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08/03/2005

  Ballooned Radiator

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Vehicle Cosworth  24V engines only
Year All
Mileage All
Repair Cost 350
Repair Part(s) Coolant Radiator

The Case of the

Ballooning Radiators

"Holmes?" said Watson. "Holmes, do be a good fellow and sit down. You are quite wearing me out with that pacing."

"Sorry, Watson.  I try to sit still, but I cannot. I become bored so easily now that I have forsaken opiates."

Watson sighed and folded up the Times. He knew he would read no more of it today. "Then shall we look at some of your mails? There might be something there to take your interest?"

Holmes' aquiline nose wrinkled. "Mails? Electric contrivances now, instead of good paper and ink," he grumbled.

Dr Watson persisted. "Nevertheless Holmes: should we not peruse them and ensure that some unfortunate person who needs our help does not find himself ignored by the very person whose opinion may be the most valuable for him to receive?"

Holmes paused for a moment, then returned to his chair and sat down. "Yes, if we must, Watson."

Watson picked up a sheaf of papers. "Now here is just the example." he exclaimed. "This is from some motor car people, the - ah - " he scanned the page "... Scorpio owners."

"Oh." Holmes' voice betrayed disappointment. "Really? Car people? I have never understood why a gentleman should wish to fiddle with those dirty contraptions. One has servants for that sort of thing."

"Nevertheless  they are good people, Holmes, I assure you. And they have a conundrum that should appeal to you." He waived the sheaf of emails.

"Have you read the messages, Watson?"

"Indeed I have, Holmes."

"Then pray divulge fully of this information, Watson, and I shall load my pipe and smoke while I cogitate. Pray do not miss out any of the tiniest part, for it is often in the slightest detail that an answer rests."

Watson nodded, adjusted his glasses and began. "Well Holmes, as I have already mentioned, the Scorpio people have discovered a problem with their radiators. Radiators are -"

"Heat exchangers placed in the front of the motor car so as to lose excess heat from the engine coolant."

"Yes Holmes, quite so. On some of the vehicles, the 24V engines to be precise, the radiators have ballooned as if submitted to a gigantic pressure. However, the owners have been blissfully unaware of this outrage. The radiators have been replaced, both by original manufacturers' replacements and cheaper alternatives, and these, in turn have ballooned. Yet no coolant has spilled."

"Yes, you  were right, Watson. This is interesting." Holmes said. While Watson spoke he was resting his head lightly on the back of his high chair, his fingertips together in front of his chest, puffing steadily at his pipe.

"The machines affected are from all stages of production - let me see," Watson turned the pages and found the list. "A saloon from 10/96 and 2/97, 2 more saloons built on 11/04 and 6/98, an estate built on 4/97 and saloons on 11/97 and 10/96. Seven in all, and all Cosworths."

"Excellent. And how many Cosworths are on this List?"

"Perhaps forty, Holmes."

"And how many DOHCs?"

"Oh, six times as many."

"Excellent. Continue, Watson."

Watson continued with the briefing. He explained that all vehicles shared the same pressure cap and all the header tanks were of a similar capacity. The plumbing of the coolant system was very similar on the three DOHC engines, having a thermostat mounted in the traditional place at the front of the cylinder head, controlling the flow of water through the heads to the radiator. The Cosworth arrangement differed markedly, in which the thermostat was mounted in the lower coolant hose to the radiator and varied the coolant flow from the cylinder heads to the radiator, depending on temperature. One owner had used distilled water and several different types of antifreeze solution had been involved.

"And that is as comprehensive a summary as I am capable, Holmes." Watson said at last. "They stand ready to bring an example of the motor car to us for examination."

Holmes did not move from his posture, his fingertips pressed lightly together and elbows resting on the arms of his chair. "That will not be necessary, Watson. I know what is causing the problem. It is the thermostat."

Watson gasped. "Really, Holmes, that is preposterous. How could you possible know - "

"Think, my dear Doctor, think! It is you who told me the answer, as you read them from the mails."

"I?  But surely ..."

"The answer is there, Watson. You just need to tease it out, isolate it and bring it into the light."

"Really, Holmes. I know how you enjoy perplexing me with these games of yours, but even I cannot believe that you can state the case with such precision. Surely there is some room for doubt?"

"None whatever, Watson, I assure you." He turned to face the Doctor and smiled at last. "Very well. It seems I must explain. Sit down, my dear Watson, and I shall pour a madeira for you while I expound." He walked over to the sideboard and lifted the decanter. "Seven facts are the essential elements in the solution. You know them, yet you do not recognise them." He poured the wine as he spoke, walked over to Watson and gave him the glass of wine. "The facts are:

1. Only 24V Cosworths are affected

2. Some 24Vs have experienced this problem several times

3. Some 24V cars have not experienced this problem at all

4. Not caused by hard water

5. Affects all production dates

6. Not caused by ageing radiators.

7. No other symptoms

"Eh?" Watson said. "How do we know ageing radiators are not to blame?"

"Really Watson," Holmes admonished him. "The second fact. Some motors have experienced this several times. This means they had new radiators installed, but they still failed."

"Ah, yes. Yes of course." Watson shifted in his chair.

"And the third." Holmes continued. "If it were ageing radiators every single early one would have failed by now, and even fact 5 confirms this, for all production dates are involved."

Watson smiled weakly. "Yes, quite so. Yes, of course you are right, Holmes. But surely excess pressure must have something to do with the pressure cap?"

Holmes smiled tightly and took a sip of his wine. "One would think so. Indeed it would be the first suspect. But clearly it cannot because of Fact 1 - all vehicles use the same pressure cap - exactly the same, mark you, Watson. But only the 24V machines experience the syndrome. With six times the number of DOHC motor cars there would be hundreds of faulty radiators reported by now. Instead we have Fact 1 - only the Cosworths are affected."

"Yes. That is so." Watson agreed. "But perhaps the header tank - "

"Fact 3," Holmes snapped.

"Or the plumbing - " Watson persisted.

"Fact 1 and 3." Holmes snapped again. "Please, Watson, keep up."

"Because of fact 3 we can rule out the header tank. Logic states that the plumbing of the coolant systems cannot be to blame; if it were then fact 3 would not be possible. Since this syndrome is unknown to the DOHC machines, we must look for some difference between the DOHC and the 24V systems that can account for all seven rules.

"Since it cannot be the radiator, the pressure cap or the header tank, nor the plumbing, then it must be the only remaining element that is both capable of failure and is different to the DOHC engines. Clearly the only candidate left to agree with all seven Facts is the thermostat."

"But an owner suggested a cylinder head gasket - and another the air bleed pipe."

Holmes snorted. "Impossible. Fact 1: gaskets can fail on any car, not specific models. Besides, Fact 7 applies - no other symptoms are noticed and they certainly would be if a head gasket had failed. The same applies to the air bleed pipe to the reservoir. This can happen to any car - indeed, it is not uncommon - so Fact 1 is breached."

Watson shook his head ruefully and sighed. "Holmes, this is remarkable. So what is your theorem?"

"That in some circumstances - not common I agree but nonetheless occasional - circumstances and a weak thermostat conspires to overheat a part of the 24V coolant system. With insufficient flow the high temperature overcomes the pressure of the coolant and a plug of steam is created. Since steam is one hundred times greater in volume than the liquid this sends a shock wave of very high pressure through the system, sufficient to balloon the narrow radiator vanes. The radiator nor any of the pipes give way, however, so there is no outward sign, while the now huge pressure forces the steam to return to coolant again."

Holmes finished his glass and put it down carefully.

"But Holmes, why does the pressure cap not let go?" Watson asked.

"A good question, Watson. I can only conjecture here. It is probable that the hydraulic shock is so sudden that the damage to the radiator vanes occurs before the pressure cap can react. Bear in mind that the radiator is connected with broad pipes to the hottest part of the engine, while the header tank has a very narrow pipe, so the hydraulic pressure in the header tank would not be the same in any case."

Watson nodded and looked wistfully at his now empty wine glass. "I take my hat off to you, my dear fellow." he said. "I shall send a message back. Er - what should I tell them?"

"I should tell them it is the thermostat, Watson. They must change the thermostat at the same time as changing the radiator. They would be best advised to flush and reverse-flush the system, too. But they should not fit a new radiator without a new thermostat to safeguard it."

"Very well, Holmes. I shall tell them. You never cease to amaze me."

"Elementary, my dear doctor."

Apologies to Conan Doyle.

EricR

 


 
 

 

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