Fixing oil leaks

Skipper's Checklist

By Alan Lucas

Rare indeed is machinery that never weeps oil or grease — especially small marine engines whose owners pay little attention to them until trouble brews. And even those who claim their engines are “so clean they can eat their lunch off them” are destined for a dose of reality one day. But what are the realities of oil and grease leaks and can regular checks prevent them?

The answer is no, not entirely. All the dedicated maintenance and careful attention to detail cannot guarantee freedom forever. We can only make regular inspections and respond to brewing problems, the first sign of a leak often being droplets in the bilge or a mystery filming somewhere on the engine or gearbox. Their source can be ridiculously hard to find because oil often doesn’t drip directly from its source, it merely spreads then drips from the lowest point.

Easiest to find

The easiest leaks to find and fix are those caused by our own mismanagement. For example, after changing the sump oil a clumsily replaced filler cap will allow it to blow out as a thick mist and an improperly seated dipstick has similar potential. The answer is simple: be more careful.

Oil leaks can also result from cracked gaskets — typically those between cylinder head and block or tappet cover and cylinder head, and oil coolers suffer gasket and O-ring failure, or their cast body might crack around the endplate bolts. With the last problem, it is important to recognise that the overtightening of end-plate bolts is more likely to increase a leak than cure it.

Regardless of cause, phantom evidence of an oil leak can appear for some time after successful repairs. This is because previously escaped oil gathers around inaccessible parts of the engine from where it drips into the bilge when the engine is hot and stops when it cools. If thorough cleaning of these areas is impossible, then be patient while all the old oil “melts off”.

Biggest cause

The biggest cause of escaping grease from such items as water pumps is an unnecessarily strong lateral pull from an over-tight V-belt. This can groove the shaft and/or wear the bearing until grease is freed to throw out of the bearing. This gets awfully messy and is best treated with new seals, bearings and a re-machined shaft — if not a new pump — and a promise not to over-tighten the belt in future.

You may or may not reach a stage where you can “eat your lunch off the engine,” but you can at least maintain a higher level of inspection than in the past and this, after all, is what check lists are all about.