Confirm it first: the 30-second fling test
Before tearing anything apart, verify the oiler is actually failing. Hold the saw over a piece of cardboard or a stump with the bar tip about 8 inches away. Run it at half to three-quarter throttle for 30 seconds. A working oiler throws a visible line of oil spatter off the bar tip. No line, or a few dry specks, means the oil isn't reaching the chain and you've got a real problem, not just a hot day and thin oil.
One number worth knowing for gas saws: a healthy oiler burns through roughly one tank of bar oil per tank of fuel. If you're refueling twice and the oil window hasn't moved, the oiler stopped somewhere along the line even if the chain doesn't look bone dry yet.
Where the oil actually flows
The path is short and every stop on it can clog. Oil leaves the tank through a pickup filter, gets pushed by a small pump (driven off the clutch on gas saws, a gear on most battery saws), exits through an outlet port on the saw body, passes into a matching hole on the bar, and rides the bar groove out to the chain. Sawdust mixed with sticky oil is the enemy at every one of those stops. Work the checklist in order, because it runs cheapest and most likely first.
The checklist, most likely first
- Tank level and oil type. Obvious, still the top cause. Fill it with actual bar and chain oil, not motor oil. Motor oil is too thin and has no tackifier, so it flings off the chain instead of clinging, and you'll see a weak fling line even with a healthy pump.
- Clean the bar's oil holes and groove. Pull the bar. Find the small oil hole near the bar's mounting slot and scrape it clear with a pick or a bent paper clip, then drag the pick down the full length of the bar groove. Measured on a saw that's cut a cord of dry oak, the packed sawdust in that groove can come out as a solid ribbon. This single step fixes the largest share of dry-bar cases.
- Clean the outlet port on the saw body. With the bar off, look for the small port near the bar studs where oil exits the saw. It clogs with the same paste. Scrape it clear and check that the bar's oil hole actually lines up with it when remounted. A bar mounted with the tensioner pin in the wrong hole can blank off the port entirely.
- Check oil viscosity against temperature. Summer-grade oil in the cold, or heavily degraded old oil, can be too thick for the pump to pull. In July the likelier version is the reverse: bargain oil thinned by heat throws a weak line and drains fast. Match the grade to the season and dump anything that's been sitting for years.
- Pickup filter and tank vent. The filter sits on a weighted hose inside the tank; fish it out and rinse or replace it if it's crusted. Then check the tank vent. A blocked vent pulls a vacuum as oil leaves, and the flow slows to a dribble after a few minutes of cutting even though the first minute looked fine. That symptom pattern, good at first then starving, points at the vent specifically.
- The pump itself. If everything above is clean and the fling test still fails, the pump's worm gear or plunger is worn or stripped. On most gas saws that's a repairable part, and on a saw under warranty it's a claim, not a DIY job. Opening the crankcase side yourself will usually void it.
Battery saws: same clogs, one extra check
Cordless saws like the Ego CS2005 or Milwaukee's M18 Fuel chainsaw use the same tank, filter, port, and groove layout, so steps 1 through 5 apply unchanged. The extra check: several models ship with the oiler set low from the factory, and some have an adjustment screw under the saw near the bar mount. Check the manual for your model before assuming a fault, and expect to top off the oil roughly every charge or two rather than every fuel tank, since there's no gas tank to pace it against.
When it's actually the bar
A bar with rails pinched shut from a pinch or worn uneven won't feed oil down the groove no matter how clean it is. Sight down the groove: if it's visibly narrowed anywhere or the rails are mushroomed over, dress it with a flat file or replace it. A new chain on a starved bar can blue and stretch inside one afternoon of cutting, which turns a free cleaning job into a bar-plus-chain bill. Fifteen minutes with a pick is the cheap version of this repair; run the fling test after every step and stop when the line comes back.