My 2004 TD4 FL1 has been running on the cool side all the time I have had it, due to the sticking termostat. Haven't have motivation to change the oem thermostat or doing the inline termostat mod either. Car has FBH and cabin heat has been ok, not spectacular. It's winter here in Finland again and I thought I'll try this ancient mod to cover the grille to block air flow to the engine bay. Ended up using xpe stuff and cut two pieces; one for the top opening and one for the bottom opening, leaving the thin middle one not covered. Immediately noticed engine temp rising to half way, which has been a rare sight earlier. Decided to do some testing using Foxwell and driving with live data on. Today we are having 2 degrees celsius here, not the actual winter yet but typical November cold. After 15 minutes of driving coolant temp had settled to 75 degrees and when letting it run idle temp rose to 85. Cabin heating blows very hot now, so the end result is that blocking the grille is an improvement - not a pretty one but functional. Looks like the temp gauge has been normalized and it stays in the half way quite wide range of temps; in my test at least 75-85 and probably way higher also.



https://photos.google.com/photo/AF1QipOitgjunr01fdV4hpmhJJaaYFzvKZQ7SL0f8cNV

Yes, the temperature gauge has been calibrated to show normal when the engine is between 75°C and 115°C. This is pretty normal for LRs, where the operating temperature can vary widely depending on load on the engine.

That would explain why, when I had to drive home 20 miles with no belt on, the gauge still showed 'N' when I got home but the engine was having a boil up !!

andyfreelandy said:

That would explain why, when I had to drive home 20 miles with no belt on, the gauge still showed 'N' when I got home but the engine was having a boil up !!

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How is the coolant tank? Are there small cracks around the filler neck? Cracking is common, which prevents the tank from holding pressure, resulting in boiling below the HOT portion of the gauge.

I figured it needed air to boil but no weeping or leaks. What temp does it need to be to boil in a closed system ? Also, could the pressure relief cap allow air in when open due to pressure?

I've read somewhere that in a pressurized system using a proper coolant/water mix the boiling point could somewhere around 150C.

Stance said:

I've read somewhere that in a pressurized system using a proper coolant/water mix the boiling point could somewhere around 150C.

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The coolant on a correctly pressurised FL1 system will start to boil at 121°C, providing the pressure is held at full cap pressure.
Unfortunately the pressure cap can loose spring tension over time, allowing the pressure to release before it's correct pressure. The coolant tank is also known to split, which prevents pressure from building, resulting in boiling below the high portion of the gauge.