Folks -

If anyone has any informed opinion here, I'd be grateful...

I've got an '09 plate FL. It's set to variable servicing, or at least was... when it had a service last year at about 18k, the dealer must have used the dashboard to reset the service interval, and it reverted to fixed interval. So, when it recently started shouting for a service near 28k, I took it in and they simply reset the counter - which means it now yells at me every single time I start the car. Their reasoning was that resetting it to variable (or "long life", as they call it) now would make the car think it's been serviced, and reset all its counters, meaning the next service would come anything up to 10k too late... better to leave it another 9.5k or so, then service it properly and move it back onto variable as intended.

Any comments? This sounds plausible, but I thought variable triggered on time since last service (2 years) *or* oil gunginess, so surely it should kick in when the crap level reaches a relevant level anyway. Alternatively, is there any likely problem replacing a variable interval with two fixed 9.5kish intervals?

Cheers...

You would be ok leaving it until around 18k but what the dealer should have done as they didn't do it right in the first place is give you a free service at the 10k and reset the counter properly back to variable.

Any comments? This sounds plausible, but I thought variable triggered on time since last service (2 years) *or* oil gunginess, so surely it should kick in when the crap level reaches a relevant level anyway. Alternatively, is there any likely problem replacing a variable interval with two fixed 9.5kish intervals?

Cheers...

That is not how variable works. There is no measurement of oil quality. It simply records how you drive the car and reduces the counter accordingly. It uses an algorithm that reduces the counter more quickly when driving cold or on full throttle than it does when cruising along the motorway at 70mph.

So, for example, you may drive 300 miles in a single trip and find the miles to service has only reduced by 250 miles but during winter with lots of cold starts and short journeys 300 miles driven could reduce the miles to service by 350 miles. Those numbers are not exact but give you the idea.

My experience with service interval resets over 4 years of Octavia ownership is that if you are on variable service then there is a 50/50 chance that when you get the car back it will have been reset to fixed! On 2 services I had to take it back to have it reset properly.

My current car is on fixed and due a service in 700 miles - still trying to decide whether to keep it on fixed or switch to variable.

That is not how variable works. There is no measurement of oil quality. It simply records how you drive the car and reduces the counter accordingly. It uses an algorithm that reduces the counter more quickly when driving cold or on full throttle than it does when cruising along the motorway at 70mph.

So, for example, you may drive 300 miles in a single trip and find the miles to service has only reduced by 250 miles but during winter with lots of cold starts and short journeys 300 miles driven could reduce the miles to service by 350 miles. Those numbers are not exact but give you the idea.

My experience with service interval resets over 4 years of Octavia ownership is that if you are on variable service then there is a 50/50 chance that when you get the car back it will have been reset to fixed! On 2 services I had to take it back to have it reset properly.

My current car is on fixed and due a service in 700 miles - still trying to decide whether to keep it on fixed or switch to variable.

There IS a measurement of oil quality as there is an oil sensor that monitors this. It does also go off journeys etc but I'm afraid it does monitor the quality of the oil.

They can stop it shouting at you every time you switch on ignition - I got fed up with the whole saga of fixed and variable they never seem to set it right, usually find it is fixed when you thought variable etc.... same on all 3 Skodas I have owned...

There IS a measurement of oil quality as there is an oil sensor that monitors this. It does also go off journeys etc but I'm afraid it does monitor the quality of the oil.

Does anyone know what kind of sensor it is that measures oil quality and where it is mounted ?

Details are sketchy but it monitors the soot levels and the temperature, as in the time taken to cool down and heat up......the longer it takes the worse the quality of the oil. One would presume that the sensor is in the pan.

Details are sketchy but it monitors the soot levels and the temperature, as in the time taken to cool down and heat up......the longer it takes the worse the quality of the oil. One would presume that the sensor is in the pan.

It monitors the temperature as this is a key part of the algorithm - you get the readout in maxidot. That is not a measure of oil quality though.

The fixed service interval is a very crude miles or time method. The variable refines this by taking advantage of huge improvements in oil technology to allow a longer interval and monitors how the car is being driven to fine tune this longer interval - it reduces miles to service based on how long the engine is driven with cold oil (hence the temperature monitor), length of journeys, time spent idling in traffic, time on full throttle.

As a chemist I would be very happy to be proved wrong on this and very interested to know what type of sensor is being used to detect soot in oil. Others have suggested in other threads that it monitors oil viscosity but as far as I know viscosity cannot be measured by use of a simple "dip" sensor - if it can then please let me know because the in-line Brookfield sheer viscometers (the size of a small alternator) we have in our processes at work are a PITA to maintain & calibrate and Ford flow cup measurements are messy! I would love a simple dip probe :yes:

Edit

As I have confessed elsewhere I am something of a data collection geek!

When I had my last 1.9TDI on variable I monitored the miles to service against mileage:

7 Aug 2009 mileage 38188 - miles to service 8000

14 Aug 2009 mileage 38997 - miles to service 7500

That was motorway mileage for a holiday in Dorset. So I drove 809 miles but miles to service dropped only 500. Even accounting for the fact that miles to service is reported to nearest 100 miles I still "gained" 100 miles from somewhere. No sensor cheap enough to mass fit in vehicles is going to detect oil quality change over 800miles - that is an algorithm at work.

Edited 18 June, 201115 yr by eccleshill

Happy to be proved wrong even if I do it myself

Done some research (ie used Google) and found references to oil quality monitors that use the dielectric constant of the oil to measure contamination and degradation.

Here is one:

http://www.gillsensors.co.uk/content/datasheets/Oil-Quality-Sensor-Datasheet.pdf

and more here

http://www.marcusfitzhugh.com/CLK/DIY/oilchk.html

That said, I am sure that the sensor is only part of the picture - an algorithm is also in place that probably does most of the work and takes the monitor output into account as well as driving conditions.

Clever stuff eh?

A'int science wonderful

In my youth you just used thicker oil when your engine started to smoked more - till the time you eventually rebuilt the engine or scrapped the car

Happy to be proved wrong even if I do it myself

Done some research (ie used Google) and found references to oil quality monitors that use the dielectric constant of the oil to measure contamination and degradation.

Here is one:

http://www.gillsensors.co.uk/content/datasheets/Oil-Quality-Sensor-Datasheet.pdf

and more here

http://www.marcusfitzhugh.com/CLK/DIY/oilchk.html

That said, I am sure that the sensor is only part of the picture - an algorithm is also in place that probably does most of the work and takes the monitor output into account as well as driving conditions.

Clever stuff eh?

Yeah the sensor is only part of it, but it does have one! It takes into account the length of journies and number of cold starts etc.