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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 cans for $150 - $450 installed, and they play a hugely important role for your motor.

Dmax modifications

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

What does a catch can do?

By nature some oil, fuel and even water escapes from the motor 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 saying 'So what; why does that matter?', and I'll cover that now. The biggest reason you want a quality catch can on a modern diesel motor is to stop the massive problem it causes when it mixes with your exhaust gas re circulation system.

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 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 losses in power and fuel economy. There are a variety of ways of cleaning motors, which can be time consuming and expensive. Avoid the build up in the first place and you'll be in a great position.

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.

How much oil does it catch?

This question is very generic, but the amount of oil, water and fuel that is caught is actually fairly reasonable. 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.

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.

Blocking the EGR

Another way to stop the build up of carbon in your intake is to block the EGR. This is 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 ECU, 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!

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 options, and settled on the HPD.

I installed it a few days ago, at 1600km on the clock. I'll monitor it, and do a review down the track of how its going, but am confident it will do its job well

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 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.

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

Overall, I'm really seriously impressed with what HPD offer. 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 Hummell. 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. 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 a catch can for $45, and fit it to your expensive 4WD. The only problem though, is it probably won't catch anything! 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.

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

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.

Future updates will come

I'll pass on how the 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.

Do you guys run catch cans? What did you fit? What do you think of it? How much oil do you catch?

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