Undertray and new sill weld patch

[Tomjones1995]

Hello everybody, hope you're all well.

 

I've had the car on some ramps in a garage and I took the opportunity while the car was in the air to check the underneath to find that the new sill welded patch was put in place where the undertray screws onto.

 

So, basically there's nowhere for the undertray to screw onto underneath and the patch is thick with road grime so I'm concerned it's going to rust all over again due to the undertray not covering it for all this time.

 

So do I just clean the dirt off the patch and drill a hole through it for the original screw or use some sort of ultra strength grab adhesive to stick the undertray to the patch save drilling a hole through it?

 

The chap didn't tell me about it and it's been like this for months.

 

Any help or advice would be greatly appreciated.

 

Thanks,

Tom

 

 

[HeavyMetalRich]

The undertray doesn't screw into anywhere near the sills. Do you mean the sub-frame (bit all the suspension and engine is bolted to) or another undertray that covers brake pipes and fuel lines etc?

 

Not to be patronising but incase you're not clear, the sills are the bottom of the sides of the car.

[Tomjones1995]

2 hours ago, HeavyMetalRich said:

The undertray doesn't screw into anywhere near the sills. Do you mean the sub-frame (bit all the suspension and engine is bolted to) or another undertray that covers brake pipes and fuel lines etc?

 

Not to be patronising but incase you're not clear, the sills are the bottom of the sides of the car.

Sorry for not being clear. I'm not referring to the engine undertray but the one for the fuel lines and such I would imagine yes.

 

It's near the sills and the welder has patched further underneath the car and hasn't made any screw holes for the undertray to secure to if that makes sense.

 

Thanks,

Tom

[HeavyMetalRich]

18 hours ago, Tomjones1995 said:

Sorry for not being clear. I'm not referring to the engine undertray but the one for the fuel lines and such I would imagine yes.

 

It's near the sills and the welder has patched further underneath the car and hasn't made any screw holes for the undertray to secure to if that makes sense.

 

Thanks,

Tom

 

Ah right, with you now.

 

Originally there would have been a stud with an open thread the same as a self tapping screw sticking out from the bottom of the car that a plastic nut would go on to secure the tray.

 

However, the cars don't actually need the extra undertrays, many don't even come with them from the factory. If you still feel you'd rather have it on though, a self tapper with a big washer will do the job, just watch for possible wiring harnesses etc inside the car if you use long screws.

 

Hope that helps!

[Tomjones1995]

Hello again everybody,

 

I've been thinking in regards to underbody rust.

 

Is it worth looking for a company or garage to underseal a car nowadays or is it just false economy?

 

The way it seems to me is it that once a car reaches about 10 years old. No matter how thorough the mechanical maintenance has been, the rust will eventually ruin the car anyway.

 

Thanks,

Tom

Edited 4 March, 2023 by Tomjones1995

[Crasher]

Rust has made a big comeback on VAG products, they were so much better from the 82 Golf 1 right through to the Golf 4 and then it all went wrong… my 200k Octavia 1U has had zero structural or cosmetic rust except where morons had used trolley jacks on the sills before I bought it and to be honest, Skoda are better than the rest of the VAG range especially Audi on the 8E and 8K A4 which suffer horrible floorpan and chassis leg rust. Even the aluminium A8 is not immune, last year we had an 8 year old A8 in and I just put my fingers through the subframe where the diff mounts, a huge job to fit a new subframe 

 

 

[Tomjones1995]

30 minutes ago, Crasher said:

Rust has made a big comeback on VAG products, they were so much better from the 82 Golf 1 right through to the Golf 4 and then it all went wrong… my 200k Octavia 1U has had zero structural or cosmetic rust except where morons had used trolley jacks on the sills before I bought it and to be honest, Skoda are better than the rest of the VAG range especially Audi on the 8E and 8K A4 which suffer horrible floorpan and chassis leg rust. Even the aluminium A8 is not immune, last year we had an 8 year old A8 in and I just put my fingers through the subframe where the diff mounts, a huge job to fit a new subframe 

 

 

 

Yes and I have two polo 9n's, both with rusting sills. One was welded last year only to already be returning 7 months later.

 

Is it worth undersealing or is it a waste of time?

 

as you say, it's rather common across the VAG group

[sepulchrave]

Underseal simply locks any existing rust and moisture in place, it should only be used on rust free areas which lack protection, i.e. freshly welded areas of clean metal.

[J.R.]

1 hour ago, Crasher said:

Rust has made a big comeback on VAG products, they were so much better from the 82 Golf 1 right through to the Golf 4 and then it all went wrong…

 

What year do you reckon was the pinnacle or sweet spot? I don't know when the golf MK4 came in also whether you meant to include that in the good ones or the start of the bad ones.

 

My MK1 Octavia was superb for corrosion protection, the MK2 seemed good but the rear sub frame and trailing arms had little or no protection, the Yeti is the same but also has to contend with the scabby zinc inclusions.

 

Subframes & trailing arms are easy to protect albeit messy with Owatrol oil but I am loathe to do that if the sills & chassis rails are going to decompose anyway.

[sepulchrave]

Early Fabia 1 is the pinnacle of noughties rust resistance, I had an '89 Passat B3 GT estate that was completely immune to corrosion and built like a brick ****house until I spun it on a diesel spill and hit a tree side-on really hard, even then I was still able to drive it home!

[Tomjones1995]

1 hour ago, sepulchrave said:

Early Fabia 1 is the pinnacle of noughties rust resistance, I had an '89 Passat B3 GT estate that was completely immune to corrosion and built like a brick ****house until I spun it on a diesel spill and hit a tree side-on really hard, even then I was still able to drive it home!

 

Would you say in that case the fabia MK1 is more rust resistant than the polo 9n?

 

I've seen other polo's for sale that have had MOT advisories stating sill corrosion of varying degrees but I've yet to look into the fabia vrs.

 

I love the platform of the MK1 fabia/ polo 9n/ Ibiza age with the diesel hot hatch sort of thing. VAG seem to of shifted away from that in favour of the turbo petrol hot hatch which doesn't prove economical enough for me.

 

But if they're all destined to corrode with no way of preserving then underneath then we're all being forced to move on through age I guess

 

 

[AnnoyingPentium]

Generally it seems the earlier you go in regards to Fabias, often the better the rust proofing is. As towards the end of production the bean counters got in and started reducing factory rustproofing etc. I've seen more Polos with hammerite and holes than Fabias, but it's not impossible. Although that's true for any car as there's a bloody myriad of factors that contribute to how and why a car rusts, where it rusts etc.

 

That being said, I've got a 2006 Mk1 with 74k miles that's now doing 12k a year in all conditions... in Scotland. Got some surface rust on the sill ends at the rear, and a bit in the rear arch tubs, I'm going to sort that out in the summer so that it at least delays the inevitable with any luck. @DoctorBoostaLot has a thread going now documenting the welding he's doing to his Mk1 Fabia, if you can do work like that, or find someone reputable to do welding work (thin on the ground getting, but still possible) then you'd be doing pretty well, I reckon.

 

So aye, a good Mk1 still has life in it, and just tidy up any rust that appears as and when it happens. If you've got a clean base for a car, then that's fine. It's easier to replace an engine than most metalwork, keep that in mind.

[KeithCheetham]

19 hours ago, Tomjones1995 said:

 

Is it worth undersealing or is it a waste of time?

 

I think the new route of protecting cars are now products such as Lanoguard which is quite thin and just sprays on, and into cavities. Plenty of videos showing it being applied.

[DoctorBoostaLot]

On 02/02/2023 at 12:55, Tomjones1995 said:

 

" the new sill welded patch was put in place where the undertray screws onto. So, basically there's nowhere for the undertray to screw onto underneath and the patch is thick with road grime so I'm concerned it's going to rust all over again due to the undertray not covering it for all this time. So do I just clean the dirt off the patch and drill a hole through it for the original screw or use some sort of ultra strength grab adhesive to stick the undertray to the patch save drilling a hole through it?

 

Upload us some pictures and lets have a look.

As others have chimed in, rubberised underseal is good - UNLESS the rust is already there and working its way around. Clear off the iffy areas, wirebrush wheel it off, rust neutralise it then some underseal / seam sealer. ONLY then try something like Lanoguard.

 

I had a Mk1 Scirocco Storm that had super rusty, alright rotten sills and sill returns, don't get me started on older Beetles, those rusted like hell. My Furby is great in comparison. My A4 Avant is much the same being a 2004/5 with very similar mileage.

 

I think the old fellas had it right, it wasn't pretty but apply your used engine oil to the underside of your car every year.

Here's another channel I follow, you'll see what I mean about rust under the seam sealer. If you approach the rust like they do here then you'll be golden.

 

 

[Tomjones1995]

Here my second polo 9n in better condition than the welded one with the loose undertray.

 

Would you say that the inner sill would probably of perished from the inside out so to speak?

 

Is it worth me wire brushing that off or would that be a waste of time?

 

 

I'm only looking to keep one of these polo's and I'm trying to decide which one is in the better condition

Edited 5 March, 2023 by Tomjones1995

[Crasher]

I think thePolo 9N has been quite good against rust unlike the 6N. It is difficult to put an exact time on the problem starting but the Golf 5 platform AKA PQ35 certainly was a step back from the Golf 4 PQ34 in respect of front wings, sills and entire rear underbody. We recently welded the back of the sills and stripped, de rusted, treated and Dinitrol sprayed the entire rear floor of a Golf 5 GTI which should last a long time.

 

 

Edited 5 March, 2023 by Crasher

[Tomjones1995]

2 hours ago, Crasher said:

I think thePolo 9N has been quite good against rust unlike the 6N. It is difficult to put an exact time on the problem starting but the Golf 5 platform AKA PQ35 certainly was a step back from the Golf 4 PQ34 in respect of front wings, sills and entire rear underbody. We recently welded the back of the sills and stripped, de rusted, treated and Dinitrol sprayed the entire rear floor of a Golf 5 GTI which should last a long time.

 

 

 

Gosh, that must of taken ages, looks like a good job.

 

I wish I had the DIY knowledge to do welding myself and the equipment. It's hard to find welder's around that will do extensive work like that these days.

[Crasher]

The hours that went into this were considerable and even more so when it looked like this

 

 

[Tomjones1995]

2 minutes ago, Crasher said:

The hours that went into this were considerable and even more so when it looked like this

 

 

 

Looks awesome!

[Crasher]

New dampers still to be fitted then and still as no choice has been made yet.