Generator Won’t Start After Oil Change – 1 minute fix

When the power goes out, I’m always surprised how many things I can’t do. Even my workshop door is electric! So when you need a generator, you need it right now! 

You are in the right place, a minute from now you’ll know how to get the juice flowing again.

The top two common causes of a generator that won’t start after an oil change, include:

Oil level low
Oil level switch fault

In this post you’ll learn more about the top two causes of a no start and how you can fix them quickly. I will also cover some other less likely but possible causes.

Check engine oil level

1 Incorrect Oil Level Will Prevent Start

I know incorrect oil level might seem too simple an answer, but for most this is the problem. All generators I know of are fitted with a low level oil switch.

The switch is a fail safe feature, preventing engine failure. Meaning, if oil level is low, the engine won’t start.

The very first step towards diagnoses is checking the oil level. Although we suspect the oil level may be low, too full is also bad.

how to check engine oil

An overfull oil level won’t necessarily disable the ignition system like a low oil level. Nevertheless it may cause plug fouling which may result in a no start. 

Check engine oil level as follows:

Place generator on level ground
Locate the dipstick
Remove and clean  Refit dipstick (do not thread threaded dipsticks to check level)
Remove dipstick and hold upright to read level

Some dipsticks can be a pain in the ass to read, try pressing the dipstick against a flat sheet of kitchen towel to highlight the level. Dipstick types and level indicators symbols vary.

Dipstick markings as follows:

Full level –  the upper mark is always the full level and the optimal oil level. Commonly  marked by the letter “F” or “Max” or simply notched

Oil level correct

Low level – it’s the lowest mark dipstick commonly the letter “L” or “Min” or a notch. This is the danger area and as you now know, it’s where the oil switch kicks in and prevents engine start

Oil level low

Hatched area – a hatched area between the low level and full level indicates an acceptable oil level. It’s neither optimal nor critical. Adding some oil here would be nice, but not strictly required

Hatched area

how to add engine oil

Adding oil is as you already know easy. It is also easy to add too much oil and you know that’s now good either. 

These small engines doesn’t hold a ton of oil and they use a splash lubrication system, meaning too much oil prevents the splash paddles distributing oil throughout the motor. A case of more being less.

Most generator engines like 5W30 or 10W30 engine oil and the average size engine will hold approx.1 quart from empty.

You can find all the tools and lubricants you’ll need here on the “Generator maintenance tools page”. If you need parts, check out the MTD parts link below. MTD sell parts for many engine makers.

MTD Parts.com- Shop Parts by Diagram Now!

Mechanics tips for adding oil:

Avoid if possible mixing oil grades
Use funnel to add oil
Add a little oil at a time, stop and recheck oil level
Use a syphon to remove excess oil

Add a little & recheck

Honda Level correct

2 Faulty Oil Level Switch

The second of of most likely causes is not as simple to fix but is simple to bypass. While bypassing the switch is not ideal, it does at least get the juice flowing quickly. More on that below.

The low oil level switch is a simple on off component fitted to the oil pan of the engine. It’s wired in parallel to the ignition system.

When the oil level is low, the switch will ground and prevent voltage from reaching the spark plug.

How to diagnose and bypass generator oil switch

Diagnosing and bypassing the oil switch is the one action. Meaning, by simply disconnecting the oil switch from the ignition system, we are eliminating it altogether.

If the switch is faulty (or oil low), your generator will start right up. On the other hand, if she still refuses to fire, we may have a different problem on our hands, and I’ve added a couple of troubleshooting links at the end of this page to help you with that.

Bypass / diagnose oil switch as follows:

Locate oil switch on the engine pan
Follow wiring to locate wiring terminal (maybe in line or at switch)
Disconnect terminal by pulling apart or removing the fastener
Attempt to start engine

Locate switch & follow wiring

Disconnect the switch

If your engine started and you are confident the oil level is correct, then you have successfully diagnosed a faulty oil level switch.

Alternatively use a volt meter set to resistance to check for continuity, you’ll need to drain the oil to check low level operation. See below.

Good sensor oil level correct

Good sensor oil level low

Note: All oil switch wiring will have a terminal for disconnecting. Thing is, they may not always be easily accessible. For the purpose of testing, it’s OK to cut the wire in a convenient place. (leave plenty of wire either side of the cut)

If you choose to leave it this way as a semi permeant bypass, tape off the raw wiring to prevent both grounding and corrosion. 

Remember if your generator is fitted with a Honda engine, it is most likely the module that has failed, rather than the switch itself. To replace the module, remove the fastener and disconnect the two conveniently located wiring terminals. Rebuild in reverse order, easy, love Honda!

Honda module failure more common

A warning for those who decide to disconnect the switch as opposed to repair it. Keep a tight eye on oil level (check with every gas fill) as your engine will now start no matter what the oil level is. As you know an engine won’t last long with a low oil level.

How to replace switch

Some models are easier to replace than others. Many Briggs & Stratton engines are a dream, and then there’s the Honda engine.

Now I love Honda motors, they are really good motors and easy to work on, but replacing the oil switch requires an engine strip down. That said, and to be fair to the Honda, it is more likely to be the oil switch module that fails and it’s easy to replace.

Honda module easily replaced

Replacing the switch as follows:

Remove oil (drain)
Locate oil level switch on oil pan
Remove sensor wire
Remove switch fasteners (usually two)
Place shop rags under the switch & remove switch
Remove old interface gasket, O-Ring etc.
Clean oil pan interface
When fitting new switch use new gasket, O-Ring etc.
Fit both fasteners by hand before using socket and ratchet to snug
Refit sensor wire & test

Less common causes of no start

There are of course lots of other possible causes of no start after oil change. While these other causes may seem remote.

Let me just say, as a mechanic with twenty five years experience, I’ve seen some really odd, seemingly not connected, remote possibility crap happen.

Anyway, here’s a few things you can check quickly:

Gas tap On?
Fuel level OK?
Switch on OK?
Choke On?
Consumers plugged out?
Fuel quality OK?
Plug wire on securely?
Try starting after removing the air filter – sign of a wet air filter, often happens by tilting the machine incorrectly (carb side down)
Try starting after removing the gas cap – sign of faulty cap
Try cleaning the spark plug – repeated starting attempts fouls spark plug

If none of this helped, then we’ll need to remove the spark plug and check for spark. If that checks out ok, we’ll need to check the carburetor bowl for dirt.

You’ll find a spark test tool together with a video on checking spark here on the “Generator maintenance tools page”.

I’ve included the following links, they may not be for generators but the engines are often identical and the test process definitely is.

“How to check spark”

“Carburetor cleaning”

You may find these other generator posts useful:

Generator surging

Generator starts then dies

Generator Troubleshooting Page

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