NOTES ON COMMON ENGINE PROBLEMS
What do I do if my engine runs rough during run-up?
Engine roughness while checking the magnetos during run-up could indicate a fouled spark plug or other ignition system problem. Accelerate the engine to run-up rpm and lean the mixture until the engine runs rough. Let the engine run for about 30 seconds. Enrich the mixture then check the magnetos again. If this doesn’t clear the roughness, have the ignition system checked by a mechanic before flying.
What if the mag drop is more than 200 rpm?
A larger than normal mag drop is not as critical as a rough mag. A smooth drop up to 200 rpm is fine. A drop greater than 200 rpm could indicate a mag-timing problem that should be checked. A mistimed magneto can rob some power from the engine and also cause engine damage.
Can I fly if the carb heat drop is 300 rpm or more during run-up?
No. A large carb heat drop, more than the typical 50-100 rpm, is caused by an exhaust leak where hot air is diverted to the carburettor. This can allow exhaust fumes/carbon monoxide into the cockpit. It can also direct hot exhaust onto components like fuel lines, possibly causing fire in the engine compartment.
Is it possible for the carburettor to ice up during ground operations?
Yes. If you don’t leave the carb heat on for at least 10 seconds during run-up, any existing ice might not melt and could cause lower power output during take-off and possible engine failure.
How do I know if my engine is developing full power during take-off?
The engine must reach the specified static rpm range (before releasing the brakes) at full rpm. Check the POH for these numbers. If the aircraft can’t reach this rpm range on the ground there may be a problem with the tachometer indication or something wrong with the engine. Possible problems include a worn propeller (fixed-pitch), improperly set propeller governor (constant-speed), mistimed magnetos, fouled spark plugs, clogged fuel injector nozzle, or a blocked muffler.
Can I take off if the oil temperature isn’t in the green?
Yes, but check to make sure the engine picks up smoothly as the throttle is slowly advanced. Cold oil doesn’t lubricate as well, and damage could occur if the oil isn’t warm enough. Engines can be started at low temperatures, but it is generally safer to preheat below -6C. Preheating improves oil lubrication, the fuel vaporizes for easier starting, and engine parts expand uniformly.
My engine runs very rough while starting then smooths out as it warms up. Is there something wrong?
Yes, there is a strong likelihood that you have a stuck valve, which is dangerous because the sticking can occur during normal operations and it can cause catastrophic engine failure. Have this symptom checked thoroughly before flying.
Can I hurt my engine by leaning too much?
Yes, at higher power settings. Follow the POH leaning instructions to avoid damage. Over-leaning isn’t a problem when running at just above idle power, so during a long taxy or a lengthy wait for take-off clearance, you can lean the engine aggressively without damage. This helps to prevent spark plug fouling, but don’t forget to enrich the mixture before take-off!
Is it okay to lean below 3,000 feet?
Yes. There is no reason not to lean during cruise, as it saves fuel and is better for the engine. Recommendations not to lean below 3,000 or 5,000 feet are intended to keep lower-altitude pilots from forgetting to enrich the mixture before descending, and are not related to any potential engine problems!
I learned what to do if my engine fails, but what do I do if there is a partial power loss?
This is more likely to occur than a complete failure. If the engine is losing power steadily, you’ll need to find a place to land quickly. For example, a gradual loss of oil pressure will result in total engine failure and a forced landing will be soon required. Whereas a fuel line or muffler blockage could cause a partial power failure but leave enough power to stay level and nurse the airplane to a nearby airport, but this will depend on terrain and weather. The bottom line for partial power loss is to treat it like a full engine failure and plan to land at the earliest opportunity.