The ventilation is blowing hot air into the interior

Hello,
Unfortunately, I couldn't find a suitable post. I own an Octavia 1 4x4 TDI PD with manual air conditioning, and I always have the following problem in the summer.

'In the summer, when it's hot and the car gets little airflow, hot air keeps blowing from the vents even though the fan is on max and the heater is set to zero, and the flap is definitely not letting any warm air through from the heat exchanger. In my old Passat (32b), the hot air only blows for a short time until the radiator and ventilation components cool down. With my Octavia, I have to wait forever for the air to get cooler.'
Yesterday I investigated and, to my disappointment, discovered that the fresh air intake area near the partition (water tank/engine compartment) gets so hot that you might think the heating is turned on.

'Now, some people will probably come and ask me why I don't turn on the air conditioning. No, thank you. Should the AC first cool down the unnecessarily pre-heated air (a waste of energy)? Besides, I can't tolerate air conditioning. The exhaust pipe/manifold/turbo etc. gets pretty hot against that partition wall near the water tank.'

Has anyone ever insulated a partition wall before?

Is there anything preventing me from removing the underbody panel in the engine compartment to improve airflow and reduce heat buildup? I understand that this might make my TDI a bit louder for those nearby. Does this panel belong to the vehicle's approval certificate (ABE)?

irisches-bier wrote:

Hello, Is there actually anything preventing the removal of the underbody panel in the engine compartment to increase airflow and reduce heat buildup? I understand that this might cause a slight increase in noise for my neighbors with their TDI. Does this panel belong to the vehicle's approval certificate (ABE)?

I'm not sure about the ABE (German approval), but it probably doesn't matter for other countries. In Germany, it likely wouldn't be approved. What speaks against it is the increased power output (CW value) and higher fuel consumption.

Naja wer Allrad fährt wird mit dieser cw Wert Änderung sicher nicht einen exorbitanten Mehrverbrauch haben. Mach sie doch versuchsweise einfach ab und schau mal ob das was bringt. Ich persönlich habe einen Golf 1J und das ist ja im Prinzip das Selbe wie dein Octavia. Beim Golf ist eine Isolation aus silbernen Dämmatten an der spritzwand. Auch kann ich keine heiße Luft bestätigen. Mal Does it check if all the cables and linkages in your air conditioning system are properly adjusted?

Air is drawn from the water reservoir, but in my case, there's a seal between it and the engine compartment, so there's no contact. The air intake is therefore located between the windshield and the hood.

The ABE (German approval certificate) might be slightly at risk due to the potentially increased noise. Otherwise, I don't think anyone will mind except maybe the TÜV inspector. However, I would recommend leaving them installed, because if you constantly suck in a lot of water from below, the cable and grounding connections in your engine bay, which may not be in perfect condition, could start to corrode prematurely!

The cables are probably fine because if the heating control knob isn't fully turned, only cold air comes in during the winter. And if there isn't a buildup of heat, the air remains cool, at least not noticeably warm.

The sealant applied to the panel between the hood and the body is perfectly fine and creates a good seal. However, it's somewhat strange that the openings in the water tank cover are designed in such a way that the air being drawn in *must* flow along the partition wall, thus absorbing a lot of heat.

The insulation (silver foil) is only in the lower area, specifically where the footwell is. It doesn't extend to the area of the water tank. Is this insulating foil a pre-formed part, or can you also get it for custom fitting? I just remember that there used to be similar foils available as an add-on for catalytic converters, which you basically had to adjust and fit yourself.

Regarding the cw-value (drag coefficient), I don't think that the lower body panel makes much of a difference. To really improve it, you would have to completely enclose the entire underside of the vehicle. What's the point of streamlining the front if the rest of the underbody and rear axle components (even on non-all-wheel drive vehicles) still generate massive air turbulence? Since I mostly drive at speeds up to a maximum of 160 km/h, it probably won't make a significant difference anyway.If someone drives aggressively, then even the best aerodynamic values become meaningless.
Kleine Abweichung vom Thema: Es wird immer versucht den Verbrauch und Schadstoffaustoß der Motoren zu optimieren und handelt sich damit immer schwerere Aggregate und Fahrzeuge ein. Das muß alles bewegt werden. Bei glatter konstanter Fahrt fällt das nicht so sehr ins Gewicht, aber die meisten Fahrzeuge werden doch im Kurzstreckenbetrieb gefahren und da geht das wohl eher negativ in den Verbrauch ein. When I think about the fact that an A2 with a 1.4L engine weighs almost 1000 kg (and it's an aluminum body, mind you), and a Passat 32b Variant 1.8L 66kW weighs 1007kg, well, that says everything.

'With my Passat, I get most of the splash water coming in through the front grille (because there's a missing panel there that I forgot to order at some point, and now it's no longer available as a spare part). Of course, all the lower parts like the transmission etc. are exposed to the moisture. However, I don't think much gets in higher up except through the opening in the front grille.'

Regarding the cw-value (drag coefficient), I don't think that the lower body panel makes much of a difference. To really improve it, you would have to completely enclose the entire underside of the vehicle. What's the point of streamlining the front if the rest of the underbody and rear axle area (even on non-all-wheel drive vehicles) still generate massive air turbulence? Since I mostly drive at speeds up to a maximum of 160 km/h, it probably won't make a significant difference anyway.

Hello, don't do that here.
False ceilings are more important than you might think.
If it were solely about fuel consumption and speed, all the underbodies would be completely smooth.
AUDI has completely clad the underbodies of its new vehicles to improve speed and reduce fuel consumption. This results in a reduction of approximately 0.3 to 0.5 liters per 100 kilometers!

Regarding downforce and maximum speed, I would rather refer to motorsports, where these aerodynamic modifications have a more significant impact. For example, a Suzuki Swift in Group H with a 1.3-liter engine producing approximately 185 horsepower, featuring a completely enclosed rear section: this resulted in an increase of 16 km/h in maximum speed at the Döttinger Höhe (a specific location).
In the WTCC, the size of the engine cover is prescribed. Certainly because it doesn't add to the weight.
In the late 1980s, several manufacturers offered underbody panels designed to increase top speed.

Back to the climate problem:
In the field of injection molding, the absolute maximum temperature for stagnation heat is a critical factor.
Even without an underbody panel, it will still be present there, but it will be reduced because there is more air movement in the engine compartment (which leads to poorer aerodynamics and increased fuel consumption!).
One thing you could try is adding more soundproofing to the firewall on the engine side.
What's even more effective is to bring fresh air into the interior space with a flexible resistance system.
To achieve this, you would need to modify the window cover. This would reduce the amount of warm air being drawn from the water tank. However, a problem with the PQ34 platform is that it already has issues with airflow, which can quickly lead to condensation inside.


Best regards, Jochen.

"Just turn on the air conditioning and set the temperature a bit warmer, then it will be comfortable without the AC blowing too cold! The automatic climate control does the same thing automatically! In my car without air conditioning, only warm air comes out! This is also because the dashboard gets very hot from parking in the sun! I always open all the windows and the sunroof; it's wonderful!"

That's the thing, I don't want to turn on the climate control, even though I could adjust the intake temperature.

I'm glad there's no condensation anywhere in the ventilation system. Otherwise, I always have problems with odors. Also, I prefer to put those few horsepower to use on the road rather than wasting energy heating the air for a little bit of comfort.

For me, an air conditioner in a car is pure energy waste. Unfortunately, there was no version of the vehicle available without an air conditioner.

irisches-bier wrote:

Bei meinem alten Passat (32b) bläst es nur für kurz Zeit heiße Luft, bis Wasserkasten und Lüftungsteile sich abgekühlt haben. Beim Octi warte ich ewig auf kühlere Luft.

Hi,

"How long does the hot air last in a Škoda Octavia if you don't start the engine but just run the blower while the car is stationary (assuming the battery is fully charged)?"

When the time is significantly shorter (similar to a Volkswagen Passat), it's truly heat transfer from the engine to the outside air.

If it doesn't make a difference, the ventilation system in the Octavia has a larger thermal storage capacity than the one in the Passat.