SportKa MOT advisories question - oil leak

AliceBanned

Good idea, thanks. It was the sandpapering which took up a lot of time last time.

Do they come battery operated? I can't park my car anywhere near a mains supply as I am in a first floor flat.

tberry6686

You can get cordless ones but they are generally more expensive probably closer to £100. (if you do opt for this make sure a battery and charger are supplied, some of the cheaper looking ones don't supply them with the Grinder)

AliceBanned

OK. I probably wouldn't fork out as much as that so I will have to do manually, unless I can hire one somewhere.

AliceBanned

OK I had a look today. I don't know why I couldn't see this before, though the sill is slightly underneath.


There is the one rusty patch where the paint has come right off, then there are loads of bubbly patches all along the sill.


I'm going to tackle the rust patch today, as it's dry and sunny, though rain is forecast later on.


The nearside sill is fine so far.


Not sure how long it will last in this case. Presume I just keep treating and respraying each time more paint comes off..then eventually deciding whether it is worth replacing the sill?

Joe_Horner

First thing, attack the whole length of it with a wire brush - manual is ok, powered (in a drill or angle grinder) is easier. The brush won't get it clean enough to treat, but it'll give the fastest idea of what you're facing. Again, the fact that it didn't fail the MOT, especially with a tester who DID advise the bits you've already done, suggests it's probably sound underneath.

Bubbles don't have to be caused by "nasty" rust. When steel rusts the rust expands (a LOT) compared to the steel it came from. That expansion can crack concrete so it has no trouble at all breaking paint up.

Even quite light surface rust can do this if it's under the paint simply because the expanded rust takes up more room than there is available. So the paint lifts, forming a bubble, to make space for it.

Wire brushing the paint off has two benefits. It allows you to see what it's really like, and it opens the area to the air which, in the short term at least, is much better than having moisture trapped under the paint.

AdrianC

One small question... How has this rust started under undamaged, unbroken paint - unless it's coming through from the inside?

Joe_Horner

It may not be unbroken, undamaged, paint. In fact, by the time it bubbles it certainly won't be.

It only take a pin-hole or very small stone chip through the top-coat for rust to start because moisture will get in and be absorbed by the primer, which holds it in contact with the metal. Te bottom of sills is a prime area for stone chips, and is rarely inspected in any detail so they go un-noticed.

That's why "rubber" type underseals can cause so many problems - as soon as the barrier's broken they hold water in place and actually speed the corrosion up.

If there's bubbling "all along" that had come from the inside then it's extremely unlikely to have passed an MOT because, by definition, by the time rust from inside shows on the outside there's a hole there.

If you look at a (removed) sill that's rusted from the inside, you'll see that the rust tends to form a shallow "crater" in the metal - so it gradually gets thinner from the outside of the rusted area to the centre. That means that, by the time anything shows on the outside, a good few inches around it are normally thin enough to shove your finger through (don't try this at home - real risk of cutting yourself on rusty edges!)

AdrianC

But if the first sign on the outside is that bubbling, it'd pass.

Sorry, you're in denial thinking that's coming from the outside on ANY car - let alone a Ka.

Joe_Horner

AdrianC wrote: »

But if the first sign on the outside is that bubbling, it'd pass.

Sorry, you're in denial thinking that's coming from the outside on ANY car - let alone a Ka.

Not when tapped with a corrosion assessment tool it wouldn't. See edit above regarding what rust from the inside looks and acts like.

I've had over 30 years experience of cutting and replacing rusted metal from cars and, by the time bubbling shows, internal rust is almost always easy to spot by tapping.

Without cleaning it back you can never know for certain, so writing the car off before doing that simple thing is nuts unless you're a garage trying to sell welding work.

AliceBanned

Joe_Horner wrote: »

First thing, attack the whole length of it with a wire brush - manual is ok, powered (in a drill or angle grinder) is easier. The brush won't get it clean enough to treat, but it'll give the fastest idea of what you're facing. Again, the fact that it didn't fail the MOT, especially with a tester who DID advise the bits you've already done, suggests it's probably sound underneath.

Bubbles don't have to be caused by "nasty" rust. When steel rusts the rust expands (a LOT) compared to the steel it came from. That expansion can crack concrete so it has no trouble at all breaking paint up.

Even quite light surface rust can do this if it's under the paint simply because the expanded rust takes up more room than there is available. So the paint lifts, forming a bubble, to make space for it.

Wire brushing the paint off has two benefits. It allows you to see what it's really like, and it opens the area to the air which, in the short term at least, is much better than having moisture trapped under the paint.

Thanks Joe, I appreciate the feedback. I have tried this time with a strong screwdriver and this bit has come off more easily - I realise I ran out of wet and dry paper to do the edges that are too awkward with the screwdriver. Pics coming up in a minutes.


It does feel like 'newer' rust in this part - I am presuming this because the silver edges are coming up quite easily and it feels moist. I have scraped over the top with a wire brush. Quite a bit more to go but will show you so far. I am going to have trouble getting to the end horizontally as it may be one patch going all the way along. Also the next panel (front) is being affected too.