I changed our Jazz anti freeze at 10 years. Although the original looked as new, it was interesting to see the silt sitting above the drain plug when it was released: lowest point of cooling circuit at radiator bottom..

Silt does build up over the odd decade

The UK is not a dusty country. Mine never appeared to be 'clogged'. They are easily cleaned with a stiff brush. I have sometimes washed them, like the filter on our Dyson.

I'm not saying you're wrong, it's years since I have looked at a car airfilter, but the filters in our house ventilation system (MVHR) have been an eye-opener.

I change them every 3 months because they are cheap, but it's surprising how much greasy black material accrues on the filter that sieves the incoming air. The installer says it's mainly diesel exhaust solids. The intake is about 20 metres from a village road that sees maybe 2,000 vehicles a day, and it's on the rear facing roof 6 metres up.

The first one I left in for 6 months and that was quite black. Not quite the same application, and it is running 24/7, even so...and it doesn't brush off either.

Interesting bit of fag packet maths - my MVHR moves about 60 litres of air per second, which seems to be about double the volume of a 1.6 litre engine running at 2500 rpm. On that basis air filter could be like my MVHR one after 6 months, if the car ran 24 hours a day. If it runs on average about an hour a day, then the 6 months becomes 12 years. Double the amount of particulate matter because it is actually on the road rather than 20 metres away and you get 6 years. The recommended change frequency for my MX-5 air filter is every 6 years or 75,000m - coincidence?

Edited by Manatee on 21/07/2023 at 16:26

John F, if you can be bothered read this..

www.machinerylubrication.com/Read/841/coolant-fund...s.

Explains it all nicely...

As for all the nonsense you keep banging on about regarding cleaning air and pollen filters with soft brushes all your ever doing is removing the dirt on the surface of the element, there is no practical way of removing the material deep within the pleats or indeed refreshing the activated carbon component that most modern pollen filters contain.

Edited by paul 1963 on 21/07/2023 at 20:42

Not all corrosion requires oxygen. Stainless steel, for example, is subject to crevice corrosion specifically in the abscence of oxygen. Big deal for sailboat rigging and keel bolt failure.

Then again, its doubtful that a car cooling system is sealed against oxygen, since coolant moves to and from the expansion tank, probably taking some oxygen with it, and hoses probably have some permeability .

Less theoretically, my last coolant looked like hot chocolate when I changed it, This might be partly due to me using a local brand of coolant, but the current Shell stuff also showed signs of rust when drained.

I also have operational confirmation of the need to change brake fluid, in the shape of a scary brake failure almost certainly due to boiling brake fluid, and much Hot Chocolate in the system when I stripped it.

I've had occaision to change the brake fluid on two other old cars in Taiwan and they were both in a very sorry state.

Re Hot Chocolate, I dont believe in miracles.

Not all corrosion requires oxygen. Stainless steel, for example, is subject to crevice corrosion specifically in the absence of oxygen. Big deal for sailboat rigging and keel bolt failure.

Thanks for this, ed - I never knew about 'crevice corrosion' and its requirement for a 'stagnant electrolyte'. But it can't be much of an automotive problem otherwise I'd have had problems long ago. The enduring continence of my 43yr old TR7 (apart from a leaky water pump 20yrs ago) continues to amaze me.

Well, DeLaurean;s and the Tesla Fantasy Folded pickup truck aside, there admittedly isn't much stainless steel in cars, but as someone pointed out, engines have a lot of aluminium these days.

Thats a similarly "passivated" metal, relying for its corrosion resistance on an impermeable oxide layer, and it can corrode badly, in a similar way, in the absence of oxygen.

I think you might be over-generalising a bit from observations on an old they-dont-make-them-like-that-any-more car.

I'm drawing conclusions from observation of an old car too, but with an important difference.

While your lack of observed corrosion doesn't prove it cant happen, my observed corrosion does prove that it can.

There is stainless steel in head gasket fire rings though. Heres Uncle Tony alleging that this gets attacked by old acidic coolant in composite gaskets. (Skip the first 5 minutes or so)

www.youtube.com/watch?v=wSn2YGY4rCY

I dunno if this is true, and if it is I dunno why MLS gaskets were the solution, but it does seem a relevant theory.

In theory, possibly. (Jeez, Uncle T doesn't half drone on......). I was inspired to dig out some old urine testing strips and dipped my TR7 decades old coolant. Pleased to note healthy looking clear light blue and pH between 7 and 8. Original 43yr old 73,000 mile head gasket still intact. No idea whether or not it has steel fire rings. In practice, supports my scientific argument expounded elsewhere never to change coolant.

<< In practice, supports my scientific argument expounded elsewhere never to change coolant. >>

I would only add the rider : ... provided its colour hasn't changed. I've seen examples of brown windsor soup masquerading as coolant.....

So have I. It's almost certainly a sign of CHG failure linking oil and coolant passages. Nothing to do with the integrity of the coolant which I agree should look as clear and colourful as when new.....as mine does in both my cars; their average age being >30yrs.

Dont think mine was.

Pretty sure it was rust, because it looked like rust, and it smelled like rust, and it settled out like rust.

i.e. not like oil.

Reminds me of coolant in pre 1970 cast iron engines. If rust it looked more like Heinz tomato soup than brown Windsor soup.