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All my previous Petrol-engined cars, ranging from 1200cc - 3000cc have all reached operating temperature within Three miles of starting, even in Winter, but I have noticed that the Octavia only just gets there at about Five and a half miles! Is this about normal for a 2.0lt Diesel? Do Diesels run cooler than Petrol or is it likely to be a sluggish sensor?
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Yes , they take longer to warm up. it's a feature of diesels.
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Ta! - that's ok then! ;-) Thought it may be a sensor or partially sludged-up in the tubes!
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cos they are more efficient - less heat as a byproduct :)
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Diesel engines have better thermal efficiency and therefore are more efficient, i.e. better MPG. But that means there is less waste heat.
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Turbos can change the characteristics, but comparing NA, relatively unstressed engines there has always been a contrast between petrols which can easily run out of cooling if bits of the system are sub-optimal (who, who has had a few old cars,has never had one overheat?) and diesels which spend a lot of their lives running too cool for complete combustion.
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I learned in thermodynamics years ago that all heat engines run more efficiently when hotter, and that that is why cars have thermostats to restrict cooling and raise the engine temperature.
I can see that diesels will generate less heat, but why does the principle of restricting coolant circulation to raise the operating temperature apparently not apply to diesels?
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I think it does it just takes longer for the coolant temp to rise. The blocks are made from a different material or thicker therefore it's longer before the heat is transferred.
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All my diesels had a thermostat, the more recent ones had PTC heaters in the HVAC system to provide a rapid warm-up for the car's interior.
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>> All my diesels had a thermostat,
The thermostat in my IDI Berlingo failed in open position. On a mild February day it didn't get anywhere near operating temperature unless near to stationary.
Roomster doesn't have a temp gauge, just a blue light that extinguishes when approaching operating temperature. The point at which it goes off on an ordinary trip to work varies by around a mile depending on air temperature.
Last edited by: Bromptonaut on Fri 2 Jun 17 at 09:24
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Worth noting that in many cars now the temp gauge isn't real. It displays a value put out by the ECU, hence they get to "normal" quite quickly and sit there, unmoved, unless something dramatic happens. It might as well just be a light (as indeed some cars have moved to).
My older Merc C270CDi takes about 15 miles to properly warm up on a cooler day. My wife has a Tiguan with the latest EU6 2 litre diesel. That'll show 90C on the temp gauge in 3 miles (and, thanks to its hefty electric booster heater, will chuck out heat almost instantly). However select 'oil temp' in the cluster display and at 3 miles it's still blank! It takes, surprise surprise, about the same distance as the Merc takes to get the oil into the 90's.
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>>..... It might as well just be a light (as indeed some cars have moved to).
>>
My daughters y2000 petrol Yaris shows just a little thermometer symbol either red of blue and no temp gauge so not a new approach.
A temp gauge is a waste of space for the vast majority of car users.
Fools lights and an automatic shouty female voice is the future :-)
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>> My daughters y2000 petrol Yaris shows just a little thermometer symbol either red of blue
>> and no temp gauge so not a new approach.
I once had an Audi 80 given to me as a courtesy car. IIRC it was a Y reg (1982). It also had a blue/off/red light instead of a temperature gauge.
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Trying to remember the science ...
A petrol engine benefits from the cooler charge (fuel air mix) to start to expand and for the fuel to therefore fully vaporise just before the spark, without this effect the fuel will not burn fully with a low fuel to air ratios hence the need for a richer mixture when the engine is cold. Additionally the charge in a petrol engines burns very, very quickly meaning that some of the energy is wasted in excess heat.
The benefits of a cooler charge are that the air is denser which means that more enters the combustion chamber for any given pressure, be it atmospheric or forced. Also damp air slows the burn meaning less energy is wasted in heat. Hence a petrol engines can feel perky on a cold, damp day and in some applications water injection is employed along with the more common place intercoolers (cooling the incoming air).
The charge in a diesel engine burns a lot more slowly giving the piston a good shove down the cylinder, rather than a sharp explosion as in a petrol engine, meaning that less energy is wasted in heat. However the slow burn restricts the number of cycles per minute (RPM) and also the efficiency is much reduced at higher RPM.
So for any given cylinder capacity a diesel engine will give bigger shove to the piston (torque) though cannot do it as often as a petrol engine so cannot ultimately produce as much power.
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>> So for any given cylinder capacity a diesel engine will give bigger shove to the
>> piston (torque) though cannot do it as often as a petrol engine so cannot ultimately
>> produce as much power.
>>
You drive with torque not power.
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>> You drive with torque not power.
>>
Hmm, kind of. You need torque though it is the force behind the push, what you need is power which torque (the size of the push) x RPM (the number of pushes).
So say, 300nm at 60rpm would only give you about 2.5hp, not much good for automotive use, though 300nm at 2000rpm would give you about 85hp, much more useful. Let's assume we are talking diesel, at say 3500rpm that torque might be nearer 200nm (as diesels are less efficient at higher RPM) though 200nm at 3500rpm would give you about 100hp so still quite useful.
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>> Worth noting that in many cars now the temp gauge isn't real. It displays a
>> value put out by the ECU, hence they get to "normal" quite quickly and sit
>> there, unmoved, unless something dramatic happens. It might as well just be a light (as
>> indeed some cars have moved to).
>>
>>
>>
That's the case in my Almera. It gets to normal in about a mile and stays there all day.
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The MX5 (a 1999 Mk2) has a pretend gauge; however it does move gradually up to 'N'. But it's well known that it is not a proper analogue for temp and it it isn't marked with actual temperatures.
The Mk1 had a proper gauge and some people go to the trouble of fitting one in their Mk2. It isn't as straightforward as swapping the gauge. I couldn't be bothered to do that. If it's going to boil, it will boil.
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>> The MX5 (a 1999 Mk2) has a pretend gauge...
My Mk3 even has a pretend oil pressure guage. The needle moves when you flick the engine, but if you disconnect the sensor it still moves! It goes to zero if you ground the wire.
I'd prefer an old fashioned oil light - I'd have a better chance of spotting it if it came on.
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I couldn't be
>> bothered to do that. If it's going to boil, it will boil.
>>
Not necessarily. If it's going to boil but you spot the gauge climbing above its normal position then you can stop and avoid the cost of a wrecked engine.
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A few light years ago I had a Datsun 160B with a proper temperature gauge. It usually went to 50% quickly, dropped to 25% when the thermostat opened, slowly crept up to 50% and stayed there. One day it went slowly to 75% and stayed there. The thermostat had failed half open and I replaced it later that day, not something you could diagnose with an ECU driven gauge or the red and blue idiot lights my recent cars have had.
Last edited by: Old Navy on Sun 4 Jun 17 at 13:05
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>>A few light years ago
Light years are a measure of distance, not time! :-D
Forgiven though as I loved my Datsuns. I had a 120Y and a later model Sunny, both the easiest cars to drive and very reliable.
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must admit i prefer a bank of nice gauges! like a few others i think a gauge gives you a more accurate warning of things that are happening - you can see things developing as opposed to a light which is either on or off! - usually on when the damage is already done!
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>> must admit i prefer a bank of nice gauges! like a few others i think
>> a gauge gives you a more accurate warning of things that are happening - you
>> can see things developing as opposed to a light which is either on or off!
>> - usually on when the damage is already done!
>>
Makes far more sense to have a gauge.
I can't imagine a bulb makes that much difference to costs overall as you still need the equipment to measure the temperature and send it to the controller for the light.
I suppose the few £ adds up over several thousand cars.
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Our two Berlingos - different marks, different engines - exhibit(ed) quite different t-gauge behaviour.
The current one may well be the artificial type mentioned above. It rises quickly to 90 and sits there all day up hill and down dale even laden and towing a tonne plus of caravan. Only time it did differently was on arrival at a French campsite more or less at top of a mountain pass. Left car stopped for 10minutes while we booked in and had brief 'franglais' chat with Madame - we're frequent returnees over 25+years. On restart gauge shot up almost to red zone and then, almost before I had handbrake off, dropped like a stone back to 90. I doubt the real coolant temp dropped by 20 or so degrees in that time.
Older one, now left fleet, would vary between 85 and 100+ depending on load. Climbing Mt Ventoux four up it got nearly to red before the fan audibly cut in and it slowly dropped back to normal.
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I would think outside of those with an interest in cars, a light is easier for people to understand or take notice of. A gauge appeals to the inner car nerd but for most it's information they'll never take notice of.
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Our 2010 petrol Corsa has no gauge, just a light that comes on if it overheats. So you have no reassuring "temp is normal" info at all and if the warning light fails you wouldnt know and could cook the engine.
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>> Our 2010 petrol Corsa has no gauge, just a light that comes on if it
>> overheats. So you have no reassuring "temp is normal" info at all and if the
>> warning light fails you wouldnt know and could cook the engine.
>>
Perhaps an alternative solution would be a tri-colour light. Green for OK, amber for problem and red for oh dear, knackered engine.
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>> I would think outside of those with an interest in cars, a light is easier
>> for people to understand or take notice of. A gauge appeals to the inner car
>> nerd but for most it's information they'll never take notice of.
>>
I agree,, if they never check the oil level or top up the screenwashers before they are empty a temperature gauge would be lost on them.
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>> >> I would think outside of those with an interest in cars, a light is easier
>> >> for people to understand or take notice of.
>> >> ..... but for most it's information they'll never take notice of.
>>
Citroen SM ( 1970-1975 ) all those decades ago tried it so it is hardly new
retrorides.proboards.com/thread/156570/quirk-design
spct2000.files.wordpress.com/2014/12/smx03.jpg?w=600
The BIG red light says STOP when a serious fault detected.
Simples
Last edited by: henry k on Sun 4 Jun 17 at 16:25
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>>>The BIG red light says STOP when a serious fault detected.<<<<
I guess that the SM had good reason if it used similar hydraulic set up to BXs of the period The brake system depended on hydraulic pressure generated initially by an engine driven pump. Your foot operated pedal released pressure to the brake system. STOP = No pressure = NO Brakes! Makes for interesting driving experience if it is your first time!
For the pedants, and in the interests of accuracy, BXs actually stored sufficient potential energy in the lifting of the rear suspension to provide pressure to allow an application of the brakes even if the pump had failed - but I am not sure that I would like to depend upon it.
Some models may also have operated the STOP indicator in the event of overheating.
Last edited by: sherlock47 on Sun 4 Jun 17 at 17:09
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I'm surprised what with all the voice activated technology the car doesn't tell you there's a fault rather than having all these lights on the dash?
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>> I'm surprised what with all the voice activated technology the car doesn't tell you there's
>> a fault rather than having all these lights on the dash?
>>
How would it tell you that there is a problem with the voice activation system ...
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>> How would it tell you that there is a problem with the voice activation system
Same way you know when the bulb has gone in the "Stop Engine" light - a very loud bang with some smoke and a sudden loss of power.
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> How would it tell you that there is a problem with the voice activation system
>> ...
>>
True best get rid of all warning systems
;)
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>> > How would it tell you that there is a problem with the voice activation system
>> True best get rid of all warning systems ;)
>>
SWMBO will not be happy :-)
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The STOP light on the BX (and Xantia) was associated with a critical failure. Could be hydraulics related, temperature or (IIRC) terminal oil pressure.
In somethin north of 300k miles in 2*BX and a Xantia I only saw it once, for low LHM caused by a dripping leak. It came on long before any loss of braking.
A quick top up of the reservoir and we were on our way. The only worrying bit was that Mrs B, who was driving, hadn't noticed the STOP light remained on after start up.
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At least one of my 306s had a "Stop" light in addition to the temperature gauge and oil pressure light. It spelt out stop in big red letters.
Last edited by: Old Navy on Sun 4 Jun 17 at 17:58
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>> At least one of my 306s had a "Stop" light in addition to the temperature
>> gauge and oil pressure light. It spelt out stop in big red letters.
Both Berlingos too and IIRC the 205. Seems to be standard issue on PSA group motors
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PSA STOP - The general problem is that when it is associated with too many diverse issues people have a habit of ignoring it! Whilst overheating or oil pressure issue may be terminal for the car, a hydraulics issue can terminal for car AND other people. Although in your case wife had not even seen it.
Something like crying 'wolf'?
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The shop I part time in had a 307 for three years for deliveries. The STOP light was permanently on for the last two of those. The car ran like a clock.
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operating temp - CGNorwich
