Rad cracking prediction / prevention?

Seems like the top of the stock rad is prone to cracking.

At what sort of age / milage are people experiencing this problem?

Mine's 11 years old in July, so I'm guessing it's only a matter of time?

I'm toying with the idea of 'capping' the radiator in this area with thin ally sheet (~1.2mm) held in place with a suitable adhesive.

Assuming the cracks appear where the plastic is at it's weakest (thinnest?), adding more strength should work??

Thoughts / comments welcomed of course.

I dont think strenghtening it will do any good matey IMO, the rad cracks because the plastic gets brittle and cracks, ive heard of people putting a new rad Top on the old one but never seen one done before,

I just bought a new one in the end easy enough job to to DIY as well

Cheers

Ian

I dont think strenghtening it will do any good matey IMO, the rad cracks because the plastic gets brittle and cracks, ive heard of people putting a new rad Top on the old one but never seen one done before,

 

I just bought a new one in the end easy enough job to to DIY as well

 

Cheers

Ian

Interesting.

Normally though their must be a force (leading to movement) to cause a crack, even in an embrittled material. My theory is if you resist the force you stop the movement and hence stop the crack forming. I may just be talking science fiction though:)

The crack occurs where the hot coolant flows into the radiator opposite the top hose entry. The hot coolant and cold rad matrix (judt below where the crack appears) causes a thermal gradient across the plastic and repeated cycling of hot to cold during each drive & subsequent cooldown causes embrittlement of the plastic, leading to a small crack forming. This then propogates with each cold to hot cycle, eventually becoming large enough to throw out quite a bit of steam.

I posted a method of repair here http://www.mkivsupra.net/vbb/showthread.php?t=83786 but JB weld can't stand the thermal gradient and heat cycling. I found Isopon P40 (fibreglass and resin mix) is a better lasting repair as the fibreglass stops the stress cracks forming. Stick it on 1/2 an inch thick from the top to the bottom of the plastic tank and all is fine & dandy.

As far as prevention goes.... it can't hurt to thicken up the material where it cracks. I wouldn't use aluminium though as this has a much different rate of thermal expansion than the plastic (glass fibre I believe) of the header tank and will probably break itself free. Probably better to use like for like.... i.e. glass fibre (P40 again?).

The number of years it lasts before failure may not be a good indicator as its probably the number of heating up & cooling down cycles it has done that is the cause. Probably better to look at mileage?? Mine went at ~80K miles.

Cheers K14, that's useful info.