What’s slowing my Lister down?
QMy Lister ST2 starts fine, but over the course of an hour the boat’s speed will drop from 4mph down to 1mph. Increasing the throttle just overheats the engine. The prop is clear. I changed the engine oil and put fresh ATF in the LH150 hydraulic gearbox. The prop seems to pulse out power. The engine seems fine. Is something wrong with gearbox or propeller?
STEVE MACK, via email
ATONY REPLIES... Firstly, leaves around the prop are very common in the autumn (and you won’t see them through the weedhatch because they drop away when you go into neutral): pop it into reverse for a moment so the leaves spin away from the prop. If not, here are some things to check.
If you have an LH150 gearbox, ATF oil is far too thin; you might have worn the clutch and brake band. It should have SAE 80 gear oil. You might also have an oval reduction box bolted to the back of the gearbox, with a separate oil filler and drain, which again uses SAE 80.
The LH150 only uses oil pressure for astern and neutral, but the ATF in the gearbox and possibly no oil in the reduction box could be causing one or other to seize up. An oil change just might solve it.
It could be partial engine seizure. Oil dilution from internal fuel leaks is one possible cause, but changing the oil has ruled that out. It can also be caused by a restriction of cooling airflow. Make sure the flywheel cover band with the air holes in it is free of dirt; you have cleared the cylinder fins of any build up of dirt; the cool air inlet into the engine bay is large enough; and the hot air outlets are properly trunked and of the correct size.
Does the stern gland get more than slightly warm? If so, it might be seizing up on the shaft. The gland might be over-tight, or the engine and shaft might be out of alignment.
Finally, it could be a fuel problem. Make sure the tank breather is clear, and try running without the fuel filler on as a test. Change and inspect the fuel filters and strainer in the liftpump: if you find water and dirty slimy stuff, the tank might need cleaning.
Gearbox and reduction box fillers