| How To Fix | Hynautic Hydraulic Engine Throttle & Gear Control System |
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The Challenge with Hynautic Throttle Systems
Hynautic hydraulic throttle and gear control systems have served vessels reliably for decades. However, with time, age catches up. These systems are now completely unsupported, with no new parts available. And when they start to fail — they fail fast.
It’s not just about when the failure happens — it’s about what fails. A common issue is a sudden drop in hydraulic pressure due to leaks. In such cases, a boat could get stuck in gear, in neutral, or even stuck at revs with no way to disengage. That kind of scenario can turn into a serious hazard very quickly.
Understanding the Hynautic System
The Hynautic system works by storing pressure in a cannister — typically filled with a 50/50 mix of ethylene glycol (without any stop leak) and distilled water. The system is pressurised to over 80–100 psi and feeds both the throttle heads and gear actuators.
What could go wrong:
- External leaks – around fittings and hose ends
- Internal leaks – worn o-rings inside slave cylinders or throttle heads
- Throttle Head Failures – leading to erratic or stuck engine control
Trying to Maintain It
For boat owners looking to squeeze a little more life out of their Hynautic system, there’s a methodical (but time-consuming) approach:
- Start at the Cannister – Check pressure (should be 100psi) and inspect for obvious damage or leaks.
- Inspect lines – Examine every hydraulic line running to the throttle and gear actuators.
- Bleed the System – Every component needs to be re-bleed thoroughly. This may have to be repeated several times, ensuring no air bubbles are present and that pressure remains stable.
This is a labor-intensive process that may only delay the inevitable.
The Better Solution: Flexball Electronic Throttle Controls
Rather than patching an outdated system, many vessel owners are now choosing to modernise completely. At THT, we recommend replacing Hynautic systems with Flexball Electronic Throttle Controls.
Flexball offers:
- Reliable, modern performance
- Compatibility with both mechanical and electronic engines/gearboxes
- Smooth, precise control
- No hydraulic fluid, leaks, or pressure maintenance
- Easier future servicing and support
With zero risk of fluid leaks and long-term reliability, Flexball controls are an ideal upgrade for vessels still running legacy hydraulic systems.
If your boat is still running a Hynautic control system, it’s not a matter of if it will fail — it’s when. Whether you’re experiencing early signs of failure or want peace of mind before heading out on the water, contact us at THT to discuss how a Flexball system can bring your vessel into the modern era of marine engine control.
