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Bill Vatter (
Posted on Saturday, 06 July, 2002 - 11:27:   Edit PostDelete PostView Post/Check IP

In another thread, Norman Geeson provided much information on the early post-war engines, and in particular he highlighted some cooling problems.

My own car has no cooling problems that I know of, but the top deck bridge area could be overheating locally without my knowledge. Norman stated that a clean block, high speed water pump pulley, and a 73 C thermostat were good things to keep temperatures under control.

In addition, I would be interested in information on what coolant is thought to be best. I have heard that while a mixture of ethylene glycol (anti-freeze) and water raises the boiling temperature of the coolant, engines will actually run somewhat hotter than with straight water because the convective heat transfer coeficients are poorer with glycol vs. water. Maybe this is actually due to inhibited boiling with glycol, as boiling heat transfer has extremely high heat transfer coeficients, and local sub-cooled nucleate boiling could be occuring in the deck bridge areas when only water is used.

Anyway, to keep my engine cool, I have been using plain water, with a corrosion inhibitor and water pump lube additive for quite some time. (The winter is mild where I live and my car is always kept inside, where the ambient temperature is always above 10 C.)

Some of my sporty-car friends are using a product called "Water Wetter" additive to their coolant that they say reduces summertime temperatures.

My car has A/C, and this will cause it to get a little hot in traffic. (However, even on hottest days it cools down to 85 or less with the A/C on when I get up to speed.) From Norman's discussion in the other thread, it is clear to me that I need to keep the idle high when stopped to cool the deck bridge area, and probably it would not be wise to run the A/C in stop-go traffic. I think that 90 C will be my decision point on turning off the A/C. It has been higher than that before but never boiling.

Any thoughts on coolant?
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Jim Bettison (
Posted on Wednesday, 10 July, 2002 - 11:47:   Edit PostDelete PostView Post/Check IP

As I said to you in the other thread; my instinctive feeling about your (possible) overheating is "If it ain't bust, don't fix it". I feel that if you do have a problem it would have have shown itself quite clearly by now; at least, that's been my experience with the Bentley and other cars. I would expect signs of local overheating to include small surges from local boiling at the hot spot(s) to appear in the top header tank if you removed the cap immediately after a hard run. Also, there might be coolant discolouration sooner than expected.
As to coolant additives: You have the physics of heat transfer, etc., much better than I do. Just a few comments: at least one Oz coolant additive supplier markets their concentrated product as "Anti-freeze, anti-boil". I understood the action of the ethylene glycol at elevated temperatures was to cause elevation of the boiling point of the coolant, thereby enabling a greater temperature differential, coolant/ambient, and hence enhanced heat transfer.
Inhibited ethylene glycol has a primary function in most of Oz as a corrosion inhibitor. There is relatively little of the continent that suffers from temperatures below 5decC. Where I live - Adelaide - has the hardest water in Australia, and Australia is reputed to have the hardest mains water in the world. True or not, "plain" tapwater is anathema to multi-metal engines; there's a thriving local industry in alloy head reconditioning. Water for cooling must be either demineralised ("distilled") or clean rainwater, Yet some service stations still put out "complimentary" water cans, filled from the local mains tap ... I first became aware of the corrosion problem when the MkVI had its first valve grind in my ownership. I went looking for info, and came across an article on corrosion inhibition in the Merlin aero engine, by an R-R engineer. R-R had tried nitrite additive, and soluble oil (which, when in contact with the cylinder wall, came out of emulsion and formed an oil film on the metal; the thermal insulation of the oil film lead to some spectacular failures) and inhibited ethylene glycol - their choice. The main purpose of the inhibitor was to retard decomposition of the glycol into glycollic acid (also not nice for engines) and they recommended a 25% IEG mix for motors, changed annually. At the change they recommended purging with a citric acid solution, followed by clear water flushes (2) and concluding with a BP non-foaming detergent washout - then refilling with 25% IEG.
Here in Oz we can take our choice of concentrated IEL, and mix your own, or buying a premix ready to go straight into the system. I choose the latter; a local firm (Tectalloy) puts up a range of coolants in 25 litre containers. They claim to mix to design targets; life (I pay a small premium for 3 year life juice - the choices are 1, 2 or 3 year). They also put it up for diesels, older cars (particularly American) with all-iron waterways, etc. If you're interested I'll try to locate a dealer in your area (if I can be told the area) or get some tech info sent to you.
Your comment about the effect of aircon is most interesting; one of our other friends has just fitted it to his Dawn and is having real overheating problems. Could you let us know some more about yours, please? What model of car? the size of unit? and the size and placement of the condenser would be most useful. Ours has a condensor area of approx 50% of the core, and is placed in the middle of the core (i.e., equidistant from top and bottom). I'll look forward with interest to any comment from Norman about management of the aircon in the circumstances you describe.
For closers: it's reputed that some people here are substituting an electric water pump for the original, with some improvement. Others are changing the fan assembly for a viscous-coupled unit, optimised for relatively low air movement (i.e., pulls a lot of air through when idling, and relies on vehicle movement at road speeds) which also shows benefits.
Comments, please?
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Martin Cutler (
Posted on Wednesday, 10 July, 2002 - 13:24:   Edit PostDelete PostView Post/Check IP

Hi Guys,

My Mk VI 4.5 litre stays relatively cool, always between 75 and 80 degrees when rolling along, but get stuck in traffic, and the temp soon soars. I don't like the look of turning the grille fins around, and you see the core easily. I fitted a 16 inch thermo fan to the front of the core, with a pull switch under the dash. When I get stuck in traffic, I pull the switch on, and the temp drops back down. I have had this installed for a couple of months now, but, being winter, haven't had to use it yet. With 10,000 miles up in the last 4 years, and minimal movement in valve clearances, I hope it is running fairly cool. I read with horror the story on the "wavy" bores, I have only once seen the temp gauge get to 100 degrees, whilst stuck in traffic, and it let some coolant out the pressure valve, but didn't boil. I think I was lucky!

Running straight unleaded is definitely cooler than running Lead replacement fuel.
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Bill Vatter (
Posted on Friday, 12 July, 2002 - 05:58:   Edit PostDelete PostView Post/Check IP


Thank you for your comments regarding coolant. I agree that in a warm climate the principal use of IEG is to inhibit corrosion, and I also agree the water used needs to be free from a high concentration of minerals. Fortunately the municipal water in my area (Atlanta, Georgia, US) is quite soft, comming from lakes and rivers rather than ground water. However, many places in the US have very hard water, which is more determined by how the water supply authority gets it rather than the geographical area.

Do you have any experience or knowledge of a coolant additive specifically intended to reduce coolant temperatures by improving heat transfer properties of the coolant? I believe that IEG does exactly the opposite, and for this reason, I choose not to use it.

You stated that the soluble oil causes problems if it gets in the combustion chamber. You should also know that if Ethelyne Glycol gets in your oil and thence to the bearings it is very destructive. An alternate anti-freeze is available in the US under the brand name "Sierra" that is chemically similar to EG but is much less poisonous and is sold as being "environmentally friendly," meaning that if animals drink it they are less likely to suffer a painful death from poison. A side benefit of this stuff is that it is also less harmful to engine bearings. Wish I could remember the chemical name. I will look at it when I am next at a store where it is sold.

Regarding A/C: A general comment here that the condenser mounted forward of the radiator makes everything except the passengers hotter, and the load of the compressor makes the engine work harder, adding to the general heat load from several points. I would like to further discuss A/C also, but I will begin a different thread under that title, so that the presence of such discussion will me most visible to others.


I believe your car would have the larger water pump/fan pulley which results in lower relative speed of these components. That is probably the fundamental reason your car heats up at idle. The addition of a supplemental cooling fan is a good solution, often used in the US also. The fans are cheap and in a Bentley relatively easy to install once the radiator shell is out of the way. However there is insufficient room for it in a Silver Wraith with operating radiator shutters. Another general consideration here is total electrical demand and the capability of the dynamo. There is not any excess electrical generating capacity on these cars, and if you want to aviod using a modern alternator, you need to be thrifty with electricity. This is a big factor with A/C which I will adress in the other thread.

I also think that many cars with corrosion-product-restricted radiator matricies are using a supplemental fan as a fix, when the fundamental cure should be to clean out the cooling system.

Another reason some cars are running hot is the removal or substitution of the thermostat. The factory thermostat opens to send coolant to the radiator, BUT ALSO CLOSES THE RADIATOR BYPASS WHEN IT IS FULLY OPENED. Use of an aftermarket thermostat for an ordinary car or removing the thermostat all together will cause the car to run hot because a significant fraction of the coolant flow will bypass the radiator. Of course the Silver Wraiths originally equipped without a water thermostat also did not have a radiator bypass either.

Changing the fan pully is easy on a later car (after about K series Bentley I think) with the fan mounted forward of the adapter hub that is pressed onto the water pump shaft. Just take off the belt and take out the 4 screws and you have the pully in your hand. The early cars have the pully behind the adapter, requiring the pully to be pulled off with the adapter and pressed on (requires removal and partial disassembly of the pump). (I have no clue why it was done like this.) I needed to remove my pulley for modification for the A/C (other thread), and for re-instalation, I drilled and tapped a hole in the center of the pump shaft so that I can press the pully back on by grabbing the shaft with bolt from the front. Of course changing over to the later style pully adapter would be a good idea, but I did not have those parts at hand, and I don't expect to need to do this job very often.
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Martin Cutler (
Posted on Friday, 12 July, 2002 - 10:17:   Edit PostDelete PostView Post/Check IP

Hi Bill,

Yes, fitting the fan was easy ONCE the grille was removed, Bl**dy Freestone & Webb use a zillion screws to set the guards in place.:-)) I replaced the radiator core when I rebuilt the car, and it runs the original thermostat, which opens at 75 degrees on the button. As for easily swapping the fan pulley, I have had to replace a fan belt, and it was in no way easy! I think I will leave it in place for a while! The car generally runs cool, but, as talked about in the other thread, heat in the front seats coming off the firewall during summer is fairly intense, the under bonnet temperature is very high. Lagging the manifolds might be a good first step. The heater core leaked like a seive when I connected it up, so I simply turned the taps off on the block. However, I have never owned a car, where, in the middle of winter, it is toasty warm in side from turning the demister fan on! Nice for warming your hands!
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Martin Cutler (
Posted on Tuesday, 15 October, 2002 - 12:54:   Edit PostDelete PostView Post/Check IP

Hi guys,

Ran the MK VI in fairly hot conditions the other day. The car seems to heat up a lot quicker with the thermo fan in place, I think it impedes the air flow when it is not running. However, with the fan running, the temp doesn't go above 80-85 degrees, and if you leave the fan running long enough, it will come all the way back down to 75. I am mindfull of the amount of amps it draws though, and it is noisy. I still have the engine splash trays on either side of the engine in place, is it common theory to take these out or leave them in to promote cooler running?

Also, I took out the webbing that is located between the bonnet and the scuttle, leaving only enough to locate the bonnet at the corners. With the fan on, heated air can now escape out the trailing edge of the bonnet. As heat rises, I think this may help a fair amount.

My hope is to be able to use the fan as little as possible, will see how things go.

I may attack a flush of the system soon, as I haven't done this for 2 years.
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Bill Coburn (
Posted on Thursday, 17 October, 2002 - 07:51:   Edit PostDelete PostView Post/Check IP

Martin's last remark about flushing stirred my memories of over heating in these engines. Since all the learned chemistry and physics applied above did not seem to address the simple problem of getting the coolant through the block. Although I confess to my experience being some 20 years old it is probably still relevant. My first engine out of SDB94 which I with much trepidation completely overhauled, went back into the car and immediately ran at 78 degrees C in ideal conditions climbed to 85 on a hot day and stuck in traffic teased the over 90's range prompting ridiculous displays of sitting in this beautiful looking car in traffic with the engine throbbing at about 2500 rpm. This always worked and I put up with it until the family recovered from forced malutrition after the first overhaul. Out came the engine again and was completely stripped including removing the water transfer tube that sprays the exhaust valve seats and exit ducts.

This was in the days when one coudn't buy those clever little lights for poking down plug holes so I made some up with miniature globes soldered to wires and lit them with my battery charger.

Gluing bits of mirror to the end of coathanger wires I was able to get a good view of the inside of the block and was horrified at the limited flow space around the sides of the cylinders caused by accumulated rust. Later experience with a 4 1/2 litre block showed some more room I this area as I recall.

Before starting my 'treatment' I filled the block several times with a strong detergent and very hot water to remove all traces of oily sludge that may have accumulated and rinsed the block thoroughly afterwards with clean water. I then blanked off the various outlets with plates and plenty of silastic, liberally coated the top of the block with thick grease and filled the whole thing with 'brickies acid" (HCL diluted 50% with water) and sat back ready to drain the whole thing and flush but the 'bubbling' was very gentle and in the end I left the whole mess to stew overnight. Next morning I flushed the block very thoroughly, did an inspection and the entire interior was probably better than new. I then blocked it up again and filled it with household bleach being the cheapest most readily available alkali to neutralise any acid that may have been remaining in the block pores.

After putting it all back together I found the engine always ran at 78 degrees except when under extreme duress (for those that live in New South Wales near the coast I actually made the Clyde in top gear while on my own) and then 85 was probably as far as it got. That Silver Dawn as an aside could pull 94 mph when she got the bit between her teeth!

I used this system for cleaning on many cast iron blocks and never had any accidents or failure. I also used a chemical recommended to me by a qualified engineer ammoniated citric acid as I recall that was used in bottle washing plants but it was very slow and very expensive.

I always made up plates to block the holes but otherwise I would put thick gaskets in place to avoid the acid getting to the originals. Always check the rear plates on the block and head for corrosion as they do rust through. The side plates do also but not probably as quickly. If you can't get the exhaust valve cooling tube out dont worry, after the acid treatment the removal of the rust will allow this.
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Martin Cutler (
Posted on Thursday, 17 October, 2002 - 09:43:   Edit PostDelete PostView Post/Check IP

Sounds like what is needed Bill. I will be going down Clyde Mountain in about 3 weeks, always enjoy that bit if road, sort of inhabited by NSW's finest these days though......
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Richard Treacy (
Posted on Thursday, 17 October, 2002 - 19:31:   Edit PostDelete PostView Post/Check IP

Yep. The Clyde Mountain is the real test of these beasties. It checks the brakes on the way down, and the cooling system on the way up. On the countless trips down there in the R-Type I always survived without using the safety ramps or any overheating (80 degrees is always max), but when a little oil reached the brakw servo it was touch and go a few times.
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Bill Coburn (
Posted on Friday, 18 October, 2002 - 09:54:   Edit PostDelete PostView Post/Check IP

Speaking of the Clyde Richard, on one trip down there was an elderly couple complete with card table and table cloth parked smack in the middle of one of the escape ramps having afternoon tea. I was so shocked all I could think to do was blow the horn. I have a measureable paranoia about trucks and my rear end on steep hills!
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Bill Coburn (
Posted on Friday, 18 October, 2002 - 09:59:   Edit PostDelete PostView Post/Check IP

Forgot one bit of information. The older cars tend to build up an oily sludge in the whole cooling system which would do little for conductivity or circulation. An old hand put me onto using a bottle of dishwasher NOT dishwashing liquid into the system for a 100 miles or so which will get the lot out usually bit not of course the stuck on solids. Using dishwashing liquid as I did once got things clean but took ages to stop the frothing.
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David Gore (
Posted on Friday, 18 October, 2002 - 10:48:   Edit PostDelete PostView Post/Check IP

David's Hint for the day - you can use the defoaming solution available at any supermarket that hires out carpet steam cleaners to fix this problem - I use "Britax" from our local Coles or Franklins supermarket - only precaution is to flush the system at least twice with the defoamer and twice with clean water to remove all residues that might interact with your coolant additives.
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Richard Treacy (
Posted on Friday, 18 October, 2002 - 16:10:   Edit PostDelete PostView Post/Check IP

Same experiences: I have seen many a picnic held on the Clyde escape ramps, but I didn't honk the horn. What I would do if the brakes failed I don't know: maybe blow the horn and hope they scatter. On dishwasher powder, basically caustic soda, I have used that as a flush every two years before flushing and refilling the cooling system. You can buy the same stuff, 100g for $20 packaged as a special Radiator Flush product (brand withheld), but good old Dishlex is just the same formula. I usually drained the radiator on the South Coast, refilled it with water and dishwasher powder and ran it up the Clyde and on to Canberra before flushing it and refilling with coolant. That work-out keeps it all clean.

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Bill Coburn (
Posted on Saturday, 19 October, 2002 - 00:26:   Edit PostDelete PostView Post/Check IP

David Gore

Would you please call Peter Chan he needs important advice!!
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David Gore (
Posted on Saturday, 19 October, 2002 - 12:17:   Edit PostDelete PostView Post/Check IP

Will do Sunday barring unforeseen circumstances - also my apologies to Britax, makers of very fine seatbelts, for the error in my previous post; the correct brand-name is "BRITEX". Also please note use of detergent/wetting agent is essential if cooling passages have been contaminated by oil from a blown head gasket - straight alkali such as caustic soda [NaOH Sodium Hydroxide] or washing soda [Na2CO3 Sodium Carbonate - preferable as it is less aggressive to aluminium/zinc components that may be in the cooling system] will not effectively remove adherent oil residues. SHELL used to make a wetting agent "TEEPOL" which could be purchased from their larger service stations - this was very good for washing contaminated glasware especially in the chemical labs where I spent my early industrial career and is ideal for this purpose.

Kind regards