Is it necessary to run engine for 10-minutes when cold starting?

[KiwiKampers]

I ask this question because on several occasions I have been parked next to a motorhome in which the driver insists on starting the engine and leaving it running for ten to fifteen minutes before he drives off. I remember this was a habit people had about twenty years ago, but with modern Diesel engines is it really necessary? It’s very annoying when they start up at 06.30am.

 

[Martyn911]

Rather interesting question , and some of the answers are equally interesting .

Actually it's totally the opposite , yes it is necessary , even more so with modern diesels and their smaller bore oil galleries . Oil is thicker when cold meaning it won't flow anywhere near the same as when it's warm , and don't forget your already using a lower viscosity to transverse those passages now . The practice is to allow oil in sufficient quantity to reach critical areas for engine survival , including the turbine , commonly called oil pressure . The same goes for stopping where the engine requires time to stabilize oil pressure before shutting down , also allowing the turbine to spool down to acceptable limits , at the same time . My mothers Mini requires around 5 minutes to stabilize oil pressure , often rocketing to an unstable 80 psi on start , before settling back to 30 psi , and that's a 1.3 . Now it could be argued , that you've got 80 psi here . Well no , it's a false reading , the actual reason is the oil is restricted due to viscosity , and pooling around the sensor position . It actually has no pressure , and imagine your turbine is furthest from the flow , running without oil on start . Even worst , running after its oil supply is shut off , still rotating at 30-40,000 rpm , at maximum temperature . Turbine temperature climbs rapidly , but it's even faster with lack of oil . It's a pretty good path to excessive wear on the main bearings , and knackered turbo's . Many high performance turbo's use ceramic bearings , but even here they are still bathed in oil .
Question , have you never not wondered why air ambulance helicopters never shut down immediately after landing ? . It's the same thing , and those bearing are ceramic . I would question 15 minutes , but yes idle for a short period .
Now while on the subject , aircon is also misused in exactly the same way . Many people are under the impression , it's perfectly fine to just shut the engine down with the aircon running full chat . Well no , the correct procedure it to switch the system off two minutes before the engine , though this can and should be done while still driving . That's why a pool of water will always appears under the parked car . Aircon is a breeding ground for all kinds of nasties , and is very rarely treated properly , and worse even rarer , serviced . This is the prime reason i would never buy a second hand motor with aircon ! .

Good luck , with giving someone a mouth full , your more likely to get a mouth full in today's world ! .

Like your post, seams like you are the only intelligent person explaining how it is. But i feel you forgot to endorse my reply. On a lorry one can’t let off handbrake to move off. I think most of the post in this forums drive vans not lorries.

 

[Bcollinson]

I ask this question because on several occasions I have been parked next to a motorhome in which the driver insists on starting the engine and leaving it running for ten to fifteen minutes before he drives off. I remember this was a habit people had about twenty years ago, but with modern Diesel engines is it really necessary? It’s very annoying when they start up at 06.30am.

Not needed and a waste of fuel.

 

[tonyidle]

Modern alternators have clutches on the pulleys and don't even charge anyway until certain parameters are met.

They do? I've seen plenty with a one-way clutch (freewheel) that is used to prevent belt resonance but not one with a clutch that can be controlled in any way.

 

[Platelet]

My old Scammell Crusader required at least a two minute wind down before switching off……otherwise damage would be done to the turbo. Those were the days.

Is that after leaving a paraffin heater underneath all night?

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[Tony50]

Even with modern diesels, start and let in run (briefly)

And when coming to a stop let it tick over again briefly.
Will prolong life of the turbo.
Was my teaching.

But 10 mins a bit excessive imo.

Correct, also never ever rev, rev the engine hard when cold or you could cause piston weld , this is where the glands on the piston scuff and jam the piston rings that reduces power , start using more oil, etc. In my younger days I went on a Hepolite piston course, and, learnt a lot.

 

[TeaBiscuit]

Idling the engine for long periods can cause more wear and tear. Modern oils run quite freely, engines reach operating temperature much faster when under moderate load (normal driving). It's better to drive off straight away.

 

[Beltie]

Idling the engine for long periods can cause more wear and tear. Modern oils run quite freely, engines reach operating temperature much faster when under moderate load (normal driving). It's better to drive off straight away.

Agreed! You'd sit for a very long time waiting for a modern engine to warm up at tickover. In the meantime you'd be hastening the demise of the DPF.

 

[nev robinson]

Totally unnecessary.Not mentioned in the handbook.Reminds me when my dad used to leave the house 10mins before anyone else to "warm up the car" (and have a fag).Running with the choke on was never a good idea then with petrol engines and never heard it necessary for diesel.

Not good for the engine at all,in fact very bad…

 

[Philip - Argos]

Hi there, I don't know if this has been raised in this thread, but a friend of mine always advised that the engine should be properly warmed up before you engage top gear (i.e. 6). I tend to use 6th gear when I get to speeds of 56+ MPH and I like to keep the RPM around 2000 revs. We bought our second hand motorhome back in 2017 (large tag axle - 3.0l Multijet engine) and within 3 months, the gearbox broke and we had to replace the complete unit. This isn't anything to do with my driving I would like to say, it's because of the life it had previously to us owning it.

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[TeaBiscuit]

With respect, the difference between 5 and 6 has no influence. It just doesn't make sense mechanically.

 

[jockaneezer]

There is an issue with some Fiat gearboxes where fifth (or sixth ?) gear was "added on" to the top of the standard gearbox as an update. There were many cases of this extra gear failing over time. This was thought to be because it was "splash lubricated" and it took a little while to get enough oil supplied to it to keep it happy. A couple of solutions were not to put it in top gear until you'd driven a few miles and it was also suggested to put more oil in the gearbox than the Fiat specification.

 

[Martyn911]

Very bad for the engine with modern diesels you you drive off directly after starting them.
Leaving them ticking over they will never reach operating temperature risking damage to the CAT & DPF and damage to the engine itself.

So Lenny B, How do I move off if the air is not up to pressure in the tanks so i can't move off, as the hand brake will not release ? Please tell me with your expert knowledge on this forum )) Think you you may be a little to much wine.

 

[airwave]

There is an issue with some Fiat gearboxes where fifth (or sixth ?) gear

Yep quite correct . The MG5TU gearbox fitted in the main to the series one 2.5 , but was also coupled to various series two motors , up to about 2001/2 , and the introduction of the ME5TU . It was actually a 5 speed box , modified from an original 4 . Fiat quite literally bolted a 5th speed cog on , and used splash feed for lubrication . It's fairly easily identified from the shifter , reverse is under 5th , on the right . There never really was a total solution to the problem , only a couple that , well to be perfectly frank delayed a failure . I have the gearbox in question , and the 5th gear bulge is clearly visible . Remove the nearside wheel for access , average repair time is around 3 hrs ! .
Yes , i do over fill the gearbox . If i remember correctly , normal fill should be around 1.3 , 1.6ltr , but i've never done that . The new recommendation is 2.3 , but i put in around 2.5-2.7 ltrs . Always a good quality , 75/90 dual range mineral , gearbox oil , changed every year . There is no dipstick , so fill through the reversing light fitting . Actual gearbox capacity is 2.9 , just don't ask me how i know , okay .
There is a further recommendation of not changing to 5th below 50mph , but here again i use a different train of thought . I use 2000rpm , which equates to about 80 kmph (or 48mph) , my speedo is only marked in km's . As in cruise , i'm only pulling around 2300 rpm , with probably between 0 , to .02 boost , giving me around 95 km ph , i doubt this will make any difference , overall . But i do feel that below 1500 rpm , it's unlikely there would be sufficient vibration for any lubrication . of far more importance , is to have the temperature off the peg , and registering .