Should you fit an oil catch can to your engine?
If you believe the hype, oil ‘catch cans’ protect your engine and clean up a factory design deficiency - the reality is very different
Modern engines are actually designed to recycle exhaust gas (it reduces emissions and boosts fuel economy) as well as poisonous crankcase vapours
QUESTION
Would you be able to do an article or video piece on whether ‘Oil Catch Cans’ are a marketing myth of actually have a valid part to play in catching so called ‘blow by’ and stop it entering the intake for reburn?
( I am assuming the manufacturers would fit one if it were needed?) My dealer will fit a diesel pre-filter (30 micron) to my V8 diesel Landcruiser but won’t fit a catch can - sighting that that have seen these cause pressure issues in the engine and blown seals.
Like your article on chipping I am not interested in fitting marketing gimmicks that actually could cause more damage than good - what is your expert view please. - Piers Cunningham
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ANSWER
If there were an epidemic of engines clagged to death from oil blow-by, then a catch can (or other systematic countermeasure) would be built in at the factory - subject to legislative compliance. Modern engines are designed to recycle exhaust gas. EGR - an exhaust gas recycling system is built in, which improves fuel efficiency and emissions performance. Additionally, engines have positive crankcase ventilation (PCV) which pumps poisonous crankcase vapours containing atomised oil and noxious vapours (hydrocarbon byproducts) into the engine so that they are burned to less harmful chemicals before they enter the air we breathe.
The PCV system includes an oil separator, designed to catch oil before it it drawn into the engine, and return it to the sump.
When these systems work properly, there’s no need for a catch can. If they become defective, the fix is to repair the system, not to fit a catch can - obviously. (Fitting a catch can is like taking Panadol for a brain tumour. It’s ineffective, but might make you feel better.)
At the regular services, the dealer should inspect the engine (and the EGR and PCV systems) to ensure they’re functioning properly.
All modifications come with what engineers call ‘feedback effects’ - inevitable changes to the system’s response flowing from some modification to the system.
(For example, upgrading to stiffer springs and stickier, low-profile tyres improves grip - the primary benefit. The feedback effects might include reducing the margin between grip and slip - meaning a sudden transition from grip to sliding, with less warning. Especially in the wet.)
For this reason, curing ‘maybe/nonexistent’ problems is a bad idea. Curing the nonexistent problem of oil blow-by with a catch can, which pressures up the system and blows a seal, allowing sump oil to escape could have the nasty feedback effect of catastrophic engine failure, and you will not be covered by warranty. In fact, engine modifications generally (and modifications to related systems) are a great way to give the manufacturer justification to deny a warranty or consumer law claim in the event of a major engine failure.
Here’s what happens in practise, if you fit a catch can, aftermarket air filter, piggyback engine control ECU ‘upgrade’, EGR ‘delete’, etc., and then your engine blows up: The manufacturer will throw you under the bus, and deny your warranty claim. You might think this to be unfair, but in fact, you will then need to hire a lawyer and commission an independent technical expert to determine the cause of the engine failure, and let a court determine who pays.
So, if you’ve got a 15yo Hilux and you’ve built it up to do mad off-roading, go nuts. But if you’ve got a new 4X4, for Christ’s sake, leave it standard, unless the thought of a $25,000 repair bill appeals.
I think a lot of these reports about clagged up engines are a consequence of never getting onto the open road and allowing the engine to function at optimum temperature in a lean-burn state, to de-coke itself and decontaminate the oil. ‘Chipping’ engines (altering the engine control ECU programming) is also an excellent way to get the engine overfuelling itself, from time to time which will cause a raft of related problems. Not getting the car serviced on time is also a risk.
If you drive every couple of weeks on the open road for about an hour, this purifies the oil, by allowing it to burn off any combustion byproducts that have blown by the rings and entered the crankcase. These contaminants are typically water and unburned fuel. If you let these build up in your oil, it reduced lubrication (bad) and also increases oil level, increasing the likelihood of overwhelming the PCV system.
If you can’t get out on the open road often enough, get your oil and filter changed twice as often. (Which would be at six-monthly intervals instead of 12 months, for most cars)
Finally, I’d suggest that when a catch can fills up with oily residue, many people view that as justification that they have cured a problem. In fact, all they are doing is collecting oily residue that the engine is designed to burn off as part of its normal operation.