If your vacuum pump is leaking oil, the usual causes are a worn shaft seal, a failed gasket or O-ring, overfilling, back-pressure from a blocked exhaust, or oil mist from a missing or spent exhaust filter. The first step is to work out whether you have a genuine liquid leak or oil mist coming from the exhaust — they have different fixes.
Liquid leak or oil mist?
A puddle under the pump is a liquid leak (a seal or gasket). A fine haze or film around the exhaust is oil mist — oil being carried out with the exhaust gas. Identify which you have before chasing it.
1. Worn shaft seal
The rotary shaft seal is the most common source of a liquid leak. It’s a wear part and is replaced during a service.
2. Failed gasket or O-ring
Leaks around the oil box, end covers or drain/fill plugs usually mean a perished gasket or O-ring. These are inexpensive parts replaced in a service kit.
3. Overfilling
Too much oil is forced out of the exhaust as the pump runs. Check the level at the sight glass and drain any excess — fill only to the mark.
4. Back-pressure from a blocked exhaust
A blocked exhaust line or clogged filter raises the pressure inside the pump and pushes oil past the seals. Clear the exhaust and make sure it isn’t restricted.
5. Missing or spent exhaust (mist) filter
Oil mist from the exhaust usually means the exhaust/oil-mist filter is missing, saturated or fitted incorrectly. A fresh mist filter (or coalescing filter element) fixes it and keeps your workspace clean.
Tracing a persistent oil leak?
We supply seal and gasket service kits, exhaust filters and full workshop repairs for every make of pump. Email [email protected] or request a quote.
Frequently asked questions
Why is oil coming out of my vacuum pump exhaust?
Oil mist from the exhaust usually means the oil-mist filter is missing, saturated or fitted wrongly, or the pump is overfilled. A blocked exhaust causing back-pressure can also push oil past the seals.
Is it an oil leak or oil mist?
A puddle under the pump is a liquid leak, usually from the shaft seal or a gasket. A fine haze around the exhaust is oil mist, usually from a spent or missing exhaust filter. The two have different fixes.
Can I fix a vacuum pump oil leak?
Yes. Shaft seals, gaskets, O-rings and exhaust filters are standard wear parts replaced with a service kit or during a workshop service. Overfilling is fixed simply by draining to the correct level.
Written by the Girovac technical team. Girovac Ltd has supplied and serviced industrial and laboratory vacuum equipment from its North Walsham workshop since 1983. Last updated: July 2026.