Cooling problems with undertrays?

[JulianEdgar]

Originally Posted by Nautilus

1. Working by hand, with no wind tunnel or other aero instrument, it's pretty hard to reproduce the Porsche design.

I am not sure why you say that, unless you choose to proceed in the dark. Lots of aero data can be cheaply, easily and accurately measured without a wind tunnel.

If deflectors before front wheels really give a delta Cd of 0.01, this drops the overall Cd from 0.32 in the 0.28 range, which is actually very good for a daily-driven car.

You cannot just ascribe Cd reductions to a car based on what the change did on another car. (Same as you cannot just add Cd reductions together to get an assumed total reduction.)

[freebeard]

I'm working on an undertray for my car and have come up with some cooling questions for anyone that knows about such things. Both my oil pan and transmission case are aluminum and extend down slightly into the airflow beneath the car. Could blocking with an undertray cause any overheating?

https://en.wikipedia.org/wiki/Thermal_paste

[aerohead]

Originally Posted by fanamingo

I'm working on an undertray for my car and have come up with some cooling questions for anyone that knows about such things. Both my oil pan and transmission case are aluminum and extend down slightly into the airflow beneath the car. Could blocking with an undertray cause any overheating? The oil temp would be somewhat moderated by the fact that the engine itself is cooled via the radiator. The transmission has an ATF "warmer" that has coolant hoses running to it, but I don't know if it also helps cool the transmission. The "warmer" has two warmer and two bypass hoses running to it, and I've no idea how it functions.

I may be able to tap into the ATF temp sensor with a multimeter, but this will only give me a voltage reading. I wont' have a good idea of how that reading correlates with temperature.

Chevrolet was allowing the following for their last-gen Corvette:
* coolant- 239 F
* engine oil- 284 F
* ECU- 221 F
* Supercharger- 289 F
* Intercooler coolant- 131 F in
176 F out
* Brake fluid- 338 F
* Transaxle lube- 284 F

[JulianEdgar]

Originally Posted by aerohead

Chevrolet was allowing the following for their last-gen Corvette:
* coolant- 239 F
* engine oil- 284 F
* ECU- 221 F
* Supercharger- 289 F
* Intercooler coolant- 131 F in
176 F out
* Brake fluid- 338 F
* Transaxle lube- 284 F

I don't have the reference but those temperatures are very, very high - I'd guess the absolute max before destruction.

For example, an engine oil temp of 284F (140 degrees C) is above the breakdown temp of a conventional oil, although not of a fully synthetic.

Those supercharger fluid temps would imply an intake air temp of over 176F (80 degrees C) - and you never ever want to see that on a forced aspiration car.

Coolant temp 115 degrees C - and so on...

The OP is now 12 years old, so I won't bother answering that.

[Vman455]

The last-gen Corvette, in its supercharged configuration, also notoriously suffered from overheating issues on track--to the point that it was recalled by GM. I wouldn't put much stock in their allowable temperatures, if the numbers posted are even credible (which, without a link to a source or a citation, is unknown).

[Nautilus]

Originally Posted by JulianEdgar

You cannot just ascribe Cd reductions to a car based on what the change did on another car. (Same as you cannot just add Cd reductions together to get an assumed total reduction.)

Of course, this is why I didn't add them together and quote a precise number, just assumed a serious drop in Cd.

VAG judged, due to late-2000s experiments with eco versions of Audis and Skodas, that underbodies and suspension control arms fare much better if covered / plated over to achieve a surface as smooth as possible. Even if the suspension arm moves all the time, they still thought it needed a "fish-flipper" surface, compared to usual shape of suspension arms.

For Mk7 Golf there is a set of underpanels similar to my own, which can be retrofitted also to "non-eco" versions:

How to retro-fit skid trays, aerodynamic under trays, & stone guards to a MK7 Golf

They also covered the exhaust bend before rear axle, which I didn't do - my pipes were too big and still needed some airflow under them to be safe.

2020 Audi A3 version of undertray set:



My setup is similar, but without the mid-car side panels, since the floor is "mostly" smooth.

[aerohead]

Originally Posted by JulianEdgar

I don't have the reference but those temperatures are very, very high - I'd guess the absolute max before destruction.

For example, an engine oil temp of 284F (140 degrees C) is above the breakdown temp of a conventional oil, although not of a fully synthetic.

Those supercharger fluid temps would imply an intake air temp of over 176F (80 degrees C) - and you never ever want to see that on a forced aspiration car.

Coolant temp 115 degrees C - and so on...

The OP is now 12 years old, so I won't bother answering that.

Yes, they were reported as maximum, but allowable operating temperatures. And this would be with a full-synthetic lube package, circa 2015.

[aerohead]

Originally Posted by Vman455

The last-gen Corvette, in its supercharged configuration, also notoriously suffered from overheating issues on track--to the point that it was recalled by GM. I wouldn't put much stock in their allowable temperatures, if the numbers posted are even credible (which, without a link to a source or a citation, is unknown).

That's gonna be AUTOMOBILE, CAR and DRIVER, ROAD & TRACK, or MOTOR TREND. When I run across it again I'll flag it.

[skyking]

those corvette temps are some nutty numbers, not a realm I would be comfortable with.

[Nautilus]

When (not "if", but "when") electrical accessories, drive belts, cooling system plastic parts, cylinder head gaskets get destroyed from 115°C (239°F) constant coolant temperatures, the repairs outweigh any monetary gain from fuel economy.