Over the last four decades, we’ve learnt that often, the hardest faults to find aren’t dramatic failures.
Instead, they’re the small, hidden things, quietly robbing an engine of performance.
Recently, our engineers were supporting a vessel following a 5000-hour overhaul on a pair of Caterpillar main engines.
Harbour trials went well, but during Sea Acceptance Trials the starboard engine wouldn’t make full power, topping out at 2160rpm and then triggering a low fuel pressure alarm, forcing a shutdown.
First up: proving what wasn’t wrong
From the outside, low power can point to all sorts of usual suspects: injectors, sensors, regulating valves, fuel pumps, filter heads.
So we did what good diagnostics demands: isolate variables and test methodically, so we could understand what was and wasn’t operating as it should be.
To locate where the fuel pressure was being lost, we swapped components at a time between port and starboard engines, with a run and re-check after each change.
This included:
· The fuel transfer pump
· The fuel pressure sensor
· The fuel pressure regulating valve
· The fuel manifold block
· The fuel check valve on the filter head.
No change.
On a follow-up visit, new regulator valves were fitted and tested, but still the starboard fuel pressure lagged.
Operating the fuel filter changeover lever caused the starboard fuel pressure to collapse far more than the port engine, indicating that something inside the filter head assembly wasn’t behaving normally.
At that point, we removed the fuel filter head and returned it to our workshop for deeper investigation.
The cause: red silicone in the priming pump
Back at Bartech, the real culprit showed itself.
The manual priming pump check valve wasn’t operating correctly and was constantly exhausting pressure from the fuel filter head. When removed, the inlet and exhaust valves inside the priming pump were clogged with pieces of red silicone sealant.
Once the priming pump was replaced and the filter head retested, it held pressure correctly again. Reinstalled on the vessel, fuel pressure improved immediately and during the next sea trials both engines reached 2200rpm with no issues.
The takeaway? Silicone is useful, but it must be controlled
Silicone sealant has its place. But this is a textbook example of what happens when even tiny fragments migrate into internal pipework and small valves:
- A small piece of contamination can hold a valve off its seat
- That can bleed pressure continuously
- And the end result looks like a much bigger fault: low power, alarms, downtime and cancelled trials
What can you do to prevent this happening to you?
When using silicone on engines (or any connected fuel/oil/air system):
- Use it sparingly and only where specified
- Keep it away from internal passages wherever possible
- Make sure internal pipework and components are clean before assembly
- Treat small valves and priming systems as high-risk contamination points
If you’re chasing a “won’t make power” complaint, especially after major work, it’s worth remembering sometimes it’s not a failing component.
It might be the smallest foreign material doing the biggest damage.
Paul
