PRODUCT DETAILS
Thermostat for Mercury / Mariner Outboard
Fits DFI Optimax 2-Stroke Models – 200HP, 225HP, 250HP, 300HP
This high-quality aftermarket thermostat is designed to maintain proper engine temperature and cooling performance in Mercury Optimax engines.
Will fit the following Mercury/Mariner DFI Optimax models:
• 200 HP DFI – USA models from serial 0G590000 and up
• 225 HP DFI – USA models from serial 0G590000 and up
• 250 HP DFI – USA models from serial 1B426561 and up
• 300 HP DFI – USA models from serial 1E001867 and up
Replaces OEM Part Number:
• Mercury / Mariner 8M0057307
(OEM part number used for reference only. This is a marine-grade aftermarket replacement.)
Why Buy from SSI Marine?
• Marine-grade aftermarket part
• UK-based stock for fast shipping
• Same-day dispatch on orders before 1 PM (Mon–Fri)
• Collection available from our Leigh, Manchester unit
• Trusted supplier with years of marine experience
• VAT invoice available upon request
• Expert help available — message us if you’re unsure about fitment
⚠️ Please confirm compatibility with your engine model and serial number before purchasing. If in doubt, contact us and our team will be happy to help.
SHIPPING & DELIVERY
Delivery & Returns Policy
Delivery
Standard Delivery
- £6: Royal Mail Tracked 24 Service
- £3.99: Large Letter - Royal Mail 1st Class Post (Untracked)
We offer free delivery on all orders over £150 (excludes outboard engines).
Orders placed before 1:00 PM (Monday-Friday) are usually dispatched the same working day.
Most parcels are delivered within 24 hours, but please allow extra time for courier delays that may occur outside our control.
For outboard engines, please contact us for a delivery quote.
Important: Please ensure your shipping address is correct before completing checkout. SSI Marine is not responsible for parcels sent to an incorrect address provided by the buyer.
Tracking Your Order
Once your order has been dispatched, you will receive a tracking number via email (after 5 PM on the day of dispatch).
Tracking is available only for parcels sent via Royal Mail Tracked 24.
Large Letter orders are sent via Royal Mail 1st Class Post (untracked).
Returns
We accept returns of unused and undamaged items within 30 days of purchase.
Returned items must be in sellable condition and include the original packaging.
Please do not tape, label, or write directly on the product's original box.
Important: Do not return items in their original product boxes only, they must be placed inside a protective outer box or bag. Parcels returned like the example below will be subject to a 20% restocking fee.
Return shipping costs are the customer's responsibility.
Please include your order details and reason for return inside the parcel.
Refunds
Refunds are issued for the item purchase price only (shipping costs are non-refundable).
All refunds will be made using the same payment method as your original order.
Items returned in poor condition or without proper packaging may incur a 20% restocking fee.
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