Member Since: 30 Jan 2012
Location: Banbury
Posts: 202
FBH Duration
Hi All, Is the FBH meant to stay on all the time in cold weather or is it meant to turn off once the engine is up to operating temperature? Mine seems to be on all the time?? I have a 25 mile commute in the mornings and the heater is still puffing out smoke when I arrive at work.
10th Dec 2012 11:02 am
DiscoDunc
Member Since: 08 May 2006
Location: Bristol
Posts: 16390
it can stay on all the time
Quote:
Supplementary heating is requested by the ATCM while the engine is running if the ambient temperature is less than 5 °C (41 °F) and the engine coolant temperature is less than 75 °C (167 °F).
The ATCM cancels supplementary heating if the ambient temperature increases to 5 °C (41 °F), the engine coolant temperature increases to 75 °C (167 °F), or the engine stops.
Duncan
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10th Dec 2012 11:07 am
Fudpucker
Member Since: 30 Jan 2012
Location: Banbury
Posts: 202
That's what I thought but the engine certainly seems to be up to temperature. The gauge is in the middle and the heating chucks out enough hot air to strip paint. What might cause it to stay on assuming the engine is at normal operating temperature? I am assuming this would be around 92-96 degrees C???
10th Dec 2012 11:28 am
Divlar
Member Since: 10 Sep 2008
Location: West Midlands
Posts: 221
Mine stays on too regardless of engine temp but turns off if outside temp more than 5 degrees.
10th Dec 2012 7:29 pm
Robbie
Member Since: 05 Feb 2006
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Fudpucker wrote:
That's what I thought but the engine certainly seems to be up to temperature. The gauge is in the middle and the heating chucks out enough hot air to strip paint. What might cause it to stay on assuming the engine is at normal operating temperature? I am assuming this would be around 92-96 degrees C???
I think you are mixing cause and effect regarding the impact the FBH is having. Also worth noting that the middle point of the temp gauge is weighted to encompass a wide range of coolant temperatures so as to not worry the customer and that the FBH has 2 modes with either a 5kW or 2.5kW output. It can cycle between the modes, including off, to maintain the correct coolant temp.
The FBH runs when the coolant temp needs it, but only when the outside air is cold. If the FBH runs for more than 72 minutes then it will shut down to stop build up of carbon deposits on the glow plug. If the coolant temp and outside air still fall in the FBH running range then the FBH will restart when the cool down phase is complete.
Land Rover - Turning Drivers into Mechanics Since 1948
Member Since: 30 Jan 2012
Location: Banbury
Posts: 202
Regarding cause and effect, i am not worried about it working as such and wasn't worried about any effect it might be having to the running of the car other than fuel economy and whether it ought to turn off once the engine was hot. Thanks for the extra info. Seems all is ok then. I wonder if anyone blocks part of their cars radiator off nowadays when its cold given that all cars have thermostats??
10th Dec 2012 9:13 pm
Robbie
Member Since: 05 Feb 2006
Location: ¯\_(ツ)_/¯
Posts: 17932
Not a good idea these days as radiators also do things like the gearbox, aircon compressor, fuel cooler etc. Thermostat on a D3 starts to open at 82degC and is fully open at 95degC.Land Rover - Turning Drivers into Mechanics Since 1948
Member Since: 30 Jan 2012
Location: Banbury
Posts: 202
Good point ref the gearbox. I would still like to know why the fbh doesn't go off though??? The engine is definitely getting hot enough. At times my 25 mile journey can mean half an hour just sat in traffic when you would expect the engine to get hot. The viscous fan coupling isn't seized and the heating is very warm so I would have thought all is ok regarding the engine getting to temperature. Then again without actually measuring it, it is hard to say for certain.
Standing in traffic often causes the diesel engine to cool down, not heat up.Mark.
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11th Dec 2012 8:42 am
Hairy Dan
Member Since: 19 Jan 2011
Location: Co. Durham
Posts: 12319
Modern diesel engines are highly efficient and this means there is little usable waste heat from the engine available to heat the vehicle on cold days, so manufacturers use FBH's in their vehicles to maintain temperature.Cheers Ian
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11th Dec 2012 9:10 am
Martin Site Admin and Owner
Member Since: 06 Nov 2004
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LR wouldn't pay for an FBH and fit it unless it was necessary 06 D3 SE / 15 LR D90 XS SW / 88 LR 90 Td5 / 68 BMW 2000 ti
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11th Dec 2012 9:21 am
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Shouldn't that read "You wouldn't have paid LR for an FBH and fit it unless it was necessary "
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11th Dec 2012 10:56 am
Fudpucker
Member Since: 30 Jan 2012
Location: Banbury
Posts: 202
The engines might be efficient but they will get just as hot as any other engine and overheat if stood in traffic with no method of cooling them down.
This is true. The thermostat on the radiator is a wierd one - operates on pressure and temperature - and I can't remember what the manual I read said about the pressure part.
It could be that the pressure side of the thermostat kept it open despite the water being cooler than required and the natural conduction/convection off the radiator in the winter is greater than the heat that gets put into it - and pulling heat off to warm the cabin up will suck alot of heat out of the engine too.Mark.
2006, D3 SE Auto - gone but not forgotten.
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11th Dec 2012 8:01 pm
Robbie
Member Since: 05 Feb 2006
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The thermostat is exposed to 85% hot coolant from the engine on one side and 15% cold coolant returning from the radiator bottom hose on the other side. This allows the thermostat to react to the ambient conditions and provide coolant control for both winter and summer use. Hot coolant from the engine passes via holes in the by-pass flow valve into a tube which surrounds 85% of the thermostat sensitive area. Cold coolant from the radiator conducts through the remaining 15% of the sensitive area. In cold ambient conditions, the engine temperature is raised by approximately 10°C to compensate for the heat loss of 15% exposure to the cold coolant returning from the bottom hose. This improves heater performance and engine warm-up.
The by-pass flow valve is held closed by a light spring and operates to further assists engine and heater warm-up. When the main valve is closed and the engine speed is at idle, the coolant pump does not produce sufficient flow and pressure to overcome the spring and open the valve. In this condition the valve prevents coolant circulating through the by-pass circuit and directs coolant through the heater matrix only. This provides a higher flow of coolant through the heater matrix improving passenger comfort in cold conditions.
When the engine speed increases above idle, the coolant pump produces a greater flow and pressure than the heater circuit can accommodate. The build up of pressure acts on the flow valve, overcoming the spring pressure, opening the valve and relieving the pressure in the heater circuit. The valve then modulates to provide maximum coolant flow through the heater matrix and allowing excess coolant to flow into the by-pass circuit to provide the engine's cooling requirements at higher engine speeds. The thermostat then regulates the flow through the radiator to maintain the engine at the optimum temperature. Maximum opening of the thermostat, and therefore maximum flow through the radiator, occurs if the coolant temperature reaches 95°C.
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