, saying Mazda updated the part. That is a retailer's claim; I could not confirm the change from Mazda, so check the part number with a Mazda parts counter.
| Seller | What it offers | Notes (as stated) |
|---|---|---|
| Good-Win Racing, Moroso ND aluminium coolant tank (61-2481) | "rugged all-aluminum replacement" made by Moroso in the USA with TIG welding; a direct bolt-in that fits the same space and mounting points as the plastic tank; its machined neck takes the factory cap | 2016-2026 |
| TascaParts, Mazda reservoir tank P51B-15-351 | the genuine part; the listing says it includes the reservoir cap and is a special order from the maker | 2016-2025 |
| Go-Parts, article on why the tank fails | a retailer's guide rating the replacement as an easy job of under an hour with basic tools; its advice when buying used is to look for a bright white tank and avoid a yellowed one | 2016-2025 |
Flyin' Miata's search results also list aluminium coolant overflow tanks for the NA and NB and a Moroso aluminium tank for the NC, and no ND tank; I did not open those product pages.
Not covered yet
- Owner accounts of ND reservoir failures, and confirmation from Mazda of the part number change.
- Aluminium radiators for the NA and NC, and Flyin' Miata's Crossflow, whose pages I did not read.
- Hoses and thermostats; some timing belt kits include a thermostat (see timing belt kits).
© 2026 Fischer Interactive LLC. Written for the Ref Sensor app's Miata users. The seller's page is the authority.