Yamaha TRX850 Oil System Woes

The Yamaha TRX850, a machine often lauded for its unique character and performance, shares its engine with the TDM850, making it a familiar platform for many Yamaha enthusiasts. However, like any motorcycle, it can present its own set of maintenance challenges. One such persistent issue, as highlighted by forum discussions, revolves around the oil level and circulation, particularly concerning the dry sump lubrication system. This article delves into the intricacies of the TRX850's oil setup and explores common troubleshooting steps for oil-related problems.

Understanding the TRX850's Dry Sump System

Unlike traditional wet sump motorcycles where the engine oil is stored in the crankcase, the TRX850 employs a dry sump system. In this configuration, the engine's oil is stored in a separate oil tank, typically located above the engine. This system offers several advantages, including improved ground clearance and consistent oil supply to the engine, especially under hard acceleration or braking. However, it also introduces complexity, with two oil pumps: one to supply oil to the engine's components (feed pump) and another to scavenge oil from the crankcase and return it to the oil tank (return pump).

Common Oil Level Indication Problems

A frequently encountered problem is the oil sight glass (or window) on the sump not indicating any oil, even after filling with the specified amount. This can be a source of significant concern for riders. Several factors can contribute to this:

• Insufficient Oil Volume: While it might seem obvious, ensuring the correct oil level is crucial. When the engine is completely drained, not only the oil tank but also the engine's internal passages, oil filter housing, and various components will be empty. This can account for a significant amount of oil (potentially 300-400ml or more). Therefore, after initial filling and running the engine, it's often necessary to top up the oil level.
• Incorrect Checking Procedure: Dry sump systems often require a specific procedure to check the oil level accurately. Typically, this involves running the engine at idle for a short period (e.g., 30 seconds) with the motorcycle held perfectly upright. This allows the return pump to circulate the oil and fill the tank. After shutting off the engine, a brief waiting period (around a minute) is usually recommended before checking the sight glass. Checking the level immediately after revving the engine can be misleading, as the feed pump may have distributed oil throughout the engine, but the return pump may not have had sufficient time to return it to the tank.
• Oil Flow Interruption: The core of the problem often lies in the oil not returning to the tank as expected. This can be due to issues with the return pump, the oil lines, or internal components.
  

  Investigating the Oil Return Problem

  When the oil level isn't registering in the sight glass, a systematic approach to diagnosing the issue is essential. Here are some key areas to investigate:

  The Oil Pumps

  The TRX850 has two oil pumps. The discussion suggests that if the return pump is not functioning, the feed pump wouldn't have oil to supply, meaning the absence of oil in the tank points towards a problem with the return system.

  Key Component: Non-Return Valve

  A critical component in many dry sump systems, and specifically mentioned in relation to the TRX850 (and TDM850), is the non-return valve. This valve, often a small ball bearing on a spring, is usually integrated within the oil pump assembly. Its purpose is to prevent oil from draining back from the oil tank into the engine when the engine is off. If this valve becomes stuck in the open position, oil can slowly drain back into the crankcase, leading to an apparently low oil level in the tank. Conversely, if it's stuck closed, it could impede oil flow.

  The exact location of this valve can sometimes be elusive, with fiche diagrams often showing it as part of the oil pump assembly. If you've had the oil return pump apart and haven't identified such a component, it's worth re-examining the pump for any small, spring-loaded parts.

  

  Oil Lines and Filters

  Ensure all oil lines are correctly connected, free from kinks, and not damaged. The oil pickup within the oil tank and the crankcase sump will have strainers or filters. A blocked strainer can severely restrict oil flow. In one user's experience, a strainer in the sump, blocked with metallic debris, was the culprit. Regular maintenance, including cleaning these strainers, is vital, especially on higher-mileage machines. The fiche diagrams can be invaluable for identifying all such components.

  The Sump and Crankcase

  The term "sump" in a dry sump system refers to the lowest part of the crankcase, which ideally should contain very little oil. If oil is accumulating in the sump and not being effectively scavenged by the return pump, it can lead to issues like smoking on startup or oil being pushed out through the crankcase breather. Checking the sump drain plug (if present) and observing the amount of oil that drains out can provide clues. A significant amount of oil here, when the tank appears low, suggests a return pump or non-return valve issue.

  Troubleshooting Steps Summary

  Here's a consolidated list of steps to address oil level indication problems on your TRX850:

  Step	Action	Notes
  1	Verify Oil Level and Filling Procedure	Ensure you're using the correct grade and amount of oil. Follow the manufacturer's recommended procedure for checking the oil level (warm engine, idle, upright position, wait time).
  2	Inspect Oil Tank and Lines	Check for any visible leaks or damage to the oil tank and associated hoses. Ensure all connections are secure.
  3	Examine Oil Pumps	If comfortable, inspect the oil feed and return pumps for any signs of damage or wear. Pay close attention to the non-return valve within the return pump assembly. Consult the Yamaha TRX850 user manual or TDM850 fiche for diagrams.
  4	Clean Oil Strainers	Locate and clean the oil strainers in both the oil tank pickup and the crankcase sump. A blocked strainer is a common cause of poor oil circulation.
  5	Check Sump Oil Level	Drain the crankcase sump to see if an excessive amount of oil accumulates there, indicating a problem with the return system.
  6	Consider Pressure Relief Valve	While less likely to cause the tank not to fill, ensure the oil pressure relief valve is functioning correctly.

  Frequently Asked Questions

  Q1: How much oil does a Yamaha TRX850 typically take?
  A dry engine fill typically requires around 3.8 litres (3800ml), but always refer to your owner's manual for the exact specification. Remember that after an oil change and filter replacement, you may need slightly more.

  Q2: Can I use a different oil than recommended?
  It's always best to use the oil viscosity and type recommended by Yamaha. Using an incorrect oil can affect lubrication and the performance of the dry sump system.

  

  Q3: My oil light is on, what should I do?
  An illuminated oil pressure warning light indicates a serious lack of oil pressure. Immediately turn off the engine and investigate the oil level and circulation. Do not run the engine with the oil light on.

  Q4: Where can I find a Yamaha TRX850 user manual?
  As indicated, there is generally one primary user manual available in PDF format for the Yamaha TRX850.

  By systematically addressing these potential issues, TRX850 owners can ensure their beloved machine's lubrication system is functioning optimally, safeguarding the engine for many miles to come.