Using coolant dye to diagnose leak

[Mozambique]

2010 V8 at 217k km, front & rear plastic pipes and water pump replaced 40k km ago, majority of coolant hoses replaced Aug 2025.

Have been through the endless system burping residual air after replacing the hoses last summer. Coolant level still dropping gradually so figure there's a leak. Added dexcool compatible dye into expansion tank, and here's the thing, when I shine my UV light on the tank, zero fluorescence? Drops of undiluted dye on the filler neck shone brightly. I used the whole 2.5in. tall bottle. Concentration too low? Need a 2nd bottle? Or does the coolant need to evaporate on the warm block and it's the dye residue which glows?

In the meantime will be doing a pressure test to confirm leak.
Any thoughts appreciated!

 

[Nechaken]

Weird.... the regular Land Rover coolant seems to fluoresce on its own I thought ?

 

[txfromwi]

OEM Rover coolant is yellow fluorescent.

 

[Longtrail]

If there's nothing in the engine bay could it be something in the heater core or rear heating system?

 

[Mozambique]

Hey, thanks guys. Using GM dexcool.
Got it into the garage and darker conditions and could leaks glowing

 

[TheCrimsonCrawdad]

Hey, thanks guys. Using GM dexcool.
Got it into the garage and darker conditions and could leaks glowing

Where did the leak end up being from?

 

[Mozambique]

Ha!
I put on new coolant hoses as PM last summer. Went mostly with aftermarket. The $CAD 30 one that attaches on top of the tstat housing was leaking at the plastic part in-between it's two hoses. No reason for this, but it was. Replaced with OEM. Also, coolant seeping from sides of radiator (plastic side parts delaminating according to my mechanic), so I replaced radiator too. Touch wood, so far so good