Blue smoke
Generator Blowing Blue Smoke
Blue or blue-grey smoke means your generator is burning engine oil. The cause can be as simple as oil overfilled above the maximum mark, or as serious as worn piston rings, valve guides or a turbocharger seal. We check the oil level, the oil use and the engine’s condition before we recommend anything, because an overhaul is the last answer, not the first.
Callout fee waived when you accept our written quote. 1-year workmanship guarantee. See prices
- Oil use checked first
- Cheap causes ruled out
- Written quote before any work
- Onsite across Gauteng
Oil reaching the combustion chamber
What does blue smoke from a generator mean?
Blue smoke is burnt oil. Oil is getting into the cylinders, past worn rings or valve guides, through a leaking turbocharger seal, or from a sump filled above the maximum mark, and it burns with the fuel.
When it appears tells us where to look. Smoke for a minute after starting that then clears points to valve stem seals, because oil seeps down while the engine stands. Smoke that never clears and oil use that keeps rising point to ring or liner wear.
Blue smoke is not the same as black smoke (too much fuel or too little air) or white smoke (unburnt fuel or coolant). If you are unsure of the colour, a short video taken from a safe distance helps us.
Fault guide
Generator blowing blue smoke: what it can mean and what to do
Blue-grey smoke usually means the engine is burning oil. We check the oil level, the breathers and engine wear. This guide separates what you can safely notice from what a qualified technician tests. One symptom never proves that a particular part has failed.
Symptom, likely cause and repair
Find the line closest to what you see. The cause is the most likely one, not a diagnosis: testing confirms it before any part is replaced.
| What you see | Likely cause | Usual repair |
|---|---|---|
| Blue smoke at start-up that clears | Oil seeping past worn valve stem seals while the engine stands | Engine overhaul |
| Blue smoke all the time, oil use rising | Worn piston rings, liners or valve guides | Engine overhaul |
| Blue smoke straight after an oil top-up | Oil overfilled above the maximum mark | Generator servicing |
| Blue smoke on a lightly loaded diesel | Long light-load running glazing the cylinders | Load bank testing |
| Blue smoke and oil in the intake or exhaust pipework | A turbocharger seal leak, where a turbo is fitted | Generator fault finding |
01
What you may notice
- Blue or blue-grey exhaust smoke
- The oil level drops between services
- Oily deposits around the exhaust outlet
02
Possible causes
Any of these can produce the same symptom. Testing decides which one applies.
- Oil overfilled above the maximum mark
- Worn piston rings, valve guides or seals
- A crankcase breather problem
- A turbocharger seal leak, on engines that have one
- Long periods of light-load running
03
What you can safely check
Look and note only, from outside the canopy. Do not open panels, covers, fuel lines or the cooling system.
- Does the smoke appear at start-up only, or all the time?
- Has oil been added between services, and how much?
- Is oil visible around the exhaust or under the set?
04
Stop using the generator and call if you notice
- A low oil pressure alarm
- Knocking or a sudden change in engine sound
- Heavy smoke drifting into buildings
If it is safe to reach, stop the generator with its normal stop control or emergency stop, keep people away, and call a technician.
05
What a qualified technician typically tests
These are technician checks, not steps to try yourself. Several involve live electrical measurement, fuel or pressurised systems.
- Oil level and oil consumption record
- Crankcase breather and turbocharger seals, where fitted
- Compression or leak-down tests where wear is suspected
06
Common repair categories
The repair follows the test result. These are the services this symptom most often leads to.
07
What to send when you book
- Your suburb and how we reach the generator
- Make, model and kVA from the data plate (a photo is ideal)
- Fuel type: diesel, petrol or gas
- How much oil has been added since the last service
- Whether the smoke shows at start-up, all the time, or only at light load
08
Related faults and services
Not sure which symptom fits? Try the generator symptom finder.
Safety before you check anything
- Exhaust contains carbon monoxide, which you cannot see or smell. Run a portable generator outdoors only, away from doors, windows and vents, and never run any generator in a house, garage or other enclosed space.
- A standby generator set to automatic can start at any moment, when the mains fails or on its exercise timer. Keep the canopy closed and stay clear of fans, belts and the exhaust.
- Generator output, the changeover and the control panel can be live, and some parts hold stored electrical energy after shutdown. Leave panels, covers and wiring closed for us to open.
- The engine, exhaust and coolant stay hot after running. Never open a radiator or coolant cap on a hot engine.
- Do not refuel a running or hot generator. If you smell gas at a gas-fuelled set, do not operate switches; leave the area and contact your gas supplier.
Carbon monoxide guidance: US Consumer Product Safety Commission: Generators and engine-driven tools (carbon monoxide).
Send the details on WhatsApp
This opens WhatsApp with a short message already typed: brand, model, capacity, symptoms and suburb. Fill in what you know and send it. Blank lines are fine.
- The data-plate photo is added inside WhatsApp after the chat opens: tap the attachment or camera icon and choose the photo. A link cannot attach the photo for you.
- Take the photo only when the generator is switched off and has cooled down. Do not reach over or into a running or hot generator, and keep away from the exhaust.
- A standby generator set to automatic can start by itself when the mains supply fails. If you are not sure how it is set, photograph the plate from a distance or send a photo of the whole set instead.
Typical repair costs for this fault
Published ranges, last reviewed October 2026. The callout is R400 – R700 in business hours and R700 – R1,400 after hours, and it is waived if you accept the quote. Your written quote after diagnosis is the price that applies.
- Engine overhaul
- R9,000 – R28,000+
Step 9: book a diagnosis visit.
Related Pages
Oil, wear and the engine
Common Questions
Questions about blue smoke
What causes blue smoke from a generator?
Oil burning in the cylinders. The usual causes are oil overfilled above the maximum mark, worn valve stem seals, worn piston rings or liners, a turbocharger seal leak, or long periods of running at very light load.
Is blue smoke serious?
It can be. Overfilled oil is a quick fix, but smoke that does not clear and oil use that keeps rising mean the engine is wearing, and the longer it runs that way the bigger the repair.
My generator only smokes blue when it starts. Why?
Oil can seep past worn valve stem seals while the engine stands, then burns off when it starts. If the smoke clears within a minute or two, seals are the likely cause rather than ring wear.
Does blue smoke mean I need an engine overhaul?
Not always. We rule out overfilled oil, the breather and the turbo first. If the engine is worn, we quote a top-end overhaul or a full rebuild and compare it with replacement.
Can light-load running cause blue smoke?
Yes. A diesel that runs for long periods with very little load does not get hot enough, which can glaze the cylinders and let oil past the rings. A load bank test shows how the set behaves under a proper load.
How much oil use is too much?
If you are adding oil between services, note how much and how often, and tell us. A steady rise in oil use is more telling than a single top-up.
Can I keep running the generator?
Check the oil level before each run and keep it between the marks. Stop and call us if the oil pressure alarm comes on, if you hear knocking or if the smoke gets heavy.
Still unsure what the fault is? Call or WhatsApp 082 057 4605 for onsite diagnosis.
Service Areas
Onsite visits across Gauteng
We come to your generator anywhere in Gauteng, 24/7. Choose your region for local suburbs, call-out details and the faults we see most there.
What to send before we attend
These details help us plan the visit and bring the right parts. Send what you can on WhatsApp; if you can’t find the model number, we still book the visit.
- Location
- The suburb or site, so the visit can be booked in the right area.
- Make and model
- The generator brand and model, if they are known.
- kVA
- The size printed on the data plate.
- Fuel type
- Diesel, petrol, LPG, natural gas, or dual-fuel.
- Controller model
- The module name on the panel, when it is visible.
- Fault or alarm
- What the set does, and any text on the screen.
- Photos
- The generator, the data plate, and the controller or alarm. Send these on WhatsApp.
Book a Visit
Tell us when the blue smoke appears
At start-up only, all the time, or at light load? Tell us how much oil you have added since the last service.
- Call
- 082 057 4605
- Message us on WhatsApp
What happens next
- We reply with questions about the generator, or to book a visit.
- A technician comes to you. For a breakdown we arrive within 1 hour.
- The fault is diagnosed on site and you get a written quote. No work starts until you accept it.
Charlie, lead technician: Degree in Mechanical Engineering, Degree in Electrical Engineering, Diesel Plant Fitter. Generator specialists since 2000.