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| andy63 Member Since: 30 Jun 2023 Location: north east Posts: 676  
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a great description , thanks for taking the time..
I wonder what the designed " limiting ambient temperature" as you call it , of a puma engined defender was designed to be..?? I know there are many variables in practice in terms of the way the cooling system has been maintained... |
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25th Mar 2025 11:59am |
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| Ianh Member Since: 17 Sep 2018 Location: Essex Posts: 2204
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These two topics make an interesting read on the use of standard UK and lower temp thermostats.
I don’t think a definitive conclusion was achieved, but those that advocate the lower temp thermostat in hotter climates when working the vehicle hard did do a fair amount of temp monitoring and analysis. So I don’t think all were a victim of placebo effect. https://www.defender2.net/forum/topic32086...thermostat https://www.aulro.com/afvb/discovery-2-a/1...ir-d2.html |
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25th Mar 2025 1:08pm |
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| andy63 Member Since: 30 Jun 2023 Location: north east Posts: 676
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Cheers for the links ian..
Quick look, they are long threads..I'll have a proper read later.. BTW.. what is the standard fitting Thermostat in a Puma..I seem to remember mine is supposed to start opening at 82 deg and fully opened at 96... and I know the 96 sort of ties in with the highest temp I usually get but accept that have sometimes had to drop into 5th to keep it there or reduce it.. |
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25th Mar 2025 1:44pm |
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| Johan_B Member Since: 20 Sep 2024 Location: Gothenburg Posts: 60  
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I skimmed through the first pages of the D2N thread and all the reported temperatures there was still to be expected. The system was still able to control the temperature and the effect of the lower opening temperature was still there. But remember, overheating (which I assumed was the problem) doesn't happen at 92 or 96 degrees. It happens at 115C or some other temperature depending on coolant and pressure in the system. So what that tell me is that these users, even though pushing the vehicle hard, was not at the limit.
One user reported that the temp was steady at 96C up to 32C ambient temperature. They seemed to draw the conclusion that that was the limiting temperature, but then there was likely a 20C margin in coolant temperature before engine protection would be activated. My statement regarding placebo referred to a perceived rise in limiting ambient temperature, i.e. that you could run at max power in higher temperature without overheating with the lower opening thermostat. LAT for our Pumas is probably not revealed, but it seems to be lower than what we would like it to be considering all reports of overheating. Legally it must be minimum 25C. But higher than that is optional for the manufacturer. But we can't blame all problems on Land Rover. In the thread there was users able to drive hard at 44C jet I had overheating problems this summer in 35C. On closer inspection my airbox lid was not properly attached, causing the engine to breath 70C air from the engine compartment. Engine becomes extra hot, charge air gets extra hot, CAC rejects extra heat in front of the radiator. That's just one example of how things can go wrong. Now add a winch and some lights in front of the radiator and who knows how bad it can become? Maybe I am drifting off topic... |
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25th Mar 2025 3:14pm |
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| Chicken Drumstick Member Since: 17 Aug 2020 Location: Near MK Posts: 856
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Ultimately the cooling system only has capacity to handle 'x' amount of heat. The thermostat has no direct impact on this at all, in fact if you removed the thermostat completely, it still wouldn't impact the total heat/cooling capacity of the system. The only impact it can have, is to allow the additional cooling (using all of the systems capacity rather than part of it) sooner at a lower temp. This may reduce PEAK numbers, because the cooling will happen sooner, but it doesn't increase its ability, it is just operating in a different part of its range now. And this 'range' is only extending the cooling on the lower temp side, not the hotter temp side. The additional cooling may impact emissions, mpg & performance. As well as make the heater worse, heater air cooler and longer times for the engine (and engine oil) to warm up. If your vehicle is overheating, i.e. going beyond the capacity of cooling system, then this will not help or solve this issue. It may, if you are lucky, make it take slightly longer before it overheats. But thats about it. The only incidental side effect I can think of, if the engine is running within limits, but at a higher temp, then you may get more heat soak into the engine bay/body sooner. Making more radiant heat for longer, that is harder to actively cool. But ultimately all car makers for many many many decades have been testing their vehicles in a wide variety of conditions. So it will still be within its expected operating range. |
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25th Mar 2025 5:01pm |
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| bear100 Member Since: 22 Mar 2010 Location: South Wales Posts: 1971  
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Thanks, some great reply’s.
I did fit a lower temp thermostat 83°c if I remember correctly? And at the time I couldn’t get my head around how it would make a difference to a hot engine? Typically before I had an issue my engine would run at 86°c pretty much consistently, then all of a sudden it would run 96-98°c, this was the start of my cooling journey! I’m currently in the middle of DIY fitting a new cylinder head as mentioned in another post, so looking for the best setup I can achieve. Think I’m still being quite sensitive to overheating! TBH I hadn’t realised that a radiator would be perishable overtime, I’ve seen a Nissens for sale for under £200 so it’s a no brainer really. 2023 Defender L663 V8 2016 Range Rover Autobiography 4.4 TDV8 (gone) 2010 110 XS Utility 2.4TDCI 2010 Range Rover Sport TDV8 (gone) 2007 Discovery HSE TDV6 (gone) 1993 110 csw 200 tdi (gone) 1994 90 HT 300 tdi (gone) 1994 discovery 300tdi (gone) 90 hybrid 3.5 v8 (gone) Range rover bobtail 3.5 v8 (gone) |
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25th Mar 2025 10:47pm |
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| Mo Murphy Member Since: 01 Jun 2008 Location: Letchworth Garden City, Herts Posts: 2310 
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Nissens we're the OEM for TD5 and TDCI radiators to Land Rover. Mine is doing sterling work cooling my M57 👍
Mo The Land Rover 90 - Many are called, few are chosen. 50 Shades of Pennine Grey |
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26th Mar 2025 5:25am |
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| andy63 Member Since: 30 Jun 2023 Location: north east Posts: 676
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One other point that I think may be worthwhile while you have ongoing work and won't cause a great deal of extra , would be to fit a coolant level alarm.. if you ever do loose a bit coolant through running hot, or a leak , I think it will give you the best chance of stopping before the overheat causes damage.. |
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26th Mar 2025 6:47am |
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| TexasRover Member Since: 24 Nov 2022 Location: Paris Posts: 1198  
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The LAT design criteria should be different per region. I lived in the Middle East (50 deg C - not often but often enough), there are a lot of Toyotas etc and it would not surprise me if they get factory shipped with a larger radiator for the ME. The ability of the radiator to shed heat (energy to be more precise) will be a function of the temperature differential between the air and the coolant. With less differential you need a bigger radiator with more cooling capacity. My defender now is from Oman where it was sold new. I have changed the radiator already and frankly I did not see any difference (if the one there was original) and when i ordered one there was no 'hot climate ROW option' so I doubt land rover would have accommodated for hot-climate markets specifically. In my experience (also had some Land Rovers in Texas USA) a new radiator can handle a lot, an old one not so much. Buying a larger radiator means you can loose more efficiency over time so they last longer, but if they are 2-3x the price its probably cheaper to change the stock radiator more frequently. |
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26th Mar 2025 8:17am |
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| Johan_B Member Since: 20 Sep 2024 Location: Gothenburg Posts: 60
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Yes, the design criteria can be different between regions but ultimately comes down to the strategy of the maker and the trade offs involved. Unless there is a hot climate pack for the Puma we are all having the same solution.
I've now read most of the two threads above. As Ianh said there was no definitive conclusion, rather they provided good example of the complexity of the dynamics inside the cooling system. In my experience, testing at steady state is one thing, you will be able to predict the temperatures and effect of any changes you do. (This is very hard to do without a test bench) Testing in transient conditions can produce a lot of counterintuitive results. Real world driving is transient to a very high degree. It should not be uncommon to see higher coolant temperatures at lower ambient temperature for example (within reason). The concern for designers is to at all times keep the temperature below whatever failing temperature there is. Fully aware that in some occasions the temperature will rise outside of optimal but below limit for short periods of time. This is the reason there is a filter on the temp gauge for the driver. Anything between, say 88C and 103C (if anyone knows the actual figures please correct me) will be displayed as nominal. Because it is, in the sense that the driver shouldn't need to pay any attention to it. If a driver frequently experience engine protection or that the temp gauge shoots up, either they are running in very high ambient temperatures at full power, or there is something in the system that has degenerated with age or got clogged. Also of course not all radiators are the same. Even if size and depth is the same, the efficiency could be different. Also if running a remapped engine with higher power, the original system will not handle the extra heat up to the same ambient temperature as before (at full power). |
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26th Mar 2025 9:16am |
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| andy63 Member Since: 30 Jun 2023 Location: north east Posts: 676
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There are many factors to consider..bigger upgraded radiators etc, which may well allow greater heat transfare for a given situation, but to me from a very non scientific practical sense and observations I've read countless times on threads the big factor with defender cooling is the flow rate..
I believe the standard radiators have sufficient capacity to shed enough heat.. But increasing the flow rate has the biggest effect on dropping the temp.. I have seen reference somewhere that even though a slower flow rate through a heat exchanger resulted in a larger differential of inlet and outlet temps , the system that was capable of shedding more heat was run at a higher flow rate with less of a differential temp..maybe it's just the overall balance of the time the coolant has to absorb heat to the time spent shedding it.. |
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26th Mar 2025 9:56am |
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| andy63 Member Since: 30 Jun 2023 Location: north east Posts: 676
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And I ment to mention that reducing the quantity of antifreeze in the mixture to a higher %of water will or should help ..again how much I'm nor sure, but as water has a far better capacity to absorb heat than antifreeze it may help..I've not played with that and would likely take a fair while to establish a trend..🤔
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26th Mar 2025 10:16am |
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| Johan_B Member Since: 20 Sep 2024 Location: Gothenburg Posts: 60
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Since, as TexasRover points out, the radiator works with the difference in temperature between the two mediums being used, a higher temperature difference will make it more efficient. Increasing the flow will ensure a higher temperature difference across the radiator, making it more efficient. Thus rejecting more energy per second but not necessarily cooling the coolant that much. The difference in inlet and outlet temperatures is not a good comparison since what we are after is cooling power, rejected energy per second. A higher flow can achieve a higher cooling power with less difference between inlet and outlet. I've also read posts on here where members have overheating problems that can be overcome by gearing down, from 6th to 5th for example. That makes sense for the above reason. But why it should be necessary is an enigma. I can think of some reasons. Detoriation in the system, i.e. old radiator, old coolant, worn pump, etc. Or, and I hope that is not the case, if the power curve has a flat top, as it appears to have, and the cooling capacity is just enough at the peak rated power at 3500 rpm, the flow will be significantly less at 2500 rpm but the power will be almost the same. If this was not considered in the design the system might be able to cope with peak power @ 3500rpm and 45C, but not 97% of peak power @ 2500rpm.  Click image to enlarge |
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26th Mar 2025 11:11am |
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