Paint for under bonnet chassis

[paul_a]

Hi the powder coating on the under bonnet cross member on my chassis right next to the exhausts has started to lift and flake a little. I’ve lifted the flaky bits off and the steel underneath is really good and solid. I guess it’s the exhaust heat that’s caused the issue. My question is what’s the best thing to put on it? Would high temperature exhaust type paint be ok or good old Hammerite. It will need something before rust sets it.
Thanks Paul

[Belle427]

Hammerite is rubbish these days, id probably clean it up well and use a brush on engine enamel in a close colour.

[kris450]

Depending on far you want to go, could also remove the manifolds and wrap the chassis tubing in some heat reflective material. Just a thought.

Sure, the below was done with no engine in so infinitely easier, but with manifolds removed you've still have decent access.

Edited by kris450 on Saturday 16th March 13:10

[paul_a]

It’s the square box section just behind the manifold, that the swirl pot fixes next to. looks like yours has been removed.i reckon I could wrap it in the same stuff you’ve used. Where did you get it from? I thought about white exhaust wrap but 1. It doesn’t look nice and 2. I read somewhere it can hold moisture, which could make things worse. Paint and your wrap could be the answer?

[kris450]

paul_a said:

It’s the square box section just behind the manifold, that the swirl pot fixes next to. looks like yours has been removed.i reckon I could wrap it in the same stuff you’ve used. Where did you get it from? I thought about white exhaust wrap but 1. It doesn’t look nice and 2. I read somewhere it can hold moisture, which could make things worse. Paint and your wrap could be the answer?

It wasn't anything particularly spectacular or wallet breaking. Got it from amazon years ago. Just had a look and that listing isn't available anymore, but any sort of heat reflective material should work. I used stuff with an adhesive backing and it hasn't lifted at all so far over the last few years.

My only tip is (at least with the stuff I used) you get one chance of applying it. The adhesive is fairly brutal but can actually be peeled back carefully. Trouble is it then loses probably 90% of its 'stickiness' and can subsequently lift off easily. So clean the cross member to within an inch of its life and make sure you're all good to go before you start applying.

But I have to admit it seems a little strange that its the cross member thats suffered. Normally the engine mounts start to sag and the manifolds get close to the chassis sides and thats what ends up being roasted. Never heard of the cross member being effected before.
Are you still running the main cat ? If so is there any chance that might be getting blocked slightly and then radiating abnormal amounts of heat ?

[paul_a]

The manifold is about 20mm away from the cross member. I’m hoping it’s just the heat and poor coating. 🥴 The chassis in general is really good.

[Rocket 88]

I have been experimenting with different paints for several years and thought I had found a good one in POR-15 but it doesn't last very long and it is expensive. Frost Auto Restoration have a vast array of paints and the Eastwood range are quite good but the best so far for me is Rust-Oleum CombiColor. Unfortunately the smallest tin is 750ml but is lasts well in the tin and gives a good hard finish. Takes a couple of days to dry in this weather. I did all the underside of my Shogun @ 3 years ago and it is still as good as the day I did it.

[Loubaruch]

paul_a said:

The manifold is about 20mm away from the cross member. I’m hoping it’s just the heat and poor coating. ?? The chassis in general is really good.

I think that you will find that corrosion on the cross member is due to leakage or condensation around the Swirl pot. As its in front of the engine where cooling air enters it is very unlikely to be heat related. Mine was also quite rusty but easy to remove and treat.

[paul_a]

Good point. It’s not corroded I’ve wire brushed it and it’s really clean and rust free. It’s just the powder coat that’s flaked off. Can I ask what you treated it with. Thanks

[Belle427]

Rustoleum combicolour as mentioned above is a good choice, not expensive and lasts in the tin once opened,
Protecting the chassis from the heat will help if you can.
I was always impressed with POR15 when i used it, stuck like st to a blanket and almost impossible to get off when cured, problem is it would need to be used quickly once opened.

[Loubaruch]

I have never been a fan of POR15 paints, vey messy and not easy to touch up and in my experience lasts no longer than other paints.
I treat derusted metal with Bilt Hamber Hydrate 80, it seals any rust and is quite happy on clean metal and does not need washing off. Then a decent red oxide primer, Bird Brand is excellent and also contains corrosion inhibitors and is Xylene based so dries quickly and thins with cellulose thinners if necessary, finally a finishing top coat of chassis paint.

[paul_a]

Thanks for all the good advise. I really appreciate the help.

[PabloGee]

When I painted my steering rack, I looked at a few things.
Possibly mistakenly decided on POR-15, but it's on and is holding up.
Clearly the steering rack doesn't take the heat battering in the same way.

Part of my research pointed me to two-pack epoxy paint, more for its hard wearing nature than heat resistance, but I hadn't heard of it before then. Might be worth exploring. Definitely consider heat protection as well though...

[s p a c e m a n]

About 8 years ago I used rust buster 121 epoxy bought from ACT, jet washed the chassis down and wiped it with a rag before painting. It's all still on the bits that I painted, looks in exactly the same condition as when I did it if I wipe it down with a cloth. Hasn't even changed colour under the manifolds from the heat and the car lived outside for 6 years so isn't a garage queen. I will say that the stuff is thick though and I should have painted around the chassis numbers as I could read them when the paint was wet but it sort of self leveled itself and filled the numbers in.

[Badgerchim]

Another vote for rust buster 121. Also added some additional protection to the top chassis rails

[paul_a]

Looks tidy. Is the extra protection the self adhesive foil on a roll? How did you apply it?

[Badgerchim]

I used a self adhesive aluminium turbo exhaust protection from a well known auction site with 50mm self adhesive aluminium tape at the ends to tidy it up.
The protection was slightly textured and thicker than the tape. I have looked back for a ref but it appears no longer available but sure there must be similar alternatives.

[TJC46]

paul_a said:

Looks tidy. Is the extra protection the self adhesive foil on a roll? How did you apply it?

Foil faced glass cloth is what your after. It is the same material as the heat shields TVR fitted to the inner wings.

You just cut it to fit on the chassis tubing, and tape it in position using foil tape.

[ads]

Sorry to Hijack but just stumbled across this thread as I am currently looking to paint my top tubes near the exhaust manifolds. My powder coating has cracked and underneath is fine surface rust which I have used a small wire wheel on a dremel to remove.

At the moment I am either looking at coating with rust buster 121, POR 15 or Bilt hamber epoxy. I'm seeing mixed reviews regarding the POR 15, bust also didn't want to hastle of the epoxy mixing so is there anything else?

In the past I have used Hammerite. I recently used Hammerite on another project and it is not the same as it was years ago so looking for something that will last longer