Mercury Optimax 90 Problems: With Effective Solutions

Are you worried about Mercury Optimax 90 problems? I know many of you’re facing these and I am here to help.

There are mainly 5 problems associated with Mercury Optimax 90. In this article, I’m going to cover the problems with symptoms and solutions. So keep reading till the end. 

Mercury Optimax 90 Problems: Table Overview

I’ve prepared a table for you to help you understand more about the issues.

ProblemBest Solution
Engine Won’t StartEnsure the battery is charged and connections are clean and tight
OverheatingRegularly inspect and replace the impeller or water pump
Oil Injection System FailureEnsure oil mixture is calibrated correctly
Noise IssuesInspect and tighten loose engine components
Fuel Pump ProblemsClean or replace clogged fuel pump or fuel lines

Next, I’ll be discussing the detailed guide for Mercury Optimax 90 common problems. However before that, I’m suggesting a related article on – Mercury 9.9 pro Kicker problems.

Mercury Optimax 90 Problems: Detailed Guide

Now let’s get started –

Problem 1: Engine Won’t Start

Encountering a situation where the Mercury Optimax 90 refuses to start can be frustrating, especially when you’re eager to hit the water. Several factors can contribute to this problem, requiring troubleshooting to identify and resolve the issue.


  • Engine does not respond when the key is turned.
  • Clicking or buzzing sounds without engine ignition.
  • Inconsistent or weak cranking.


  • Low battery voltage or faulty connections.
  • Fuel supply issues, such as a clogged fuel filter or empty fuel tank.
  • Ignition system problems, such as a faulty starter motor or ignition switch.


  1. Ensure the battery is charged and connections are clean and tight.
  2. Verify that the fuel filter is not clogged and the fuel tank has an adequate supply of fuel.
  3. Inspect and replace a faulty starter motor or ignition switch if necessary.

Problem 2: Overheating

Overheating is another issue that Mercury Optimax 90 owners may encounter. Excessive heat can cause damage to the engine components and lead to performance degradation if not addressed promptly.


  • Engine temperature gauge indicates overheating.
  • Loss of power or acceleration.
  • Boiling or bubbling sound coming from the cooling system.


  • Insufficient coolant or low coolant level.
  • Malfunctioning thermostat.
  • Blockage or restrictions in the water intake.
  • Worn-out impeller or water pump.


  1. Check the coolant level regularly and ensure it is at the appropriate level.
  2. Inspect and replace a faulty thermostat, if necessary.
  3. Clear any blockages or restrictions in the water intake to ensure proper cooling.
  4. Regularly inspect and replace the impeller or water pump as per the manufacturer’s recommendations.

Problem 3: Oil Injection System Failure

The oil injection system of the Mercury Optimax 90 is responsible for delivering the right amount of oil to the engine. A malfunctioning oil injection system can result in improper lubrication, which can lead to engine damage.


  • Excessive smoke emission from the exhaust.
  • Engine performance issues, such as reduced power or misfires.
  • Oil leakage or oil level fluctuations.


  • Clogged oil injectors or oil lines.
  • Faulty oil pump or oil pressure sensor.
  • Improper oil mixture due to incorrect adjustment or calibration.


  1. Regularly clean and maintain the oil injectors and oil lines to prevent clogging.
  2. Inspect and replace a faulty oil pump or oil pressure sensor, if required.
  3. Ensure the oil mixture is calibrated correctly by following the manufacturer’s guidelines.

Problem 4: Noise Issues

Excessive or unusual noises coming from the Mercury Optimax 90 can be a cause for concern. Unwanted noises can indicate underlying problems that require attention to prevent further damage to the outboard motor.


  • Rattling, grinding, or knocking sounds during operation.
  • Whining or squealing noises from the belts or pulleys.
  • Loud or abnormal exhaust noises.


  • Loose or worn-out engine components.
  • Damaged belts or pulleys.
  • Exhaust leaks or issues with the muffler.


  1. Inspect and tighten any loose engine components to eliminate rattling or knocking noises.
  2. Replace worn-out belts or pulleys to address whining or squealing sounds.
  3. Check for exhaust leaks or muffler issues and repair or replace the affected components accordingly.

Problem 5: Fuel Pump Problems

The fuel pump plays a crucial role in delivering fuel from the tank to the engine. If the fuel pump malfunctions, it can lead to poor engine performance, stalling, or complete engine failure.


  • Engine hesitates or sputters during acceleration.
  • Loss of power or inconsistent engine performance.
  • Difficulty starting the engine.


  • Clogged fuel pump or fuel lines.
  • Malfunctioning fuel pump relay or fuel pressure regulator.
  • Faulty fuel pump motor or wiring issues.


  1. Clean or replace a clogged fuel pump or fuel lines to ensure proper fuel flow.
  2. Inspect and replace a faulty fuel pump relay or fuel pressure regulator as needed.
  3. If the fuel pump motor or wiring is faulty, consult a professional technician for repair or replacement.

That’s everything I had to share about Mercury Optimax 90 Problems. I hope you’ll find your problem common from this guide. It’s time to say bye bye but if you want you can check another article on – Mercury 115 2 Stroke Problems.

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