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Mark Taxis
Frequent User
Username: mark_taxis

Post Number: 74
Registered: 4-2007
Posted on Sunday, 26 October, 2014 - 11:14 am:   Edit PostDelete PostView Post/Check IP

The radiator in my Mk 6 special is showing signs of age and will need some attention in the near future.
As the radiator will be out would there be any advantage in blocking off the steam valve and slightly pressurising the system
Will pressurising the system do any damage? and if it is safe to do so what would the recommended maximum pressure be.
Thank you
Mark
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Martin Cutler
Prolific User
Username: martin_cutler

Post Number: 209
Registered: 7-2007
Posted on Sunday, 26 October, 2014 - 05:20 pm:   Edit PostDelete PostView Post/Check IP

Hi mark,

I'm far from an expert here, but i think the steam valve has a spring in it, which would offer some degree of pressurisation. Pressurising will raise the boiling point, but i would never let my car get that hot. Ran up to the southern highlands on friday, got to 80 degrees up catherine hill, any higher and i would have stopped and let it cool down. 33 degree day, fairly warm. I would leave it standard.
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Bob uk
Unregistered guest
Posted From: 94.197.122.72
Posted on Monday, 27 October, 2014 - 03:35 am:   Edit PostDelete PostView Post/Check IP

The steam valve is RR speak for pressure relief valve.
All car water cooling systems MUST have a relief valve otherwise known as an expansion valve especially if a expansion tank is fitted.

Have the radiator recored. Then refit and pressurise the system to the specified pressure to test the valve. There is no advantage to upping the pressure as this engine runs at 75c. Fit new thermostat. Antifreeze.

(Message approved by david_gore)
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Mark Taxis
Frequent User
Username: mark_taxis

Post Number: 76
Registered: 4-2007
Posted on Thursday, 30 October, 2014 - 08:20 am:   Edit PostDelete PostView Post/Check IP

Thank you for the replies.
I will leave the steam valve as is
Mark
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NORMAN GEESON
Unregistered guest
Posted From: 82.6.223.129
Posted on Sunday, 02 November, 2014 - 09:42 pm:   Edit PostDelete PostView Post/Check IP

Mark

I notice that you have asked the same question on other web sites with similar replies. The moral here is don’t believe all you read!

In the interests of recording correct data these replies unfortunately demand some correction. If the system is not fully understood, then there is no chance of any successful alterations.

First of all, a true study of some of the history of this MKVI cooling system. Originally the system ran at 4 psi, with spring loaded relief valve on the radiator header tank and a filler cap on the top horizontal surface of the radiator header. Contrary to some replies the water pump seals, were and still are, no problem at this pressure, in fact at 3750rpm with the thermostat closed R-R report cooling system pressures of 7 psi. However when the Siam 4.8 ltr engine ran with an air conditioning plant the water pump seals were reversed so that the seals were “pressured” into position and system pressurisation introduced.

The relief valve (steam valve) tended to stick mainly through lack of use and it had an unfortunate ability not to release the vacuum caused when the system cooled down. This vacuum being relieved by the collapse /bypass of the water pump seal. In this situation this air joined the air pocket in the top of the water pump. A situation that could do with relief in any even by bleeding this trapped air into the radiator header tank. N.B The pump top casing is higher than the cylinder head.

Subsequently the relief valve plunger and spring were removed and the system ran unpressurised as a pure thermo-syphon system, which has no need of any relief valve. It was then found that in certain circumstances coolant poured from the unrestricted overflow pipe when the car experienced heavy braking.

To combat this, about November 1949, the radiator filler cap was moved from the top of the radiator tank and repositioned on the sloped section of the top tank, this prevented overfilling of the radiator. Around the same period the relief valve plunger and spring were reinstated BUT with the plunger drill through its centre. These modifications were done merely to stop water loss in hot conditions during braking.

In unrestricted form, thermostat open, the temperature gauge shows an operating temperature of 75 degrees, note my comment “gauge shows”. This is misleading and catches out many mechanics and owners. As late as April 1960 R-R were recording 3.5 inch bore engines with rear end temperatures 13 degrees higher than the gauge reading! On newly run in engines, in good condition and with super clean coolant passages 88 degrees was the normal recorded temperature adjacent to No 6 bore.

A number of cars have been pressurised to at least 4psi, mostly after having the top radiator tank strengthened. In these circumstances the radiator header tank has been coupled to a remote small expansion tank ( ex. Jaguar / MG) with a modern pressure cap. To be safe the thermostat should be changed to the waxstat type. Those with the experience of these particular engines in different operational conditions have been wise enough to equalise front and rear temperatures by piping coolant from adjacent to no 5 / 6cylinder back to the water pump inlet or top tank.

In modern times, I understand, these mods have been completed by our most famous R-R and Bentley repairer and was done on a few cars by R-R for the Queen’s tours of some commonwealth countries.

I am not suggesting that you pressure your system, nor would I suggest you do not, I have merely provided you with some facts, with no assumptions.
}

(Message approved by david_gore)
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Mark Aldridge
Prolific User
Username: mark_aldridge

Post Number: 162
Registered: 10-2008
Posted on Monday, 03 November, 2014 - 08:35 am:   Edit PostDelete PostView Post/Check IP

Norman, I have a 1956 S1. Does the above apply, and is there any merit in a restricted bypass on the heater to facilitate greater cooling of the back of the engine ? Also, what is a waxstat, is this a modern version of the standard thermostat or a Peugeot stat ?
I have modified Austin 7 and BMC "A" series engines to create a water return from the back of the head with good effect on uprated engines.
Mark
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Mark Taxis
Frequent User
Username: mark_taxis

Post Number: 77
Registered: 4-2007
Posted on Wednesday, 05 November, 2014 - 08:07 am:   Edit PostDelete PostView Post/Check IP

Norman
A very interesting article, many thanks
Mark
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Bob uk
Unregistered guest
Posted From: 94.197.122.92
Posted on Wednesday, 05 November, 2014 - 10:45 am:   Edit PostDelete PostView Post/Check IP

Straight sixes have always suffered from the cylinders that are furthest from the water pump overheating. The A series mod I did to combat this problem was a tee piece in the heater pipes to create a bypass from the non water end to the bottom hose. This evened the cooling out enough so that a bigger radiator was not necessary, how ever the heater was weak.

I saw a liner from a big Volvo diesel engine that was badly pocmarked on the outside due to the engine idling for days on end because the starter was faulty. The water pump cavitated the water which collapsed against the liner.

When I brought my Jeep which has a straight six I checked the rear of the engine and found the rear was ten degrees hotter. I flushed the system with a garden hose etc and an amazing amount of muck came out and now both the heater and cooling system work much better. I reckon every three years. And of course always have at least 25 % glycol in the system.

It would be a shame to fit a normal rad cap because the large plastic cap is much better looking. The steam valve and plastic cap can be made to work well by careful attention to detail. A smear of water proof grease on the steam valve bits helps. The catch tank idea is good and maybe something period looking from an auto jumble would work, something made of brass would look nice. Any part that is higher than the rad cap will have air most likely, as long as the water flows through the area ok then it will be fine. Water pumps are surprisingly powerful especially so when the clearances are correct. There is a device that fits in the top hose that detects water and is silent until no Water then it sounds. Think it's £50 or so. Also hand held infra red temp thingy from maplins is very handy. Check brake temps as well and servo.

I have never seen a six cylinder stat but I believe that a stat from a big diesel engine might do the trick. The truck parts shop have books with measurements of the stats. These are about £25 each so not too pricey.

A tip for checking rads is to see how much water the rad will take and indeed the whole system if the book says 20 pints and there is only 18 then maybe there's 2 pints of clag in the system.

(Message approved by david_gore)
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NORMAN GEESON
Unregistered guest
Posted From: 81.97.26.213
Posted on Wednesday, 05 November, 2014 - 12:25 am:   Edit PostDelete PostView Post/Check IP

Mark

A 1956 S1 would benefit from some by- passing of coolant from the rear end of the block/head and how it is done depends on the cooling pipe layouts. For instance in my car, a Bentley R Type, the heater matrix is continually fed with coolant whatever the weather just to ensure a through flow of coolant. Of course this will not work if the matrix is full of debris, collected as the matrix is the lowest point in the cooling system! Actually providing a full by-pass, albeit restricted, can be done on these cars by short circuiting the heater pipes. My car has been used for many experiments and I have needed to keep the cooling system standard at the rear, otherwise it would have a permanent by-pass at the rear.

Some years ago my friend Lloyd Missen in Sydney conducted extensive tests on his Silver Dawn proving that returning coolant from the rear was helpful in evening out temperatures, he used a number of thermocouples in his experiments.

Returning to your S1, some of the military versions of this engine had a rear end top hose, that is to say coolant return was taken from the rear of the engine specifically to even out temperature gradients. From memory this idea was discussed with the intension of using it on the car engine, but not taken up. In the case of the S1 car engine I would restrict the return flow using a 6mm bore restrictor. So you will not go far wrong by copying the R-R idea.

Your car will have a “none bulge” port cylinder block that does not have additional coolant passages around the exhaust valve seat, and as the exhaust port is the second largest heat generator to coolant on this engine it needs all the help it can get. The block listed in the parts list is actually the bulge port type. As you may have noticed these engines start to protest when subjected to consistent speeds above 3000 rpm not at all liking the long piston stroke and exhaust port.

For interest R-R modified Silver Cloud 1’s and also other cars for procession work, by reinforcing header tanks, shrouding the fan, pressurising the system (4 lbs if I remember correctly) and in some instances, (certainly Phantom IV) fitting additional galley radiators underside, with electric pumps. The last two mods apparently allowed operation in 40 C with 6 mph following wind. I don’t know how they mastered the fuel vaporisation in procession, nor can I remember if they fitted the air conditioning type of water pump.

The waxstat was one of the first wax type thermostats that we all know today and eventually became a trade name. The original version would not handle coolant system pressurisation but was quickly redesigned to rectify that shortfall. An alcohol type bellows thermostat is not suitable for coolant pressurisation systems and forced the introduction of waxstat type units fitted to about every car today.

If you do experience overheating I would not suggest adapting pressurisation to cure the problem.

(Message approved by david_gore)
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Mark Aldridge
Prolific User
Username: mark_aldridge

Post Number: 165
Registered: 10-2008
Posted on Thursday, 06 November, 2014 - 05:05 am:   Edit PostDelete PostView Post/Check IP

Norman, Thanks for the advice. The only occasion the car has overheated was this year after about an hours continuous running at 60-65 mph on a very hot day and the temp gauge only went above normal when I stopped to fill with fuel and ,whilst stationary with with the engine off it tipped about 1/2 pint of coolant out of the overflow. After topping up and on the move again the temp reduced to normal. The problem has not re occurred. However, the heater bypass idea is worth a try if only to help the back cylinder.
Mark
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Martin Cutler
Prolific User
Username: martin_cutler

Post Number: 212
Registered: 7-2007
Posted on Tuesday, 11 November, 2014 - 07:00 pm:   Edit PostDelete PostView Post/Check IP

Hi Norman,

What are your thoughts on leaving the tap open at the rear of the block, and running a hose through a heater matrix under the bonnet, then back to the heater outlet on the water pump? The heater outlet on the head on B256MD is closer to the front of the head.
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Jan Forrest
Grand Master
Username: got_one

Post Number: 696
Registered: 1-2008
Posted on Tuesday, 11 November, 2014 - 10:53 pm:   Edit PostDelete PostView Post/Check IP

A couple of years ago I acquired a small convertible with a useless cab heater. No amount of ordinary flushing would make it work. Despite the extremely limited access I disconnected both heater pipes and shoved the business end of a garden hose into the outlet and turned on to full. After a moment's hesitation I was rewarded with a solid plug of rusty gunge from the inlet tap end followed by a stream of clean water. I left the water running for a couple of minutes and now the heater in that little car is the best of all my cars.

In short: Do it!

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