How much  a used generator is worth? What are the most important checks to do? Find out how to choose a  used generator   even if you do not have special skills in the mechanical or electrical sector!

(Video at the bottom of the page)

If to buy a generator we have to avoid only 6 mistakes  ( so to speak), when  buying a used generator, the situation gets complicated and it is crucial to be able to select a generator without ending up on something that can reveal a bad purchase.

The main concern is not the fact that someone before us used the generator, but rather is it the fact of not knowing if he used it with scrupulous and careful attention.

The ideal thing is to get along with an expert, a professional who knows what to look at and can distinguish a deal from a mass of problems

It's natural though that if you're reading this article you probably do not want or cannot get a hand lended from anyone, so let's go straight away with the information you need to not fall into a wrong choice.

Identifying the Generating Set: Is It Really It? Has it been tampered with?

A key step before proceeding with any test is to identify the generator unit by verifying that the data on the plate conforms to the documents submitted by the vendor.

Verify the identity of the generator, verify that no tampering has been occurred.

We are talking about changes that compromise its operation. Let's take some examples:

The emergency stop was inhibited; The shutdown system has been changed; the EC caps have been removed from the engine; the switch has been replaced with one having different characteristics, the operating logic has been changed, changes have been made to the chassis or bonnet, etc etc.

Without documents it's never a deal.

We will often make similarities with cars. An Unlocked Generator Set and like a car without a circulation card.

Some people make the mistake of thinking that a generator can later be equipped with the documents needed for its use, but this can never be taken for granted.                      

Issuing documents, especially when it comes to products from other manufacturers, is an expensive operation that many  tend to underestimate.                       

Actually issuing documents for a machine we did not design and we did not build is a great responsibility towards the user and to those who designed i considering the main risks and residual risks.                      

It is crucial when you look at a used generator  to ask the owner to show you the generator's documents.                       

These documents are the certificate of conformity, user manual, maintenance manual. Sometimes the user manual and the maintenance manual are in the same brochure. If you want to deepen the topic, we have dealt with this topic in another article dedicated to generic set documents.                     

Drawings, technical sheets, and other material are useful and very important elements but are not indispensable, and above all they are not mandatory for doing business with a generator set.

Reissuing the documents due to the loss of the originals may be required through the intervention of the original manufacturer.                       

Reconfirming the compliance of a generating set binds the certifier to produce a complete technical file and a residual risk analysis.                       

In addition to being compliant with the regulations in force, the documents must comply with the identification plate on the generator set. The plate must bear the CE marking, the power of the generator, the generator model, reference standard, and other  technical data to identify the machine and its operation.                       

A generator set without documents could not be sold, and in any case could not be installed and used.                       

A generator with a certificate of conformity can be installed, but cannot be used if the user manual  is not present on site.                       

The recertification of a generating set provides for the availability of documents useful for issuing a new certificate. They are the documents relating to the main components of the generator, for example the diesel or gasoline engine, the alternator and other components of the electric board.                       

Hours to work, year of production, but not only.

Working hours are important but must be evaluated taking into account the context in which they worked.

Let's take an example to understand the concept: Would you prefer a used car that has 100.000 km mostly on the highway or one that has  run 100.000 km on a mixed path?

Is it better having a generator that worked a few meters from the sea , a generator that worked in a sand quarry, or a generator that was in emergency service at the mall? Salt, sand, or the quietness of a technical room in the underground of a building?

In the case of the generator, we must first evaluate whether the operating hours have been totalled in a continuous or emergency mode, then try to understand in which environment it has worked.

The engine, this is what you must never neglect.

Take a look at the engine .

There should not be excuting fluids. Check the belt that is usually well visible.


During a cold start a black smoke or a white smoke may be normal.

Black smoke: In the case of  black smoke  during operation, there is probably an excessive consumption of oil , from the dirty oil filter, or the presence of exhausted engine oil.

White Smoke : The emission of white smoke during operation requires deeper checks because it can mean a lot of things. It could be caused by a low amount of coolant, by the presence of water in the diesel, an injection delay, a cracked piston, the head gasket, etc.

Please note that during operation at load, the smoke increases considerably.



Check the status of the anti-vibration pads: with the engine off and cold push the coupled alternator motor to one side. The engine must move and return to position without residual oscillations.

Do not neglect this detail, it is a matter that only experts control. A generator that is proposed as "equal to the new" will have all the kit of anti-vibration in excellent condition.


Cooling Radiator

Open the coolant cap: there must be no oily residue,  which indicates a possible fall in the head seal.

You could repeat the control before starting and after the test run. Be careful during these checks, the liquid temperature is burning.


Noise Frequency and Voltage under load

Consider when the load is switched on, if the motor reacts promptly by returningvoltage and frequency to nominal ones.

Quality and Pressure of Lubricating Oil.

When the engine is cold, check the oil level, and with a cloth score if there is a possible presence of solid residues, a symptom of engine wear.

When th engine is hot, open the oil filler cap, there may be a natural outbreak of hot vapors but there must not be an oil spill.

Connections and wiring

Check that the system is in order and that there are no traces of burnt or rigid or deteriorated conductors.

Security systems

The generator must automatically switch off for low oil pressure, high coolant temperature.

Try also the emergency stop button. (Required). Shutting down should take place within seconds.


Operating test .

If you are purchasing an automatic generator, simulate the lack of network by selecting "Automatic" mode from the control panel. The generator must start the engine in 5 few seconds.

It may not be enough to start the engine and check that the voltage is at the nominal level. The best test is the load, at least 50% of the load that the generator can withstand. A charge test could be paid as it involves a technician and there is a natural fuel consumption.

The Alternator, fundamental but never verified.                  

The alternator is one of the most neglected components in the generator, although it is also one of the most expensive after the first engine.                       

More than half the problems experienced by a user who has a used generator is to find surprises on the alternator.                     

In fact, on the 90% of the generating sets only engine maintenance is often performed and often not complete, reducing the replacement of filters and lubricating oils.                        

A regularly maintained and revised alternator by a qualified and experienced personnel has relatively high life expectancy.                       

One of the reasons why the alternator is never verified by the user who intends to buy a generator set is the general lack of expertise in understanding the aspects to be verified in the alternator                      

It is important not to ignore the fact that the alternator is made up of rotating parts that are subject to vibration and mechanical stress which over time can create wear and then fail to adequately repair them.                       

Few people know that the mono-support alternator, equipped with a single headset bearing, has a well defined maintenance plan that provides for replacing or lubricating the stand regularly.

The control panel.

The control panel is essentially an electronic component. Make sure it is the original one assembled by the manufacturer of the generator, if it's not the case, ask for information on the kind of intervention performed.

Remember that if the control panel is replaced on a generator set without the necessary adjustments, the operating hours start from zero.


Clear signals but almost (all) ignore it.

It's not all. There are signs that only a watchful eye can notice. In fact all that we have explained in this article is 50% of what you should know, a share of all respect that will allow you to avoid throwing away your money.

From whom to buy a generator set used ?

Used generating sets can be found by private vendors who have ceased their activity, from specialized dealers and dealers.

The suggestion is always to turn to a builder first because he will not take the risk to put into service used machines  that could bother him and make him bad publicity.

Resellers and small craftsmen are an unknown, in our region, for example, there are companies that retrieve scrap of years 80 and restructure without a criterion and without producing really valid documents.

Manufacturers or their dealers, on the other hand, often take over generating units that have not accumulated a large number of hours and sell them at competitive prices.

Used yes

Watch the Video with Tips to Purchase a Used Generator That Works. What to check, what to ask, what are the most important things and all you need to be sure that the use you've identified is actually what you need.

Watch the video with tips for buying a used generator that works. What to check, what to ask, what are the most important things and everything you need to make sure that the used one you have identified is actually the one that is right for you.