General Auto stop/start

[Panda2023]

Hi Everyone. Not sure where else to post this, so here goes:

Just took delivery of a 71 reg XC90 B5. It is the "early 2022" software edition.

That particular build deleted the ability to disable the stop/start function.

...Volvo dealer told me there is nothing THEY can do....but there are people who can program it to stay off (at least until they update the software). They also said it may affect the remaining new vehicle warranty here in the UK.

As it spends most of its life on motorways, my biggest fear is driving fast then exiting to a set of traffic lights.....and presto... the engine switches off and stopping the lovely lubricating oil from circulating around the engine and turbocharger. I can see a problem with this particularly on the turbo, and particularly after a fast drive, it will be running quite hot. I just want to avoid at all costs repeating what happened to my RangeRoverSport a few years ago.

The stop/start can be stopped by depressing the brake and the throttle together...but that gets tedious really quick.

Someone online calculated (using published assumptions) that the stop/start system will save on average £2.67 per year in fuel. Which as we know can be completely obliterated by fast or spirited driving. It does nothing for the "environment" and "climate change".

Question:

1. do you have this concern/fear?

2. do you know anyone who can permanently disable this system?

Many thanks,
Andrew
2022 XC90 B5

[racerx67]

I don't worry about this issue to be honest..

But I understand some of the issues you feel may be a problem.


So the first one with the turbo spinning and not being lubricated is a non issue to be honest. The turbo impeller is a low mass part so is quite responsive, that small amount of turbo lag you feel is that mass effect taking a moment to spool up. So as you slow down the exhaust gasses also have less pressure to create any boost so the turbo will slow down significantly as you slow and will be spinning at the same speeds as it would if you had been driving slower and come to a stop. So the worry about a lack of lubrication is not so much an issue.

OK so to the driving the car fast, I don't know what you feel as driving fast as for some driving fast can be very different to someone else's idea of that. Continuous high rpm close to the red line is what I would call driving fast and 99% of the people I know would never actually push a car that hard on the road. The heat from that kind of driving will be significant through the exhaust side of the turbo but again much of that can be self regulating as the turbo also has a cold side with the alloy intake side acting like a heat sink. The bearings are just a plain bearing so they do get a good oil supply and compared to a much higher revving performance engine the volvo is not really a highly stressed engine with a turbo putting high levels of boost through it. The volvo engines will keep the engine fan running for up to 6 minutes after the engine stops to stop heat soak from hot engine parts causing problems and this includes the turbo. If the 2 litre engine was a fire breathing high boost 400 bhp+ engine then it would be a bigger concern.

My background is motorsport both as an engineer and as a competitor. So I don't mean to cause offence if you feel I am not saying you do actually drive fast enough to cause these issues, it is just I know personally only a hand full who could or would push a car or bike hard enough to actually risk engine issues with constant high RPM. Issues can happen with any turbo over time but most of those issues are either maintenance issues or manufacturing issues. I have worked with a few turbo engines from a 1.9 litre 115 bhp Renault diesel through to a 1400 cc 350BHP motorcycle. Both of those examples had different issues. The bike had the turbo centreline mounted lower than the oil level and would leak oil out of the turbo at low RPM when there was not enough gas pressure to overcome the oil pump pressure too and we needed to fit a scavenge pump to actually pump oil away from the turbo into the sump when the engine was running. We had no issues with too little oil on that very high revving (compared to a car) engine. The Renault was known to have turbo failures and we had a brand new turbo break the impeller shaft within 20 miles of being fitted. The only other time we saw a turbo fail was in an engine that had been used for towing and had been worked hard and had done over 120,000 miles with suspect service intervals.