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RV DIY Fluid & Filter Maintenance

RV DIY Fluid & Filter Maintenance

One thing most everyone knows about us is that we appreciate the ability to do much of our own RV maintenance and repairs, DIY-style. We know when to call on the pros – and we do! But, there are lots of maintenance items that we regularly tend to ourselves. Among them is regular attention to fluids & filters. So, in today’s post, we’re sharing our RV DIY fluid & filter maintenance processes, in case you’d like to follow along.

What RV Fluids Do I Need to Check & Maintain?

There are several RV fluids that motorized rigs need to have checked regularly and maintained. We’ll go through each one-by-one, but first a couple of notes.

Fluids should be checked routinely and before long trips. This is a great way to keep things running well in your RV, and to stay on top of what’s needed prior to driving a long distance.

Let’s run through the steps to check the various fluids in your RV:

Engine Oil

  1. Remove the dipstick.
  2. Clean the oil off the dipstick with a rag or paper towel.
  3. Re-insert the dipstick.
  4. Remove the dipstick again, and check the level (near the end/bottom).
  5. If the level is below the “full” line, add oil as needed.
  6. Recheck the oil level on the dipstick.
Checking RV oil is an obvious item of RV DIY fluid maintenance

We regularly check our rig’s engine oil when we stop for fuel or when we’re heading out on a trip (after the engine has been running for a while, but has cooled long enough for the oil to have drained back into the pan).

Think of motor oil as your engine’s blood supply. It’s the single most crucial fluid in your driveable RV, without which your engine would self-destruct in short order.

Be sure to check your owner’s manual for the appropriate type of oil for your RV’s engine. You may also need to take into consideration the weather where you’ll be traveling for proper oil viscosity. Your owner’s manual will specify which viscosity is best for travel in warm climates, and which should be used during colder weather.

The ideal way to check your engine oil is with the engine and oil warm (so the oil flows more easily), but after the engine has been shut down and sitting long enough to allow the oil to drain back into the pan. The RV should also be as level as reasonably possible when checking oil level.

If you’re planning to head out early in the morning to head to your next campsite, the engine of course won’t be warm after sitting all night. While it’s not ideal to check the oil when the engine is cold, it’s better than not checking it at all, and will still show pretty close to accurate on the dipstick.

Our preferred method is to drive to our campsite, and get set up at the site. Then, with the RV leveled and the engine still warm (so the oil has drained back into the pan), we check the dipstick so that we know it’s okay ahead of our next driving day.

Part of our PTI (pre-trip inspection) on departure morning includes looking under the engine area for any signs of fresh oil leaking out. If we confirm the proper level upon arrival, and there’s no puddle under the engine before departure, we’re comfortable our oil level is good.

The engine oil and filter replacement interval is generally based on time or mileage (for example, once per year, or every 7,500 miles, whichever comes first). Follow the maintenance schedule in your owner’s manual to know when it’s due.


  1. NEVER open the radiator cap on a hot engine!
  2. Visually check the coolant level in the overflow tank.
  3. Some coolant overflow tanks have a clear site glass to confirm the level.
  4. If the coolant is low (or not visible) in the overflow tank, open the pressure cap to check the level in the radiator. (Again NEVER do this when the engine is hot!)
  5. Check the fluid level.
  6. Add coolant as needed to fill the radiator.
  7. Replace the pressure cap and close it securely.
  8. Add coolant to the “cold level” line in the overflow tank.

Coolant replacement is usually required less often than engine oil replacement. That interval can often be extended by using long-life coolant. For example, we use red OAT (Organic Acid Technology) coolant in our RV, which doubles the replacement interval.

Even so, because of the volume of fluid involved in the process of draining, flushing, and replacing an RV engine’s coolant, we don’t typically tackle this as a DIY RV fluid & filter replacement project, and let the pros handle this for us.

Transmission Fluid

Our rig being professionally serviced - not all things are good RV DIY fluid & filter replacement projects

Even though we do much of our own maintenance and repairs, we regularly have our rig professionally serviced.

While it’s certainly possible to change the transmission fluid of your RV as a DIY project, many RVers, ourselves included, choose to have it replaced at a professional shop. That said, you can check the transmission fluid level by taking the following steps.

  1. Warm your engine before checking the fluid level.
  2. Remove the dipstick with the engine running.
  3. Clean off the dipstick with a rag or paper towel.
  4. Replace the dipstick.
  5. Remove the dipstick and check the level, again with the engine running.
  6. Add fluid if the level reads below the “full” line.

NOTE: Some transmissions have the ability to run their own diagnostic routines that report on fluid level. The Allison transmission in our diesel pusher does that. Follow the instructions in your owners manual for details.

Also check your owner’s manual for the proper type of RV transmission fluid to use. Be very careful here because the wrong type of fluid can damage your (very expensive) transmission.

Power Steering Fluid

Here again, a flush of the power steering fluid is often best left to the pros, but you can check and maintain your power steering fluid as part of your RV DIY fluid & filter maintenance plan. If you don’t see a cap marked “power steering”, check your owner’s manual for the location of the power steering reservoir. Check the level by following these steps:

  1. Remove the dipstick
  2. Clean the dipstick with a rag or paper towel
  3. Replace the dipstick
  4. Remove the dipstick again and check the level
  5. Add fluid if the level is low, however, be sure not to fill higher than the “max fill” line

Your RV owner’s manual should state the type – and possibly even the brand – of power steering fluid you should use. New power steering fluid is usually clear, and older power steering fluid is generally brown.

Brake Fluid

Note that most diesel motorhomes have air brakes (and air ride suspension systems), and don’t have brake fluid. You can expect to find air brakes on Class A diesel-powered motorhomes – the biggest and heaviest RVs. So, the following steps generally apply to gas-powered RVs.

Checking or changing brake fluid may not be a RV DIY fluid & filter replacement project for you

Class A diesel rigs like ours have air brakes so we don’t have a brake fluid reservoir to check. But, if you have a gas-powered RV, you can check your brake fluid using the steps noted below.

Locate your RV’s brake fluid reservoir and check the level of the brake fluid by taking the following steps:

  1. Clean off the top of the reservoir so that no dirt/debris falls into the brake fluid when you open the cap.
  2. Remove the cap to open the reservoir.
  3. Visually inspect the fluid level to make sure the brake fluid is about half an inch from the top.
  4. If your brake fluid level is at or above the “MIN” line, don’t add fluid. If the brake fluid level is below the “MIN” line, add the proper brake fluid to just under the “MAX” line, taking care not to overfill.

Windshield Washer Fluid

The maintenance of windshield washer fluid is one of the easiest tasks on your RV DIY fluid & filter maintenance checklist, and probably the task you’ll do most frequently, depending on how much you drive your RV. Check the level of your windshield washer fluid and top it up as necessary:

  1. Identify the windshield washer fluid reservoir and check the markings on the side.
  2. Open the cap and add fluid as necessary.
  3. Be sure to use low-temperature windshield washer fluid if there’s a chance you’ll be RVing in below-freezing conditions.

Hydraulic Fluid

Diesel-powered RVs have a dedicated hydraulic system (and sometimes a hydraulic filter) for powering components of the engine & chassis, but gas RV engines don’t.

But, no matter what way your RV is powered (gas or diesel), all RVs that have hydraulic leveling jacks and/or slides will also add checking the hydraulic fluid levels of those systems to your RV maintenance checklist for fluids.

Even though diesel RVs have engine hydraulics, they’ll likely have a separate hydraulic system for the leveling jacks and/or slide-outs as noted above.

Check your owner’s manual for the location of your hydraulic fluid reservoir(s). The reservoir has a dipstick, so you can check the level using the same steps as you used to check your oil and transmission fluid levels. If you need to add hydraulic fluid, be sure to check your owner’s manual for the appropriate fluid to use for your RV.

The replacement of hydraulic fluid, however, is a task best left to the pros.

Don’t Forget Your RV Generator

The Onan generator in our RV

We regularly change the oil, oil filter, air filter, and spark arrestor in our Onan RV generator.

Generator Engine Oil

As part of any RV DIY fluid & filter maintenance plan, it’s also important to check the oil in your RV generator’s engine routinely as well. Depending on where your RV’s generator is located, this could require getting under your RV to check (and change) the oil.

Your generator has a dipstick just as your rig’s engine does, and you can check the oil using the same steps noted above for checking the RV engine oil.

Most RV generators require oil and filter replacement every year, but check your owner’s manual to be sure what’s called for on your particular make & model.

For a visual step-by-step guide to the process, you can watch our video on our annual Onan diesel RV generator maintenance, where you’ll see us change our generator’s oil & oil filter, replace the air filter, and clean the spark arrestor as well.

Generator Coolant

You’ll want to check the coolant level in your generator, too. Here’s our post and video on changing the coolant in an Onan diesel RV generator. If nothing else, this should help you to see where the coolant in your RV generator is located.

What Filters Do I Need to Change on My RV?

Air Filter

Changing your air filter regularly is a good practice and can be part of your RV DIY Fluid and Filter maintenance list. It’s a good practice to change your air filter whenever you change your oil, or when specified by the owners’ manual.

Changing our RV's air filter is an easy and important RV DIY fluid & filter replacement task

Changing your RV’s air filter is an important part of regular RV maintenance.

To change your air filter simply consult your owner’s manual for the location of the filter. Remove the filter and write down the information written on the side of the filter or take the filter with you to the auto parts store.

Air cleaners on diesel pushers can be both specialized and large. Here’s a video showing how we replace ours.

Oil Filter

Your oil filter should be changed whenever you change your oil. If you change your RV’s oil yourself, change your oil filter at the same time.

If you take your rig to a shop for an oil change, they should do this automatically as part of the job.

Fuel Filter

The fuel filter on an RV is an important filter to maintain. Your RV’s fuel filter removes potentially harmful contaminants that could be in the fuel, keeping it out of your engine. Follow your owner’s manual for required intervals, or take it to a pro.

Power Steering and Transmission Filters

The power steering and transmission filters may be fairly accessible, depending on your rig. But here’s the thing – changing the power steering fluid can be dangerous if there are air bubbles left in the line. (The same is true of the brakes.) This isn’t a risk we want to take, and isn’t one we recommend.

Similarly, while transmission filters are usually pretty easily accessible and can be changed as a DIY project, we’ve always had a service location do ours because there are a number of gaskets and seals that need to be handled carefully, and a lot of fluid to manage.

Generator Oil, Air, & Fuel Filters

In the first video above in today’s post, we showed you how to change the generator’s oil and air filter.

The following video will demonstrate how to change the fuel filter. (For reference, we have an Onan 7.5 kilowatt QuietDiesel generator. If you have a different model, be sure to check your owner’s manual for possible differences in the procedure.)

A Note About DIY RV Maintenance Tasks

Doing your own RV and generator maintenance is great, but there can be a bit of a learning curve to certain aspects of these tasks. Several of them you may already know how to perform, and you may have done so regularly for years.

In some instances, simple instructions or some step-by-step guidance from our videos may be all you need to become acquainted with some of the other tasks. But as we’ve noted more than once in today’s post, some maintenance tasks are really best left to the pros.

Not Interested In RV DIY Fluid & Filter Maintenance?

Not the type to tackle your own RV fluid & filter maintenance projects? You’re in luck! Cummins is offering a special, limited-time promotion for RV engine, chassis, and generator maintenance discount. Check out the details here:

No coupons found.

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Friday 28th of January 2022

Think you forgot a filter. If a newer diesel MH, the Freightliner Dealer a couple of years ago, changed a filter in the DEF reservoir


Friday 28th of January 2022

Thanks for adding that one in, Walt! Us drivers of old (2005) rigs can sometimes forget about DEF!

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PLEASE NOTE: We're handy RVers, not professional technicians. We're happy with the techniques and products we use, but be sure to confirm that all methods and materials you use are compatible with your equipment and abilities. Regardless of what we recommend, consult a professional if you're unsure about working on your RV. Any task you perform or product you purchase based on any information we provide is strictly at your own risk.

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