Q: Dissimilar Metals in a Modern Cooling System

addo · Post by **addo** » 01 May 2011, 10:38

First a point - I'm not looking for recycled Googling, more hoping for words of anyone here who has a qualified opinion (whether by education or hard knocks) on mix-n-match metals in a modern French car's cooling system.

Say - typically we have in the cars, an alloy head, iron block or sleeves, aluminium radiator/heater, brass noses to the coolant sensors and possibly a silicon bronze impeller on the water pump. Assume a modern spec coolant but no exclusive choice.

If one were to replace a fancy set of multi-legged hoses with fabricated manifolds and simple joiner hoses, what might be the ideal metal: Welded aluminium tubing, silver soldered copper or brass, TIG welded stainless or brazed steel tubing?

I'm stressing the French car bit due to fragility of the heater core; one doesn't want sacrificial action upon its innards!

Cheers, Adam.

HDI · Post by **HDI** » 01 May 2011, 10:56

Stainless steel, without question. Use 316L and it will be inert to all intents and purposes in the application. In a past life we had a family company which was involved in hose, pipe and fittings so I've had experience of this sort of issue. In industry where it's often very important to prevent contamination in a circulating system, 316L SS was the material of choice unless chlorine, brine or some other chemicals were present.
Actually, this is one of the reasons why car manufacturers often specify to use distilled water for cooling systems, to prevent corrosion and sacrificial deposition from possible chemical contamination in mains water.

andmcit · Post by **andmcit** » 01 May 2011, 11:04

Pal of mine graduated from Imperial College, London and is a smart bunny
but also a big big Citroen fan and we've had a conversation on this thread
topic many times in the past. There's a T elbow on a Cx which is made of
licqorice and a brass pluming fitment that makes an identical replacement.
My pal would always be on my case to coat the inside with enamel paint
to create a barrier to the plumbing fitment and give me the shivers about
cooling corrosion especially as it happens the fine coiling that runs inside
the vanes of the heater matrix like some wild helter skelter.

That all said, there's a significant chance of corrosion with the
aforementioned plumbing fitting than the cylinder head, block and
radiator/matrix. I don't believe engine manufacturers would have
doggedly stayed with these dissimilar metals if they didn't go the
distance accepting these designs were made before our more throw
away disposable modern day. The worry would be a weak anti freeze
coolant that allows the innards of the matrix to disintegrate, block and
then leak.

It'd be worth slicing a Xantia matrix to see if the fine spiral vane element is
the same potentially vulnerable design.

Andrew

addo · Post by **addo** » 01 May 2011, 11:14

Thanks, gents. 316L would be one of those "lifetime" products, I think - seems like the one to chase. Can a Parker tool bead the stainless or is it easier to add a ring of weld to seal the rubber hoses?

My steel supply bloke would probably have a crack at it - makes a change from welding commercial balustrades.

A smartarse mate suggested Titanium! It was all the funnier because he's so tight with money.

Re the Valeo heater matrix failures - I am yet to see one fail at the bends, which is where their tech bulletin implies risk to be greatest. Our local water is fairly soft overall, but heavily chlorinated.

Cheers, Adam.

HDI · Post by **HDI** » 01 May 2011, 15:23

Well you could use Ti, one of the Duplex stainless grades or even Inconel ! Actually, the very best grade of stainless for this application would be 6MO. However, they would be far from cost effective and would not offer any substantial improvement in performance over 316L.
They also wouldn't be available in the range of practical products that 316L is off the shelf.
Instead of roll beading just look for a supplier of hose fittings and look for serrated hose tails. They are available in a wide range of sizes and are very convenient to use in this sort of application.

Post by **CitroJim** » 01 May 2011, 19:00

addo wrote: Re the Valeo heater matrix failures - I am yet to see one fail at the bends, which is where their tech bulletin implies risk to be greatest.

I've seen it happen on a couple of 205s Adam, but never on a Xantia (so far). My belief is that they fail on the O rings joining the pipe extensions to the matrix proper...

The 205 ones failed because the cooling systems in each case had been filled with plain water and scale had built up to act as a fine abrasive.

addo · Post by **addo** » 01 May 2011, 21:33

Jim - yes, that mode of leakage (distortion/seals) has been observed here, too.

HDI - by serrated, do you mean hose barbs?

HDI · Post by **HDI** » 02 May 2011, 10:26

Yes, the industry term is serrated.