Failed rad....cause that very few check for.

Nissan doctor

I had a car in today which gave a chance to show an extremely common cause of cooling system failures..but one which is rarely diagnosed or even checked for, and one which many may not even have heard of or considered.

Many people will be aware that radiators can leak and need to be replaced, some from impact damage, some from leaks between the plastic end caps and the core, but if you have a radiator that seems corroded and/or has pin hole leaks in the aluminium core then there is likely to be another reason....a bad earth!

A bad engine earth will cause the coolant to become electrically changed which will then lead to a chemical reaction with the alloy called electrolysis. This can corrode alloy in days if the charge is high enough(in the case of this car, it was inspected only a couple of weeks ago and had no leaks) and is a very common problem as cars get older and earth points become corroded or electrical systems earth/wiring breaks down.

Most people see corrosion on a failed rad and don't think much of it but think for a moment, the rad is alloy, clean water can't corrode it, coolant is specifically designed not to corrode and even salt etc from road grime would only effect the surface finish of alloy, this leaves only electrolysis as the cause but if you haven't diagnosed it and just fit new parts, then you haven't carried out a permanent repair.

A couple of pics:

The leak in the end of the rad,



And with the cover removed, you can see that the alloy core has developed a pinhole.



Checking for electrolysis couldn't be any easier, you simply use a multi meter with the positive probe dipped into the coolant reservoir,



The reading above shows 214mV(just over 0.2V) with the engine running. Any more then 0.1V(100mV) is enough to cause electrolysis.

In lieu of turning every single individual electrical system on and off to see if the voltage reading in the coolant changes, a simple way to remedy the problem is to add an extra earth point between the engine and body and check the reading then,

A makeshift earth strap for testing,





And with the extra earth in place, a reading of just 12.6mV(just over 0.01V) comes back so you know that you have found the cause and the solution is to simply add an extra, more permanent earth which will prevent the new radiator from being corroded in the same way.

So there you go, how an electrical system issue can cause the failure of your cooling system!

Thanks for reading..

Captain Slow IRL

That's impressive, something you'd never even think to consider!

langdang

Nice post ND. Would there be a voltage between the engine and body too, before adding a new good earth? Or is it only noticeable in the coolant? ( Bothering me thinking about why the coolant would be at different potential to the engine -Not really up on the whole electro chemical side of things! )

shamwari

***Cue a large number of boardsies heading to their cars with voltmeters in hand*** :pac:

Great post ND, can I ask what sort of car this was?

Kopparberg Strawberry and Lime

shamwari wrote: »

***Cue a large number of boardsies heading to their cars with voltmeters in hand*** :pac:

Great post ND, can I ask what sort of car this was?

was my own car for this one

2004 volvo s80 2L turbo

JohnBoy26

Electrolysis is a big problem in steel boats. If an earth leak occurs it eats the metal at an alarming rate.

Excellent post, very interesting reading.

Pj!

Thanks ND.

Learn something new everyday.