Rustproofing surface corrosion

[Vince70]

My old Z3 is going in the garage for the winter months from November onwards but on it’s last mot it had an advisory for surface corrosion underneath so just wondered what’s the best thing to coat the underneath in.

I was told by the tester it was due to not using the car but I don’t want it getting any worse.

[Mally]

My MOT man says old engine oil. Drips everywhere though.

[Tamworthbay]

Dynax UB was from bilthamber. Best stuff I have ever used with amazing ‘creep’ so penetrates very well.

[Vince70]

Thanks as I’ve got loads of old engine oil so I will get the Poundland paintbrushes out but do like the sound of using the Dylax ub I just wondered would I need many cans.

[sierraman]

Old engine oil is crap, it washes off quite quick. I’d wire brush it back, then use Flag Rustconverter then Waxoyl over the top.

[bolognasal spray]

Whatever you decide on, I think it's a good idea to apply it to bone dry surfaces - because, if let's say you were to use a wax oil or under-seal type product, and let's say the surface to which these were applied were damp, you would effectively be trapping the damp onto the already corroded or pitted areas. This then facilitates further corrosion because it's created tiny pockets of moisture and air, which are needed for corrosion to occur. This at any rate is the tame mechanic up the road's view - he offers a very decent oil-spray service, however he all-but refuses to apply it unless he thinks the vehicle is very dry. 

 

I say all of this, but I have to also mention that a few decades ago, I place near to where I used to live had a Finnegans franchise and the treatment was steam cleaning and wax "oyling". Vehicles went in, were sprayed with steam to clean them, and then the owners were told to drive round the block to "dry" them. As if this would work! But it was apparently the official Finnegans prep. Perhaps they just didn't want to create a more thorough process that would involve a less straight-through process. I dunno.

 

I wondered if what might be a good idea would be to, yes, wait until the underside is really dry. Then, as a first coat, spray with ACF50 - I appreciate it's expensive and messy, and difficult to apply. But then, after that, do a more trad wax oil coat over the top (after letting the ACF50 settle in for a few days. I wonder how well that would work. Loads of people in bike world swear by ACF50.

[bolognasal spray]

Agree on the wire brush bit. Really not looking forward to that job though.

[Tamworthbay]

Thanks as I’ve got loads of old engine oil so I will get the Poundland paintbrushes out but do like the sound of using the Dylax ub I just wondered would I need many cans.

Two cans will do the underside of a decent sized estate car, one will do a fiesta sized car. It’s not the cheapest but is the best and a lot cheaper than paying for someone to weld it up. I think it was about £15 a can the last time I did it but the cans are huge, about twice the size of a normal aerosol.

[Tamworthbay]

Still £15 a can

https://www.bilthamber.com/dynax-ub

Or the paint on tins of it are half the price.

[Pat Earrings]

Just bought 2 cans of the Dynax UB. Didn't have an idea of coverage but cheers Tamworth for the info,helped me to bite the bullet! Plan on preserving the good underside of the Mazda through the winter!

[MikeR]

when ever I jack up the car I give the under carriage a fondle with a cloth to remove any dirt

 

followed by a can of pound land black spray paint ...

[Honey Badger]

If your keeping the car the dynax is a good investment as it costs more but lasts longer, as Tamworth said it creeps into seams well and is self healing I believe.

 

Engine oil is pointless as it has no viscosity so it will wash/drop off quickly, it's not good if you have a cat either.

[fordperv]

My MOT man says old engine oil. Drips everywhere though.

Do it then wait for next m.o.t and see if there's an advisory about an oil leak

[D Spares & Tyres]

Old engine oil is crap, it washes off quite quick. I’d wire brush it back, then use Flag Rustconverter then Waxoyl over the top.

Waxoyl? You may as well piss all over it for all the good that will do.

[D Spares & Tyres]

If your keeping the car the dynax is a good investment as it costs more but lasts longer, as Tamworth said it creeps into seams well and is self healing I believe.

 

Engine oil is pointless as it has no viscosity so it will wash/drop off quickly, it's not good if you have a cat either.

No but it's really amusing if your neighbours have one. Preferably a white one

[Rusty_Rocket]

Waxoyl? You may as well piss all over it for all the good that will do.

You're not wrong there. When I had my Cavalier, I sprayed black waxoil everywhere, including through the rear light apertures so it ran in between the inner and outer rear arches, down into the rear of the sills.

Imagine my joy, when big rust holes started appearing in said panels. When I stripped the car down, the metal had actually started rusting under the waxoil, with the wax happily sitting on top of the shale in the bottom of the various box sections.

It's utter rubbish imo; I reckon the car would have lasted longer if I hadn't bothered rust proofing* it in the first place!

 

Interested to see if the modern equivalents are any better.

[Tamworthbay]

You're not wrong there. When I had my Cavalier, I sprayed black waxoil everywhere, including through the rear light apertures so it ran in between the inner and outer rear arches, down into the rear of the sills.

Imagine my joy, when big rust holes started appearing in said panels. When I stripped the car down, the metal had actually started rusting under the waxoil, with the wax happily sitting on top of the shale in the bottom of the various box sections.

It's utter rubbish imo; I reckon the car would have lasted longer if I hadn't bothered rust proofing* it in the first place!

Interested to see if the modern equivalents are any better.

I did some back to back tests on a few different ones, I used stone chip, old hammerite, new hammerite, waxoyl, Dynax, normal underseal and bare metal. After three months of hanging outside only the old hammerite and Dynax were rust free, after six months the underseal and waxoyl were barely better than nothing at all. I left them outside for a couple of years and thickly applied old hammerite was still good as was the Dynax. The Dynax is. Ichihara easier to apply though and more forgiving of less than perfect surfaces. And you can’t get the decent hammerite anymore as the new stuff is shite. For the point of fairness I should point out that my old race team was sponsored by Bilthamber for a while and I was most impressed by the guy who owns them. He learnt his trade doing stuff for oil rigs so knows a thing or two about preventing rust. I use nothing else now even though I have to buy it, sadly the days of a few tins as freebies are long gone.

[Bradders59]

I wont use anything but Bilthamber products when treating rust. 

[Scruffy Bodger]

The old skool trick round here is an engine oil and diesel mix. The diesel being thinner penetrates and sticks about longer. Take a look at the tin work on any old tractor near where they get filled with fuel, the paint work may be dull but the tin will be intact even if the mudguards have completely disintegrated.

[lesapandre]

I'd not advise using old engine oil. Its a carcinogenic substance once its been used in engines - getting it everywhere is not recommended. All the rest of the advice seems good. HSE advice:

 

http://www.hse.gov.uk/mvr/topics/oil.htm

[bigfella2]

I once got told by a mechanic that underseal mixed with used engine oil works well, doesn't dry out like underseal so always stays a little tacky. Never used it though. Agree with above that bilt hamber make some nice rust treatment products

[dollywobbler]

Vactan is bloody good stuff. I'd recommend it, but the horror of rubbing down can't really be avoided. You need the flaky crap gone to ensure the converter is getting down to the actual rusty metal. 

[DodgeRover]

Vactan washes off though in time unless you paint over it?

[Tadhg Tiogar]

Still £15 a can

https://www.bilthamber.com/dynax-ub

Or the paint on tins of it are half the price.

 

Hmmm...maybe a coating of FE-123 followed by several of Dynax UB?

[bolognasal spray]

The old skool trick round here is an engine oil and diesel mix. The diesel being thinner penetrates and sticks about longer. Take a look at the tin work on any old tractor near where they get filled with fuel, the paint work may be dull but the tin will be intact even if the mudguards have completely disintegrated.

 

Let me just say something quick about the use of diesel. For a couple of years I owned a W650 - I've actually got some pics of it, Here it is:

 

 

When I bought it it was totally free from any kind of corrosion. And it was pretty much the same when I flogged it - the above is a pic I took for my eBay listing.

 

But one thing had changed - and that was the occurrence of pitting on the rear spokes (note that the spokes on these bikes are not stainless but mild steel - supposedly because they offer slightly more give, and thus comfort - but in reality, almost certainly because they cost less). On the rare occasions the bike suffered a bit of damp from a ride on winter roads, or acquired some condensation when being wheeled back into a warm-ish garage, this pitting actually started to show the tell-tale signs of orangey rust developing.

 

None of this was at all serious - and could easily be remedied. But the question arose - what was causing it? After all, the spokes on the front wheels remained utterly free from even the slightest signs of pitting, never mind corrosion.

 

The only difference between front and rear wheel was that the latter accumulated some amount of "fling" - i.e. very small splats of lubricant from the chain. I always and only ever use EP90 (thick gear oil) to lube chains. I couldn't fathom for a moment that this was causing corrosion or pitting. Surely if anything it would be creating a barrier between metal and moisture? Yet oxidation was clearly happening.

 

One other difference between front and back wheels was in play though. I was using diesel to clean the chain prior to squirting the EP90 on. So, strictly speaking, the EP90 was actually a mixture of that and small amounts of diesel.

 

I could only really conclude that the culprit here was the diesel. Because surely the front and rear spokes were the same steel? Well - of that we can't be absolutely sure. But nevertheless. In any case, I personally decided the diesel was doing something. I wondered if it contained some strong detergent-type ingredient that was acting as a degreasing agent on the EP90? Or if there was some sort of acidic additive in there?

 

The reason I'd been using diesel (this had been going on for a couple of years, a couple of times a week), was because I thought it offered the same cleaning properties as paraffin but at a fraction the cost. Paraffin is the preferred fluid - but definitely dearer these days. Regardless, I went back to paraffin after the W650 spoke saga, and don't use it for anything now. I'm not saying anyone anywhere should follow my lead - just that my own experience seemed to suggest there was a weird and potentially harmful to steel component in modern diesel.

[Shirley Knott]

+1 on the Bilthamber suggestions, I've used on various stuff, most recently my 940. It goes on very nicely, looks the part and seems to protect well too.

 

 

 

 

 

 

 

As others have said best to get the underside of the car 100% clean and dry before application, I jet washed the up on stands and then gave it a week under the carport to fully dry off. Also make sure to give any areas of surface corrosion a rub back and treat with Hydrade80/Vatcan etc first too.

[MikeR]

EP90  may be worth checking out for its corrosive properties

 

years ago I had a Fiat and I wanted to top up the gearbox ...

 

EP was not to be used as the Extreme Pressure additives would de-solve soft bearing metals from what I could find out ..

 

only ordinary 90 was to be used

[dollywobbler]

Vactan washes off though in time unless you paint over it?

True. It doesn't form as much of a barrier as Bilt Hamber stuff. It does arrest the rot though.

[jon.k]

I used dinotrol on my mx5 and it has been great. This was about 8 years ago and it’s still rust free. They do various aerosols and the mx5 fanboys swear by them.

 

On parts which had light corrosion I painted POR 15 rust paint. It is no good on rust free parts but it sticks to rusty bits and apparently stops it getting worse. It worked on the suspension arms which still look black and shiny 3 years later, where they were previously beginning to pit. I, fairly sure it’s not rusting underneath the paint. I don’t know what it’s made of but don’t get it on your hands; I’m fairly sure I still have a spot of it stuck on my skin now.

 

I’m about to do the same process in my 305, but I’m going to take it to the local lorry mot place to get it it steam cleaned first then wait for it to dry out.

 

 

Spraying oil and diesel all over the bottom of the car is pretty irresponsible, surely. I thought we have all moved on a bit since those days.

[steveo3002]

most important bit is scrape back loose underseal , no point in painting or waxing over top

 

my methods ...if you can clean it back to clean metal then nothing better than epoxy like jotun jotamastic 

 

for bangers /cant be too bothered i clean the area off and brush grease on with a paint brush , lasts a year by which time you should be jet washing it and checking it again , also go around any exposed threads , brake pipe ferrules etc and grease them