HDI temperature gauge

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tony1
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HDI temperature gauge

Post by tony1 »

On my old ZX the temperature gauge was right in the middle when it was up to working temperture. On my HDI it does not get this far (about 80%).Is this correct for a HDI because it runs at a lower temperture to a petrol engine, or do I need to investigate further?
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Post by Peter.N. »

As long as its reading somewhere in the normal section and the temperature comes up reasonably Quickly (slower in this very cold weather) and the heater works allright,it should be OK. Temperature gauges/senders are not renowned for their accuracy.
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Post by AndersDK »

Peter just told you -

- and you are right : the HDI runs with less heat loss than a petrol.
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Post by Rostami »

My HDi (110HP) very rarely gets near the 90ºC mark. It is mostly just a little above 70ºC.

Even when driving at high RPMs and the engine oil gets over 100ºC the engine water temperatute continues below 90ºC. (naturally when driving fast the engine is better cooled down due to air flow)
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Temp

Post by paulbx »

My Hdi Xantia has temp numbered markings at 60 /90/ 110 in normal weather (for the Uk) it sits between 60 and 90- so I guess about 75/80 C.

This all seems normal. It does not have an Oil temp gauge which is useful as it woudl only be anotehr dial to strate at and worry about!

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Post by tony1 »

That is interesting, as the HDI thermostat should start opening at 83C & be fully open open at 99C. So I would expect the temperature gauge to run at above 83C. I guess it just shows how inaccurate the gauges are.
I think I'll change the thermostat when I change the antifreeze.

Which does raise another question. when do you change the antigel? citroen do not have it as a service item. the bottle is marked "Longue duree" ! Looking on the forum the opinion seems to vary between 3 & 5 years.
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Post by Kowalski »

AndersDK wrote:Peter just told you -

- and you are right : the HDI runs with less heat loss than a petrol.
Have you ever noticed that often, diesel models have bigger radiators than their petrol equivilents? Diesels often have oil jets to cool the underside of the pistons where as petrols don't have them as often.

Diesels lose less heat out of the exhaust pipe than petrols BUT their cooling systems have to cope with the engine putting more heat into its water / oil. This is because of their high compression ratios (and high combustion temperatures) as well as the fact that they're turbocharged. Indirect injection diesels are even worse for heating themselves up because of the even higher compression and the extra surface area that the swirl chambers give. In short you're right that diesels lose less heat than petrols but of what heat they do lose more of it ends up in your oil and water.

The temperature your engine runs at is governed by the thermostat, these don't last forever and can get coroded so that they leak. In effect they're always stuck partially open even when they're closed. Its winter now so you can't really expect your engine to get as hot as it does in the summer, I know that in the summer the temperature gauge on my TD will go up if I make the engine work hard, where as in the winter the gauge stays where it is regardless.
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Post by RichardW »

"BUT their cooling systems have to cope with the engine putting more heat into its water / oil. "

Eh? Most of the heat the cooling system dissipates is due to the thermal inefficiency of the engine. For a petrol this is typically around 30%, for a diesel 40%. If the engine is 90 BHP, that's approx 68kW, which means (at full chat) the radiator is dissipating 158kW for the petrol and 102 kW for the diesel. This is why diesels take so much longer the heat up in the morning - especially the hyper efficient Common Rail types.
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Post by Kowalski »

RichardW wrote:"BUT their cooling systems have to cope with the engine putting more heat into its water / oil. "

Eh? Most of the heat the cooling system dissipates is due to the thermal inefficiency of the engine. For a petrol this is typically around 30%, for a diesel 40%. If the engine is 90 BHP, that's approx 68kW, which means (at full chat) the radiator is dissipating 158kW for the petrol and 102 kW for the diesel. This is why diesels take so much longer the heat up in the morning - especially the hyper efficient Common Rail types.
Not all of the inefficiency of an engine can be accounted for by energy that is lost via the radiator, the majority of the energy goes out of the exhaust pipe, your exhaust pipe gets hot.

Diesels take longer to heat up because generally they have more thermal mass, e.g. they are heavilly made and have large capacity cooling systems / big radiators etc. They also tend to have oil coolers, this means that the water is cooled by the oil, which warms up the whole of the engine.
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Post by AndersDK »

Tx Richard -

I was beginning to sweat :?
As I understand it :

1) we are talking a HDI/petrol heater gauge dispaly comparison in this thread
2) the HDI (or should'nt we really call it an EDI for EXTREME high pressure Direct Injection ?) is much more efficient because of the better fuel atomising and hence more efficient combustion.
3) more efficient combustion leads to less fuel consumption at same power output
4) same power output at less energy (fuel) - means less energy wasted as heat loss.
5) as a consequnce HDI engines have some means of initial heating of the coolant (heater plugs or oil burners).
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Post by Kowalski »

AndersDK wrote:Tx Richard -

I was beginning to sweat :?
As I understand it :

1) we are talking a HDI/petrol heater gauge dispaly comparison in this thread
2) the HDI (or should'nt we really call it an EDI for EXTREME high pressure Direct Injection ?) is much more efficient because of the better fuel atomising and hence more efficient combustion.
3) more efficient combustion leads to less fuel consumption at same power output
4) same power output at less energy (fuel) - means less energy wasted as heat loss.
5) as a consequnce HDI engines have some means of initial heating of the coolant (heater plugs or oil burners).
I agree with all of your points apart from number 2.

This is a little off topic but.... The atomisation is better because of the higher pressures but that only makes the engines cleaner, it takes very little fuel not being burnt to produce visible smoke.

The XUD was indirect injection, these have a lot of surface area to lose heat into the head with. The HDI is direct injection it has a much lower surface area and that helps with the efficiency. Compression ratio could be a factor in efficiency too, I'm not sure about the exact numbers here. In principle higher compression gives better efficiency but it also gives higher temperatures, and higher temperatures mean more heat gets lost into the block. There will be an optimum value for compression ratio to get maximum efficiency. Most current engines have settled around the 18:1 mark, (where as the XUD is more like 22:1) there has to be a reason for this 18:1 figure, its either optimum efficiency, noise or emissions....

Since the pressure on HDI is only 20k psi and not the 30k that VWs PD does you can't really call it extreme pressure ;)
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