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MGTF Treating the underside for winter

8K views 21 replies 11 participants last post by  gnu 
#1 ·
Hello again,, Is there any value in having the underside of my MGTF treated with some kind of protection to survive the winter? There appears to be several treatments available costing around £300 which seems a lot, unless anybody can suggest cheaper alternatives.
Best wishes, Mick
 
#3 ·
Thanks for that advice slatept, my only problem is !'m 6'3" and nearly 18 stone with no facility for ramping the car up! I think if I got underneath, I wouldn't come out again! However, its something I could suggest to my local classic car garage and get a price from them, especially if you recommend Waxoyl, which gives me something to go on.
Thanks again, Mick
 
#4 ·
I 'undersealed' mine a few years back as there was a bit of rust on the panel that close off the handbrake mechanism- and I was probably bored and had a tin of TETRA-SEAL in the garage for about 20 years from my Imp/Stiletto days.
Jack and support the rear as you would do for any job, on stands and safe-then pop the under-seal in a tin of scolding hot water for 1/2 Hr and it paints on nicely and has the desired effect-Oh, and it prevents water ingress! Im 65 years old and about 100 kg, but I manage that sort of job easily. You just need to finish doing the rear to over half way, then swap over the jack/axle-stands and prop/paint the front. The MOT man wasn't too impressed but they only want newish cars in and out . He did say to me 'typical of you old Boys'-which I took as a compliment.

It is also a good bit of advice to wire-brush, treat and hammerite the subframes- which is challenging, but worthwhile and takes a lot longer in situ.
The OP asked is there any benefit?-Yes, it helps prevent rust and corrosion. Wax-oil or any gun-applied wet treatment go that extra mile, but its best one on someone else's driveway or premises....don't ask me how I know this...
 
#6 ·
I 'undersealed' mine a few years back as there was a bit of rust on the panel that close off the handbrake mechanism- and I was probably bored and had a tin of TETRA-SEAL in the garage for about 20 years from my Imp/Stiletto days.
Jack and support the rear as you would do for any job, on stands and safe-then pop the under-seal in a tin of scolding hot water for 1/2 Hr and it paints on nicely and has the desired effect-Oh, and it prevents water ingress! Im 65 years old and about 100 kg, but I manage that sort of job easily. You just need to finish doing the rear to over half way, then swap over the jack/axle-stands and prop/paint the front. The MOT man wasn't too impressed but they only want newish cars in and out . He did say to me 'typical of you old Boys'-which I took as a compliment.

It is also a good bit of advice to wire-brush, treat and hammerite the subframes- which is challenging, but worthwhile and takes a lot longer in situ.
The OP asked is there any benefit?-Yes, it helps prevent rust and corrosion. Wax-oil or any gun-applied wet treatment go that extra mile, but its best one on someone else's driveway or premises....don't ask me how I know this...
Thanks Guys, that's extremely helpful and food for thought!
Best wishes, Mick
 
#7 ·
I had one of those £100 jobs where they spend an hour and slap some stuff on done by one of the MG dealers about ten years ago... but looking under the car a year or so later it was probably a waste of money (Having had a Land Rover and painted the underside of that with Waxoil I was happy to pay someone else to do the MG at the time.)

Then about five years ago I had it properly cleaned off, any rust treated and it was then painted/sealed by the MGF Centre, I think that cost around £300 and they had the car a couple of days to do it. It looked great and the car sailed through several MOTs but this year 'all of a sudden' we found a fair bit of rust hidden under it. I guess it must have done some good but I think it can also hide problems.

I certainly wouldn't bother with a cheap treatment again but if the car is new and in good shape then it might be worth looking at having something done properly, if you are planning to keep it a while.
 
#8 ·
I had one of those £100 jobs where they spend an hour and slap some stuff on done by one of the MG dealers about ten years ago... but looking under the car a year or so later it was probably a waste of money (Having had a Land Rover and painted the underside of that with Waxoil I was happy to pay someone else to do the MG at the time.)

Then about five years ago I had it properly cleaned off, any rust treated and it was then painted/sealed by the MGF Centre, I think that cost around £300 and they had the car a couple of days to do it. It looked great and the car sailed through several MOTs but this year 'all of a sudden' we found a fair bit of rust hidden under it. I guess it must have done some good but I think it can also hide problems.

I certainly wouldn't bother with a cheap treatment again but if the car is new and in good shape then it might be worth looking at having something done properly, if you are planning to keep it a while.
Thanks very much Bromsgrove, as you say if I intend keeping the car, which I do, then its worth making the investment for long term peace of mind. My MGTF is 2004 but only done 18000 miles and full service record for every year and although I say it myself, looks immaculate. So I think I'm going to go for it. I have the benefit of Mercury Motorsport Ltd, Fife, just a couple of miles down the road who specialise in classic cars so will get a quote from them and let you know what they say.
Best wishes, Mick
 
#9 ·
I do Rustproofing for my job, if your paying £300 your just having someone covering over any problems that are there.
Waxoil is a waste of time as within 12 months it will be flaking off.
For something like a TF I would be charging £550 and spending a week working on it.
First removing as much rust as possible, then treating with a rust converter.
Next step is coating with zinc primer then filling and box sections, sills etc with Dinitrol wax.
Before a final coating of Shutz to seal it.
The one day Rustproofing jobs are just trapping rust under a coating.
 
#11 ·
I do Rustproofing for my job, if your paying £300 your just having someone covering over any problems that are there.
Waxoil is a waste of time as within 12 months it will be flaking off.
For something like a TF I would be charging £550 and spending a week working on it.
First removing as much rust as possible, then treating with a rust converter.
Next step is coating with zinc primer then filling and box sections, sills etc with Dinitrol wax.
Before a final coating of Shutz to seal it.
The one day Rustproofing jobs are just trapping rust under a coating.
Wow! that throws a different light on things and makes me realise there is more to this than I first imagined. I will have to think twice about what to do next, if anything at all!
Thanks again, Mick
 
#10 ·
Undersealing (in whatever form) is really only fully effective on a brand new car. I would recommend that if you do treat an older car, it should only be done in the summer, or at least when the car has not been out in the wet for a considerable time, and so any rust will be thoroughly dried out.

Once rust has started, it is very difficult to remove it 100%, and any moisture that gets sealed in will simply make the rust continue under the sealant - the only difference will be that everything will look fine for a year or two until you suddenly find that you can stick your finger through the panel!.

Treating the underside properly is a job which would be frighteningly expensive for a proffessional to do for you as you really need to remove all of the rust already present - this means chemical treatment, not just grinding off what you can get at and covering up the rest!. If you do the job yourself, you can take whatever time you need, and use something like Deox Gel to dissolve all the accessible areas of rust before using a rust neutraliser to try to stop (or at least slow down) any deep pits of rust or areas that cannot be got at to remove completely.

Be aware that the rust neutralising products really only neutralise the surface of the layer of rust and leave an inert layer which shields the underlying remaining rust from air and moisture. If there is damp in this to start with, the rusting will continue until all the moisture and air/oxygen is exhausted, by which time you may have a hole in the panel. Such products are not the universal cure-all that some people think - they do help, but they are unlikely to stop all the rust completely unless you can get the neutraliser to penetrate right down to the bottom of the rust (which takes many hours of repeatedly soaking the surface before the previous application has a chance to dry).

Personally, I would then only repaint effected areas under the car, and only use an underseal in areas which are exposed to wear and damage, such as exposed areas in wheel arches, and behind road wheels where it will protect against flying stones. Elsewhere underneath, I would leave it as bare paint so you can see where any future rust areas start to develop before they become serious. I wouldn't use ordinary Waxoyl type products except internally within doors and sills as it tends to wear off in the areas that need protection.

The bottom line is that simply undersealing the whole underside of an older car looks very impressive and tidy when first done, it almost always ends up making matters worse, not better.
 
#19 ·
Hi Pete, I most certainly do! I've obviously read lots of reviews and they constantly say about height restriction and the seating is too high, which is balderdash, as I am living proof! I find the driving position really comfortable with a couple of inches to spare with the roof closed and all the instruments clearly visible.
I have to point out that my 171/2 stone is very proportional and a 36 inch waist, so I won't be using the car to go to any sliming clubs just yet!
Cheers, Mick
 
#20 ·
Lots of good replies. My two penn'orth is that there are different levels of rust protection - there is a difference between simply 'arresting' rust and having the full de-rust/protection treatment. The full derust and protection treatment will indeed be quite time consuming and involved and I can well believe the poster who says he does it for a living and it will take a week. It took me several uncomfortable weekends under the car, chipping away/using a burr in a multitool to remove most of the rust on the frames (there are lots of hard-to-get-to places, especially around the rear subframe), then came the chemical rust treatments, then the underseal and spraying Dinitrol Cavity wax inside box sections, sills etc. The hardened purists remove the subframes entirely and have them derusted and galvanised!
On the side of less effort, one of the tips I have picked up from watching Youtube American car 'rustoration' channels is that (again, as has been said) some of the rubbery spray on undercoating treatments simply trap water next to the chassis once the coating fails, and causes more harm than good in the long run. To get around that, it seems popular (and cheap) to use some stuff called 'Bar and Chain Oil' (in the USA) and coat the underside with that when the car is dry. It's a thick, sticky oil used for chainsaws and the like. It never really truly dries out totally so can't crack or flake, and seems to be persistent long enough that it doesn't wash off the first winter. A little bit of dust on it doesn't matter, it just forms part of the protective film.
I went down the DIY rust removal route at home with wire brushes, a Dremel tool and a pointy hammer and then treated with rust converter to passivate any remaining rust, then went over everything with two coats of Hammerite Underbody Seal with Waxoyl (it's bituminous and black) or a similar bituminous Dinitrol 4941 underseal spray . I injected Dinitrol ML Cavity wax into all the box sections and sills (the bodywork must be dry for this).
So, I'd say the first question is whether you want simply to stop the rust getting any worse (with minimum effort) or try and 'zero' it back to bare metal where it occurs and go down the full derusting and re-undersealing route. Rubbery underseal coatings do seem to be a trap to avoid...
 
#22 ·
I’ve gone down both professional and DIY routes. My low mileage rust free ZT I had professionally treated with Mercasol, and my 50k miles R25 I did myself with Bilt and Hamber products. I’ll wait and see whether it’s worth it, but it’s given me peace of mind in the mean time.

Tbh I always prefer to treat rust rather than leave it, but each to there own...

DIY R25 job:
 
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