110tim · Nov 22, 2019

after a 30 mile run in near freezing temperature, out of curiosity I felt the lower radiator hose and to my amazement it was stone cold and the upper hose was not that hot ,you could hold your hand on it without getting uncomfortable. The thermostat was replaced recently by a genuine part and the temperature guage reads normally with the needle in the middle,although on this occasion it was slightly to the left indicating that the coolant was probably not quite up to temperature I understand that BMW M47's run cool but is this normal ?

Avocet1 · Nov 22, 2019

110tim said:
after a 30 mile run in near freezing temperature, out of curiosity I felt the lower radiator hose and to my amazement it was stone cold and the upper hose was not that hot ,you could hold your hand on it without getting uncomfortable. The thermostat was replaced recently by a genuine part and the temperature guage reads normally with the needle in the middle,although on this occasion it was slightly to the left indicating that the coolant was probably not quite up to temperature I understand that BMW M47's run cool but is this normal ?

Yes, I think so. It looks like your new thermostat is doing its job! Was the heater warm enough? It's a very efficient engine, so it will reject very little heat into its cooling system. If the top hose was warm and the bottom hose was cold, the thermostat was probably almost closed, keeping the heat in your engine, where it should be. If you did the same run on a hot Summer day, you might find that the top hose was a lot hotter and the bottom hose a fair bit hotter. Again that would be the thermostat doing its job.

Nodge68 · Nov 22, 2019

110tim said:
I understand that BMW M47's run cool but is this normal ?

Yes, perfectly normal. The radiator only gets rid of excess heat. If enough heat is being dissipated by the heater and from the engine block, then there's no need for the radiator to get rid of any more, so the thermostat remains closed.

110tim · Nov 23, 2019

Avocet1 said:
Yes, I think so. It looks like your new thermostat is doing its job! Was the heater warm enough? It's a very efficient engine, so it will reject very little heat into its cooling system. If the top hose was warm and the bottom hose was cold, the thermostat was probably almost closed, keeping the heat in your engine, where it should be. If you did the same run on a hot Summer day, you might find that the top hose was a lot hotter and the bottom hose a fair bit hotter. Again that would be the thermostat doing its job.

thanks for the reply, the heater was on but not fully and obviously sucking what little heat there was in the cooling system, I found it very strange that after a long run the radiator hoses were so cool I am used to older less efficient engines

110tim · Nov 23, 2019

Nodge68 said:
Yes, perfectly normal. The radiator only gets rid of excess heat. If enough heat is being dissipated by the heater and from the engine block, then there's no need for the radiator to get rid of any more, so the thermostat remains closed.

Thanks for the reply Nodge, I am used to older less efficient engines that get hotter, nice to know that this is normal

Avocet1 · Nov 23, 2019

Yes, modern (by which I mean last 20 years or so) diesels have come on in leaps and bounds when it comes to efficiency. I can remember being a young engineering student in the mid '80s and we have a visiting lecturer (a thermodynamics engineer fro Ford, I think) come to talk to us about engine developments. One of the brighter kids asked him if he envisaged the time coming when engines would become so efficient that we'd struggle to get enough waste heat out of them to power the heater. He laughed, in a slightly patronising way and said that he didn't think they'd ever get that efficient. Roll-on 20 years and we now need fuel burning heaters or they'd never get up to temperature in Winter!

GrumpyGel · Nov 23, 2019

Avocet1 said:
Yes, modern (by which I mean last 20 years or so) diesels have come on in leaps and bounds when it comes to efficiency. I can remember being a young engineering student in the mid '80s and we have a visiting lecturer (a thermodynamics engineer fro Ford, I think) come to talk to us about engine developments. One of the brighter kids asked him if he envisaged the time coming when engines would become so efficient that we'd struggle to get enough waste heat out of them to power the heater. He laughed, in a slightly patronising way and said that he didn't think they'd ever get that efficient. Roll-on 20 years and we now need fuel burning heaters or they'd never get up to temperature in Winter!

Rubbish, my L Series dates back to 1960's BMC's favourites and I struggle to get any heat out of the heater.

Mind you, if I top the coolant up, there's enough to flow through the heater and it toasty then

Jayridium · Nov 24, 2019

Avocet1 said:
Yes, modern (by which I mean last 20 years or so) diesels have come on in leaps and bounds when it comes to efficiency. I can remember being a young engineering student in the mid '80s and we have a visiting lecturer (a thermodynamics engineer fro Ford, I think) come to talk to us about engine developments. One of the brighter kids asked him if he envisaged the time coming when engines would become so efficient that we'd struggle to get enough waste heat out of them to power the heater. He laughed, in a slightly patronising way and said that he didn't think they'd ever get that efficient. Roll-on 20 years and we now need fuel burning heaters or they'd never get up to temperature in Winter!

Incidentally, we have now hit a tipping point where for any given volume of engine displacement, a modern turbo diesel engine beats the output of a naturally aspirated petrol engine. Twenty years ago, petrols were making ~100bhp a litre, diesels were making 45-50bhp per litre. Nowadays, turbo diesels can make north of 110bhp per litre, and a trazillion lbft of torque.

GrumpyGel · Nov 24, 2019

Jayridium said:
Incidentally, we have now hit a tipping point where for any given volume of engine displacement, a modern turbo diesel engine beats the output of a naturally aspirated petrol engine. Twenty years ago, petrols were making ~100bhp a litre, diesels were making 45-50bhp per litre. Nowadays, turbo diesels can make north of 110bhp per litre, and a trazillion lbft of torque.

But in real terms are they any more fuel efficient that 20 years ago?

There are loads of stories of Evoques and DSports only getting about 20mpg - that's 1/2 of what I get out of my 20 year old lump.

Nodge68 · Nov 24, 2019

GrumpyGel said:
But in real terms are they any more fuel efficient that 20 years ago?

There are loads of stories of Evoques and DSports only getting about 20mpg - that's 1/2 of what I get out of my 20 year old lump.

Fuel efficiency is a very complex subject, which is affected by many outside variables. However as a rule, the more emission control stuff an engine has, the less efficient the engine will be.

dfossil · Nov 25, 2019

My lightweight S2A gave b*ggerall out of it's heater - must have been decades ahead of it's time

- possibly other factors at work

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