Rotax 903 engine

October 16, 2026

Rotax 903 ACE Engine

for SEADOO and WILLIAMS jet boats

The Rotax ACE 903 engine (often called the Rotax 900 ACE) is a 4-stroke, 3-cylinder inline engine designed by BRP-Rotax, known for its lightweight design, low fuel consumption, and reliability. It powers some Sea-Doo jet skis and the majority of WILLIAMS jet boats. At Rotax Tender Parts, we offer maintenance and replacement parts for these applications: oil filters, spark plugs, sensors, and transmission parts. Check the model and year, and use the original OEM part number to find the compatible equivalent.

Rotax 903 - Specifications

Find parts for your Rotax 903 ACE engine

Engine parts
Fuel system
Ignition
Sensors
Electrical parts
Cooling
Oil and filters
Gaskets and seals
Impeller housing parts
Other

Which models use the Rotax 903 ACE engine?

WILLIAMS Boats:

Since 2016: WILLIAMS 280 Minijet.
Since 2017: WILLIAMS 345 Sportjet
Since 2017: WILLIAMS 395 Sportjet
Since 2017: WILLIAMS 435 Sportjet (Rotax 903 engine)
Since 2019: WILLIAMS 285 Turbojet,
Since 2019: WILLIAMS 325 Turbojet

SEADOO Jet Skis:

2014–2026: Spark 2UP / 3UP and TRIXX
2014–2015: Spark 903, 2UP / 3UP versions
2016: Spark 2UP HO 900 ACE; Spark 2UP iBR 900 HO ACE; Spark 3UP iBR 900 HO ACE
2017: Spark 903 and 903 HO, 2UP / 3UP / iBR versions; Spark TRIXX
2018: Spark P-1 60 hp, P-1 90 hp, P-1 iBR 90 hp, P-2 90 hp, and P-2 iBR 90 hp
2019–2020: Spark DT NA / TRIXX 2900
2017: GTI 903; GTI SE 903; GTS 903
2018–2020: GTI 90
2017–2026: GTS equipped with the Rotax 900 / 903 ACE (continued versions to be confirmed)
2018: GTS 90

Check the installed engine, year, and OEM part number for each part before ordering.

Common Rotax 903 ACE Parts

Click an "Add to Cart" thumbnail to add one unit to your cart and access the cart. If the version or set requires a selection, the "Choose Version" thumbnail opens the product page. The name and part number also open the product page. This non-exhaustive list brings together parts whose product pages list the Rotax 903 engine. Confirm the year, part number, dimensions, and installation before ordering.

Part	OEM Part Number	Function
Rotax ACE 903 Oil Filters, Set of 4	420956123	Oil filtration. Rotax ACE 903 engine
Spark Oil Filters, Set of 2	420956124	Oil filtration. Rotax ACE 903 engine
Spark Oil Filter, Single Unit	420956124	Oil filtration. Rotax ACE 903 engine
CR8EB Compatible Spark Plugs, Set of 3	5297925; CR8EB	Generic compatible spark plugs. Spark; Williams 280 and 285 / 325 since 2019.
35 A / 12 V Relay, Single Unit	278002822 / 278003828	Electrical switching. Rotax ACE 903 engine
35 A / 12 V Relay, Set of 5	278002822 / 278003828	Electrical switching. Rotax ACE 903 engine
Starter Solenoid Relay	278000513 / 278002347 / 278001802 / 278001766	Electrical switching - Williams 280; Turbojet 285 / 325 since 2019 and some older generations.
12 V Power Relay	278003012	Williams 280 battery disconnect switch depending on the product page; Turbojet 285 / 325 from 2014–2018.
Sea-Doo / Williams Throttle Body	420893144 / 420893141	Air intake control - Rotax 903 engine
Throttle Body Presented as OEM	420893141 / 420893144	Air intake control - Rotax 903 engine
Spark Throttle Body, Other Offer	420893141 / 420893144	Air intake control - Rotax 903 engine
Spark Air Filter Kit	Unspecified	Air intake control - Rotax 903 engine
Ignition Coil	420666142	Ignition - Rotax 903 Engine
Ignition Coils, Set of 3	420666142 / 420666141	Ignition - Rotax 903 Engine
Sea-Doo / Williams Starter	420893830 / 420892426	Starting- Rotax 903 Engine
Spark Starter, Other Offer	420893830 / 420892426	Starting- Rotax 903 Engine
Crankshaft Position Sensor	420966575 / 420966570	Measurement and Control (Sensors) - Rotax 903 Engine
Camshaft Position Sensor	420664045 ; Williams 02-1089	Measurement and Control (Sensors) - Rotax 903 Engine
Camshaft Sensor, Other Offer	290664040 / 420664045	Measurement and Control (Sensors) - Rotax 903 Engine
Spark Camshaft Sensor, Other Sheet	420664040 and Cross-Referenced Sheet	Measurement and Control (Sensors) - Rotax 903 Engine
Right Throttle Position Sensor	278002283 / 004-525	Measurement and Control (Sensors) - Rotax 903 Engine.
Compatible Water Temperature Sensor	278002895 / 278001016	Measurement and Control (Sensors) - Rotax 903 Engine.
Original Water Temperature Sensor	278002895 / 278001016	Measurement and Control (Sensors) - Rotax 903 Engine.
Coolant Temperature Sensor, Other Offer	278002895 / 278001016	Measurement and Control (Sensors) - Rotax 903 Engine.
Voltage Regulator / Rectifier	710001103	Electrical Circuit (Magneto) - Rotax 903 Engine.
ACE 900 Crankshaft Seal Kit	420450165 / 420850220 / 420450080	Transmission - Rotax 903 Engine.
Spark Cylinder Head Gasket	420431812 and Cross-Referenced Sheet	Sealing - Rotax 903 Engine.
Stator Cover Gasket	420431640	Sealing - Rotax 903 Engine.
Output Shaft Sleeve	420947573	Transmission - Rotax 903 Engine.
Drive Shaft Boot Kit	295501148 / 271001762	Transmission - Rotax 903 Engine.
Spark Crankshaft Locking Tool	529036272 / 80-115B	Accessory and Workshop Tools
LEOCH AGM 12 V 25 Ah Battery	Manufacturer Reference LDC12-25	Electrical Circuit - All Jetskis or Tenders with a Rotax 903 Engine (Except SEADOO SPARK Jetskis)

Common Rotax 903 ACE Problems

The symptoms below may concern several components or systems. These are possible causes, not a diagnosis or troubleshooting guide. A single symptom is not enough to identify a part to replace.

The engine does not start: have the battery, starting circuit, electrical supply, wiring, connectors, fuel supply, and ignition checked according to the model's procedure.
Engine misfires: the check may cover the spark plugs, ignition, injection, fuel, sensors, wiring, and compression.
Lack of power: distinguish between an engine fault and a propulsion unit problem. The intake, fuel supply, ignition, compression, turbine, and wear ring must be evaluated according to the installed configuration.
Fault code displayed: note the exact code and the circumstances of its appearance. A code may concern a circuit, a power supply, or a signal; it does not confirm on its own that a sensor is defective.

To learn more about fault codes, consult our Rotax fault code list for Sea-Doo and Williams and our guide for decoding Rotax fault codes on Sea-Doo and Williams. Check that the information you consult applies to your model.

How to identify the correct ROTAX Ace 903 part?

Don't know which Rotax part to choose? Send us a photo of the part, its OEM reference, and the model of your engine or your Williams / Sea-Doo. Add the year and, if available, the engine identification number. We can help you identify the appropriate replacement part.

You can also use our automatic part recognition tool by clicking:

Identify my part from a photo

Rotax 903: Frequently Asked Questions - FAQ

What is the Rotax 903 ACE engine?
The engine designated Rotax 903 ACE or 900 ACE in our catalog is used on certain Sea-Doo personal watercraft, notably the SPARK range, and jet boats Williams, primarily on the MINIJET (280), TURBOJET (285 and 325, after 2019), and SPORTJET (345, 395, and 435) ranges. Check if your machine is affected using the detailed list above.
Where can I find the Rotax engine serial number?
On the Rotax 903 ACE engine, the serial number, generally consisting of 8 digits, is located on a plate attached to the intake manifold.
Are Sea-Doo Rotax 903 ACE parts compatible with Williams boats?
All parts related to the engine block are identical for Jet Skis (personal watercraft) and WILLIAMS boats. However, check the elements specific to marine use (notably the exhaust line, which has a catalytic converter on boats), the transmission (shaft, stuffing box carbon ring...), and the propulsion unit.
Which Sea-Doo models use the Rotax 903 ACE engine?
All SEADOO Spark, Spark TRIXX, GTI / GTI SE 903, GTI 90, and GTS 903 / 90. Consult the models and years above, then the compatibility of each part; this list is not exhaustive.
Which models of Williams boats use the Rotax 903 ACE engine?
The 280 Minijet, 285 / 325 Turbojet since 2019, and 345 / 395 / 435 Sportjet Std are equipped with the Rotax ACE 903. Consult the detailed list above.
Should the information for Rotax supercharged versions be applied to the Rotax 903 ACE?
No: the compressor and 1503 overhaul instructions do not apply to the 903 ACE because it does not exist in a supercharged version (no turbo or compressor). All Rotax 903 engines are called "naturally aspirated".
What engine oil should be used in a Rotax 903 ACE?
Generally, BRP XPS 4T 5W-40 synthetic oil. This oil is the same for the Rotax 1503 and the Rotax1630.
How much oil does a Rotax 903 ACE engine need?
Approximately 3.4 to 3.6 liters depending on the exact crankcase configuration. Note that, during an oil change, not all the oil can be removed, with some remaining inaccessible at the bottom of the crankcase. Generally, the volume of oil that can be replaced during an oil change is between 2 and 3 liters.
How to properly check the oil level of a Rotax 903 ACE?
- Start the engine and run it with an appropriate water supply if it is out of the water, or ride briefly to bring the oil to its normal operating temperature.
- Briefly increase the RPM to about 4,000 to 4,500 RPM for about 15 seconds to ensure the oil is fluid and circulating.
- Immediately stop the engine using the start/stop button or remove the kill switch cord.
- Wait about 30 to 60 seconds to allow the oil to drain back into the reservoir / oil crankcase.
- Top up gradually only if necessary, then check the level again using the same procedure.
Which oil filter is suitable for the Rotax 903 ACE engine?
Our catalog offers the 420956123 for Sea-Doo personal watercraft and ACE 903 powered Williams boats.
Which spark plugs are used on a Rotax 903 ACE?
The recommended spark plugs are NGK CR8EB spark plugs. Rotaxtenderparts.com offers compatible generic NGK CR8EB spark plugs, Rotax part number 5297925, in packs of 3.
How often should a Rotax 903 ACE engine be serviced?
First service after break-in: to be performed between 10 and 25 hours (oil change and oil filter replacement, hose and clamp checks, and general inspection). Regular full service : every 50 hours or once a year.
Why won't my Rotax 903 ACE engine start?
Several systems may be at fault: battery, electrical supply circuit, fuel (fuel pump), or ignition. Note the symptoms and any fault codes before having the engine checked.
Why does my Rotax 903 ACE start but lose power when accelerating?
A check must distinguish between fuel, ignition, intake, or compression problems and propulsion unit problems. Indeed, a foreign object stuck in the propulsion unit will affect the power of your machine without affecting the engine's performance. This symptom therefore cannot, on its own, determine which part to replace.
Why is my Rotax 903 ACE engine overheating?
Possible causes may be a loss or poor circulation of the coolant, a thermostat fault (not opening correctly), insufficient raw water flow (clogged exhaust cooling circuit, pinched hose, intake of algae or other debris, closed tow valve when one exists... ) or heat exchanger problems. Consult our article on overheating. Our article on engine overheating provides general clues to check for your model.
Why does my Rotax 903 ACE run erratically or misfire?
The diagnosis may cover the spark plugs, ignition, injection, fuel, sensors, wiring, or compression.
What problems can affect the Rotax 903 ACE engine?
Starting difficulties, misfires, power loss, overheating, or electrical faults are possible symptoms. Frequent oxidation of electrical harnesses, and a poor ground on the engine block have been documented, among others. This presentation does not constitute a ranking of their frequency on the 903 ACE.
How to read the Rotax 903 ACE fault codes?
Follow the display procedure for your model or use a compatible diagnostic tool. Consult our fault code guide while checking its applicability to your installation.
What do the Rotax 903 ACE fault codes mean?
They indicate detected anomalies, not necessarily a defective part. Consult our Rotax fault code list then the model documentation to confirm their interpretation.
How to tell if a Rotax 903 ACE fuel pump or injector is defective?
Fuel pump: check the 12 V supply, listen for a brief hum for 2 to 3 seconds (pressurization), and check the fuel pump pressure (at least 56 psi). Injectors: disconnect them electrically one at a time, or carefully remove them from the engine to see if they spray when the engine is started. Caution, these operations must be carried out with all necessary precautions.
How to identify the correct spare part for my Rotax 903 ACE engine?Check the OEM reference, engine version, model, and year, or send us a photo, or use our visual recognition tool built into this site. It's simple and fast, take a photo of your part, and, if we have this part, you will be immediately directed to the relevant product page.
Where to buy replacement parts for Rotax 903 ACE?
Consult the product pages in the table above at Rotax Tender Parts for the offered replacement parts, or a brand dealer for original parts. Always confirm the compatibility and nature of the product before ordering.