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Coolant Temperature

Discussion in 'TD5' started by tom1979, Aug 4, 2021.

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  1. tom1979

    tom1979 Well-Known Member

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    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.
     
  2. sierrafery

    sierrafery Well-Known Member

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

    kermit_rr Green Member Full Member

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    My radiator had a small amount of dirt on it, blocking air flow. Washed that off and it runs cooler
     
  4. tom1979

    tom1979 Well-Known Member

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    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
     
  5. Mario110

    Mario110 Active Member

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    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°.
     
  6. tom1979

    tom1979 Well-Known Member

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  7. sierrafery

    sierrafery Well-Known Member

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    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.
     
  8. tom1979

    tom1979 Well-Known Member

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    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.
     
  9. Mario110

    Mario110 Active Member

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    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.
     
  10. tom1979

    tom1979 Well-Known Member

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    Many of the genuine thermostats are stamped 88*C.
     
  11. Mario110

    Mario110 Active Member

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    :eek: It's a mess with spare parts....
     
  12. tom1979

    tom1979 Well-Known Member

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    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.
     
  13. sierrafery

    sierrafery Well-Known Member

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    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.
     
  14. Discodevon

    Discodevon Well-Known Member

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

    sierrafery Well-Known Member

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    The best is PEM100990LR
     
  16. Discodevon

    Discodevon Well-Known Member

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

    sierrafery Well-Known Member

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

    Discodevon Well-Known Member

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    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?
     
  19. sierrafery

    sierrafery Well-Known Member

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    With such big tyres better put a PEL500110
     
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  20. tom1979

    tom1979 Well-Known Member

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    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.
     
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