Warming up a diesel?

[en13]

Hi all

Tried searching the forums to see if there's anything on this but there seems to be none.

What's your take on warming up diesel engines before going off? A search on google says that it's not necessary- just drive but don't rev it too much and the engine will warm up with your driving... apparently idle warm ups don't help anything.

what do you think about this and are there any mechanics who can verify anything? i'm not a carhead so i don't know any better.. my mechanic told me to always warm up idle for 5 minutes with my 1994 Golf 3 GL.. but his specialization is jap cars.. don't know if there's much of a difference with jap/euro..

[Logzy]

Start car, idle for 10 seconds, drive.
Idling is not good for the car and will not warm it up.

The 2.0 TDI's they say to drive and rev to 2500 (no more, no less) when cold and then 3000 when temp is on 2 white marks, then whatever i guess once its fully warm.

The reason for this is to stop the VNT cloggin with soot etc.

[gldgti]

this is a good question... it does depend on a few things.

for the new tdi owners, then what logzy has said would be sensible.

for drivers of older cars, you need to keep some things in mind:
- if you have a turbocharger fitted to your engine, it isn't nice to work it hard while the engine (hence oil) is cold. keep off the pedal until the temperature is warm so that you do not incur excess wear of turbocharger bearings. - likewise, if you stop after some serious driving, allow the car to idle for a minute so that the turbocharger may cool down, also to save the bearings.

- if there is no turbocharger, the same applies but the main care should be taken with not using high rev's until the oil is warm.

[TDI Dude]

Question then, mainly for gldgti.... new tdi's also have a turbocharger yes? so wouldn't same apply for the turbo bearings also on the newer cars???

[gldgti]

Question then, mainly for gldgti.... new tdi's also have a turbocharger yes? so wouldn't same apply for the turbo bearings also on the newer cars???

technically, yes.

if i owned a new TDi, thats how i'd drive it, and cool it down also. however, i did not say this at the risk of being grilled by people who know better.

also note, i believe that for reasons of "user practicality", VW intend the high grade oil and fine tolerance bearings to eliminate the "need" for this special treatment - joe bloggs does not want to buy a diesel car if he has to treat it differently from any others...

but, as an engineer, i know it to be fact that if you treat your turbocharger well by letting the bearings cool slowly with lubrication, it will certainly last longer.

[TDI Dude]

Thanks for that and I wasnt 'grilling' just asking as there seems to be 1,000 theories about how to treat a diesel these days. I'm a little old school as I learnt about cars by tinkering on a HJ Kingswood 202 and that you had to look after especially in winter (warming up etc) And thanks again gldgti for your answer to my question.. appreciated

[en13]

hmmm... so we technically should warm it up for a while- say a minute? and also then cool it down? how do you cool it down- just by idling?

sorry never had a diesel before

[gldgti]

Thanks for that and I wasnt 'grilling' just asking as there seems to be 1,000 theories about how to treat a diesel these days. I'm a little old school as I learnt about cars by tinkering on a HJ Kingswood 202 and that you had to look after especially in winter (warming up etc) And thanks again gldgti for your answer to my question.. appreciated

its not you i'm worried about... hehe

[gldgti]

hmmm... so we technically should warm it up for a while- say a minute? and also then cool it down? how do you cool it down- just by idling?

sorry never had a diesel before

when you drive fast, and you produce lots of boost, the exhasut gas temperature goes right up. this makes the turbine very hot, which then soaks through into the turbocharger bearings.

while the engine is running, you're ok because the oil keeps pumping through the bearings. but if you have been hard at it, and you stop the engine, the oil flow stops but the heat saoks through the turbine and into the bearings. this makes them hotter than ususal. this puts undue stress on the bearings and shortens theire life.

by allowing a no load scenario, like idleing, you have a period of normal oil flow, and low heat production, allowing the turbocharger temperature to stabilise before cutting off the oil supply. this means that when the engine cools down after shutdown, the bearing will not become any hotter than it was before, and is happy

[TDI Dude]

its not you i'm worried about... hehe

Well hang on then give me 5 mins and I'll turn then!!!!

[en13]

thanks guys! i feel more confident now. the car has been delayed yet again but at least i'm learning new things!

[gregozedobe]

My $0.02 worth (these are just my personal opinions, and like everyone else I have no hard scientific data to back it up with, but it makes sense to me):

Drive off (gently) straight away. Excessive idling can contribute to glazed piston rings (particularly with a new VW TDI engine). The engine will get to proper operating temperature much quicker with a bit of load on it.

After a few minutes of gentle driving you can start to use a bit more accelerator pedal and revs (but not over 2,500).

When the coolant AND oil is properly warm (may take another 5 minutes after the engine coolant is up to 90C) then you can use full accelerator and rev up to 3,500 (yes, even on a brand new engine). I wouldn't do this in every gear all the time, but reasonably frequently will help your engine run in better (it increases the combustion pressure, which pushes the rings harder against the bore, which helps avoid glazing and creates a better seal/"fit").

Even if you want to drive for maximum fuel economy you should use at least 2/3rds accelerator pedal at least once or twice an hour to help prevent the variable vanes in the turbo from sticking (and besides, it's fun )

TDIs that are run in with varying revs (no cruise control allowed during the first 2,500KM) and frequent application of full accelerator tend to have better compression, run better and get better fuel economy than those that are always babied and driven very gently.

I always drive gently for the last 3-5 minutes of any journey to allow the turbo to cool down a bit before switching the engine off when I get to my destination. Similarly if I have to stop suddenly after working the engine hard (eg driving up a long, steep hill) I will allow the engine to idle for a few minutes so everything can cool off with good circulation of coolant and engine oil (generally I try to avoid idling where I can). If you switch off with a very hot turbo heat soak can cook the engine oil on the turbo shaft, leading to damage and possible turbo failure.

[en13]

thanks again gregozedobe- now i know the difference between oil and water temp! never knew there was a difference...

do you also recommend changing oil at 5000?

my friend has a toyota prado (diesel) and says that the oils are specific and special, so i shouldn't change them before the service schedule tells me to... i'm not quite sure if this is accurate- as you can tell, i don't know much about engines at all so this forum's collective brain and experience really helps!

[Mischa]

thanks again gregozedobe- now i know the difference between oil and water temp! never knew there was a difference...

do you also recommend changing oil at 5000?

my friend has a toyota prado (diesel) and says that the oils are specific and special, so i shouldn't change them before the service schedule tells me to... i'm not quite sure if this is accurate- as you can tell, i don't know much about engines at all so this forum's collective brain and experience really helps!

your friend is right, you need to use the right oil only available at dealers unfortunately. its around 80$ for 5L plus 18$ for the filter and a few bucks for the sump bolt. as long as you use the right oil and filter theres no reason not to change the oil between services its what i do.

[jets]

My $0.02 worth (these are just my personal opinions, and like everyone else I have no hard scientific data to back it up with, but it makes sense to me):

Drive off (gently) straight away. Excessive idling can contribute to glazed piston rings (particularly with a new VW TDI engine). The engine will get to proper operating temperature much quicker with a bit of load on it.

After a few minutes of gentle driving you can start to use a bit more accelerator pedal and revs (but not over 2,500).

When the coolant AND oil is properly warm (may take another 5 minutes after the engine coolant is up to 90C) then you can use full accelerator and rev up to 3,500 (yes, even on a brand new engine). I wouldn't do this in every gear all the time, but reasonably frequently will help your engine run in better (it increases the combustion pressure, which pushes the rings harder against the bore, which helps avoid glazing and creates a better seal/"fit").

Even if you want to drive for maximum fuel economy you should use at least 2/3rds accelerator pedal at least once or twice an hour to help prevent the variable vanes in the turbo from sticking (and besides, it's fun )

TDIs that are run in with varying revs (no cruise control allowed during the first 2,500KM) and frequent application of full accelerator tend to have better compression, run better and get better fuel economy than those that are always babied and driven very gently.

I always drive gently for the last 3-5 minutes of any journey to allow the turbo to cool down a bit before switching the engine off when I get to my destination. Similarly if I have to stop suddenly after working the engine hard (eg driving up a long, steep hill) I will allow the engine to idle for a few minutes so everything can cool off with good circulation of coolant and engine oil (generally I try to avoid idling where I can). If you switch off with a very hot turbo heat soak can cook the engine oil on the turbo shaft, leading to damage and possible turbo failure.

Very good comments. I would also add to cool down when driving hard & fast & pulling over for fuel [I know not very often in a diesel] The electric water pump will keep circulating coolant but as already mentioned the oil flow will stop.