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Idly browsing used cars cos I'm bored.
SCR diesel engines (the ones with ad blue or whatever it is in VW world) are only on the newer cars which are around £20k at the dealer - older cars without it are more the sort of price I'd be looking at, around £15k. I say old - 4 years and 30k miles isn't really old.
I like the idea of SCR because it results in less pollution and in theory better engine performance as stuff like EGR isn't necessary, or not as much; and the previous generation of engines are the ones affected by the emissions scandal I think so they are either polluting or knobbled. Is there any real-world difference, in terms of driving, efficiency, refinement etc?
I was looking for a VW van last year and deliberately got a lower mileage 2016 T6 van with the 140hp non adblue engine rather than a higher mileage newer 150hp adblue engine.
Not 100% sure why but guess didn't want adblue as just felt it was something else to go wrong. Maybe a stupid attitude, will let you know in a few years time!
are the older ones euro6 compliant? I'd be careful of buying a euro5 engine depending on where you want to drive it.
I think it's less to go wrong tbh. On paper, it's a better solution than EGR in all respects.
Hmm, apparently VW TDI SCR engines also have some EGR.
I've got a 2.0 TDi AdBlue engine in my Superb, I don't know if it's SCR, that's a new one on me.
Anyway, the engine is great, a good spread of economy and performance if you want it. It's a bit annoying when the Adblue warning pings as it gives you about 2000 miles notice, and it's loud bing and warning symbol, but it's cheap and easy to buy. I bought a massive container of the stuff in ASDA for £8, it'll last me 6 months or more.
molgrips
Full Member
I think it’s less to go wrong tbh. On paper, it’s a better solution than EGR in all respects.Hmm, apparently VW TDI SCR engines also have some EGR.
this!
A lot of engines need SCR, EGR and LNT to comply wit Euro 6b+ and will need them for Euro 7 probably. That said Isuzu have got a PU that is managing without SCR.
P-Jay
Free Member
I’ve got a 2.0 TDi AdBlue engine in my Superb, I don’t know if it’s SCR
AdBlue = SCR
I’ve got a 2.0 TDi AdBlue engine in my Superb, I don’t know if it’s SCR, that’s a new one on me.
Not sure if adblue is a trade name or something, but yes it's the chemical that's added as part of the SCR process. I think the generic name is DEF?
Your normal catalyst works by using the residual air to burn off the residual hydrocarbons. SCR works in the same way for NOx, but needs Urea adding instead of air.
AIUI the EGR works at low engine loads but has to close at high loads, which is when SCR kicks in. In principal I guess it's possible to build a big lazy engine that can do without it. But then you run against other constraints like fuel economy which favour smaller engines with larger turbos.
Not sure if adblue is a trade name or something, but yes it’s the chemical that’s added as part of the SCR process.
Ah cool, yes Adblue is a trade name, manufactures have to pay to use it.
My Superb has 'AdBlue' on the cap, but I'm sure the dash warning uses the generic "DEF", my mate's Hyunadi only uses DEF.
SCR = Selective Catalyst Reduction, with the primary thing is catalyses is NOx.
AdBlue is just a name for the Urea solution used as part of the process.
EGR also targets NOx, by reducing combustion temperature to lower than the temperature at which NOx is produced.
Anything Euro 6 with SCR, still needs EGR to ensure NOx levels are maintained until the SCR system is up to temperature and working, at which point EGR can be reduced allowing higher combustion temperatures. I say reduced, as it's still used as part of the measures to ensure combustion temperatures don't reach valve and piston melting temperatures.
Whether to chose between something with or without SCR, I probably wouldn't let it sway my decision. It's like lots of other systems, the vast majority work without problem, but you do always risk the chance of something expensive failing.
Out of all the cars/vans I see with AdBlue problems, they've always stemmed from driver misuse. Usually something being ripped off, or far more likely, they've let the system run dry to the point the vehicle enters non-start.
Lorries on the other hand, any faults are likely to be a failed NOx sensor, at £600 a go to replace.
If you want it for the emissions improvement then it is probably worth getting one compliant with Euro 6b (manufactured after late 2018 I think). Some euro 6 ones had it but only used it in the situations needed to get through the emissions test. Euro 6b introduced a real world element to the test so it has to use the system a bit more often (although it’s still not perfect - ours doesn’t seem to use any when towing). It means topping up between services (which our old euro6 VW didn’t need) but I prefer to stick some in every few months and spit out less NOx.
Wikipedia suggests that all B8 diesels are SCR but the used car search on Sinclair lists SCR separately in the model name.