Onan Fault Code 33 [Cummins Generator Overheat]

A Onan generator may report a code 33, overheat.

You may need to replace:

  • sensor
  • radiator
  • fan belt
  • water pump
  • Coolant
  • Oil


Check the coolant and oil levels.

Owners report this issue happens after 1000 hours.

Note that it will shutdown itself if it gets too hot.


Fault code 33 status led will blink 3 times, pause, then 3more.

Here is a video of how one person fixed overheating:



  1. Low coolant level: Insufficient coolant can lead to overheating. Check the coolant level and add more if necessary.
  2. Blocked or damaged radiator: A blocked or damaged radiator can impede the flow of coolant and lead to overheating. Inspect the radiator for damage or debris, and clean or repair as needed.
  3. Faulty thermostat: A malfunctioning thermostat may not regulate the engine temperature properly, leading to overheating. Replace if needed.
  4. Faulty water pump: A damaged or malfunctioning water pump may not circulate coolant effectively, causing the engine to overheat. Inspect the water pump and replace it if necessary.
  5. Leaks in the cooling system: Leaks can cause the coolant level to drop and lead to overheating. Inspect the entire cooling system for leaks, including hoses, connections, and seals, and repair as needed.




Troubleshoot an Onan generator

  • Check the fuel level: Ensure that the fuel tank has enough fuel to run the generator. A low fuel level can cause the generator to shut off or run poorly.
  • Check the oil level: Check the oil level and add oil if necessary. Low oil level can cause the generator to shut off or run poorly.
  • Inspect the air filter: The air filter prevents dirt and debris from entering the generator’s engine. A clogged air filter can cause the generator to run poorly or not start at all. Check the air filter and clean or replace it if necessary.
  • Check the spark plug: The spark plug ignites the fuel in the generator’s engine. A faulty spark plug can cause the generator to run poorly or not start at all. Replace if necessary.
  • Check the battery: The battery provides power to the generator’s starter motor. A weak or dead battery can cause the generator to not start or run poorly.
  • Check the carburetor: The carburetor mixes air and fuel to provide the engine with the correct fuel-to-air ratio. A clogged or dirty carburetor can cause the generator to run poorly or not start at all. Clean or replace it if necessary.
  • Perform a diagnostic test: If the above steps do not resolve the issue, a diagnostic test should be performed by a trained technician to determine the exact cause of the problem. This may involve using diagnostic software to analyze the performance of the generator’s engine and electrical system.


Q: What is an Onan generator, and is it related to a mythical ancient god of electricity?

A: Ah, the mighty Onan generator! While it may sound like it has divine origins, it’s not directly related to any mythical gods of electricity. Onan is actually a reputable brand that specializes in manufacturing reliable and powerful generators for various applications. But hey, if you hear any low hums or mysterious sparks, you never know—maybe it’s channeling some hidden electric powers!

Q: Can an Onan generator power my entire neighborhood during a blackout? I promise to throw the best block party ever!

A: As much as we’d love to see an Onan generator transform your neighborhood into the ultimate block party paradise during a blackout, its capabilities do have limits. While these generators are designed to provide backup power, the size and capacity of the generator will determine the number of appliances and devices it can power. So, you might have to scale down your block party dreams just a tad. But hey, a well-lit living room and some catchy tunes can still create a party atmosphere!

Q: Can an Onan generator produce enough energy to power a UFO? I’m asking for a friend who’s planning an intergalactic road trip.

A: Ah, the allure of intergalactic road trips! While an Onan generator is quite powerful, it’s unlikely to produce enough energy to launch a UFO into space. They are better suited for powering RVs, construction sites, or providing backup electricity for homes. Your friend might need to seek some advanced extraterrestrial technology for their spacefaring adventures. But hey, if they find a way to power a UFO with an Onan generator, we’ll be the first to buy a ticket for that interstellar journey!

Q: Can an Onan generator spontaneously break into song? I could use some entertainment during a power outage!

A: While an Onan generator won’t serenade you with a chorus of power ballads, it does have a special talent for providing a reliable and uninterrupted power supply during outages. So, you might have to find other sources of entertainment—like a good old-fashioned board game or a candlelit storytelling session—to pass the time. But hey, if your generator starts humming a catchy tune, make sure to let us know, because that would be quite the showstopper!

Q: Can an Onan generator power my coffee machine and keep me caffeinated during camping trips? Asking for the sake of humanity.

A: Ah, the eternal quest for caffeination during camping adventures! Fear not, for an Onan generator can indeed power your coffee machine and provide you with that precious liquid fuel to kick-start your day. Just imagine waking up in the great outdoors, the smell of fresh coffee wafting through the air, and your trusty Onan generator ensuring that your caffeine cravings are satisfied. It’s a match made in camping heaven!