09 AugUsing Dinitrol 3125 and 4941

For the past 7 years since it’s restoration, my Spitfire has had all four wheel arches Waxoyled to prevent rust. So far it’s done the job, but I wanted to try something different as I’m not a great fan of the Waxoyl finish.

Although Waxoyl is clear, dirt sticks to it and cannot be cleaned off (without removing the Waxoyl). Consequently, after many months of road use, the wheel arch looks like this:

waxoyl wheel archhttp://triumphspitfire.rickbaines.com/wp-admin/post.php?post=285&action=edit&message=1

Not the prettiest of sights, and once it gets covered in dirt, the advantage of being able to see the condition underneath is removed. The eagle eyed amongst you will have already identified this as the right rear wheel arch, this article will be tackling the left rear only.

First job was removing the old Waxoyl – messy! To speed things up I filled an old spray bottle with white spirit – WD40 also works well for this. Spray it evenly all over the Waxoyl, then with some paper kitchen towels get it smeared all over so it sinks in. The old Waxoyl will come off with enough persistence, and pressure washing with water can help things along. Even though the old Waxoyl wasn’t airborne, I still covered the brake drum in an old carrier bag just in case.

On the final stretch of cleaning, use plenty of white spirit as this is effectively degreasing the wheel arch. Try remove the white spirit with a clean paper towel once you can’t see any more Waxoyl, and let it dry off thoroughly. You may need to touch up stonechips – I had a few, though fortunately these hadn’t even got surface rust as the Waxoyl had seeped over the chips to continue protecting the car.

Clean wheel arch:

clean wheel arch

clean wheel arch

clean wheel arch

It was a particularly hot and humid day, and I also had the Dinitrol 3125 in a bucket of hot water. I think this was overkill, as if anything it flowed too well!  Because these photos were taken after spraying, you can’t see the sheets under the car to catch drips or the carrier bag I placed over the brakes. This was done for both types of Dinitrol, though the 4941 didn’t drip at all so the sheets weren’t as important.

The Dinitrol was applied using the free spray gun you get from rejel.com, using a compressor at 6 bar (about 87 psi).

dinitrol 3125

The 3125 is brown and very runny, you apply it first so it seeps into all these ridges. I also smeared a bit behind the inner arch at the lower edge (out of view here) with a latex gloved finger, just to make sure it covered well.

dinitrol 3125

It really does seep into every seam! You want plenty on that flat ridge, many Spitfires have rotted here, and you can see repairs have been made here to mine during its body off restoration.

dinitrol 3125

Make sure the wheel arch lip gets plenty, as this area is particularly difficult to clean and is a notable rust trap.

dinitrol 3125

dinitrol 3125


The photo below shows how the 3125 looked the next day after allowing it some time to dry. You probably wouldn’t have to wait this long, around 4-6 is probably sufficient but I had the time so didn’t mind. It was still slightly tacky at this stage, though I expect that would go even if you didn’t apply the black 4941 afterwards.

dinitrol 3125 dry


The final stage was applying the 4941. The way this went on was very different, it’s much more controllable and doesn’t really run at all. Because it is black, in dark places like wheel arches it can be easy to miss areas so an inspection lamp is handy. I had to touch a few bits up the next day that were a bit thinly applied, because looking at it later that evening with a lamp showed them up.

dinitrol 4941

You really could do with masking up the outer body panels for this one, as it’s slightly harder to get off with white spirit than the 3125 – but it will come off.

In the ridge between the inner panels and the outer rear wing panel, you can see I’ve left a bit that should’ve been cleaned off, this was deliberate. I’m not fussed about having a bit of a black groove there if it means added protection, and you don’t notice it unless you’re looking closely.

dinitrol 4941

Notice how all the spot welds, repair patches and other marks on the bodywork still show through, even though the finish is slightly mottled. I really like this feature as it means you get a very OEM appearance.

dinitrol 4941

The finished wheel arch below. Once the car is driven for a bit, the rear leaf spring will settle down and the gap between the wheel and the top of the arch will be a lot smaller.

dinitrol 4941 finished

I’ve tested this since and any dirt does easily wash off, it’s a very impressive product. It was very very slightly tacky after drying, however it had a thorough 200 mile roadtest to Spurn Point involving heavy rain, muddy trails, sand, stones and some spirited driving and came back looking perfect, and that was just a day after I’d applied the last of the black 4941. It is no longer tacky at all and feels like a really strong finish. The real test will be on salty roads, but so far I have full confidence in it.


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8 Responses so far.

  1. Aaron Brown says:

    Being lazy; all I did was to brush them down; put kurust on the rusty patches (LOTS!); then beige (YEY BEIGE!) anti rust primer; then a bit of red topcoat; then some 99p underseal from the 99p store 😛

    I don’t care how it looks; just as long as it doesn’t get any worse!

  2. Rick Baines says:

    At least you’ve done something! Most of these cars rot from being completely neglected. Just make sure you remove the underseal two years or so (depending if you use it in winter, more frequently if you do) to check everything is fine underneath.

  3. David says:

    I`m going to do the 3125 4941 combo everywhere I can under my car and the wheel arches. I hope that neither run when un-heated in cool temps because I have a brush only. Are both products very runny cold or did it just go like that after you heated it up alot ?

  4. Rick Baines says:

    3125 is definitely more runny than 4941 when they’re either heated or cold. Consistency of both is way less viscous than clear Waxoyl.

    I think when cold, they’re probably both too runny to get anywhere near a perfect brushed finish, looks wise, but you could certainly get good coverage and penetration using a brush. If you care about appearances, I’d say spray it, if not, brush will be fine.

  5. David says:

    Wow, that was a super fast reply, thankyou.
    The appearance does not matter since I live on the coast of Wales with high farming activity so my car is always muddy underneath as soon as I drive anywhere.
    The problem is farm muck, high salt from living on the coast and abit of neglect on my part have meant that I have had to pay someone to cut out both rear wheel arches on my car and rebuild and spray.
    I was worried about how runny 3125 was because brushing anything thinner than wood stain is a nightmare, so messy and wastefull with more dripping and splashing than is going onto the surface. Would you say that 3125 is more thick or thinner than wood stain ?

  6. Rick Baines says:

    One thing I’ve been wanting to develop for a while now is a plastic wheel arch liner for the rear wheel arches, like the ones modern cars have. That way all the mud and salt would hit the liner instead of the metal, and you could dinitrol behind it making the protection extremely strong. That’s what Triumph TR4-6 owners do, just a shame nobody makes a pre-moulded one for the Spitfire.

    Its definitely not thinner than wood stain, though if you’re expecting problems and don’t want to risk buying it to try it out, I guess what you could do is brush Waxoyl clear on then cover it with 4941 – I see no reason why you shouldn’t be able to mix the products. I know from first hand experience that Waxoyl brushes on extremely well, the finish you see in the first photo on this page is brushed on Waxoyl (plus months/years of dirt).

  7. Aaron Brown says:

    Gosh that’s a blooming shiny suspension and brakes! Mine’s all original; but it hasn’t really been looked after and looks horrid :/