Underbody rust/corrosion - how are cars holding up?

Bossworld · November 13, 2020, 16:21

This year's MOT had an advisory, 'corrosion on under body of vehicle' - the only other MR2 I've got for a reference point (where I've spent a substantial time under it) is my mum's which is 6 months older and not particularly any better or worse.

It's never come up on the previous MOTs, is it fair to say it's subjective/at the tester's discretion? Car's only done about 2.3k this year so it shouldn't be anything particularly new.

Subframe was brand new from Toyota 3 years ago and the suspension, arms, PAS pipes, rad etc. have all been replaced so I've no major concerns, but other than a post on here a few months back about someone replacing their front subframe with one cut out of another car, it doesn't seem to get mentioned much.

I'd assume a 16 year old car would have varying degrees of rust underneath unless it had never seen rain or winter?

I've searched and seen some people have undersealed, or dynaxed it but I haven't got the time or desire to wire wool the entire underside given I'm also using the garage for Zwift/spinning at the moment.

Thoughts from others? The family wagon (10 years old) is going into the same test centre this weekend so interested to see if it's just his 'favourite thing' to flag, a la:

http://www.omegaowners.com/forum/index.php?topic=141363.0
https://forums.mercedesclub.org.uk/index.php?threads/corrosion-advisory-on-mot-on-car-i-am-hoping-to-buy.175795/

1979scotte · November 13, 2020, 16:27

My experience is that they all need wire brushing and zinc primer.
Even the latest 06 cars especially if they've been driven throughout the year and/or parked outside.

Joesson · November 13, 2020, 16:38

@Bossworld
My 2 has been a garage Queen since 2011, but it does show some signs of corrosion underneath. This was referred to several MOT ' s back when the front coil springs were mentioned. I rectified that and no further comment. But it seldom gets wet and it is seldom out of the garage overnight when condensation can form.
If your car is outside 24/7 then it will be subjected to the weather, condensation and road splash, not to mention winter salt. Unfortunately corrosion is progressive, it is slow burning and if regularly fuelled with moisture and oxygen (and particularly salt) it will progress.
Perhaps 'corrosion on under body of vehicle' is the 'advisory of the month' you may have further info after this weekend's visit.

Carolyn · November 13, 2020, 17:16

One needs to spend a couple of days underneath - with all the nappies (front and rear), off the car.

Wire-brush all the rust you can find. Use a good rust convertor/treatment like Bilt Hamber and let that cure, then zinc primer and then paint.

Then, once a year, get under and treat anything that appears. The car will last and last...also - seal the subframe and pour in some preserver- like waxyoil.

If you use it all year and good pressure wash underneath with 'Salgon' to remove salt residue is also good.

scm2004red · November 13, 2020, 20:07

Mine is a heck of a lot rustier than my Porsche which has just had it's 36th birthday, probably not helped by spending a lot of it's life on the south coast!

Bossworld · November 13, 2020, 20:43

Yeah I think mine lived in Saltburn before it moved further up the coast to me, but I don't run it in winter and it lives in a garage during that time.

Thanks everyone, food for thought but probably a task for the next owner, will report back on whether the Mini gets flagged for the same

puma2 · November 14, 2020, 10:19

mine has been treated in the being of last month just to try and help it out for the bits you dont see.
i think all of our 2s could do with some work on this now due to age and to make they last that little bit longer.

some mot tester do like a big scredriver to make holes were they should not be.

Bossworld · November 14, 2020, 11:20

Mini went straight through (child seats mentioned, under trays not ) but different tester at the same garage so no way of comparing. Never mind

Joesson · November 14, 2020, 11:59

Quote from: Bossworld on November 14, 2020, 11:20Mini went straight through (child seats mentioned, under trays not ) but different tester at the same garage so no way of comparing. Never mind

Don't be too disappointed 😉

Gaz2405 · November 14, 2020, 18:09

I spent a good couple of days undermine last year with a wire brush, treated then underbody rubberised paint then a covering of underseal.

All the wheel arches have been done too.

Will probably do it every year or so to keep up with it.

Mr2paul · November 14, 2020, 18:35

Yes iv done all my old cars, but not ever going to the extent of sanding and painting etc. For me that is too much work lol.
Trusty hand sprayer with thinned down black wax oil,,,, so it sprays ok and doesn't set,,,,,wire brush away the worst and spray it. With black you can see where you've been and you don't need a special pump.
I would of asked the question to the garage to show me their concern or take it back and ask them, we can only quess at your corrosion so better ask them really. My method has served well over the years. For instance if your doing brakes etc, why not give a quick spray around ? That's my method.

Bossworld · November 14, 2020, 20:14

I think the crux of it, is that it's a subjective matter, but that it's happening to most of them that aren't summer use only.

Regards subjectivity, the Mini usually goes to a B M W dealer as for years they only charged £40 and gave it a valet too.

Last year they'd upped it to £55 and I didn't want to trek back from town due to the virus; hence going locally. But last year Mini noted my rear discs were corroded - no mention of it this year.

It's good to see everyone's staying on top of their cars (or in this case, under!) I'm not planning on doing anything else to mine before it sells (and it went back in my garage literally the same evening as the MOT pass) but take on board the point about treating areas as you're working on them - I did the same for the top of the frunk areas when I made new hard brake lines a couple of years back.

Mr2paul · November 14, 2020, 21:20

Credit to you boss world. I'm glad you get my point that it's not a once n forever or never, but an evolving process. If no rust here then don't spray, if rust appears there, brush off n spray. Literally 2 min job while your at summat else or hopefully just before you take the stands out lol.
How many have done it handbrakes and have not taken the opportunity to give 2 mins tlc to a corroded bracket etc. From what iv seen then it's most. It's not hard but I do realise some do not or cannot crawl about under a car especially at this time and rely on others to fix which can be very expensive tbh.
Underbody treatment £20 plus labour plus vat == £££££££. I'm lucky in that I can just about do it , tho it's getting much harder.
When I can't do it myself, do you think I will pay those prices ?
Nope,, I'm from Yorkshire n can't justify the cost ! Tho I can justify lowering springs 🤔🤔🤔

Jimbo · November 14, 2020, 21:45

Anyone taken there's to a specialist? When I was looking at an RX8 as a sensible family car (4 seats and 4 doors (ish) met the requirements...) they were sorting out a club discount somewhere for cleanup and treatment, including all the hard to reach places. If you've got the space and time then fitting it in when doing other work sounds like a great plan, of you're not working on the car yourself then paying to get it done once every few years might make more sense.

1979scotte · November 14, 2020, 21:50

Quote from: Jimbo on November 14, 2020, 21:45Anyone taken there's to a specialist? When I was looking at an RX8 as a sensible family car (4 seats and 4 doors (ish) met the requirements...) they were sorting out a club discount somewhere for cleanup and treatment, including all the hard to reach places. If you've got the space and time then fitting it in when doing other work sounds like a great plan, of you're not working on the car yourself then paying to get it done once every few years might make more sense.

Not sure its a job i would trust others to do properly. Reckon they'd just spray muck all over it which if its already rusted isn't much good.

Bossworld · November 14, 2020, 22:34

Quote from: 1979scotte on November 14, 2020, 21:50
Quote from: Jimbo on November 14, 2020, 21:45Anyone taken there's to a specialist? When I was looking at an RX8 as a sensible family car (4 seats and 4 doors (ish) met the requirements...) they were sorting out a club discount somewhere for cleanup and treatment, including all the hard to reach places. If you've got the space and time then fitting it in when doing other work sounds like a great plan, of you're not working on the car yourself then paying to get it done once every few years might make more sense.

Not sure its a job i would trust others to do properly. Reckon they'd just spray muck all over it which if its already rusted isn't much good.

That and the cost factor really. There are some specialists who'll do it carefully, take photos and the rest throughout the process, but hard to justify £700 odd on cars that are worth circa £2k.

A quick online search suggests common pitfalls inc getting gunk on you for years to come when you're spannering lol

Mr2paul · November 14, 2020, 23:42

I agree, you can get covered in rust, shit, Debris's, but spray away n you get the satisfaction that it's done right for no money. As said iv got 5ltr wax oil coming for £19 n it will last years, just thin it down for hand spray. Iv got a big comp but it's not worth the trouble for air tools tbh.

iffyT · November 15, 2020, 23:00

I'm using ACF 50 as it's what the PO was using. It's a 'fluid film' converter and self healing barrier. You need to apply yearly with a pump sprayer. Underbody looks great so I think it works.
Cost me £25 for a quart from ebay.

Chriss · November 23, 2020, 00:44

Mine is in great condition, a little surface rust starting to form around the rear engine mount and the rear sway bar but the body is perfect.

Akayfortyseven · February 23, 2021, 13:54

Bumping this,

Whilst my engine is out and suspension off, I am going to get rid of some scabby bits. Nothing too bad.

I want to take the rear quarters off and treat there as well.

Any recommendations of treatment products?

I was going to use a converter/treatment, zinc primer and then either colour coat or hammerite to finish.

Joesson · February 23, 2021, 14:02

Quote from: Akayfortyseven on February 23, 2021, 13:54Bumping this,

Whilst my engine is out and suspension off, I am going to get rid of some scabby bits. Nothing too bad.

I want to take the rear quarters off and treat there as well.

Any recommendations of treatment products?

I was going to use a converter/treatment, zinc primer and then either colour coat or hammerite to finish.

As I reported very recently on another thread:

https://www.bilthamber.com/

This company produce a range of anti corrosion products.

Other products from other companies are available.