Oil Catch Can - Positive Crankcase Ventilation

TL;DR Keeping the intercooler clean

It will soon be 4 months that I'm Caterham-less, lovelorn with the car now in need of the aluminium bonnet be properly prepared and painted in the right colour as the paint shop messed up.

Anyway, I had the opportunity to look at my original intercooler one afternoon at House of Speed, and found it rather oily and disgusting inside. I was told it was nothing unusual, and I know for a fact that my engine does not consume any measurable quantity of oil.

Spending zero time driving around gives me some extra time to think and go deep into that kind of matter. So I did.

What happens is that the PCV system (positive crankcase ventilation) is just an small hose that goes from the top of the camshaft cover to the air intake. Wikipedia says those systems were invented during WW2 to allow deep fording with tanks. I confirm there is a small hose between the oil dipstick tube and the air intake on my WW2 Jeep too.

An effective solution for a closed-circuit ventilation of the crank case, with the following effects :

✅ the crank case is not under pressure from unavoidable leaks of the piston rings (even more of a concern on a turbocharged engine)
✅ no humidity from the exhaust gases remain to transform the engine oil into mayonnaise
✅ no oily mist is vented to the atmosphere or in the engine bay
❌ all that oily, moist and sooty crap is fed to the turbo and gunks up the intercooler, making it less effective at exchanging heat
❌ said crap also gunks up the cylinder head and intake valves - on a direct injection engine there is no gasoline flowing and keeping everything clean up there
❌ burning those fumes could decrease the octane level and increase the risk of detonation

A good solution seems to be an in-line non-ventilated, 2 ports oil catch can. I got one with internal baffling and a filter. With 300ml capacity volume, it is quite compact (imagine a Coke can...) but surprisingly heavy, more on that later.

It will be inserted in the path between the valve cover and the hose that goes to the air intake, and should keep most of the gunk out of the intake by condensing it in the pot while remaining compliant with the regulations that ask for a closed circuit.

One downside is that it will need to be kept  in check and emptied once in a while. It's probably not an issue on a Caterham on which the engine oil is replaced every 5000 km; but I can see why this is not installed on all passenger cars that run 30 000 km between oil changes.

If you want to know more about all that, have a look at those two YouTube videos from Engineering Explained : "What is an oil catch can ?"  and  "Do oil catch cans actually work ?".  This comparison was also very intersting. Funnily enough, the one I got is closer to the one in that 6 years old video than the one on the Aliexpress listing.

My first idea was to treat myself (once more) with a nice branded one. But at 10 times the price of a virtually identical item available from Aliexpress, I went for the cheap option. We're talking a whole 14€ VAT and postage included.

I placed the order on a Friday and the kit arrived on the next Wednesday morning, their logistics are really impressive.

Build quality is good but it will need to be cleaned-up a bit, as there are a few burrs and metal shavings left and right. You wouldn't want any of that in your air intake and turbo.

Measurement time : the "baffle" grid is about halfway down the pot, only leaving 80 ml of effective capacity. I should probably shorten the support and get it closer to the head of the unit and aim at 120ml or so. In the beginning it would probably be good to monitor it every 1000km or thereabout to get an idea of how fast it fills up.

Regarding weight, we're at 398g with an extra 30g for the (metal) hose fittings(*). I think the branded model comes with plastic fittings, I will look into that.  The pot itself is 116g of which 14g for the large grub screw used as a drain plug(*). Let's find a nylon one. Top bracket is only 20g with screws. Head unit with filters is 262g, I'm sure we can remove half of that with the CNC, and shorten the thread of the brass mesh filter too.  (* note for future self, plug is most likely 3/8 NPT and hose barb fitting would be M16x1.5 thead to 1/2" hose)

Materials are :
- aluminium : pot, head, barbed fittings, circular baffe, standoff (35mm long, 8mm hex with a M6 thread)
- steel : mounting bracket and screws, internal "flaps" plate, drain plug
- brass : "50µm" filter with support 

My plan is to 3D-print a prototype for a bracket that would be attached using the screws that secure the bar that carries the expansion tank across the engine bay. Or there might be some available threads on top of the pedal box, let's see. Once happy with the layout, we will CNC a carbon fibre version. 

All I know it that it must be kept away and safe from the exhaust system as we're dealing with flammable fluids.

Update on Aug 25th :
- I have since drilled a third M4 hole on the top and sourced M4 x 6mm stainless steel screws (painted black) to attach the pot to its bracket. The latest version of the band-name one has that upgrade, so why not.
- About tubing, I actually have about a metre of 12mm silicone hose I bought to cover the greased tie rods threads, a perfect fit to the pot barbed connectors.
- On the engine side, Caterhamparts.co.uk shows that the end of the hose is 14mm. So should be the nozzle on the cam cover. Not an issue for the silicone hose asthe wider part of the barbed connectors is 14mm too. I've ordered a 12mm to 15mm adapter to connect to the air intake hose. I'll propably need to grind the wider part down to 14mm as I don't expect that part to have any elasticity.

Update on Sep 3rd :
- Grinding the 12mm to 15mm adapter was not necessary, I had to cut it short to a length similar to the connector on the cam cover (ie remove 2 barbs).
- In order to add rigidity and be able to curve the engine hose at a steep 90° angle, I've inserted 12mm OD springs in the silicone. I got a pair of 300mm long 12mm dia. (0.8mm wire) compression springs from Amazon, and cut one in half, using 150mm on the end of each hose on the engine and air intake side. The spring even goes down the 14mm connector of the cam cover, that's a perfect fit.
- The catch can itself is attached on the battery bracket, using a pair of 2mm aluminium bars with 5mm holes, and a pair of screws+nuts.

Update on Sep 21st :
- Two days ago I was still doubting the necessity of the oil catch on my car as nothing had been collected in spite of the 1500km I had driven already.
- Today, 1800km in, I see that it did finally collect some expected mayonnaise. I don't know if it took all that time to build up crap in the silicone hoses that's now pooling into the pot, or if the lenghty motorway drive is somehow involved.