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Bob Clare
United Kingdom
278 Posts |
 Posted - 23/01/2005 : 12:05:48
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This is a message directed firstly at Peter Arnell and William Opie since they instigated the debate some time ago in the (dare I say it?) Octagon MGCC Bulletin, but hopefully may prompt thought amongst others.
I've been looking for an elegant way to make sure that my NB runs at something around 80C rather than the 50C which it struggles to reach now. I tried several radiator blind designs but they all required complicated mechanisms to ensure adjustment without the need to stop the car. None of these was very satisfactory.
I turned up the Octagon Bulletin for 11/97 and began the process of assembling the thermostat and clip etc recommended.
Yesterday I got a call from Chris Lewis as a result of his reading my bit in our Bulletin about oil leaks. In the course of converstaion I mentioned my intention to fit a thermostat in-line as per Peter Arnell/William Opie. Chris immediately raised a real concern and that is that even if a by-pass hole is provided to allow water to flow through to the radiator and thus activate the thermostst, the rate of flow may well be so reduced that the hot-points in the head will overheat and form a steam barrier to the coolant, leadin to a cracked head!
So, I post this warning for anyone who has made this mod or is thinking of it and for me, it's back to the drawing board - unless anyone knows better of course.
Bob Clare |
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Cymber
United Kingdom
966 Posts |
Posted - 23/01/2005 : 18:53:50
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Thermostats
My MG does not have a MMM engine but an XPAG unit. However, I worked for many years as a diesel engine development engineer and I agree with your reservations about using a thermostat in a thermosyphon cooling system. I would not use a thermostat without a coolant pump and a bypass pipe so that there is circulation when the thermostat is closed, certainly not on an engine asvaluable as these.
Maurice. |
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Bob Clare
United Kingdom
278 Posts |
Posted - 24/01/2005 : 13:27:28
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Thanks Paul & Maurice,
Perhaps I should have made it clear that my NB engine does have a water pump. Even so, Chris Lewis reckoned that without a by-pass al la XPAG engine et al, the effect of low flow in the head would cause the hot spots to create a film of super-heated steam around them thus making overheating even worse by cutting off the hot spot from the limited water flow.
My PB engine, without pump, does indeed heat up rapidly to 80C in winter and in summer boils at the drop of a hat (or more accurately, whenever I end up in a traffic queue). I've been contemplating a pump but haven't got round to fitting one. Also have a fan to fit but haven't got round to that either!
Looking forward to more comments
Bob Clare |
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Peter Green
United Kingdom
1682 Posts |
Posted - 24/01/2005 : 17:52:44
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Bob,
Your position as Triple-M Registrar is obviously keeping you away from the garage otherwise you would have fitted the water pump and fan.
Peter. |
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kimber
United Kingdom
1529 Posts |
Posted - 24/01/2005 : 18:16:05
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| Whilst talking about fans, can anybody explain to me the reason why P-type engines have a pulley wheel on the front of the crankshaft? I have never seen a P-type fitted with a fan (have you?) and the single pulley is presumably inadequate for a belt driven blower? So, what was it there for? |
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rbm
United Kingdom
141 Posts |
Posted - 26/01/2005 : 12:54:21
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I would have though the problem with putting a thermostat in to a thermo-sypon system would be getting the thermostat to open in the first place, as you wouldn't have a thermal loop. The water heated by the engine rises to the high point in the system (the hot leg), sucking cool water from the bottom (cool leg) if in essance block the cyclick flow of water the thermo-syphon stalls. Yes the heated water will rise to the top, but at a far far slower rate as the temprature diffrence between the engine water ways and the hot leg will be small and you will have a 2 way flow in the hot leg as cooler water is sucked back down into the black to replace hotter water trying to flow out of the block.
This is my own view, but would you be happy to put a restricting thermostat say halfway round you gas central heating system?
Richard |
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Cymber
United Kingdom
966 Posts |
Posted - 26/01/2005 : 21:28:52
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I have to dissagree with Paul Duncombe when he states that a small hole drilled in the thermostat flange is adequate as a bypass, it simply isn't big enough, I would say that the bypass should be around 1/2" bore to be effective. The bleed hole wants to be small otherwise it can prolong the warm up of the engine, it is only there to prevent airlocks when filling and to allow some hot water to reach the thermostat capsule. Thermostats with a plastic bead suspended on a jiggle pin to close off the bleed hole when the engine is running are quite common to prevent the slow warm up problem.
Maurice. |
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rbm
United Kingdom
141 Posts |
Posted - 27/01/2005 : 08:57:34
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Paul, I have to agree with Maurice, the small hole in the flange of some thermostats is to allow a small amount of coolant flow to reduce the chances of air locking. In the 1990's L/R had this problem with the 1.8k Rover engine, the engines partialy air locked with intresting results a modified hose kit with new type bypass and thermostat was fitted at service (- this also showed the long term problem with the k engine, head locating dowels being plastic they melt!)
based on this Land Rover fix I would suggest if you want to go down the road of a thermostat in a termosyphon engine you would need to have a chamber with the thermostat (so the hot water would surround the thermostat) in it in the top hose, and a bypass rail from this chamber to the bottom hose, the rail would need to be at least 1/2 inch diameter.so in essance you would end up with 2 thermosyphon circuits.
the thermostat would have to fitted with the normal hot leg outlet at the top or the hot water would not cycle arrround the radiator at all.
The Rover/Land Rover part number for this thermostat body is PCH001190
it is a 3x3 inch cylinder containing the thermostat, with 3 pipe outlets. I havn't used one so you would have to have a look and decide for yourself.
Richard |
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rbm
United Kingdom
141 Posts |
Posted - 28/01/2005 : 10:17:53
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Paul, have you been running this set up for a while? I'm interested because I had never thought of running a thermostat in a water pumped system with out a bypass and what effects this would have.
Is the engine standard (compression/cam etc.)?
Do you suffer from any pump cavitation?
Richard |
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rbm
United Kingdom
141 Posts |
Posted - 29/01/2005 : 08:36:39
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Paul,
seams like we have hi-jacked this thread
thanks for the further info, makes intresting reading.
cheers
Richard |
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John
United Kingdom
51 Posts |
Posted - 02/02/2005 : 14:06:10
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| Hi, I am a new member,with a PB and would like to fit a thermostat as discussed in this column. Does anyone have a part number or details on a unit that will fit the top hose??? many thanks. John |
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captainlegless
United Kingdom
24 Posts |
Posted - 02/02/2005 : 15:10:45
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Thermostats
After talking to Paul I fitted one about 2 months ago to my standard PA with water pump and so far in cold weather have had no problems. Having read all the comments about by-passes etc. I have decided to increase the effective by-pass area by drilling a few more small holes in the flange. As far as I can see this will work exactly as a modern engine by-pass. I don't think I would fit a thermostat without a pump though.
Colin Wallace.
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KevinH
United Kingdom
156 Posts |
Posted - 02/02/2005 : 15:16:25
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John,
The thermostat is Halfords part no HTK610 ú6.99 - Paul Duncombe gave details in a post dated 30/7/2004. Make sure the bulb points TOWARDS the head.
I've just fitted one - it easily slips in the top hose. I drilled two 3mm holes in the surround to ensure that there will always be some water flowing.
Previously, my PA struggled to get above 50-55degC, and now it is 70+degC at 50+mph, and is almost 80degC in urban areas. It also heats up quickly, so I'm very pleased with this mod. Long term I shall want to monitor the water temperature on the head side of the thermostat in case it fails.
My PA is currently unsupercharged and fitted with a water pump and modern cored radiator - I'm not sure how a thermosyphon only system would perform with a this setup.
Hope this helps,
Kevin |
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captainlegless
United Kingdom
24 Posts |
Posted - 02/02/2005 : 15:20:49
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Hi John,
Missed page two of the forum, so didn't answer in my last posting.
The thermostat you require is Halfords HTK610. I assume you have a pump and you will need to drill the flange to act as a by-pass. (See previous erudite discussions on the subject). Hope you get yours fitted before Bob does! On that subject I acquired a reserve fuel system 25 years ago and am only just fitting it today!
Colin |
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Cymber
United Kingdom
966 Posts |
Posted - 02/02/2005 : 19:48:47
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Paul, I would set it to about 90 C for an overheat warning. Engines are at their best when hot, the hotter the better so long as they don't boil.
Maurice. |
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KevinH
United Kingdom
156 Posts |
Posted - 02/02/2005 : 20:29:36
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Paul,
I've too have been thinking about a better way of monitoring the water temperature on the head side of the thermostat. I guess the best (engineering-wise) would be to re-mount the guage sender in the rear end of the water manifold. That would be obviously non-original and the water manifold would need to be modified but it would monitor the temperature in exactly the right place.
I've looked through the Maplin catalogue, and there is a temperature sensitive transistor that could be encapsulated and fixed unobtrusively to the part of the water manifold that can't be seen - it would need a simple bit of circuitry to sound a buzzer or maybe flash the charge light on and off, but that's getting a bit complicated!
A better solution could be to find a small enough temperature switch (the sort that are used to switch car radiator fans) and fit one in the water manifold where it can't be seen easily. The manifold would still need to be modified though, but it could be very easily used to operate a warning light/buzzer.
Anybody got any better ideas?
Kevin
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