I had a similar situation. Coolant level was at max when cold, but the low coolant light would come on after about an hour of driving. This may be how long it took for coolant to circulate through the auxiliary radiators or long enough for it to leak enough to trip the warning light. I think there is an electric water pump for the aux rads, so they may switch on after some condition is met (like coolant temp above x). My driver side aux radiator had a leak. Easy to check if you pull the wheel arch liner. The common leak starts at the top. Seems to be an issue with early p300s, not sure what years are affected. Saw a post that the 2024 p300s have deleted the driver side aux radiator. I guess thats one way to fix it.

 

About a month ago, this started happening with my '22 P400 at around 52k miles. Happens 1-2 times a week when the engine is hot and clears after the truck sits overnight. When it happens, I always check and the level is always the same - near the max level, maybe a bit over. I figure it's a bad sensor.

 

It's exceedingly worrisome to me that a service advisor would send you off saying it's normal to to need to top off the coolant.

I say this because the system is a closed lopped. Meaning there is no reason for consption of coolant.

I admit I could be wrong here as I'm no mechanic. However, for there to be missing coolant it must be leaking from a hose or radiator directly. It just doesn't get 'consumed'.

 

Its a closed system it is absolutely not normal to have to top it off. I just had the low coolant light come on this weekend. Took it to the dealer and it is a leaking hose going to the turbo charger. First time in four years it needed coolant (well except when I drained the aux radiators when I relocated them for larger tires

 

I had recently started getting low coolant level warnings too. Coolant must have a pinhole leak somewhere - nothing to see, no puddles, no significant odour, and no signs of a head gasket leak in oil or exhaust so its a mystery. Mostly see it if I change direction quickly so must be the float or sensor in the reservoir. Still, frustrating. My LR3 had this issue too but that was the float becoming "waterlogged" for lack of a better term...fix was to replace the resevoir - then it was fine. Hoping not the same issue here.Will have a pressure test done next maintenance.

 

I had a low coolant warning on my P400. Checked and the tank actually was almost empty, so I filled it up so I could get it to the dealer. They ran a pressure test and said it was leaking from the turbo pipe o-rings.

I recommend everyone check their coolant levels periodically, when I saw the warning I thought it was gonna be a phantom light but it actually was very low.

 

Thanks for the note - I'll mention that when I take it in and have them check! Much appreciated. Best I get to it before it becomes serious.

 

I've got an odd one — there’s a light coolant smell in the engine bay once the vehicle warms up. That was traced to the turbo O-rings, which were replaced, but the repair didn’t solve the smell inside the cabin.

When the heat is on, the odor only comes through the driver’s side vents (left-hand drive). The two front vents on the left side of the dash carry it strongly, and in the second row, it’s only present through the left vent on the rear center console (behind the fridge). The passenger-side vents are completely clean — you can put your nose right up to them and smell nothing — but the driver’s side vents have a strong maple syrup or butterscotch odor.

The dealer is still investigating. The system passes pressure tests, but I suspect the issue lies either with the feed into the heater core or a small leak near the firewall where vapor could be getting pulled into the fresh-air intake before being circulated into the cabin.

Curious if anyone else had something similar?

 

So I ended up much as the previous author noted - I had to replace the line that runs under the turbo, and I had to replace the coolant reservoir because the sensor was pooched (seems the sensor is bonded in the tank and almost impossible to remove). Dealer said its a pretty common issue on the Defender. Was more an annoyance than a debilitating issue but was not cheap to replace. Dealer had parts on hand. I also learned the Range Rover had a similar issue for years (a decade?) and LR finally replaced the plastic tube with an aluminium one. Why they didnt do the same on the Defender is beyond me. A known issue but NOT covered by any recall and warranty had expired. Such is life. (My LR3 also has had a coolant leak since birth...drives me nits - and I've changed the reservoir there too. Clearly LR has issues designing robust cooling systems.

 

Check the pump, on mine it passed all the tests but leaked when warmed up/ hot.