weasley

Fast idle also helps compensate for extra electrical load (heater fan, a/c, heated rear screen, heated mirrors, heated seats (if fitted), lights etc).

When I did mine the car had towbar prep so I only had to remove the trim in the boot to access the pre-fitted wiring loom. That was a bit awkward but not difficult - sorry, I don’t know about the front trim.

Id recommend you don’t do it when it’s cold as this will increase the chance of breakage. And if you’re fitting a towing module it’ll need coding to offer all of the features.

The only broken spring I have ever had was on a Renault Mégane - there's no rhyme or reason to it, just a new normal.

Turbo piping?

I guess it’s a risk vs reward judgement. Had my Yeti five and a half years and used the hooks extensively. Never once had need of a spare wheel though.

The couple of times I needed parts I found getting them directly from a Skoda dealer to be the quickest and often cheapest option.

A bulk oil temperature of 150°C is pretty high, although still well below the maximum it would see in the engine. Of course if the bulk oil is hot that means it is getting heated up a lot somewhere around the engine, so it could be overheating there. Oil film thickness varies with oil viscosity, so a very hot oil will be very thin which will lead to a very thin oil film - possibly thin enough to prevent metal-to-metal contact. And as you discovered, an air-cooled engine is more accurately an oil-cooled engine. Even a so-called water-cooled engine gets a significant cooling effect from its oil.

Apologies if I came across as aggressive - absolutely not my intent. I have participated in so many oil topics on the internet over the years that I try to present who I am and how I know what I am saying simply to try and establish some credibility. I have great respect for engineers - I work with many and am interested in the subject, although am a chemist myself. I also tend not to say who I work for because I want to present factual, objective information rather than being seen as a sales pitch. Sometimes this means I have to bite my lip because I see people saying things about my company's products which I know to be totally untrue, but I have to be careful what I say as lots of it is confidential and to challenge any mis-truths may give away something proprietary. Not saying this is happening here, just presenting you my background and the decades of oil topics I have tried to steer in the right direction!

And just to present my credentials, if I may, I have been working in lubricant R&D for 28+ years for one of the well-known oil brands. I've worked on everything from motorcycle to ship engine oils, as well as transmissions, turbines etc.

A very cold oil will be thick, meaning a very thick oil film will form between moving surfaces. This balances nicely with a cold engine, where the clearances are larger and need a thicker oil film. However a cold oil will not be working fully - some of the chemicals used in it don't really activate until 60+°C, so although a cold oil will do a basic lubrication job, you won't get the full protection it can provide. Hence why most engine wear happens during warm-up.

That's how the nomenclature was first developed, but it isn't really like that any more. What you say is largely correct, but doesn't quite go far enough. The "5W" is saying the oil is behaving like a '5' grade would when cold and the "30" bit is saying it is behaving like a '30' grade would when hot. In this case a monograde 30 would be too thick when cold and a monograde '5' would be too thin when hot, hence the multigrade performance and nomenclature. In reality the two halves of the visc grade are tested under very different conditions. The 'W' (for "winter") number is tested under very cold conditions to determine if the oil can flow and pump when cold - one test is called the 'cold cranking simulator' (CCS) and one called 'mini rotary viscometer' (MRV). For an oil that is "xW-yy", the CCS is tested at -(35-x)°C and the MRV i tested at -(40-x)°C. An oil has to flow and pump effectively in these tests in order to pass them. The yy number is mostly derived from a simple viscosity test at 100°C (oil falling through a tube and timed between two marks).

Pretty close! Take a look here. Your "runniness" is effectively the inverse of viscosity.

As @Wino says, oil viscosity varies continuously with temperature, down to the point at which it 'freezes' and up to the point it boils or catches fire. The viscosity classification (eg 5W-30) gives some idea of how the oil behaves when cold (the 'W' number) and when at 100°C (the second number). 100°C is considered to be a typical bulk operating temperature but obviously in the course of doing its job the oil experiences a wide range of temperatures, from cold start to the top piston ring or piston undercrown. If you can look at the technical data sheet for an engine oil, the value that helps you understand the effect of temperature on viscosity is the viscosity index (VI). The higher this number, the less the viscosity changes with temperature. So, an oil with a VI of 120 will vary more than an oil with a VI of 150. If both of these oil have the same viscosity at 100°C then the lower VI oil will be thicker when cooler and thinner when hotter than this. The relationship is not linear - it is a fairly complex logarithmic relationship. I would consider an oil to be 'warm' around the 60-70°C mark - this is the temperature that some of the active ingredients really start getting to work properly. This isn't the final operating temperature and I wouldn't expect an oil temperature (measured in the sump) to stabilise here. In an engine the oil does warm up significantly slower than the coolant, largely because the coolant is thermostatically controlled and only the small portion within the block is circulated at first, whereas all of the oil is circulated all of the time, so is a significantly larger mass to heat and is exposed to the cooling effect of the sump. I recall that in my Yeti TDi the oil would just about reach 90°C on my 30 minute work commute in the winter and would cool noticeably during any time spent idling.

That’s automatic a/c - you set a target temperature and the unit blends warm and cold air as needed to achieve it. Manual systems just allow you to set a fixed ‘blend’ and adjust up or down yourself to achieve a comfortable temperature. From the symptoms I would have suspected a sensor, as described by @Scotwall.

Dunno - found the picture from an old discussion on here. Car is/was in Australia

Aah, I had missed the India context. Yes, I have experienced the night-time traffic of Mumbai, Delhi, Ahmedabad and a few other places - the use of lights does seem to vary between none at all to everything switched on to maximum! A pair of driving lights may well be a good solution.... something like this:

I always thought the pre-FL halogen lights were pretty good - I upgraded to some Osram Nightbreakers which made them even better. Check the aim is right too.

What towbar is it? Can you simply remove it?

I was just adding extra info with the backwards/dye/tracer thing, for interest. On the “00” thing, I have seen more than one person get confused between 508 00/509 00 and 508 88/509 99, hence why making the point. It is an unlikely mix up to make though since the latter spec is aimed at poor fuel quality countries.

Someone at the back wasn’t paying attention! Yes, you’re right that new VW engines get “longlife 4”, a low viscosity fuel economy oil based on ACEA C5 but the spec is 508 00/509 00. Unlike before, the new oil is not backwards compatible - the new oil can not go in older engines. To protect against this the 0W-20 oil is dyed blue (the blue dye mixed with pale amber oil actually makes it look green) to prevent misapplication and it also contains a tracer element, so that it can be determined after the fact if an engine had the correct oil in it. Both these factors are built in to the VW spec so are mandatory for any oil claiming 508 00/509 00.

Not necessarily. As I said, an oil could sail over the bar but get no extra credit for it. This is where the oil companies attempt to show how their oils are differentiated from others and hence worth the extra. Unlikely to be identical - even if a big name made the oil for another seller, they would likely not give away their ‘good stuff’ but would make something that just sneaks over the bar and is appropriately priced.

Quite! Another way to achieve an approved oil is to buy an off-the-shelf option from one of the major additive suppliers (there are only four globally). They will have done all the hard work and spent the significant amount needed on testing (multi-millions) and will sell it to a marketer who just needs to blend it in the right base oils and register it with VW. Or an oil blender may make it for other brands, hence why you can get Halfords or Amazon oil, since neither of them develop or manufacture oils.

“Fully synthetic” means that all of the base oil in the oil is from a nominally synthetic source. This can be either synthesised from smaller molecules (eg PAO and esters) or refined and then hydrocracked from mineral oil. The result is a base oil mix with high resistance to degradation and good high and low temperature viscosity properties. Any other synthetic term generally means the oil has a blend of some synthetic base oil and some mineral. However the important thing is the performance, not the ingredients. If an oil manufacturer can achieve high performance using good additives in a partially-synthetic oil then well done them. Bear in mind that the specification is like a high jump; all you need to do is clear the bar - you get no extra credit for sailing way over the top. That said, the VW specs are a pretty high bar to clear. Finally, the ‘ash’ created when oils burn comes from the additives, not the base oils. The additives contain elements such as calcium, magnesium and zinc, which form solid oxides when burnt. These ashes collect in the DPF along with the soot that they are designed to collect (soot is from partially burnt fuel). The regen process can get rid of the soot, since it is mostly carbon, but it can not get rid of the metal oxides as they don’t burn, hence they accumulate over time and eventually permanently block the DPF. The VW 507 00 spec has an engine test that specifically tests for DPF blocking and many engine oil specs include a ‘sulphated ash’ test limit; typically 0.8% max for DPF-ready oils.

I do. The VW 507 00 specification is a document published by VW and regularly updated. It includes all expectations of an oil that are required to be met in order to be approved. This includes a long list of physical and chemical laboratory tests (eg viscosity at various temperatures and shear rates, element levels, ash, pour point, volatility etc) as well as a list of engine tests that must be run and passed, looked at wear, piston deposits, sludge, DPF blocking, fuel economy etc. To hold a formal approval you must carry out all the tests at accredited test facilities, achieve results that meet VW’s limits, declare your formulation precisely and commit not to alter it beyond the limited variance that is allowed and then send all this data to VW with a fee, they will inspect and verify it, and if all ist in ordnung you get a letter of approval for that formulation under that brand name for a defined period of time. Only then can you formally claim to have a VW approval. Over time the approvals expire; they can be reapproved, which usually means a limited bit of validation work unless VW have updated the specification in the mean time, meaning you have to meet the new requirements which can mean the need to completely reformulate and start from scratch. Such changes are signalled well in advance though, giving time to get products ready for the latest spec version. Also worth mentioning that to achieve VW 507 00 you must have ACEA C3 and you have to also have VW 504 00 (for petrol engines), hence you will (or should) always see an oil with VW 504 00/507 00, which is collectively and colloquially known as “VW longlife 3”. Finally, be careful with the spec numbers. The full specs are 504 00 and 507 00, not just 504 and 507. In this case it is not a problem as there are no other 504 or 507 specs, but there are some VW specs that have the same first number and different suffices, making a huge difference. For example there’s 505 00 and 505 01 and more recently there is 509 00 and 509 99, which are vastly different specs.