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o4dn

Member Since: 08 Jan 2010
Location: South West
Posts: 530

2009 Defender 90 Puma 2.4 SW Alaska White

PEL500110, too cold?

Hi all,

This weekend, I replaced the coolant in MY2009 Puma 2.4 (10 years, as per the schedule) and also changed the thermostat for a PEL500110 (as suggested many times on this forum). The new thermostat is a brand new, genuine LR part.

Previously, the coolant (as measured with the Scanguage) would sit around 93°C, sometimes reaching 100°C under load, whereas the CHT (Cylinder Head Temperature) would often go well above 100°C.

Now, with the PEL500110 fitted and the new coolant (Havoline XLC diluted at 50%), the collant temperature does not exceed 84°C and often go as low as 78°C, whereas the CHT does not exceed 88°C.

The car drives fine, the temperature needle is right in the middle, yet I fear that might be too low for the operating temperature... what do you reckon?

“A Land Rover immobilized is a moral defeat for the driver and bad publicity for the vehicle, […] it's up to you to do justice to your Land Rover!” - Land Rover Driving Technique.
--
2009 2.4 Puma Defender 90 SW
1979 Land Rover Series 3 88"

15th Jul 2019 11:09am

Marks Landy

Member Since: 09 Feb 2015
Location: Cheshire
Posts: 296

As long as you bled the air out the system I wouldn’t worry.

15th Jul 2019 12:29pm

o4dn

Member Since: 08 Jan 2010
Location: South West
Posts: 530

Oh sure, we followed the WSM procedure to the letter and it worked well, so I reckon it's bled correctly.

It's more the temperature that worries me... I mean, for sure, I knew installing the PEL500110 which opens at 82°C instead of 88°C previously would result in a lower running temperature, that was the goal, but that's a lot colder than I was expecting... “A Land Rover immobilized is a moral defeat for the driver and bad publicity for the vehicle, […] it's up to you to do justice to your Land Rover!” - Land Rover Driving Technique.
--
2009 2.4 Puma Defender 90 SW
1979 Land Rover Series 3 88"

15th Jul 2019 1:18pm

dorsetsmith

Member Since: 30 Oct 2011
Location: South West
Posts: 4554

PEL500110

82°C, soft spring rate.
This is the PRT usually suggested for retro conversions on MGFs and pre-2003 MG TFs.

Specifications and additional product information Discovery 2 - All 2.5L TD5 diesel engine models from (VIN) 5A476243 on - Quantity Required - 1
Freelander 1 - All 1.8L petrol engine models from (VIN) 1A000001 on - Quantity Required - 1

PEM100990 is a PRT (pressure release thermostat) for a MGTF LE500.
87°C, medium spring rate.
Defender 2007 on Thermostats- All 2.5L TD5 diesel engine models defender

15th Jul 2019 1:31pm

o4dn

Member Since: 08 Jan 2010
Location: South West
Posts: 530

@dorsetsmith, I'm not sure I'm following, you mean PEM100990 would be for the Puma and PEL500110 for a Discovery TD5? “A Land Rover immobilized is a moral defeat for the driver and bad publicity for the vehicle, […] it's up to you to do justice to your Land Rover!” - Land Rover Driving Technique.
--
2009 2.4 Puma Defender 90 SW
1979 Land Rover Series 3 88"

15th Jul 2019 2:11pm

dorsetsmith

Member Since: 30 Oct 2011
Location: South West
Posts: 4554

yes

PEM100990

Puma 07 to 2016 and defender TD5 1998 to 2006

PEL500110

Discovery 2 - All 2.5L TD5 diesel engine models from (VIN) 5A476243 on -
Freelander 1 - All 1.8L petrol engine models from (VIN) 1A000001 on -

15th Jul 2019 4:49pm

o4dn

Member Since: 08 Jan 2010
Location: South West
Posts: 530

Right, that's the point, several people on here have changed the original PEM100990 for a PEL500110 to get lower temperature, but I am surprised that it gets that much lower

15th Jul 2019 5:55pm

Balvaig

Member Since: 19 Feb 2016
Location: Fife
Posts: 719

2016 Defender 90 Puma 2.2 Landmark LE Corris Grey

I am not sure you have the science correct. A thermostat merely operates at a fixed temperature. It cannot lower the temperature in a system. The opening temperature determines the speed of raising the temperature to a fixed point after which the mechanical heat will determine the final temperature. As long as the mechanical heat exceeds the opening temperature of the thermostat then it is this final heat which you will measure.

So as your final temperature exceeds the thermostat opening temperature the measured heat is determined by the cooling capacity of the system (i.e the radiator etc)

I would suggest that the fact you have changed fluids is the reason there is a difference in temperature, not the thermostat.

By using a lower opening temperature thermostat you will delay the warming up period of the engine as coolant will reach the radiator sooner ( especially in winter). However the final temperature will not change due to the thermostat as your engine temperature exceeds the opening temp of the thermostat.

Probably opened a can of worms here.

15th Jul 2019 6:27pm

o4dn

Member Since: 08 Jan 2010
Location: South West
Posts: 530

Oh sure, the maximum cooling capacity of the entire system does not depend on the thermostat, however the thermostat regulates the running temperature under normal circumstances.

Anyway, I found out the old thread, it was https://www.defender2.net/forum/topic32086.html

Looks like my observation are in line with others, so I guess this is expected

15th Jul 2019 6:53pm

Balvaig

Member Since: 19 Feb 2016
Location: Fife
Posts: 719

The other scenario is that the old thermostat was sticking partially closed, which would result in the temperature being higher due to lack of cooling by the radiator.

15th Jul 2019 6:56pm

BrickBox

Member Since: 05 Oct 2021
Location: Wales
Posts: 618

2008 Defender 110 Puma 2.4 USW Zermatt Silver

Evening bump on this thread. When you have swapped to the cooler running thermostat, which one did you buy? Genuine one only, or are other brands sufficient? 2008 2.4 110 Utility XS.

28th Aug 2023 6:34pm

TexasRover

Member Since: 24 Nov 2022
Location: Paris
Posts: 790

2002 Defender 110 Td5 DCPU Chawton White

Personally I would go genuine on this and the right part number for the application.

Perfectly affordable and just as stated in this thread the actual temperature rating is important and colder is NOT better even in warmer climate, so best to go with what Landrover considered to be the correct temperature.

If a system overheats there is not enough capacity to cool. Unless of course the thermostat is broken fitting a cooler thermostat is not going to make any difference.

Engines that run too cool don't have optimal lubrication and or combustion.

Capital punishment should be reserved for those mechanics that remove thermostats (not possible in most LR applications).

28th Aug 2023 8:14pm

BrickBox

Member Since: 05 Oct 2021
Location: Wales
Posts: 618

Brilliant- thank you.
It’s just a bit of evening reading and learning. I’m not looking to purchase a thermostat right now. 2008 2.4 110 Utility XS.

28th Aug 2023 8:23pm

Dinnu

Member Since: 24 Dec 2019
Location: Lija
Posts: 3188

2012 Defender 90 Puma 2.2 CSW Santorini Black

And old thread, but worth mentioning

dorsetsmith wrote:

Freelander 1 - All 1.8L petrol engine models from (VIN) 1A000001 on -

Not familiar with the Freelander, but on the Rovers with the K series engines, the thermostat was on the radiator outlet / engine inlet, so might also be one of the reasons why the opening temperature of the thermostat had to be lower. 1988 90 Hard Top, 19J Diesel Turbo, Shire Blue - Restoration ongoing
2012 90 CSW, 2.2TDCI, Santorini Black

28th Aug 2023 8:23pm

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