Idling a Diesel engine on cold start

manisinghb

manisinghb

manisinghb

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Hi guys,

Apologies if a similar thread has already been opened elsewhere but because this is such a conflicting issue I thought I'd ask the question again, especially since the cold weather is upon us!

I have a 2008 Ford Mondeo, 2 litre diesel. My wife drives the car on a daily basis BUT she only drives it 6 miles each way, a brief commute for a diesel - I know! She was complaining of it being sluggish in the mornings, and making rattling noises. So I would start the car when I leave home (app. 15-20 minutes before her) and she said the car was driving amazingly!

However, recently a lot of family and friends and mechanics and internet forums have been saying this is bad or good on the engine, and I can't tell! So thought I'd get some more insight here...
 
I don't think leaving the car to warm up by idling is beneficial at all. A lot of the wear on an engine happens before it is up to temperature, and leaving it idling takes a lot longer to warm the engine than gentle driving. The manual of pretty much every car I have driven explicitly said not to leave the car idling to warm it up. It might run a bit better when warm, but it is a lot better to warm it up by driving normally.

Also, I don't know if that car has a particulate filter, but If it does I'd imagine it will clog up pretty quickly with that kind of use.
 
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Dont leave it running to warm up, my neighbour does this with his Q7 TDI at 6am it is annoying, nearly as much as his 10 seconds of cranking.... I think he has since worked out what glow plugs are for.

tom_e said:
I can't see how any damage can come from leaving a car idling and letting it get a bit of warmth in it before you get going.
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Then you dont understand engines.
 
lord filbuster said:
I don't think leaving the car to warm up by idling is beneficial at all. A lot of the wear on an engine happens before it is up to temperature, and leaving it idling takes a lot longer to warm the engine than gentle driving. The manual of pretty much every car I have driven explicitly said not to leave the car idling to warm it up. It might run a bit better when warm, but it is a lot better to warm it up by driving normally.

Also, I don't know if that car has a particulate filter, but If it does I'd imagine it will clog up pretty quickly with that kind of use.
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Yes has a particulate filter, been driving it to the in-laws to get a good run in to help clear it but obviously this is once in a blue moon. Is this the best way of clearing the filter - taking it for a 30 minute constant drive at 60mph+?

Also, I agree with all your points on the idling but my concern is that the 2 litre engine isn't warming enough by the time she reaches work 6 miles away, could that be having negative effects in any way apart from on the filter clogging?
 
It sounds like the wrong car was bought for the job. Diesels take longer to warm up than petrols and this kind of usage profile is not what they're best for, and what they'll be the most reliable at doing.
 
manisinghb said:
Yes has a particulate filter, been driving it to the in-laws to get a good run in to help clear it but obviously this is once in a blue moon. Is this the best way of clearing the filter - taking it for a 30 minute constant drive at 60mph+?

Also, I agree with all your points on the idling but my concern is that the 2 litre engine isn't warming enough by the time she reaches work 6 miles away, could that be having negative effects in any way apart from on the filter clogging?
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I'd imagine that the car is just barely up to temperature after 5 miles or so, but it would still be better to drive it gently there from cold, not leaving it to idle.

A quick blast up the motorway is the usual recommendation to keep the DPF clear. To be honest, regular short journeys aren't particularly good for any car, but if you give it a good run every week or so, and it is serviced regularly, I wouldn't lose any sleep over it.
 
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Chuk_Chuk said:
Could you please explain what damage happens to engines when they are idling and warming up?
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Most of an engines wear happens when it's cold as the lubrication isn't doing it's job as well as when it's hot. Idling prolongs this so more wear occurs, also sitting at idle oil pressure will be lower than driving, again providing less protection. Finally even though your engine may warm up nothing else will have like gearbox, brakes etc so you can't just go hooning off after leaving it to 'warm up' on the drive for 15 mins. - This is a classic thing for people with performance cars to do.

Everything i've ever read or heard has led me to believe starting up and then immediate gentle driving is the kindest on the vehicle.
 
Even if you aren't worried by the additional wear that can occur from extended cold running:

1) It's illegal to leave a car unattended with the engine running.
2) If left unlocked and a thief takes it (increasingly common in winter), you insurance is very unlikely to cover you.
 
sovietspybob said:
Most of an engines wear happens when it's cold as the lubrication isn't doing it's job as well as when it's hot. Idling prolongs this so more wear occurs, also sitting at idle oil pressure will be lower than driving, again providing less protection. Finally even though your engine may warm up nothing else will have like gearbox, brakes etc so you can't just go hooning off after leaving it to 'warm up' on the drive for 15 mins. - This is a classic thing for people with performance cars to do.

Everything i've ever read or heard has led me to believe starting up and then immediate gentle driving is the kindest on the vehicle.
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First and foremost I didn't realise you were talking about leaving your car for about 15 minutes (To which I agree is pointless). I assumed we were talking about leaving it for about 30 seconds to 2 mins.

I agree with your comment about the engine oil but not with the others.

For brakes, i'm pretty sure fluid temperature doesn't matter. As long as the fluid remains incompressible the brakes should function as normal. Also I'm unaware of steel brakes having an operating temperature. The lubrication around this parts would surely be rated to operate at all temperatures since the moving parts themselves do not generate any heat and therefore can not heat the lubrication.

I haven't seen data for transmission temperatures, but is the operating temperature really going to be that high? Also if the car is left in the neutral the friction generated by the input shaft would contribute to the heating of the transmission fluid up to operating temperatures?

edit: Also driving off too early would increase the number shaft rotations during the low lubrication period and therefore increase wear.
 
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A gearbox isnt as sensitive to wear additives like engine oil. Typical anti wear additives need to be atleast 60C to work and idling an engine rather than introducing load means the engine see more revolutions at sub 60C. Plus things like cam bearings..... actually this is pretty much a thread a week ago ?
 
Jonnycoupe said:
A gearbox isnt as sensitive to wear additives like engine oil. Typical anti wear additives need to be atleast 60C to work and idling an engine rather than introducing load means the engine see more revolutions at sub 60C. Plus things like cam bearings..... actually this is pretty much a thread a week ago ?
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So it's a balancing act, between leaving the car long enough to get some oil circulating around the engine (since all the oil would have drained to the bottom) and moving off as soon as possible to get the engine generating as much heat as possible to heat the oil as quickly as possible?

I don't know, was there a thread on this a week ago?
 
manisinghb said:
...Is this the best way of clearing the filter - taking it for a 30 minute constant drive at 60mph+?
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Depends on the car.
Generally yes.

For Lexus it's above 3000 RPM for 20 minutes or so.
Gets it up to heat then the 5th injector fires fuel into the exhaust to increase the temp more to burn out the carbon.

Once cycle complete - Drive as normal.

Some cars only do it above 50MPH, some don't use the 5th injector.

Should say in your manual though :)
 
Captain Fizz said:
Depends on the car.
Generally yes.

For Lexus it's above 3000 RPM for 20 minutes or so.
Gets it up to heat then the 5th injector fires fuel into the exhaust to increase the temp more to burn out the carbon.

Once cycle complete - Drive as normal.

Some cars only do it above 50MPH, some don't use the 5th injector.

Should say in your manual though :)
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Thats a Lexus system (similar in a Renault too) however Ive yet to see a VAG with this system. They dont have an additive.
 
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