What’s producing heat under bonnet overnight?

[dash]

Two defrosted circles on the bonnet suggest some heat beneath, but from where? As far as I’m aware there’s only the injectors anywhere close (and there are 3 of them!!).
Battery seems ok (monitored regularly using BM6), so not a significant energy drain.
Anyone else noticed this?

[APS]

As the outside temperature drops, the engine will take longer to cool down than the bonnet and is effectively giving off heat until it is the same as the ambient temperature.

[dash]

Not this time. Car has been unused for 2 days.

[APS]

Re-read my reply. This is just a question of thermal inertia. The same will apply to the ground underneath the car which will also contribute some heat that flows up through the engine bay.

[Kental]

Are the frosted bits where the sound deadening is so blocking the ground effect

[APS]

1 minute ago, Kental said:

Are the frosted bits where the sound deadening is so blocking the ground effect

Exactly. There will be openings in the sound deadening for the wash nozzles and these areas will be kept warm by the engine and ground beneath while the frost forms.

[flash22]

2 minutes ago, APS said:

Exactly. There will be openings in the sound deadening for the wash nozzles and these areas will be kept warm by the engine and ground beneath while the frost forms.

the washer jets are in the scuttle tho

It is more likely RTF/paint contamination it just froze at different rates

or the local fox/cat has sat on the car when it was still warm

parked under a carport or tree may explain the 4 drop marks in a row

[donkeychomp]

2 cats?

Alex

[Ralph H]

This is mine tonight same holes in snow. 
 

no idea what causes it. 

[TonyHSD]

Heat trapped in that spot. 
As explained by others and I seen these on any car , any make, any model. 
Perhaps not in electric ones. 

[MikeSh]

52 minutes ago, TonyHSD said:

Heat trapped in that spot. 
As explained by others and I seen these on any car , any make, any model. 
Perhaps not in electric ones. 

As the exhaust is between the engine and firewall the back of the bonnet will have a bit more residual heat than the front. The pattern is almost certainly due to the underlying structure of bracing and cladding material if there is any.

[APS]

16 hours ago, Ralph H said:

This is mine tonight same holes in snow. 

Open the bonnet and take a photo of the underside. There will be some clues there.

 

[Cyker]

Or maybe these are the new alternative to Crop Circles!   

[Ralph H]

3 hours ago, APS said:

Open the bonnet and take a photo of the underside. There will be some clues there.

 

That will have to wait until the weather warms up a bit or I have to fill the screen wash, it’s cold and dark out there! And my security camera can’t see under the bonnet 

[Rhymes with Paris]

1 hour ago, Cyker said:

Or maybe these are the new alternative to Crop Circles!   

Could also be aliens 👾 up to mischief.

There is a lot of that going on up here in the frozen North, well midlands really, but still chilly.

[TonyHSD]

As someone else said previously the heat from the ground and anything else around has been trapped exactly at this spot and no matter if there is bonnet cover or not this is the top part of the engine bay and any warmer air will be trapped there. 
This is also the favourite place of any rodents or other animals when it’s cold. Plus the plastic cable insulation seems like a tasty snack to all these little fellas 🦫🐁🐭

[flash22]

YC bonnet

Mk4 (a bit mangled)

[TonyHSD]

Car not used for over 24 hours. Same spots as any other car. 

 

[Benzowner]

It could be the hybrid system power to the/from the engine/brake system. Not sure if the hybrid Battery powers down when the car is switched off.

[dash]

I’m sure the HV Battery is disconnected when the car is switched off (relays on the HV Battery are opened)

[APS]

23 hours ago, flash22 said:

Mk4 (a bit mangled)

That seems to reflect the patters in the frost perfectly. Note the air channels that lead from the sections on either side of the centre section to the top of the bonnet. That's what I mistook as "crop" nozzles.  🙂

[flash22]

the structure and outer skin are also bonded together