I wasn't aware of PSA's 5-year antifreeze so can't comment on suitable alternatives. However this is a good time to issue a reminder that it is extremely important to use the correct antifreeze, especially in engines where aluminium is used for major parts like the block and/or head.
The pressure pulses (vibration) in an engine, especially a diesel engine, can cause cavitation erosion. This is the forming of minute gas bubbles on the surface of the metal which then implode and wear the metal away.
Cavitation was responsible for the cylinder block to erode around the liners in my niece's Peugeot 106 diesel. This let the coolant leak into the sump and repairing the engine cost her about £1500, far more than the cost of using the proper antifreeze at the proper concentration!
We ought to drop the term "antifreeze" as this suggests something that is needed only in the winter. It is really "coolant conditioner" and it is vital to use the correct grade, to keep it in all year round, and to replace it at the specified intervals.
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I hope it is understood that cavitation occurs only where the metal is in contact with coolant. I didn't make that very clear.
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Cavitation can occur anywhere in the fluid its pressure falls below the boiling point. This is usually on pump suctions where low pressure forms, and then the bubbles collapse as they hit the impeller and the pressure rises. In your niece's case it was probably the other way - the local temperature rose above the boiling point adjacent to the cylinder walls. My guess is probably that this was a combination of the wrong coolant, and poor circulation (maybe also as a result of the coolant!).
For an axample of cavitaion take a look at the propellor on an outboard motor - most will be pitted - this is cavitation in action.
Richard
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EuroCarParts sell the original antifreeze. Buy one more bottle than you need if your car doesn't have a header tank as you waste some when bleeding and running the system the first time.
www.eurocarparts.com is what you need.
Ben
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Last time I tried Eurocarparts would not send fluids through the post - understandable I suppose.
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Richard,
What I meant was that the cavitation occurs within the coolant and not where there is air next to the metal. My original posting didn't make this clear - and my follow-up posting wasn't much better!
As you said, cavitation is very common in water pumps. However, cavitation around cylinder liners is also a known phenomenon, especially in diesel engines, and evidence of this was found in the remains of my niece's engine. The rapid build/decay of cylinder gas pressure makes the walls of the cylinder 'pulsate' and this causes the cavitation.
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I forgot to mention that cavitation erosion around cylinder liners is likely to be found only in engines with wet liners, such as used in PSA diesel engines. Engines with interference-fit liners (and any with the cylinders bored directly into the parent metal of the block) are very unlikely to suffer this.
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Thanks for all of your comments. I would have thought that cavitation in the coolant would be prevented by the high static pressure in the system, up to 2.5 bar in my engine. This would certainly be looked for during engine development, and attended to. Another problem is caused by localised boiling at hot spots. The damage looks very similar. Luckily my engine is iron, bored in the block with Al head. However, PSA diesel head gaskets are a known weak point. (Probably because they have few others).
I'll follow up the source suggested for the PSA coolant - thanks.
As a general point, it's well worth establishing where approved consumables really come from, given how many are used per car life. For example, there is a saving of £20 per PSA engine if the specified Dayco cambelt is purchased from a factor. I'm fed up being robbed each time by this cosy maker/dealer alliance.
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Dizzy, why do you think that this damage was caused by cavitation, and not by straight-forward galvanic/bi-metallic corrosion? Corrosion would cause the alloy cylinder block to act as a sacrificial anode. It would also have the same root cause, neglect of the anti-freeze.
I've usually met with cavitation in pumps, moving hot water, where the suction at the pump inlet causes boiling; the bubbles of vapour implode as they pass into the high pressure area at the pump outlet. I can't imagine any similar pressure fluctuations in the engine cooling system, other than in the water pump. Please explain.
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PS. Sorry, I'd read this at work and hadn't noticed your later post of 20:04 which explains the cause of the cavitation. I hadn't heard of this.
I would have thought that neglect of the corrosion inhibitors in the coolant, causing corrosion, would be a more common failure mode. Presumably neglect of the anti-freeze concentration would lower the boiling point, making cavitation more likely.
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afm,
Cavitation around wet liners has caused a lot of concern, not just with car engines but also with heavy duty diesel engines. I'm fairly sure that it affects engines with cast iron blocks as well as aluminium, though I assume there would be less erosion with cast iron.
I believe that the coolant inhibitor for these engines works by coating the components with a film that lessens erosion. You may be right that modification of the boiling point also comes into it.
My work in diesel engine design taught me that using the correct coolant additive (antifreeze) is very important. My old BMW has a petrol engine and doesn't have wet liners but I still take no chances with the coolant. I spend a bit more than perhaps I need in buying expensive BMW-branded additive. I use it at 40% dilution and change it at two years as specified.
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All the XUD units are cast iron block, and have no liners - I think only the smaller 1.4 and 1.5 units fitted to AX/Saxo/106 etc had alloy blocks with liners.
Still, XUD requries good antifreeze to prevent electrolytic corrosion between the head and block.
Richard
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Not entirely relevant but cavitation can be a problem in large steam boiler houses and distribution system.
Pitting and corrosion of steel pipework directly after steam traps is common and can be prevented by using heavy duty threaded copper tube although more usually by an additive being added to the make up boiler feed water.
The cause of cavitation is the sudden drop in pressure after a steam trap.
Water at 100psi with a temperature of around 320f is suddenly exposed to lower pressure in the condensate line and flashes back into steam with resulting corrosion.
The other problem is when the condensate returns finally back to the steam boilerhouse, and is discharged into a receiver at low level to be pumped back into the hot well at high level.
The receiver is exposed to atmospheric pressure and again flashes off to steam making it difficult for the pumps to operate as designed.
To prevent this various schemes can be used including a flash steam receiver en-route to the boiler house where the condense is induced to flash off into low pressure steam and used for some other purpose such as water heating or laundries.
Using additives works to a degree by coating but does give other problems which can be reduced by adding yet another additive and so on.
Sorry not really motoring related I know but I did find your information on cavitation interesting and wasn't aware it could occur on a car cooling system where I imagined the pressure remained constant. Although after your comments I could imagine a situation in the water pump area if air was present.
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I'm sorry, my senility has been playing me up again ...
I've just remembered that it was erosion of the liners, not the block, that let the coolant into the sump in my niece's Peugeot 106 diesel!
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That would be how cavitation was diagnosed, galvanic corrosion would have attacked the block?
See also; www.babcox.com/editorial/tr/tr110046.htm
This has some information on this OAT stuff that I?d never heard of. I hadn?t heard of cavitation erosion by flash steam either, which is relevant to my job. Spirax Girdlestone pumps spring to mind.
I?m involved with HVAC systems, chilled water systems with volumes of 1,000 litres are not unusual. In this application, it?s usual to test the levels of corrosion inhibitors and top-up if necessary. Dumping several thousand litres of toxic mono-ethylene glycol into the drains is not done. My understanding is that the corrosion inhibitors are intended to adjust the pH to 8 or 9 (to prevent galvanic corrosion) and to add oxygen scavengers. In hot systems, any dissolved oxygen will react with the glycol, forming acidic compounds and causing very rapid corrosion.
I?ve always been dubious about changing the coolant every 2 or 3 years. Won?t the life of the coolant depend on how much oxygen it is absorbing? In some systems the coolant might last 5 years whilst in others it may have turned bad within a few weeks. Are coolant test kits available? Presumably the coolant manufacturers are content with us buying new coolant every 2 years, whether we need it or not, even though this involves illegally dumping toxic solutions.
Ethylene glycol is very toxic. I once found an article on a sailing site about using it as a wood preservative & stabiliser, but haven?t been able to find it again.
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AFM, I'm also unsure on this oft repeated advice on changing anti-freeze.
My 1998 vectra bought from new does not show renewal of coolant at any period on the service booklet even though it goes up to many years. It does for the Tigra and Calibra though.
Called in my local dealership and the Manager checked this for me and confirmed this to be correct.
Pleased about this because access to the radiator bottom hose is virtually non existent.
However being of the belt and braces brigade I decided to draw most of the coolant from the expansion container out and replace with new.
In to the Vauxhall main dealer to buy a litre of vauxhall anti-freeze. On the container it says compatible with all Vauxhall coolants but it was blue exactly as Bluecol whereas the coolant in the Vectra is yellow.
Queried this and the storeman says I've never seen a vauxhall anti-freeze which is yellow. However now reading your article from babcox I imagine the yellow would have been the OAT coolant as described being used by GM since 1995 and having a service life of 5 years or 150,000 miles and not recommended to be mixed with ordinary glycol.
Too late.
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That would be how cavitation was diagnosed, galvanic corrosion would have attacked the block?
I think so, though it wasn't me who did the diagnosis. A local engine machinist/rebuilder couldn't find out what was causing the coolant to enter the sump. They assumed it was a failed head gasket and they machined the head face and twice replaced the gasket in attempts to cure the problem. They were then told about the possibility of it being erosion of the liners. That is why the repair cost £1500 -- my niece (actually her dad - i.e. my brother) ended up paying for all the unnecessary work and parts as well as for the eventual replacement of the liners, etc.
David W knows the machinist I'm referring to; he too has come across their "machining the head will cure all" philosophy. Unfortunately I didn't know anything about the matter until it had been finished and paid for.
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afm,
Interesting and useful antifreeze info on the Babcock website. Thanks for that.
One thing that surprised me was the mention of mixes stronger than 50/50. Our chief chemist worked closely with antifreeze manufacturers in the mid-80s to develop a new antifreeze suitable for the Perkins Prima engine and I was involved in documenting the composition, use and performance of both the standard antifreeze and this new one. I clearly recall that mixing propylene glycol or, I think, ethylene glycol above 50% with water actually raised the freezing temperature, not lowered it. If I recall correctly, this was due to stratification, i.e. the water and additive will not mix properly at these strengths.
Any chemists out there who could comment on this?
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The info on that website could be incorrect. I did a search for OAT AND antifreeze using Google. That site just happened to be the one of many that I chose to read. Their figures suggest that the 50/50 mixture would give a 10 or 12 degC increase in boiling point, compared to plain water, at 15 psi gauge pressure. The pressure maintained in the cooling system by the cap would also make a contribution to delaying cavitation.
A Renault 21 engine I worked on had wet liners. The Haynes book said that turning the engine with the head off could move the liners, requiring the liner/block seals to be replaced. Such mundane negligence might be a more common cause of failure than cavitation. A colleague & Renault enthusiast told me that Renaults recommended filling with anti-freeze and distilled/deionized water. The calcium salts dissolved in most hard tap water will consume some the corrosion inhibitors.
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Quite a lot of heavy duty diesel engines have wet liners and I understand that these often suffer from perforation due to cavitation unles the correct inhibitor is used. Perkins engines don't have wet liners nowadays but the light-duty 4.107 of the 1960s had them and I don't recall any cavitation erosion problems. I wonder if this was because the cylinder gas pressure extremes were not as severe as on modern engines so there was less in-out vibration of the liner walls?
By the way, it it usual to rig up some kind of holding-down clamp for wet liners down to prevent movement when the engine is turned with the head off.
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