keeping engine running all day

[funkshun]

So, I do a courier route 5 days a week, its about 3 hrs, 75 miles of driving, and i make about 7 stops a day, each for about 5 minutes.

For the first two months after getting the TDI i turned the car off at every stop. I was recommended last weekend to keep the car running, and lock the doors with a second key. My friend made example of diesel trucks always keeping their engines on when parked. So, my reasons for doing this was to prevent wear and tear, and to keep the engine temp consistent throughout the day, but oddly I seem to have noticed an increase in mileage.

Does restarting the engine really use that much fuel, or am I imagining it? Any technical reasons as to why keeping the engine running all day (like example of keeping turbo temp consistent) is much better then stopping and starting?

Thanks!
tom

 

[gottdi]

Not turbo temp but turbo back pressure. It has been noted here that the turbo needs to have that pressure behind the seal to give it long life. It has been stated that long idle times can ruin the turbo seal and cause runaway which if not stopped at once will destroy your engine. So here is the reason not to do that. Yes, starting can use a bit of fuel but the amount you save in fuel may just become void when you destroy your engine. If your out delivering your package and your seal decides to take a dump and start sucking in oil causing a runaway situation your car will be toast by the time you come back. Now you don't have a car to finish your daily run and a bill of at least $4000 for another engine. What would you do. The Truck diesels use different turbos than the TDI. Yes it's a diesel but not the same class as a diesel big rig. I'd rather take the small hit in mileage than spend a ton on a new engine. Heck your getting dynomite mileage anyway. Why bicker on that small amount used to restart your car.

My .02 worth.

 

[DrewD]

Idling contaminates the oil faster with blowby gasses and unburned fuel that gets past the rings. The big rigs have large oil pans and easily hole 10 gallons or more of oil so idling isn't as much of an issue for them I assume.

 

[Mike_M]

My friend made example of diesel trucks always keeping their engines on when parked.

1) TDIs are not trucks.
2) Most truckers that still do that are doing so AGAINST the recommendations of the people who build the engines and the trucks. They're usually doing so either to generate electricity (instead of a generator) to run accessories while they're sleeping, or because they're expecting bitter cold that will make the truck hard to restart in the morning.

Does restarting the engine really use that much fuel, or am I imagining it?

Likely, you're imagining it, or it's getting cooler outside which is the real reason for your fuel economy increase. TDIs like cooler air, and do rude things like pull back the timing when they have hot air. Pulling back the timing kills fuel economy.

Any technical reasons as to why keeping the engine running all day (like example of keeping turbo temp consistent) is much better then stopping and starting?

On the contrary, idling for extended periods is WORSE on the engine. When the turbo is not under boost, oil leaks through the turbo seals and is burned by the engine. Not good for it. The turbo temp drops dramatically within a few seconds of letting off the throttle, and is likely not much warmer than a couple hundred degrees while idling, so it's no more "smooth" then if you were shutting it off.

Shutting off the engine for 5 minutes shouldn't vary the coolant temp very much, and as long as coolant temp stays above about (IIRC) 50°C (122°F), it won't matter anyway. I think that's the temp at which the "warm-up extra fueling" stops, and I know it's the temp at which the coolant glow plugs shut off.

I'd recommend going back to shutting it off at every stop, unless you know it'll be less than 1-2 minutes. Extra starter wear is a real problem too, and if you make a couple dozen stops a day, you can end up prematurely burning up a starter. I'm not sure how hard it is to do so, though. I don't think the starters are particularly fragile...that's just heavy-duty usage.

If any of the experts, or any actual TDI mechanics, disagree please feel free to tell me I'm full of crap...as long as you quantify why.

Mike

 

[Joe_Meehan]

With out the turbo issues I would say keep it running. However under the current conditions, I would suggest turning it off. In reality I doubt if the average cost difference would be enough to worry about.

 

[BioThomas]

I see the arguments for turning the car off at every stop, but what about the concept of letting the turbo cool, before turning a car off. In other words, I was under the impression that one is supposed to let the car idle for a minute, or two before turning it off, because the turbo is too hot and needs time to cool down, while lubrication is supplied.

 

[Joe_Meehan]

.. what about the concept of letting the turbo cool, before turning a car off....

That is only for old turbos, like from the 70's The current ones don't need it.

 

[greenskeeper]

If it was possible to have an AIC on our cars, then I'd say it would be no problem. Got one on our truck and I am able to adjust the idle from stock all the way up to 1500rpm. Nice.

 

[BioThomas]

That is only for old turbos, like from the 70's The current ones don't need it.

Oh, I didn't know that. I was reading all the discussion about busted turbos, etc and never checked the model years that this would apply to.

So, tell me, what is different about the two types of turbo.

 

[eb2143]

That is only for old turbos, like from the 70's The current ones don't need it.

That is incorrect.
It is still recommonded to let our VNT's to cool, but only in select cases. For example, I drive 35 miles one way to work, but on the way home and the way to work, I have 5 minutes off the highway. This is sufficient time for the turbo to cool down.

There is no way to know exactly unless you have a guage, but I believe those that do have a guage have found that after driving for extended periods on the highway at 75, the turbo is cool enough to shut down after < 1 minute.

So, unless you drive you TDI extremely hard or live/work right off the highway, idling to cool down the turbo is not needed BUT there IS still a maximum recommended shut-down temperature on the VNT-15, 17, 20's.

Back to the original post...It is a fairly tough call. I don't believe you need to worry about your starter because a hot-start puts very little stress on the starter, I would be more worried about the turbo (I remember a post of a guy who knew a guy who had gone through multiple turbo's using a TDI as a taxi overseas) As for fuel, I think a fairly accurate figure is that a start takes about 10 seconds of idle...so your wasting diesel by leaving it on.

I would agree that unless your stops were 1-2 minutes, shut down.

Bad for Turbo
Bad for Oil
Wastes Fuel

Worthwhile because...?

 

[Joe_Meehan]

So, unless you drive you TDI extremely hard or live/work right off the highway, idling to cool down the turbo is not needed BUT there IS still a maximum recommended shut-down temperature on the VNT-15, 17, 20's...

True. Thanks for the correction.

 

[eetsoot]

Was it the Lupo, that had the programming that would shut the car off at a light and as soon as you took your foot off the brake it would start the again? Evidently VW didn't think starting the car was a mileage killer.

 

[scooperhsd]

For all the reasons listed above - I'd shutdown on your stops. Better on your car, etc. YOu might want to learn how to replace the starter (not hard).
As far as cooldown - if you're driving town-type driving before parking for the stop - I'd say don't worry about it.

Oil - Instead of using the cheapest stuff, you may very well find it worthwhile to get the BEST oil you can find - say the Mobil 1 5w40 Turbo Diesel Truck, or one of the VW 506.01 spec oils, do oil analysis and go for extended change intrevals. It could very well save you money in the end.

 

[funkshun]

thank you everyone, I knew it was best to ask because I did't have enough knowledge to make the right choice. I will shut down, because it is mostly side roads, varying speeds from 30-55 and my stops are usually more then 2 min. I do use the mobil delvac, also run BP Premium, and I'm not worried about saving the extra on the mileage, as its great as is. I will note that after highway driving 55+ it does make sense to cool down for a bit (although not as long as would be needed in older engines, as my friend may have been informed) before shutting off, and if I have to evenutally replace the starter, well that is not that bad compared to the other possibilities that could arise.

THANKS!

 

[hank miller]

Most trucking companies have a policy against idling the engine in the trucks.

I know at least one company will not let the truck go faster than 55mph (set in the computer), if the truck has been averaging less than 7mpg. That works out to about an hour of slow driving after letting the truck run overnight. Since drivers are paid by the mile, this means $6 less to them. (And drivers know plenty of tricks to get around this)

The drivers leave the truck running because they cannot sleep in Florida without AC, nor can they sleep in MN without heat. (seasonable of course, in MN summers you need AC)

New trucks are starting to come with small engines to run just the AC, and generator (and heater).

 

[Fortuna Wolf]

Lesse, anecdotes...
On the highway I tend to average about 800-900 F EGTs. Coming off the highway the EGTs quickly drop to below 400F in 30 seconds or less.
If I'm putting around a residential area and pull into my driveway its already at 250F and I just shut it down. I don't think there's any reason to idle longer than the time it takes you to pull into your parking space and unbuckle your seatbelt unless you've been rallying

 

[wjdell]

IS 5 minutes really that long - I suppose its right there at the edge - Every time you shut your motor off the coolant stops flowing and the heat goes up before it goes back down. Shutting it off may be good for the turbo - but I am not so sure its best for the engine.

 

[Joe_Meehan]

IS 5 minutes really that long - I suppose its right there at the edge - Every time you shut your motor off the coolant stops flowing and the heat goes up before it goes back down. Shutting it off may be good for the turbo - but I am not so sure its best for the engine.

The heat in the engine does not go up. There is no additional heat being added. What may go up is the temperature of the water in the cooling system because it is still absorbing heat from the engine, but it is no longer being cooled. The only way the engine gets more heat is when it is actually running.

 

[wjdell]

Test for yourself

 

[dabear95]

Lesse, anecdotes...
On the highway I tend to average about 800-900 F EGTs.

With AC on? How fast? where is your probe?


Comments:
I average 550-650 at 75MPH. There is an odd exit ramp where I get off on the way home and sometimes I run it up to 800 or so. I do notice that with the AC it takes a bit longer for the temps to come down. In my opinion if you count to 30 and shut down you are all set unless you were just running the 1/4 mile...


Jason

 

[whitedog]

I'm glad you decided to shut it down during your stops. I was going to mention that with 75 miles per day for five days means you only ran half a tank of fuel to check your mileage. This isn't nearly enough of a sample to check for a change in mileage.

I mention this just because I wanted to contribute something before going to bed.

 

[funkshun]

I'm glad you decided to shut it down during your stops. I was going to mention that with 75 miles per day for five days means you only ran half a tank of fuel to check your mileage. This isn't nearly enough of a sample to check for a change in mileage.

I mention this just because I wanted to contribute something before going to bed.

i wasnt counting milage, but I was watching the needle which seemed to be going down slower then other weeks, although that probably was not happening and is far from accurate method of calculating. thanks again.

 

[Gil]

I agree that it is not a good idea to let the engine idle.
Does anyone know if I adjusted the "gas" pedal to about 1500 rpm and let it run like that for an extended period of time?
The reason I want to do this is to power an inverter for my house in case of a power outage.
I know that my inverter won't tax the TDIs electrical system because we have a 1000 watt altenator and one big battery. The inverter is only 750 watts and will run my furnace, tried it.
thanx Gil

 

[TornadoRed]

So, I do a courier route 5 days a week, its about 3 hrs, 75 miles of driving, and i make about 7 stops a day, each for about 5 minutes.

For the first two months after getting the TDI i turned the car off at every stop. I was recommended last weekend to keep the car running, and lock the doors with a second key. My friend made example of diesel trucks always keeping their engines on when parked. So, my reasons for doing this was to prevent wear and tear, and to keep the engine temp consistent throughout the day, but oddly I seem to have noticed an increase in mileage.

I'm going to disagree with everyone else -- at least on the margin.

I drive about three times as far as you, and make about three times as many stops. If I know it will take 5 minutes or longer, I shut off the engine. If I am at all concerned about the possibility of auto theft, I shut off the engine.

If, based on my experience that it will only take 1-3 minutes, and if I estimate that the risk of auto theft is very very low, then I let the engine idle and lock the vehicle with the valet key.

I think it is better for the engine to keep the oil and coolant flowing. I think it is better for the electronic components if they do not experience even slight voltage surges during each engine restart. Cranking over the starter 5 or 6 times a day is better than 15 or 20. And in the summer it is nice to come back to a cool vehicle.

As for the turbo... everyone's experience is going to be different, I suppose. But I fail to see the difference between five minutes of idling at one stretch, versus five minutes of idling broken up in 60-second increments at stop lights. Oil continues to flow through the turbo when at idle, does it not?

Thus, I fall into the camp of those who say let the engine idle during short stops.

 

[Fortuna Wolf]

Ok, I advanced my timing and went on the highway again. EGTs were between 650 and 750, But like said, its an automatic. I got great mileage though, just watching the fuel gauge. I should be able to get 600 miles on this tank.

 

[Benjamin]

My 2 cents as a pizza delivery driver who can shut off the engine and restart sometimes 20-30 times a night is that the turbo new for me is $1000 plus all my labour, the starter I can get a new bosche for $200 and a lot less labour. Granted I work in a shop as an apprentice mechanic, I would much rather change the starter then the turbo. My starter at 305000 km's is close to going, the last 50000 km's has been doing delivery, before that it was a normal work to home car. Math and labour wise, shut the car down, cheaper in the long run, and less of a headache.
My 2 cents atleast

Ben

 

[weedeater]

I'm surprised no one has mentioned how low the oil pressure becomes at idle when the oil is hot, and how this will affect long-term operation.

 

[oldiesel]

Shut it down???

The UPS guy shuts it down every time he gets out,regardless of how long he expects to be out of the truck.His new truck is diesel and i doubt anyone has better opinion on that subject than UPS. my$.02

 

[Joe_Meehan]

The UPS guy shuts it down every time he gets out,regardless of how long he expects to be out of the truck.His new truck is diesel and i doubt anyone has better opinion on that subject than UPS. my$.02

I believe they do that to keep the trucks from being stolen. Of course when you think about it, that is a very good reason.

 

[doppx006]

Why is there not an optional High idle or idle controller kit? Pickups/Semis all have them to maintain engine temperatures in cold weather so oil does not become contaminated. I know Dodge offers a kit, CHevy has an aftermarket one, and I know the powerstrokes have a kit u can buy, although they all have a automatic controller but that is only for cold weather. I used my controller on my Dodge for AC even in teh summer. Just kick on the exhaust brake and ramp the rpms to warm it up.