Oil Catch Cans. Is It Worth Fitting One?
 

I keep reading about various ways of cleaning the internals of engines (carbon cleaning, seafoam, Terraclean, walnut grit) due to the buildup of carbon, which has been made worse in recent years with the re-circulation of exhaust gases through the system.

I'm just wondering if it would be worth installing an oil catch can, to at least try and capture some of the muck that is being re-circulated back through the engine, rather than it going through the system and being baked onto the engine internals.

I think catch cans are for the 1980's and before. Our cars already go one better than that - the oil separator with a sort of Dyson tornado inside that captures it and drops it back into the crankcase, a catch-can was a predecessor that just had baffles and filled up until you emptied it.

The oil vapour is fairly harmless as long as there's not too much of it. The exhaust gas recirculation (EGR) is the real problem as it mixes soot from the exhaust with hot oil to make tar. EGR is a particularly stupid response to emissions control since the tiny impact it has on warm-up times and emissions output is completely wiped out by the loss of efficiency and performance once it's blocked up the inlet tracts.

Pre-EGR engines (D2) got a little dirt on the throttle body and in areas of stagnant airflow in the inlet tract, but even at 200K performance is barely affected. The best thing you can do with an FSI or TDI engine is to disable the EGR in software and then remove the inlet and manually clean out all the crud. With the EGR disabled it won't build up again.

Hmmm! Sounds like something to consider. I'm thinking specifically for the D3 S8.

I asked ECS Tuning in USA this very question (they sell a catch can kit). They told me it wouldn't make much difference on the S8.

After getting the carbon cleaning done, I've taken to using Wurth intake cleaner ever thousand miles or so as a preventative measure. I was surprised that, after my first application, 3000 miles after the physical carbon clean, I could feel a difference. That implies that carbon had already began to build up again.

Cheers for that. Nice to see a seller tell the truth about the products.

Pardon the pun, but it may be worth me trying the intake cleaner, at least on the 4.2 daily to begin with. The S8 doesn't get driven that much, and will soon be going under wraps for the winter.

It seems I am mistaken on this as the FSI engines don't have EGR, contrary to many threads on the various forums. Lots of people call the secondary air valves 'egr valves' since they're in a similar arrangement to EGR valves on diesel engines, but in fact they work completely opposite to EGR. It appears that the FSI engines are in fact no different to the port-injection engines in this regard so all the crud that builds up is purely from oil vapour! Colour me surprised.

In that case, a catch can may actually help, but only if it removed all the oil vapour, which can be quite a challenge. Looking at the SSP for the 4.0TT it seems Audi have gone to much more trouble to achieve this separation than in previous engines to try and solve the problem. There is an aftermarket device which is commonly used on marine engines called the Provent, made by Mann & Hummel, which is also quite popular with the TDI crowd. If there's any space under the bonnet of a D3 S8, this might be worth investigating:

http://forum.a8parts.co.uk/attachmen...1&d=1544968511

This may be one of those instances where I might just try it myself, and see what the results are like. Having watched countless videos of oil catch cans in use, I don't see why anyone would want to see this crud being fed back into the engine, if they had a choice. Fair enough, it isn't standard equipment, and then becomes a serviceable item, but if it helps reduce the build up of crud over time, then it might be worth trying.

One of the names I came across for 'quality' oil catch cans was Mishimoto, and emailed them a while back, with a recommendation from them on which of their models to choose from. I'll have to do some more reading on the ProVent, but a quick Google shows them as costing around the same £120 mark.

Since the S8 doesn't get used much, I might even put it in the 4.2 D3, as it's more of a daily use car. If it functions and manages to trap a significant amount of oil, then I can contemplate adding it to the S8 as well.

Honestly, I never thought about oil tanks, but I can't say anything.

I learned a little lesson from someone on here about EGR on the D3's (and presumably other FSI engines) where the valve overlap between exhaust and inlet strokes is such that some exhaust gases remain in the cylinder for EGR purposes.

EGR should have been fitted to all petrol engines since the 70's. Its purpose is to reduce the production of Nitrous Oxides formed during high combustion temperatures (by reducing combustion temperatures). It does so reasonably successfully, but at a cost to engine efficiency.
So far as emission requirements are concerned, the D2 should have EGR in some form. But in the case of the D2, the indirect injection helps to wash the inlet valves with solvent (petrol).