Turning a diesel engine on and off - harmful?



My boyfriend has an '81 VW westfalia van. It’s diesel. In these days of energy conservation and global warming I insist on turning the van off while he runs into the store, even if only for a few minutes. He claims that turning the engine on and off is harmful to the starter because it’s diesel. I just want to find out if he knows what he’s talking about.

I did some research and found that the emissions from a light-duty diesel van are much, much lower than every other vehicle except a light-duty diesel car.

I was surprised at how much lower they actually were.

So he may be right about this one.

The answer to this final question may be the deciding factor.

Thank you in advance!


Wow… a diesel vanagon that’s still running! Congrats!

Click and Clack get this question every so often and their answer is usually that the woman is right. There is nothing particularly harmful about leaving it running for a few minutes-- the amount of diesel used and pollution created is basically negligable. Nor is turning it off and starting it back up going to significantly shorten the lifespan of the starting system, diesel or not. Each of you can keep doing what you’re doing and quit worrying about it.

As for the emissions, there’s different kinds of emissions that come out of a tailpipe. The ones that used to be the main concern were the particulates, which create smog and other air-quality issues. Diesels, especially the older ones, produce a lot more of these. What’s arguably the bigger concern nowadays are the greenhouse gasses, specifically carbon dioxide, which diesels emit less of because they usually burn less (carbon-based) fuel than their gasoline couterparts.

The particulate emissions are more of a local issue, so if you live somewhere like LA or Phoenix, you may be able to argue that every little bit of soot your van doesn’t chug out while he runs in is a little bit less brown the sky will get.


Diesels have a very high compression ratio so they are hard on starters. But they use very little fuel when idling, truckers leave their diesels running all the time except when they will be down for days at a time.


I wouldn’t worry too much either way. Diesels have very little fuel consumption/emissions at idle. Starting them does put a little higher load on the starter/battery, but they are designed for it.


This isn’t true with newer trucks. The newest trucks are required to have generators so that they don’t idle at all while parked. The trucks from a few years ago are required to have idle systems that keep the trucks from idling more than 30 minutes. They have idle control systems that work with a thermostat and monitor the batteries. When the truck interior gets too cold, too hot, or the batteries start to drain past a certain level, the truck starts back up. It takes some getting used to when you sleep in a truck that routinely starts and shuts itself down all night, but it does save fuel and reduce air pollution and, of course, causes excessive wear on the starter.

I would not let this vehicle idle for more than a few minutes, unless I was having problems with the starter or the battery. The fuel savings might be negligible, but the reduction in particulate air pollution isn’t. Have you ever tried to breathe the air at a truck stop where the trucks are idling? Testing has proved that the pollution from an idling diesel engine is significant. That is why more and more cities are making it illegal to let diesel trucks, even the new cleaner ones, idle at all. Do the world a favor and treat this van like you would a gas burning car. If it is going to be more than a few minutes, shut it off.

Jeremy Hoyt
Professional Driver


If you think your 81 VW diesel is clean running, pull into a garage, close the door and leave it running while you sit in it. Let us know how it passes THIS emissions test…


The city where I live started a no-idle progarm last year. All city employees other than bus drivers are to shut their vehicles (city or their own when on the job) off when parked. The rationale is fuel savings, air pollution reduction, greenhouse gas (CO2) reduction and general wear reduction. The chief engineer delivered a paper on the subject to our lubrication club and it was well received. The program will now be promoted to the general public. The only reason for idling an engine should be to warm up a very cold car or truck so the engine has enough power, and the windows are clear enough to drive off safely. Years ago, when we lived in an apartment, the milkman parked his van below our bedroom window and left his out-of-tune engine running. Since he could not lock the van door, I threatened to turn off the truck and thow the keys down the storm sewer. He quickly became reasonable and stopped idling.


The main reason truckers leave their trucks running all the time…is due to the cold temps. When temps drop to near 0…it’s much easier to just leave the truck idling then trying to get it started. I got hooked on watching the Discovery show Ice-Road-Truckers. They are up in Canada for 3 months hauling 10,000 loads to the Diamond mindes in Canada over 300 miles of frozen lakes. Basically their trucks are running 24/7 or the three months they are there. Their only down time is when the truck is in for maintenance…like a oil change.