[Closed] Engine undertray

Don't bother.
They do very little on most cars and fall off for fun.
The genuine parts are made of cheap, nasty plastic with cheap, nasty fixings (which is why you see so many flapping in the breeze, especially on VW's), I can't imagine eBay copies are going to be of better quality.

I'd not totally agree tbh, they keep crap off the underside, which is useful in winter and if you do any dirt driving. Some cars have a lot of exposed stuff under there, on mine frinstance the aux belt can get blasted with crap, as well as assorted sensors etc Situational this, some cars will probably benefit more than others.

Definitely not essential though.

I got a cheap ebay one, it's better than the OE. Replaced the OEM fasteners with decent ones where i could and got a set of ebay fasteners for the ones that aren't easily substituted (didn't want to fit rivnuts or thread holes).

Mine fell of about 40k ago. I've not noticed the difference.

I've been driving it around and I've not noticed any difference although I did notice everything seems very exposed underneath. Audi want £400 for a set of undertrays. The ebay copies are £70.

bikemike1968
Don't bother.
They do very little on most cars and fall off for fun

Would you like me to list the important things that the undertray does on a modern car?

Assuming your car was built in the last 10 years, if it had an undertray, you want it to still have one fitted!

Assuming your car was built in the last 10 years, if it had an undertray, you want it to still have one fitted!

When mine started to disintegrate the garage's advice was take it off and leave it off. Didn't even offer to take my money for a new one.

Would you like me to list the important things that the undertray does on a modern car?

I'm sure that the manufacturers could give you a great list of the benefits they provide in managing the airflow under the vehicle and in the engine bay.

However, they completely negate this by making them out of the cheapest plastic they can find and attaching them with tuppence fasteners.
This ensures that most are missing by the time the car gets to five years old.

Would you like me to list the important things that the undertray does on a modern car?

Go on then, enlighten us.

Mine does a very good job of catching my sockets so I can find them six months later when I do a service 🙂

they improve airflow and help the emissions figures and mpg by a very small amount. Keep dirt and debris from pipes and electrics. Can hide a multitude of sins from a MOT tester. Most importantly they fall off and do your tits in when it comes to servicing. Its perfectly ok to run without one fitted allot better than a badly fitted or damaged one.

parkesie - Member

Most importantly they fall off and do your tits in when it comes to servicing.

😆 When I finished nailing my mondeo back together after the turbo swap, I thought I'd finish the job properly and put the undertray back on. It was genuinely the second most pain in the arse part of the entire operation (after fitting the replacement oil feed for the turbo, which Ford put in a very nearly impossible to reach place, because they are terrible human beings.) What a pain in the baws.

Heatshields is the other one... The hardest part of rebuilding a brake system shouldn't be removing the bastard heatshield without amputating your fingers.

So it's sounding like it's best to have one on. How much sound proofing do the genuine parts do? I noticed they have this on them. I will have to see if I can get a used undertray. The new parts from Audi are a little much for some plastic that could fall off.

I once got a cheap ebay one to replace the broken inspection hatch section of the one on my old Vectra. It fit perfectly and was £400 cheaper!

How much sound proofing do the genuine parts do?

Slightly sideways question but has anyone ever cut holes in their under tray to make it possible to do an oil change with the tray still in place? Should be possible with the nut-style filer housing... or would said cheap plastic get torn up by aero forces? It would be great to be able to speed up oil changes as I need to do em every 5 months or so

Maybe I was being sucked into what the Audi parts department guy was saying. He said it helped soundproofing. So I'm getting the feeling I might as well buy the £330 cheaper ebay part then.

Also makes it nigh on impossible to figure out what the clunking is on my Passat. Reckon its the exhaust but it'll be such a pita to check that I haven't.

jam bo
Go on then, enlighten us.

Right, here goes:

1) drag reduction. Smooths underfloor airflow, means your car gets good economy at high speed

2) Lift reduction: Keeps air from building up under front of car and hence reduces front end lift, especially at high speed

3) Optimum cooling performance: Modern cars are powerful and need a lot of cooling. All the cooling systems, be that engine water, engine oil, aircon, intercooler/LTR, transmissions and even power steering all have airflow that is precisely managed on it's passage through the front of your car. The undertray plays a critical part in this, allowing the hot air ejected from the engine bay to be channeled away correctly as designed

4) Protection. You might not think that thin plastic tray is doing a lot, but it is. Keeping water splash and even stray gravel out of your FEAD and the vast number of electrical and electromechanical components under the bonnet. You might think spending £200 on a bit of plastic is expensive, but if you kill the AC pump clutch due to water ingress of FOD then suddenly you'll wish you spend that money!

5) Noise reduction. A modern car needs it's undertray to pass the legal noise limit tests. You might like how your car sounds, but your neighbours probably don't want to hear you rattle off to work in your diesel at 5 in the morning everyday 😉

6) Exhaust emissions and exhaust line component heat management. The way your catalyst or DPF heats up is highly dependent on the air flow around it. Don't come running to me complaing your DPF has sooted up when you've been driving with the undertray missing. Likewise, if you car sets fire to the dry grass field you just parked in because your hot catalyst could touch the dry grass, i don't want to know

But other than that, what have the [s]Romans[/s] engine undertrays ever done for us?? 😆

My undertray had been loose and bumping on any rough or uneven road, rattling and banging, so I asked the garage about it when the car went in for its MOT in June, most of the fittings had broken, and they advised me to just have it taken off and leave it off, as it didn't offer that many advantages and many cars didn't even have them.
And to contradict maxtorque, the car is much quieter now, it doesn't sound any louder on startup and pulling away, and it's such a relief not the have the perpetual rattling and knocking from it.

Don't bother. They do very little on most cars and fall off for fun. The genuine parts are made of cheap, nasty plastic with cheap, nasty fixings (which is why you see so many flapping in the breeze, especially on VW's)

My brother had a brand new T5 long wheelbase converted into a camper. The commercial T5 didn't have one fitted as standard. A stone flew up into the engine and completely wrecked it. It was only six months old.

Try your local scrap yard - breakers - vehicle dismantlers what ever thier called these days .

My engine fell out today. Pretty sure the undertray went some way to catching it...

No luck with scrap yards / breakers. They say most of the time the fork lifts destroy them. What's the thickness of the plastic like between the cheap eBay parts and the genuine ones? I have managed to fine new pair of genuine parts for £200. That's half the price of the dealer parts. Are the genuine parts worth an extra £130 over the cheap eBay ones?

What's the thickness of the plastic like

Thin, but functional.

I've replaced a couple on commercial vehicles (Renault Master). No idea if they are all from the same supplier, so they may vary in quality.

I'm with Max^^ up there on the need to have them.

Hth
Marko

Thanks Marko. I definitely want to put them back on. I just can't decide if I'd be best just spending the extra and get the genuine Audi parts. Cheap eBay ones are £70. Genuine Audi are £200. But presumably the genuine ones will be better quality?

I stick some bacon & sausages on my car's undertray & they are just about done by the time I get to work. Lovely.

In my experience the aftermarket engines trays (alot seem to be made in Poland) are just as tough as the OE ones but may take a bit more lining up to get fitted properly, plus don't have the hollow molded plastic blocks that some OE ones have on the inside surface.

So what do the hollow molded plastic blocks do?

Correct me if I'm wrong, but combining your username and the fact you're looking for an Audi undertray, I'm going to assume you own a diesel A2, circa 2001?

If you do, keep an eye on the owner's club forum, A2OC, as quite often enthusiasts buy a dying A2 and break it up to sell off cheaply to forumites. I know, right.

Undertrays come up fairly regularly but are quickly snaffled when they do, so you need to be on the ball.

EDIT oh and if you are looking for an A2 undertray, just ensure you buy the right one - petrol and diesel A2s have different mounting designs for the undertrays iirc.

I have an A6 estate. Just using it as a mobile shed really for my bike.

despite some of the arguments for them, mine began falling off so removed it, its been five years now and zero problems. Forget it unless youre precious about your car.

I have an A6 estate. Just using it as a mobile shed really for my bike.

Drat, I thought my detective hat was working! 😆

I was going to get an A2 but wanted something a little bigger.

It was the cheap ebay clips that did for mine.

Other than that, there must be an element of insulation otherwise mine wouldn't have been lined in sound deadening material. It definitely sounds clunkier and I have been noticing a lot more grot getting into the engine bay, my advice would be to replace it if you can.

On the air channeling - look at your wheel arches and chances are on the front there is a vent - that will be for brake cooling which is generally accepted as a Good Thing.

Put it this way - why would manufacturers spend the time and money fitting them if they didn't perform a function?

They are a pain but mainly due to people removing them causing damage or not using anti-seize on the bolts when refitting. We even had one garage drill out all the rivets attaching the plastic part to the aluminium frame before realising you just unbolt the aluminium frame on our landrover 👿

Every car I have had with one fitted has had a MUCH cleaner engine bay and in a lot better condition with less rusty and hard to remove bolts and thus much easier to work on than one without.