Coolant Temperature

tom1979 · Aug 4, 2021

Hi all, I have an Android head unit on my D2 so I can monitor the ECU readouts whilst driving. Towing our not-so-small caravan last week I noticed the coolant temp at 99*C (60mph, flat road, approx 20*C ambient). Changing down a gear to go up a hill the temp dropped down to 91*C. Since then after some testing it seems if the revs are higher the coolant sits around 90*C. As a test on a flat road today I set the cruise control the 50mph in 5th gear, temp went up to 97*C. Changed down to 4th and reset the cruise control and it went down to 90*C.

I can't tell if it's a thermostat issue? I'm pretty sure it's not an airflow issue as the vehicle is moving at the same speed, and I also fitted a new OEM viscous fan last week. Could the extra revs opening up the bypass valve make for better cooling? I cannot remember what thermostat I used, it would have been an OEM or genuine one but I have noticed that not all are stamped with the temp and the ones that are can vary.

Cheers.

sierrafery · Aug 5, 2021

tom1979 said:
Could the extra revs opening up the bypass valve make for better cooling?

Hi. IMO it's not the bypass valve but the higher rotation speed of the viscous fan which circulates more air

kermit_rr · Aug 5, 2021

My radiator had a small amount of dirt on it, blocking air flow. Washed that off and it runs cooler

tom1979 · Aug 5, 2021

sierrafery said:
Hi. IMO it's not the bypass valve but the higher rotation speed of the viscous fan which circulates more air

I hadn’t thought of it that way! It could possibly be the radiator then, that’s the only thing that wasn’t replaced when the engine went in

Mario110 · Aug 17, 2021

In germany you can get 3 different types of the thermostat, opening at 86°, 93° and 96° if I remember correctly. I had the 93° (by mistake) and the temperature was around 95° - 97° going up to 105° at a hill. So I changed the new thermostat to the original one opening at 86°.

tom1979 · Aug 17, 2021

I swapped my thermostat out for a 78*C version, sits at low 80's now consistently. I havent towed with it yet. I want to try and test the old thermostat but not sure of the best way with it off the vehicle (Testing Td5 Thermostat off the vehicle | LandyZone - Land Rover Forum)

sierrafery · Aug 17, 2021

tom1979 said:
I swapped my thermostat out for a 78*C version, sits at low 80's now consistently. I havent towed with it yet. I want to try and test the old thermostat but not sure of the best way with it off the vehicle (Testing Td5 Thermostat off the vehicle | LandyZone - Land Rover Forum)

It's a whole mess around these thermostats. The 78*C version vas originally conceived for V8? i know about the soft spring "warm weather" type for Td5 which opens at 82, the optimal running temp for Td5 is around 90*C, below that you get higher EGT at the same load cos it's slightly overfuelled.

tom1979 · Aug 17, 2021

sierrafery said:
It's a whole mess around these thermostats. The 78*C version vas originally conceived for V8? i know about the soft spring "warm weather" type for Td5 which opens at 82, the optimal running temp for Td5 is around 90*C, below that you get higher EGT at the same load cos it's slightly overfuelled.

I've been testing this for a few days with different driving styles and haven't seen any noticeable change in EGT. I agree low 80's is a bit low, but mid 90's is a bit high leaving little room for error. I think the 82*C hard spring thermostat (PEM101020) is probably the better option but they are not available.

Mario110 · Aug 17, 2021

Yes 82° is the correct one (not 86° like i mentioned before), it's starting at this temperatur and is full open at 96°, so 97° like mentioned in the first post is ok in my point of view. During my observations with the wrong thermostat and 105°, the gauge doesn't show anything so I'm pretty sure that there is some room for higher temperatures because the coolant system is under pressure.

tom1979 · Aug 17, 2021

Mario110 said:
Yes 82° is the correct one, it's starting at this temperatur and is full open at 96°, so 97° like mentioned in the first post is ok in my point of view. During my observations with the wrong thermostat and 105°, the gauge doesn't show anything so I'm pretty sure that there is some room for higher temperatures because the coolant system is under pressure.

Many of the genuine thermostats are stamped 88*C.

Mario110 · Aug 17, 2021

It's a mess with spare parts....

tom1979 · Aug 17, 2021

Mario110 said:
It's a mess with spare parts....

Quite a lot are not stamped or marked at all. I know the higher temps are ok but I would personally prefer to see low 90's normal running temp and mid to high 90's towing. Over 100 i don't think is a good idea even if LR think so.

sierrafery · Aug 17, 2021

tom1979 said:
Quite a lot are not stamped or marked at all. I know the higher temps are ok but I would personally prefer to see low 90's normal running temp and mid to high 90's towing. Over 100 i don't think is a good idea even if LR think so.

Yes, around 90(+/-2) is the best. A bran' new Td5 with clean coolant circuit won't exceed that even with the genuine thermostat but as they are getting old the cooling is not so performant anymore.

Discodevon · Jun 20, 2022

So guys which is the best thermostat to get then, I’m thinking of changing mine soon

sierrafery · Jun 20, 2022

Discodevon said:
So guys which is the best thermostat to get then, I’m thinking of changing mine soon

The best is PEM100990LR

Discodevon · Jun 20, 2022

sierrafery said:
The best is PEM100990LR

Thank you sir, will order this week, Is it still ok if I do towing etc?

sierrafery · Jun 20, 2022

Discodevon said:
Thank you sir, will order this week, Is it still ok if I do towing etc?

It's OK as long as your cooling system and engine management is OK and you dont have bigger tyres

Discodevon · Jun 20, 2022

sierrafery said:
It's OK as long as your cooling system and engine management is OK and you dont have bigger tyres

Thanks running 265/7516 defender td5, I live in a really hilly area in the south west (uk) when I had my nanocom plug in a couple years ago with the trailer on the back it beeped at me saying coolant temp warning but then went after I had reached the top and backed off the throttle a bit is that ok?

sierrafery · Jun 20, 2022

With such big tyres better put a PEL500110

tom1979 · Jun 20, 2022

Discodevon said:
Thanks running 265/7516 defender td5, I live in a really hilly area in the south west (uk) when I had my nanocom plug in a couple years ago with the trailer on the back it beeped at me saying coolant temp warning but then went after I had reached the top and backed off the throttle a bit is that ok?

I've got genuine thermostats and pretty sure I've got some 78*C ones too (stamped). Let me know and I'll sort you out at trade

I run the 78*C one on my D2 and have not seen coolant temps higher than 84*C.

Coolant Temperature

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