Sierra 9555CAT4 5W-30 Semi-Synthetic Catalyst-Compatible Inboard Engine Oil — 5 Qt
Free returns on all eligible orders
You have 30 days to request a return. All sale items are final sale.
Semi-Synthetic 5W-30 Engine Oil for Non-Turbo Inboard Marine Engines
Sierra 9555CAT4 is a semi-synthetic 5W-30 engine oil engineered for non-turbo inboard marine engines equipped with catalytic converters. Built on premium base stocks with an industry-leading additive system, it meets and exceeds both FC-W Catalyst Compatible and FC-W specifications — as well as API SM category requirements — making it the correct choice for modern inboard engines where catalyst protection matters.
The 5-quart size covers a full oil change on most inboard applications in a single container.
Key Benefits
- FC-W Catalyst Compatible and FC-W certified — meets API SM requirements
- Advanced ZDDP additive technology prevents phosphorus depletion, protecting catalytic converter life
- Enhanced detergent package suspends and prevents sludge buildup
- Reduces friction to maintain consistent engine performance
- Resists thermal and oxidation breakdown under extreme operating temperatures
- High shear stability maintains viscosity and prevents excessive thinning under load
Application
Designed for non-turbo inboard marine engines equipped with catalytic converters. Confirm your engine manufacturer’s viscosity and catalyst-compatible oil specification before use.
Parts Desk Insights
This is the right oil for customers with modern non-turbo inboard engines — particularly those with MerCruiser or similar catalyst-equipped systems where using a non-catalyst-compatible oil can damage the converter over time. Best use case: annual or seasonal oil changes on catalyst-equipped inboard engines where the manufacturer specifies a 5W-30 FC-W Catalyst Compatible oil. The 5-quart size is a natural fit for a single full-change, which makes it easy to sell as a complete service item. Always verify the engine’s catalyst compatibility requirement — not all inboards need this spec, but those that do should never run without it.
Shipping information
In-stock and OEM parts: ship same or next business day.
Locally warehoused items: ship within 3–4 business days.
Special-order items: timeline confirmed after order.
Returns & warranty
Returns & Satisfaction Guarantee
We stand firmly behind the quality of every product we sell. Your confidence matters to us — and we back it with a straightforward 30-Day Satisfaction Guarantee.
If you are not fully satisfied, you may request a return within 30 days of delivery. All returns must receive pre-approval prior to being sent back. Unauthorized returns will not be accepted.
To qualify for a return:
Item must be in new, unused condition
Product must be in its original packaging
All parts, components, hardware, manuals, and accessories must be included
Packaging must be undamaged and suitable for resale
Important:
Electronics are strictly inspected. No returns on open-box electronics. Exceptions may apply only with prior written approval. Any electronic unit that has been installed, powered, activated, or altered may not be eligible for return.
We are serious about product integrity — and equally serious about taking care of our customers. If there is ever a product issue, contact us immediately so we can make it right.
For return authorization, please contact our support team before shipping anything back.