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Driving along today, heard a massive scraping sound, pulled over and the heat shield (assume it’s from the exhaust) had fallen off.
I know it’s an mot fail, but what purpose does it actually serve. I have a 300 mile drive on Friday and don’t want the car bursting into flames. Does the heat shield protect the fuel tank from overheating (which I assume would be really bad)
Depends where it was from. There are heat shields all over a car. None that I can think of would be an mot fail.
Agree that it depends where it has fallen from. The original Ford KA exhaust ran close to the spare tyre and the tyre degraded quickly because of the heat so it can be a bad idea.
As a retired mechanic I would not worry about it.
300 miles on a motorway in a wet and windy country is extremely unlikely to get anything very hot.
Most the time they are to protect the stuff around them from sustained and repeated heat so I doubt your car will burst into flames on a UK journey. Probably worth replacing it when you get a chance though.
It appeared to come from middle of the car.
Depends
Very much this... if you are vaguley mechanically minded and semi aware of how hot the exhaust can get in relation to it's proximity to something important...you can read between the lines a little bit.
The old Fiesta of my namesake had a fancy pants custom exhaust on it.. there was a ford OEM heatshield above the rear box that was made of metal that was litterally not thicker than a disposable BBQ tray, and it corroded, started rattling like a B'stard... I took it to the specialist I used at the time, I think it was Tony at Pumaspeed IIRC, as he did the engine conversion and a bunch of other Mods for me, and I asked what to do...
He looked at it, said they all fall off eventually as they are made of cheese, and just ragged it off with his hand and said 'there you go, fixed!"
And that was that. Never had any problems*
*YMMV.
Are they specific to a car, it looks just like a random bit of aluminum roughly cut to fit round my exhaust? Ie can I pop to kwikfit tomorrow and get them to fit a replacement (the bolt holes have failed on my old one), and if so anyone know the rough cost? As I’m skint..
Dying is unforunately a certainty.
However the heat shield falling off car is unlikely to cause it! They eventually fall off most cars so anything 10 years old you see probably missing a couple already!
Heat shields are only a fail if it creates a fire risk with a part of the fuel system, 6.1.3
"Only fail a vehicle for missing heat shields if there’s a risk of fire with other fuel system components."
In practice I suspect you have to be unlucky for that to ever arise, because the tester has to a) know there's a shield missing, which they might not, which also gives them plausible deniability so they can choose to pass you without risk to their licence, but also because b) the fire risk is so open to interpretation.
But aside from fails, they can still be a really good idea. Backboxes and catalytic converters especially can get very hot and sometimes you have stuff nearby that doesn't want to get hot- spare tyres, alternators, bits of plastic. Contents of your boot, sometimes! Weird unexpected stuff, like on a mk3 MX5, the right hand engine mount can get cooked and harden and fail early. I mean, in general global car platforms mean the heatshields are designed for the hottest place they sell the car, but that doesn't mean there can't be little local bits that don't want to be hot.
I've zip tied a couple back on. What you'll find it the aluminium corrodes around the retaining bolts and fall off. Either remove bolt, fit a washer and tighten back on, or try and zip tie. The only ones I've made sure stayed on are any near the fuel tank.
I suspect it’s protecting the fuel tank from the exhaust and you will blow up in a spectacular fire ball!
Or you could be fine.
Probably one of those 😉
My son's aftermarket exhaust melted the edge of his fuel tank. Very lucky as he was driving the NCN500. Only found out when back home and there was a smell of petrol. Tiny hole developed in tank. New tank job and re-routed exhaust. Could have been rather 'warm'.
As above, purely depends. The back shield rotted off my Mondeo (yay galvanic corrosion!) and I DGAF, if it had been the one at the DPF I'd have been concerned. Anything around high temperature parts is worth sorting but the rest, meh.
Due to the daft way the engine works, my car occasionally shoots flames out the back (on track), it runs much higher exhaust temps than most other cars - It has one heat shield (around manifold)
You'll be fine, you won't be throwing out huge EGTs on a motorway jaunt.
Some heat shields also provide some protection from fire if you drive into a dry grassy field! Unlikey at this time of year!
That would probably be on a DPF if anything
If the bolts will come out, penny washers also known as repair washers will hold it nicely.
Wiring it in place might cause a really annoying rattle.
I just fixed my wife's car that had manky rusty in-situ bolts for its heat shields with some of these:
https://www.ebay.co.uk/itm/222643636677
Dunno of they're the same thing as penny washers but the original nuts had evaporated and these took me (a doofus) less than 10 mins to change the car from 'rattling death machine' to 'normal for a nissan note'.
Is your car in orbit? If so, be very careful on reentry...
Penny washers won’t work as the original mounting holes have all snapped off