Is a catch can important on a modern turbo diesel?

If you own a modern turbo diesel without a catch can, you’ll probably look back in the future and wish you’d fitted one. You can get a variety of different brands and models of catch can kits for $150 – $450 installed, and they play a hugely important role for your motor.

The only reason you’d not bother fitting one is if you are going to sell the vehicle after a couple of years. However, its still an attractive item for a lot of buyers due to the longevity improvements they provide.

Dmax modifications
A catch can is one of the most important mods you can do to a turbo diesel

What is a catch can, and what does it do?

By nature some oil, fuel and even water escapes from the motor during normal operation and ends up in the crankcase. In standard form, this film of oil is sucked back through the positive crankcase ventilation line (PCV) and ends up in your air intake, where it goes back into the motor to be burnt in the combustion process.

A catch can sits in between your crankcase and the PCV, and it is designed to separate the fluid and mist from the air that makes its way through and catch it in the bottom of the unit.

Some catch can’s have filters in them, and others use mesh, steel wool or a variety of combinations. If its just a can with an inlet and an outlet, you have bought one that won’t work very well!

Isuzu Dmax Catch Can
The new catch can on our Dmax

Why is it so important?

I can already hear you asking is a catch can worth it? Is it actually important? I’ll cover that now. The biggest reason you want a quality diesel catch can on a modern motor is to stop the massive problem it causes when it mixes with your exhaust gas recirculation system (EGR).

Turbo diesel motors have had exhaust gas recirculation systems now for some time, where a portion of the exhaust gas is recycled back through the motor.

This isn’t a massive issue, except that by nature your exhaust gasses have carbon in them, and when this black soot mixes with an oil mist, it sticks to anything that it can.

Without a catch can, your engine’s air intake system cakes up with sticky black muck and soon becomes badly restricted.

You only have to jump on Google Images and look up EGR intake clean to get an idea of how bad this actually is. Left without being cleaned, you will suffer significant losses in power and fuel economy.

There are a variety of ways of cleaning motors, which can be time consuming and expensive. If you can avoid the build up in the first place you’ll save a heap of headache.

The second reason catch cans are very important is because oil reduces the efficiency of your intercooler when it covers the pipe work. The colder the air going into the motor the better it performs, and if your intercooler doesn’t function as it should you are missing out on its potential.

The oil catch can benefits are simple; your intake stays clean which improves economy, power and reduces your long term maintenance costs.

How much oil does it catch?

This question depends on lots of different factors, but the amount of oil, water and fuel that is caught is actually significant. In 10,000km you should easily get 50 – 300 ml of fluid.

What ever you don’t catch goes straight into your engine. Not good. Any mechanic worth their weight will tell you that much oil going into your intake is not good.

Catch can legalities

Catch can’s are 100% legal, and on some well designed diesels they actually come as standard. Sadly, this isn’t the case for your average 4WD motor.

In the past, people would just run a pipe to the inside of their chassis, and let the oil film run into the chassis, for ‘rust prevention’! This is not legal, and is one of 32 ways to make your 4WD illegal.

Catch cans and warranties

There’s a lot of comments online stating that fitting a catch can will void your warranty. Whilst there is some merit to this idea, its more complicated than a black and white arrangement. Isuzu themselves sell a catch can on 4JJ1 truck engines as a factory fitment, and if its correctly engineered you should have no issues. On the flip side, a poorly designed catch can or one that isn’t emptied regularly, or doesn’t have the filters replaced can cause excess back pressure and make things leak.

Either way, the catch can has to be directly related to the failure. You can’t have a rear differential failure warranty claim declined because you fitted a catch can, as the two have nothing to do with each other. Want to know more? Check out do aftermarket accessories void your warranty?

Blocking the EGR

Another way to stop the build up of carbon in your intake is to block the EGR. This is also not legal, and yet a massive number of people do it. You can do this a number of ways; electronically by tricking the ECU into not using the EGR, or mechanically by installing a blanking plate.

By doing this though, often the ECU will pick up that there is a ‘problem’ and will throw a code with the check engine light come up. Also, if you are caught tampering with any emissions gear on your 4WD, you can be fined huge money.

I believe in NSW the fine is up to $250,000 for an individual! That said, as far as I know there hasn’t been anyone fined near that amount, but they are starting to crack down on it.

Beyond that, the EGR actually provides some useful engineering benefits; its not just there for emission controls. By turning it off, you are changing the way the motor was engineered to run, and a huge amount of money and time goes into designing a quality 4WD motor.

By blocking the EGR you still end up with the oil going into your intake anyway, so its only half a fix.

The HPD catch can on our Dmax

The first accessory I bought for our Dmax was a catch can, from HPD. I spent many hours reading and researching the best catch can options, and settled on the HPD (which as it turns out was a mistake).


After 34,000km of testing on our Dmax, and reading an independent study on catch cans I’ve removed the HPD catch can in favour of something that catches a LOT more oil.

If you want to know more, have a read of this; Why I’m removing my HPD Catch Can. Spoiler alert; the Provent Catch cans are far more effective. My HPD Catch Can Review isn’t favourable.

For the full test results including the 5625km the Provent 200 ran on our Dmax, check this out – Provent vs HPD Catch Cans. In terms of oil catch can reviews, make sure there is some independent, scientific research before you commit to buying something!

EDIT – After running the Provent 200 Catch can for about 35,000km, I’ve caught somewhere in the realm of 1200ml of oil, which is pretty incredible.

Why the HPD catch can?

At $385 delivered to your door, the HPD catch can is one of the more expensive ones on the market. Here’s a couple of reasons I initially chose them:

100% Australian made

Billet aluminium and stainless steel brackets made to exceptional quality

Dipstick for checking the oil level

Substantial volume to catch oil, meaning it doesn’t need emptying very often.

Inlet and outlet both high up meaning even on weird angles when 4WDing its never going to run back into the motor

Maintenance free. No filters to replace

It comes in a kit for the Dmax, and several other vehicles. Bolts, fittings, hoses, brackets and all.

Quality gates hose used in the kit which is the same size (marginally bigger) than the factory hose.

Highly recommended by a huge variety of people (even without any sales motivation)

These have 4 stainless steel pieces of mesh on the inlet and the outlet. The idea is the air flow is disrupted going through the mesh, and causes the oil mist to stick to it and fall into the catch can.

Isuzu Dmax catch can
The HPD Catch can kit to suit Isuzu Dmax models with the 4JJ1
HPD Catch can Dmax
The bottom unscrews from the catch can
HPD catch can screens
4 removable screens held in place by a circlip either side and rubber o-rings in between on the inlet and outlet

Things I wasn’t entirely happy about with the HPD catch can

When I purchased and fitted the HPD catch can, I was fairly impressed with it. However, in the interest of being 100% honest, there were a few things I wasn’t 100% happy with and I’ll mention them below:

I found a tiny piece of wire from the mesh at the bottom of the catch can when I received it, presumably from when the mesh filters were installed. The edges of the mesh filters are cut and have strands of wire that are not meshed together, and are not overly strong. It would never have made it into the intake, but it shouldn’t have been there.

The instructions are ok, but not amazing. Some extra photos would be great, and using a standard motor (not one with aftermarket intercooler hoses!) in their photos would be helpful.

The bracket rubs on the brake line unless you bend it over. I was aware of this, but only through reading online about it. Simply bend the brake line a little out of the way.

The intake clamp rubs on the catch can if you don’t move it around, and will damage the can if left for a long time (and make an annoying noise). This could easily be part of the instructions.

You have some adjustment for the way the catch can sits. I couldn’t get it to sit clear of everything; if I twisted it around the hose rubbed on the air filter intake hose, and the other way meant the outlet sat over the dipstick a little.

I opted for the later as you can just twist the outlet around when you want to lift the dipstick out, but its not perfect. You don’t want things rubbing on each other on a vehicle; they will wear out over time.

The hose clamps that come with the kit are not adequate for the OEM plastic barbs. On the catch can it fits snugly and the spring clamps lock it on well. On the Dmax barbs though, the hose is just a smidgen too big, and the clamps don’t apply enough pressure to lock it on. I can pull the hoses off the barbs very easily even with the clamps on. Never mind; replace them with 2 hose clamps and you are laughing.

No pressure relief valve.

HPD fitting instructions
Fitting instructions from HPD

HPD vs Provent

The other contender for catch cans on the Dmax was the Provent, made by Mann and Hummel. These are quality gear (make sure you get genuine ones), but they are massive. They also don’t come in a kit for the Dmax, and you have to replace filter cartridges every 45 – 70,000km at about $70 each.

Based on everything I’ve read online, I’d say the Provent probably catches marginally more than the HPD (EDIT: Not anymore; I’ve since learned they catch a LOT more). They are a German engineering company that runs a proper filter. You’ve got to expect that sort of result.

However, there were things that I didn’t like about the Provent (like its size, inlet and outlet position, pressure created etc) and I decided on the HPD instead.

Not all catch cans are equal

Yep, you can go on eBay and buy an oil catch can for $45, and fit it to your expensive 4WD. The only problem though, is it probably won’t catch anything! If you want the best oil catch can, stick with a Provent 200!

There is some pretty intense engineering that goes into the design of a quality catch can; a steel box with a hose in one side and out the other is not going to do much. The best oil catch can may not be the prettiest looking.

Make sure you buy genuine too; there are a lot of rip offs, specifically around the Provents.

Diesel Catch Can Problems

Like everything, there’s no free lunch. A poor quality catch can has the potential to cause issues if it restricts the flow too much, or is not emptied regularly enough, or not maintained well. The solution to this is to get a well engineered and proven catch can, and look after it.

I have heard of people having issues with restrictions and blowing rear main seals, but with a good catch can this should be avoided providing you empty it regularly!

Returning the oil back into the engine

Some people take the oil collected from a catch can, and tip it back into the motor. You can do this, but I wouldn’t. For starters, its often got moisture in it, and even fuel thats escaped the combustion process. The oil is not good quality; get rid of it.

Is a catch can necessary?

If you are wondering are catch cans worth it, you’ve got some decisions to make. There’s a lot of diesel motors out there that don’t run catch cans, so they are not an absolute must fit.

However, if its your vehicle and you plan to keep it for more than a couple of years a good catch can should be considered important. I wouldn’t own a modern turbo diesel without one.

Future updates will come

I’ll pass on how the diesel catch can goes in the future – maybe after 5000 – 10,000km. For now though, I know its another thing ‘fixed’ and it will save a lot of headache down the track.

EDIT – If you missed the updates, I’ve removed the HPD catch can and fitted a Provent 200 which catches significantly more oil.

If you want to see the rest of the 4WD build, check this out – Isuzu Dmax build for touring Australia.

Do you run a catch can? What did you fit? What do you think of it? How much oil do you catch?

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  1. Hey Tony,

    Western Filters have a diagram showing the way the Provent filters work. The air enters at the top, and is spun around, through the outer of the filter, and the oil drops out the middle, into the bottom. The clean air then returns to the PVC, and the oil falls down into the hose where you can drain it out.

    I wouldn’t run a copy of a catch can unless it was on a vehicle I didn’t really care about; the risks just don’t seem worth it to me.

    All the best

  2. I bought a provent (copy) catch can.
    Reading the fitting instructions and examining the filter arrangement was a bit worrying.
    The whole thing seems back to front.
    1) the air to be filtered enters at the top, and through the filter, to the turbo out, the bottom!!
    2) This means that any drops of oil drip down into the bottom and can be sucked back into the turbo.
    3) The oil collection space is very limited, compounding the problem
    4) Normal filter practice is from the largest filter area (the outside) to the smaller (inside) this one does the opposite.
    I can see it keeping out any half bricks and lumps of carbon out of the works, but dropping the separated oil back into the “cleaned” air seems a dumb idea.
    Any comments,Aaron?

  3. Hi Dodgy Dave,

    Thanks for your opinion. Perhaps you could explain why so many modern diesel engines have them factory fitted, and why you think they should be left alone? This would certainly add a bit more weight to your comment

    All the best

  4. Dodgy dave says:

    I agree with the fellow that said it’s a farce….it’s just a fad you 4×4 warriors are into at the moment…leave your modern diesels alone

  5. Hi Neale,

    I’d welcome your own independent research on the topic; more than happy to have a critical discussion about it. You don’t think that car manufacturers have to balance the cost of the vehicle and its maintenance against sales targets?

    Do you believe vehicle manufacturers do everything they can to make a vehicle last as long as it could?

    All the best

  6. Sounds like nonsense pushed by manufactures of catch cans and/or confirmation bias from those that have been sucked in. Service your car according to manufactureers warranty

  7. Hey Dave,

    The amount you collect is relative to the blow by, and condition of the motor. 100ml for 20k seems a bit low, but if its new it takes time to fill the filter before it actually catches oil in the hose. Keep an eye on it, but it should be fine

    All the best

  8. Hey

    Installed a Provent in our 125,000km old Jeep Grand Cherokee, running the 3L V6 turbo diesel. I was really surprised when I drained it (after 20,000km as I thought the service guys did it) and only got 100ml out of it! Is that normal?

  9. Hey Bruce,

    The hoses pop off when they’ve got oil inside, especially around where the hose clamp and barb are. I’d say there’s a good chance that the hoses weren’t cleaned when they were put back. That said, the Provent won’t stop every last millilitre of oil going through, but it will stop most of it.

    Keep an eye on it, but I’d say it won’t happen again if its been well cleaned, and you’ll be good long term.

    All the best

  10. Bruce Bailey says:

    Hey Aaron , I liked the article , I have a Provent on my 2014 Colorado , Ive done about 15k with it and collected about 300mls of oil , I empty it about every 5k or so , I’m happy but do have a question , I had an intake system clean done a month back and whilst travelling the hose connected to the throttle body blew off , no probs it just wasn’t fitted correctly after the clean but I did notice that the inside of the throtle body and inside the intake hose that blew off were covered in wet oil , is that normal ?, we have done about 5k since the clean was done.
    Cheers Bruce

  11. Hi Sam,

    You are correct, and that would be a good test to do. However, as you say, every vehicle is different and getting two identical setups is almost impossible in the real world.

    At the end of the day though, the build up is the primary reason for a catch can, and if that wasn’t a problem you’d probably not bother fitting one

    All the best

  12. The effectiveness of a catch is obviously related to how much oil, water etc. It catches; Some are better than others from what I see. But different engines in diffetent mechanical condition and states of wear, using diffetent oils and driven in very different conditions, will produce varying amounts of blowb and oil vapour. All things been accounted for, Should we not actually do tests where a camera is put into to the manifold and intercooler and EGR valve to see how much gunk has accumulated after so many K’s, with and without a catch can?

  13. Hey Levy,

    Thanks. You won’t get a formal answer from Isuzu, except that they don’t endorse the use of aftermarket accessories. That said, the fact that they sell their trucks with the same motor with a genuine Isuzu catch can should speak volumes. You can actually buy this catch can and fit it to your 4JJ1 if you prefer.

    The only people that will give you answers are the dealers, and some will say it will void your warranty, and many will not. The fact remains that they can’t decline a warranty claim unless its directly related to the component you’ve fitted. For example, if you fit a catch can and the rear springs break in half, they can’t say the catch can caused it.

    The grey area is that they can blame something and not give any further evidence, and then you are left trying to fight them, which isn’t a great place to be. It can be done with independent mechanical services, but its just a pain in the backside.

    Ultimately you have to make a call, and do what you are comfortable with. Speak to reputable diesel service centres, and go off their advice and what you are comfortable with

    All the best