 | Home > Puma (Tdci) > Engine braking vs brakes |
 
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| Lou Sparts Member Since: 15 Apr 2012 Location: Kent Posts: 1501   
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When i was taught to drive (a very long time ago) drum brakes on cars would very quickly overheat and fade so i was taught to use the same gear to go down a hill as you would need to go up it ! 2005 Td5 90 XS
Steve |
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1st Sep 2013 4:05pm |
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| Glynparry25 Member Since: 16 Feb 2009 Location: Miserable Midlands Posts: 3015  
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THere are a few things to consider........ Personally (electro mechanical engineer) I would say you are causing considerable damage to your engine.
You are using excessive revs with the engine cold- this will cause a lot of wear on engine parts/ components. In the same situation you need to slow down- keep the revs below 3000 (about 2-2500rpm ideally). To do this you have to balance the brakes-eg, release until 3,000 brake until 2,000 release..... and so on- we are talking about gentle braking- not slamming the anchors on. I have used this technique for many years and never had brake fade/ overheat even when towing. Engine braking was a big thing with older drum brakes (overheat easily and retain the heat) but not as bad with calipers, and even less so with vented disks. The saying now is: 'Engine to go, brakes to slow' End of the day, excessive wear on brakes will cost you the maximum of £250 (pads, disks and fluid) where excessive wear of your engine could cost in excess of £10,000. Glyn   |
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1st Sep 2013 5:13pm |
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| Birdy Member Since: 07 Oct 2011 Location: Côte d'Azur Posts: 865  
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“a very long time ago… i was taught to use the same gear to go down a hill as you would need to go up it”
Still holds good today, did the Route des Grandes Alpes at the beginning of June as soon as the Col de la Bonette (2,802 metres, highest paved pass in Europe) was opened, you would NOT want to be coming down hills like that for mile after mile in high gears and using the brakes! Peter |
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1st Sep 2013 5:35pm |
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| Lou Sparts Member Since: 15 Apr 2012 Location: Kent Posts: 1501
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Fresh or recently changed brake fluid is a must if visiting mountainous areas as brake fluid is hydroscopic so absorbs moisture from the atmosphere,this moisture will boil in the extreme heat generated in the calipers during prolonged braking and can cause vapour locks and loss of braking. 2005 Td5 90 XS
Steve |
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1st Sep 2013 5:50pm |
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| limbrickh Member Since: 05 Oct 2012 Location: Canterbury Posts: 20 
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Glynparry25, what you are saying pretty much makes sense. I think I need to use the brakes more. I will also warm the vehicle up thoroughly before heading down.
Sockpuppet - nice explanation! K9F - I don't think the rev hang (or engine ramp) is influencing this because it is staying in one gear (not 1st) so the idle speed would have dropped after a few seconds (it should have anyway!). But yes, the 2.2 doesn't seem to have the engine braking I'm familiar with in older vehicles - someone somewhere mentioned that modern Common Rail diesels are especially bad at engine braking because they always provide a little bit of fuel. Is the TDCI a Common Rail? One question still in my mind though...why is the engine not coming up to temp? With the talk (in the other replies) of compressed gases generating heat (plus the small amount of diesel being burned) and a closed thermostat I would have thought heat would gradually build up. Is the heater on a separate cooling circuit than the radiator and some fluid keeps circulating around the engine even when the engine thermostat is closed? Thanks for your input everyone! |
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2nd Sep 2013 9:14am |
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| jimbob7 Member Since: 06 Jul 2013 Location: uk Posts: 2055 |
Defenders are "over cooled",truck engines are the same,a hot engine on a cold day will soon cool down if the engine is only idling,If your defenders not fully warm to start with that probably won't help either + large amounts of very cold air passing over the radiator/engine.
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3rd Sep 2013 7:03am |
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| robharvey Member Since: 14 Dec 2009 Location: Durban Posts: 86  
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I'll take an uneducated stab at this one, as it's happened to me before as well, in similar conditions to yours. Modern diesels do not fuel when going down hill in gear, therefore if there is no fuel to be compressed no heat can be generated. Add to this very low ambient temps and you actually see your engine temperature going down. I'm sure someone more technically minded will either tear my theory apart, or elucidate it better than I can. |
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3rd Sep 2013 11:59am |
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| Glynparry25 Member Since: 16 Feb 2009 Location: Miserable Midlands Posts: 3015
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Pretty much as mentioned above.....
The engine is generating minimum heat The water is circling the block, goes through the heater matrix where it is cooling down (like a radiator) when you blow the very cold ambient air through it to create hot air in the cab- When the girlfriend's Daihatsu Feroza thermostat failed shut we were able to drive home without it overheating by putting the heater temp to full and fan on max- not bad during the Cyprus summer (35-40 degreesC) But it was a bit warm even with the roof off and the windows open. Viscous fan- this will still be spinning and blowing very cold air over the engine further reducing the temperature. The combination of the three above will prevent your engine heating up. Two things were mentioned in the thread that will get the engine warmer faster: Expensive: Webasto heater- theses are awesome- a few members have installed these and there is loads of handy information from these members and their threads (Fron what I remember dgardel did a very very good write up). Very Cheap- 'Radiator muff' This prevents the cold air being blown over the engine (helps keep the hot air in the engine bay). 
Exmoor trim radiator muff- many others out there of varying prices and quality 
*EDIT*
TDCi- Turbocharged-diesel Direct Common-rail Injection (GEEK SMILEY) Glyn |
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4th Sep 2013 8:41am |
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| Skye_Rover Member Since: 29 Aug 2013 Location: Skye Posts: 85  
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You have been advised incorrectly regarding CR Diesels adding fuel all the time. Unless someone at a calibration stage has made a dogs dinner of the idle governor calibration, no fuel is added whatsoever on the over-run, above an engine speed of circa 250rpm above idle speed. Certainly the Puma 2.4 is not calibrated to add fuel in the way that you mention. This is one of the main advantages of a Diesel, in that you burn no fuel on the over-run. You are correct to use engine braking in the way that you first posted. All LR Diesel calibrations are robust against this sort of use, and there is a specific test in the calibration schedule for cold + altitude long descent, followed by a variety of "difficult" (for the engine) driving styles. Other manufacturers do not necessarily test this type of running. For a Diesel, adding a small amount of fuel after a long descent can give white/grey smoke issues, due in no small part to the engine having cooled down around the pistons, but without the coolant correction mapping to compensate for pilot quantity and timing. Any heat release from pumping losses is small compared to the heat release from fuel burn, hence your cooling system is doing too much work, even just through the heater matrix and bypass circuit (your thermostat should be closed with minimal leak-past the diaphragm). However, if you measure your oil temperature, it will not be dropping so far from normal, therefore you will not be doing damage to your engine (assuming you are running on the recommended oil Castrol Magnatec 5W/30 for Ford) as the oil is what keeps the bearings happy! Roads? Where we're going, we don't need roads. |
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4th Sep 2013 10:05am |
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| Naks Member Since: 27 Jan 2009 Location: Stellenbosch, ZA Posts: 2638 
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I'd recommend also going down using engine braking. Provided the engine has oil, there shouldn't be any long term damage --
2010 Defender Puma 90 + BAS remap + Alive IC + Slickshift + Ashcroft ATB rear 2015 Range Rover Sport V8 Supercharged
Defender Puma Workshop Manual: https://bit.ly/2zZ1en9 Discovery 4 Workshop Manual: https://bit.ly/2zXrtKO Range Rover/Sport L320/L322/L494 Workshop Manual: https://bit.ly/2zc58JQ |
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4th Sep 2013 10:50am |
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| JamesSmith2013 Member Since: 05 Sep 2013 Location: Glenwood Posts: 1 
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My ballot goes to Engine braking..Engine brakes decrease the occurrence of brake malfunction by utilizing the Engine to slow the rig. They boost the effectiveness of braking, save cash by decreasing wear and rip on the tires and brake system, and boost safety.
 You should check here Oil Change Mission ViejoLast edited by JamesSmith2013 on 7th Sep 2013 6:54am. Edited 1 time in total |
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6th Sep 2013 4:57pm |
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| Naks Member Since: 27 Jan 2009 Location: Stellenbosch, ZA Posts: 2638
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Using engine braking will prevent this type of accident. Inexperienced driver came down a long pass on brakes only, cooked them and....
-- 2010 Defender Puma 90 + BAS remap + Alive IC + Slickshift + Ashcroft ATB rear 2015 Range Rover Sport V8 Supercharged
Defender Puma Workshop Manual: https://bit.ly/2zZ1en9 Discovery 4 Workshop Manual: https://bit.ly/2zXrtKO Range Rover/Sport L320/L322/L494 Workshop Manual: https://bit.ly/2zc58JQ |
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6th Sep 2013 5:26pm |
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| VeeTee Member Since: 06 Mar 2011 Location: Somewhere Posts: 1512 
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That is wat I learned too... The descent of the Stelvio Pass (2758) in the first week of June (road was snow free, but 1.5 m of snow next to the road at the top) I did with engine braking with occasionally some pulsed added braking. Revs where not more than 3000 rpm, and engine temp approx 60-65 at times (digital gauge). I think it is safer to slow down with engine breaking and save the brakes for if / when it is really nessecary. If the brakes are overheated when you really need them in emergency, you have a problem. Click image to enlarge Cheers, Vincent 1959 Polynorm 1/4 Ton Trailer, Olive Drab Green (sold) 1970 M416 Military Trailer (Camping Trailer Conversion), Epsom Green (sold) 1975 Series III 88 V6, Light Green (sadly sold) 1996 Defender 110 CSW 300 Tdi, Epsom Green (sold) 2000 Freelander 1 TD4 3-drs, Silver (sold) 2006 Freelander 1 TD4 5-drs Facelift Automatic, Tonga Green (sold) MySite |
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6th Sep 2013 6:27pm |
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| SteveS Member Since: 05 Oct 2010 Location: Devon & Berkshire Posts: 388  
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Rad Muff is a waste of time in this case - cold engine will mean that if the thermostat is working properly the radiator will be out of circuit and not passing any water through. As for keeping the engine bay warm(er) I think this will only have a very small effect. Took my truck 4000miles north of Arctic Circle roughly half with Muff on and with Muff off - made no obvious difference at temps of -20 to -40C. The Defender engine bay is just too airy. BTW - fit a Webasto block heater - this will put heat in the engine and you will get the benefit on the cab heater too. The cab fan (on a TDCi) takes masses of heat out of the engine - probably less so on yours. You can fire up the Webasto on a timer or when you get back to the vehicle press the button and by the time you've got everyone sorted the block will be warm and the cab warming up
Personally I would go down on the gears with the occasional stab on the brakes to keep the speed and revs sensible. Once you start to get brake fade it is hard to recover from as the more you apply the brakes the worse the problem gets and is a vicious circle. I'd rather wreck an engine (which I doubt) than try to stop a runaway with no brakes by trying to crash down the gears and a truck full of family screaming.....your choice I guess |
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7th Sep 2013 6:37am |
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