Piston Slap: Snowballing Concerns with Auto Start-Stop Systems
Greg writes:
I just read your article about someone wanting to disable their Start/stop function.
I have a 2022 MB GLS 450 (with the M256-E30 DEH LA-R, in-line six engine) with the ISG (Integrated Starter-Generator). My concern is that the engine oil does not lube the turbo bearings when the engine shuts off.
I read that MB did include an electric water pump to keep coolant flowing, but I could not find any information about oil pump flow. I keep my ISG off to safeguard the turbo bearings. I have noticed that when I have not manually turned off the ISG, under some conditions the engine will maintain a slightly higher RPM or may even re-start even when stopped.
Perhaps, MB has allowed for some conditions when the engine should not be off. My issue is when exiting a highway and then stopping at a red light, waiting for my turn to continue. This is when higher RPMs were present and then an immediate stop. I’m hoping for a good solution.
Sajeev answers:
Just so everyone is on the same page, running the engine to let the turbocharger’s bearings cool down is a real concern. It even resulted in an aftermarket solution called the Turbo Timer. The value of such a “cool down” has been deemed irrelevant with the advent of water-cooled turbochargers. That’s provided you change the oil and coolant regularly and don’t run your car in a 24 Hours of Lemons endurance race.
My confidence increases because I suspect Mercedes has another solution in place—as you’ve noticed, the system will restart when necessary. Finding documentation is difficult, but oil temperature is likely one (of the many) variables that factor into the ISG’s system tuning, with a measurement taken from the oil temperature sensor.
Something like an electric oil pump (similar to the aforementioned water pump that remains active) would theoretically be nice, but odds are it’s unnecessary. And implementation would be nearly impossible, as all vehicles use a mechanical oil pump buried within the engine. Even a complex and expensive dry-sump design still needs a mechanical pump at the bottom of the motor to get the system primed and pumping.
Mercedes’ ISG system (and all the others like it) are already exceedingly complex, and engineering a workaround for the oil pump introduces more points of failure. If there’s one place you want less complexity, it’s the oiling system. Failure in this area is far more likely to cause permanent engine damage, so the solution for you is simple:
- Trust Mercedes’ ISG programming to keep the engine running when oil temperatures mandate it.
- Change the oil and coolant regularly.
- Don’t skimp on oil quality.
- Do an oil analysis test as often as you need to ensure your vehicle is operating in a healthy manner.
- Have the “plumbing” for both oil and cooling systems inspected on a regular basis, and fix leaks to the system as soon as possible.
All this talk is enough to make me want a new EV over a new turbocharged vehicle. But that’s neither here nor there, so now I leave it up to the Hagerty Community to chime in!
Look this feature is done to get a government credit so they can still sell you a more powerful car. With out it you would get a smaller and less powerful engine in many models.
The Button in most shuts it off.
The turbo issue is more to do with poor care and in some cases low quality units.
I drove my turbo for ten years with no issues. Good proper oil and changing it was all I did. No cool down times no other games.
Water cooled housings and synthetic oils were game changers.
This is more a political issue. So understand where the people you vote for stand on issue involving your vehicle. If you are missing on this what else are you missing.
Read this on off cycle EPA credits. Also Google it. It is something we all need to understand.
https://arpa-e.energy.gov/sites/default/files/Hula_EPA_2018_04_13%20ARPAe%20off-cycle.pdf
Many of us know. Just like “flex fuel”, but the E85 pump fuel isn’t 85%, it’s all over the map, but the MFR got fuel economy credit.
I’d rather pay a gas guzzler tax and get what I want. Which is exactly what I did.
You’re on to what’s behind everything in these comments. The EPA minions spend their days refining rules that defy logic. Taken together, the average person is being overwhelmed with changes that affect every aspect of life…
Have you heard the one about gas cooktops??
I did a lot of work on start-stop systems for a major OEM. I’ve driven a number of different akes with this feature, they all have their own way of accomplishing this goal.
Reading these comments brings me back to intervening many owners and hearing many concerns
First, a simple solution in most cars is to slightly release the brake pedal when stopping or stopped to allow the engine to restart if you are really concerned about lubrication. You can quickly adapt to this if you want to, although I understand you may not be so disposed.
Also, if you are looking for a new vehicle, a hybrid can remove any concern about the car re-starting because the battery power allows a quick & smooth takeaway when the light goes green. Again I know this might not be appealing to some
I really like the brake pedal trick. Thank you for sharing!
I have often made a game of the soft stop. I try to stop and soft on the brake to keep it from kicking in.
To be honest I got tires of turning things off so it gave me time to play with it and find the limits.
The lack of knowledge here is the greatest issue.
Auto stop/start is an unnecessary evil from those who want to tell us what to do. Its all about EPA gas ratings. If turning your car off for a minute or so saves any gas at all I’ve never realized it on MPG on my cars. But, I have burned through starters. I could never find how to disable it on my Charger and put in two starters in 93,000 miles. Currently have a Cadillac CT5 550T and an XT4 and both have a button on the console. I just hate having to push it all the time.
My bigger concern has been committing to cars that are turbocharged. Cadillac recommends/requires synthetic oil which I’ve been using. XT4 has 52,000 and CT5 has 21,000. Both are doing OK. CT5 gets 93 grade gas and all on line discussions I’ve read say to stick to that for the twin turbo V6. So I do. I do think modern turbo design is better. I had a 1987 Pontiac Sunbird GT Turbo back in the day. What a screamer of a car. Turbo took it to 165hp from 96hp. But it did it without an intercooler or other wise system add ons. So despite 2500 mile oil changes that turbo puked at 34,000 miles. When it was replaced, I had a post-oiler installed. Car went from 4 quarts to 5, and the extra quart would go in a reserve bottle when you stared the car. That was stored, mostly cold, and when you turned off the car a check value would open and cold oil would run over the bearings while the turbo itself spun down. Those turn at 100,000RPM+ and don’t stop spinning just because you turned off the car. So without an oil supply the bearing could burn and coke the oil. Mine did and there was nothing to be done about it. Just a bad design, or one that with more known about them now they are designed differently. I still idle my cars down before turning them off, not sure if that’s needed anymore but it can’t hurt. But with all the systems things on each of them, not sure I will run either one past 100,000. There is comment about longevity of modern cars in comments above this one and I think they have merit. So much in expensive hardware on cars today that future exposure to costly repairs seems inevitable, not a “what if”.
So, are there no downsides to the A.S.S. in a non-turbo car? I checked with my mechanic and he reports no increase in the frequency of starter replacements since A.S.S. has become popular in the last few years.
My concern about the start-stop system is that it has its own battery, and what else, if anything, is on that same battery. My 2018 vehicle has had 3 new “auxiliary” batteries replacing dead ones. Granted, the first couple were on warranty, but now have been driving with the start-stop light on the dashboard lit for the last 7 months. Mileage has gone down, so there is concern there, but question if there is any cost saving, replacing the battery versus fuel saved by having the engine shut down at road stops. The other question still looms big, as to whether or not there is anything else on the start-stop circuit that needs that battery. If nothing else is on that battery, it comes to a cost analysis as to whether the cost of fuel saved outways the cost of the battery. At present, I have no definitive answer, so the start-stop light stays on.
I can’t stand these things. Thankfully none of my cars have this system. My Dad turns it off on his car every time he starts it. Doesn’t like the stumbling start it does everytime it restarts.
My wife’s car is a 2019 MINI Countryman (189hp flavor) fitted with the foolish stop/start device, but the 2019 year model was the last to feature a dashboard toggle switch which permits the driver to disable the feature outright. My mechanic claims that these stop/start devices have pretty conclusively been linked to premature starter motor wear and failure.
FWIW.
B
Your mechanic is just making up things to support his bias. It is well known and well documented that the starter motors in vehicles with auto start/stop are much more robust than those without and real data has shown that they last *longer* on average, even with auto start/stop in use all of the time.
Our 2022 Clubman S has a off toggle switch. Once you are used to the system operating, I really don’t find it to be a big deal
I’ll just leave this tidbit here:
If auto start/stop was installed on every vehicle on the road today, and if it yielded *only* 1 MPG improvement in fuel economy, a conservative estimate is that over 7 BILLION gallons of gas could be saved. Thou shalt not complain about the cost of gas nor foreign oil dependence if thou complainest about auto start/stop and other fuel-saving technologies. All of the easy efforts for improving fuel economy have been done. It’s about finding 1 MPG here and 1 MPG there now.
The ASS system on my wife’s 2017 Buick Envision drove me nuts to the point I considered selling the car before I found a module that plugs into the wiring harness going to the hood switch that disables it. The shudder you felt every time it started made you think the car was falling apart. Much happier now. My 2020 XT5 also has an auto start system that you have to turn off every time the engine is started and which has become a part of my engine start routine, but at least it can be disabled with the simple push of s button on the dash. I must say however, that in the event I do forget to turn it off, the restart is much smoother and less noticeable on the 3.6L V6 in it than it was in the Buick 4 cyl Turbo.
Thank goodness we have older vehicles so no worries about turbo charged engines or automatic stop/start and all the other gadgetry.
Yep – these systems have become so complex – I’m reminded of the Arthur C. Clarke quote – “Any sufficiently advanced technology is indistinguishable from magic.”
My 2024 Integra Type S has no start/stop system, thankfully. Worrying about the turbo bearings isn’t even half of it. Every time it shuts down, there’s a brief period of no oil pressure to the engine bearings. I’ve seen numerous information bulletins from many manufacturers that are studying bearing wear on these vehicles.
I’m glad I got two of the last “large” displacement naturally aspirated V6 vehicles available from Honda. I still go a little overboard on oil change frequency (at 30% oil life), but I keep ‘em long term.
As for EVs, they can keep them. I’ll hold out until hydrogen ICE becomes a reality.
I have found (at least with my 2021 Explorer) that if I brake lightly and do not “mash” on the pedal, the auto start/stop does not engage.
24 hours of Lemons 🍋 🍋 endurance race? Pleas tell me this was an automotive pun, and that you know the race is the 24 hours of Le Mans. BTW, I hate that start stop feature. If a car doesn’t have a way to disable that, I wouldn’t buy it.
It is a pun, there is a race called Le Mans, and here’s a third thing I’d like to show you:
https://24hoursoflemons.com/