Technical Under engine tray raising the engine compartment and cab temperature?

[xj25vm]

I have a Xsara Picasso which is 15 years old and 150k miles and the lower engine bay is pretty rust free mainly due to it having an engine under tray from factory. On my 2016 Ducato, with 200k miles, which didn't have one, after replacing the oil sump which was pretty much rusting to bits, and cleaning up rust on other components in the lower engine bay, I decided to fit a full under tray to similarly protect from rust - including the two side modules and the middle one. After doing this, during longer drives in the UK this summer (1-3 hours), the temperature in the cab would become pretty unbearable at times. The outside temperature might be at 21-23 Celsius, while the cab would go to 32-34 Celsius - even with the windows open about 25%, and driving at 50mph (no aircon fitted). I checked the vents and there was no sign of warm air coming through. It somehow seems that the under tray is keeping much more heat trapped in the engine bay, which then transfers to the cab area. I've just done another 200 miles run yesterday/today, in much cooler temperatures outside - about 11-13 Celsius - and the cab is finally comfortable, and even the engine pulls much batter, with about 2-3 mpg better economy on average.

Does anyone here have experience with under trays on Ducato - or similar vehicles? I'd really like to keep it on if possible, as the rust protection - specially during the winter season - is really obvious to me based on the experience with the Picasso. Thoughts appreciated.

 

[the green vanper]

The battery in the x250/x290 is in a plastic box located under the middle passenger legs. I assume the heat can get into the cab through there.

It's only covered by the plastic cover. And eventually some internal carpet / mat. I'd insulate the cab floor, including the battery compartment covers. And the steps. With some kind of armaflex or similar. Steps have lots of room underneath.

 

[Jockstrap]

Similar simple questions used to be raised for example about air scoops in the bonnet, and lowering suspension.

The answer is not one factor. Radiated heat from the sun and poor or lack of bonnet insulation no airflow, so what's the engine bay temperature?

Each to their own. Personally with the state of roads and winter salting, like wheel arch guards the benefit is there.

 

[xj25vm]

The battery in the x250/x290 is in a plastic box located under the middle passenger legs. I assume the heat can get into the cab through there.

It's only covered by the plastic cover. And eventually some internal carpet / mat. I'd insulate the cab floor, including the battery compartment covers. And the steps. With some kind of armaflex or similar. Steps have lots of room underneath.

Isn't the battery box located rear of the subframe - and thus not in the engine compartment and not exposed to heat from the engine? Same for the steps - they don't seem to be anywhere near the engine bay? If there is heat coming in from the engine bay, I am guess it is probably coming through the engine firewall/bulkhead area.