How often do you need to empty a catch can?

Catch cans collect a fairly significant amount of oil, and need draining often. Granted, there’s a huge variety of different quality catch cans on the market and some almost never need emptying, but as a general rule, how often should you drain a catch can?

If you’ve been following along for a while, our Provent 200 catch can review showed that we are collecting around 250 – 300ml of oil every 10,000km, and I’m sure that goes up when we’re towing, or working the vehicle hard.

Provent Catch can after 5625km
How often do you need to drain your catch can?

What happens if you don’t drain it?

I guess we’ll start at the beginning; if you have a catch can installed, and you don’t ever empty it, what will eventually happen? You might chuckle, but this happens all the time, and I’ve met people who have good catch cans (like a Provent, or Ryco), and had no idea that they had to change the filters, or drain it.

Ultimately, what happens is the oil level grows, until it covers the filter, and causes restrictions in your PCV. This will put extra pressure on your seals, and you’ll have an oil leak either from the catch can, or from somewhere else in the motor, which is not good news at all. You can also end up with a considerable amount of oil flowing into your intake, which can end very badly if it diesels away.

Provent 200 filter
If you don’t drain it, your filter will block up and cause all sorts of issues

You absolutely need to empty your catch can on a regular basis, but there are a couple of variables:

How big is your storage?

On the Provent catch cans, a lot of your storage is the drain hose itself. My advice when fitting this is to run a decent length hose, and even loop it if you can, so you can hold more oil. You soon get sick of draining the catch can, and anything you can do to make it longer is a good thing.

How much blow by do you have?

I’ve heard of people blowing seals because they didn’t drain their catch can once in 5000km, and on some vehicles that is enough running time to generate enough oil to well and truly fill a catch can.

Most vehicles that are healthy won’t do more than 300ml per 10,000km, and you can get away with slightly longer durations, but its not worth pushing the friendship.

Diesel smoke isn't great
If your engine is tired, you’ll catch a lot more oil than a new, good condition one

What do we do?

When we were around home, I was doing it around every 1000km. However, since being on the road full time, this is too often as you are doing it all the time, and I got sick of it, so pushed it out to 2000km, and then 2500km. 

I think you can probably push it to 3000km, and some even do 5000km, but that’s too much for us.

Dmax and camper
I try and drain our Provent 200 every 2500km at maximum

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