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MG MGB Technical - thermostat gasket
| well my '74 b started to run rich due to a leaky carb and the engine temp went up to 190 for 5 minutes....now my fail-safe thermostat locked open..its only about 1 year old. seems simple to just replace thermostat as Ive done this countless times on countless cars before without even thinking...but this time Im thinking about it since i have some choices for thermostat gaskets...i ordered a a gasket at the same time I ordered the new thermostat (not a fail safe) from moss...and it is cork. I went down to autozone to get thermostat rtv sealant (high temp) and they actually had a rubber -cellulose fel pro gasket for $.99 for mgb. So I am thinking to use the rubber-cellulose gasket with permatex rtv silicon on both sides of gasket and not the cork...ive head some people only use the rtv sealant and no gasket....what is best here? thanks in advance. |
| jjralston |
| J- The Original Equipment gasket sets had a thin circular gasket that was to be inserted into the recessed thermostat seat in the cylinder head, prior to seating the thermostat. Since most gasket sets no longer have this gasket, put a thin bead of the Permatex Ultra Black RTV Gasket Maker sealant into the groove before setting the thermostat in place. When you press the thermostat down in order to firmly seat it, some of the sealant will ooze out past it. Wipe away the excess sealant material and let the assembly cure for an hour or more. As for the gasket issue, the engineers at Fel-Pro have come up with a solution called the PermaDryPlus® Water Outlet Gasket (Fel-Pro Part # 35562T). Originally developed to deal with leakage-prone, warped, or corroded thermostat housing flanges, they are constructed of edge-molded silicone rubber on a rigid carrier, providing a superior fit, as well as both high heat and pressure resistance. The rigid carrier prevents over-torquing, while the molded rubber assures a secure seal. Install your new gasket, then the water outlet elbow, and then after coating the threads of the studs with antisieze compound, secure the housing with Nyloc nuts placed over thick 5/16" machine washers. These Nyloc nuts are preferable to split machine lockwashers because you do not have to use excessive torque to compress a set of split machine lockwashers and thus risk crushing the rubberized gasket. Do not make the classic mistake of overtightening the Nyloc nuts until a large portion of the sealant material appears. Simply tighten them until the gasket begins to bulge outward directly adjacent to the studs. Using this system you should never have a problem with leaks, and your coolant outlet elbow should come off easily. Because the studs that secure the thermostat housing to the engine block project downwards into the water jacket, it would be prudent to install studs made of stainless steel and coat their threads with a flexible sealer such as Fel-Pro Gray Bolt Prep in order to prevent coolant from rising up the threads and causing corrosion in the future. These studs are made by ARP and are available from Advanced Performance Technology. The mounting nuts of the studs should be torqued to 8 Ft-lbs. As for the thermostat, you do not have to resign yourself to the use of a conventional wax pellet thermostat. Prestone is marketing an updated version (Prestone Part# 330-195) of what is called the "balanced" thermostat that was originally designed and marketed by Robert Shaw Controls. The 3-port construction equalizes the coolant pressure from above the valve (radiator side) to the higher, pump pressure side, hence the use of the term “balanced”. This allows the thermostat to open effortlessly and accurately no matter what the rate of coolant flow or the engine speed happens to be at that particular time. Non-balanced designs are prone to being forced closed when the coolant flow abruptly increases, such as during sudden increases in coolant pump speed. While its effectiveness is not immediately obvious when you first installed, its superiority does becomes more obvious while driving at sustained high speeds (70+ MPH). A balanced thermostat keeps the coolant temperature within 2 degrees compared with temperature fluctuations of up to 20 degrees with a conventional thermostat. Consequently, the operating temperature is more constant at highway speeds, and when under the strain of heavy loads, it takes longer for the inevitable rise in temperature to occur. The balanced design is such that it is not influenced by variations of coolant pressures as engine speed increases and decreases, and that means that it is better able to more accurately control the operating temperature of the engine than the wax pellet type thermostats. In conventional thermostats, the piston must make a large stroke to open the thermostat far enough for adequate coolant flow. Unfortunately, the long stroke compromises durability. In this case, the engineers achieved a shorter stroke with a uniquely-designed flange and poppet. This design increases the longevity of the thermostat, yet still allows adequate coolant circulation. The Robert Shaw design is also far less prone to failure. In other thermostat designs, the bypass valve stem is welded on. The weld tends to fail under stress. To eliminate this problem, in the Robert Shaw design, the entire copper cup and bypass stem are manufactured from a single piece of metal. By making the strut assembly from brass instead of steel provides another benefit: brass, being more malleable than steel, can be precisely formed in order to maximize coolant flow. Most manufacturers use a one-piece rubber diaphragm in order to seal the charge and drive the piston. If the rubber seal ruptures, the thermostat then fails. The piston is activated by a temperature-sensitive mixture of metallic powder and wax. Some thermostats use an all-wax charge which responds slowly to temperature changes. Other designs mix copper powder with the wax for faster response, but the copper quickly separates from the wax. The Robert Shaw design uses a process to maintain suspension of the copper powder in the wax so that the fast response will not deteriorate and the thermostat will not "stick-open" to cause the engine to run cool. The Robert Shaw design uses two separate parts: a diaphragm to seal the wax, and a stem seat or plug that drives the piston. The rubber material for each part is formulated especially to meet each part's unique requirements. Wear or damage to the stem seat still allows the thermostat to operate satisfactorily. |
| Steve S. |
| The cork gasket works just fine if assembled dry and nyloc nuts are used on the studs so that the cork gasket is not over compressed. Sealing the thermostat to the head as suggested by steve is a waste of time - I have never seen a ring gasket fitted under the thermostat - even on original low mileage engines which have never previously been touched. The housing gasket overlaps the edge of the thermostat and provides the seal. The MGB engine water cooling system is a pump assisted thermo syphon type and the pressure generated by the pump is very low - the system simply does not experience abrupt changes in pressure and the thermostat won't be forced closed. It is held open by a strong spring and is closed by the wax capsule. There is also a bypass drilling between the head and pump which allows some circulation of water when the thermostat is closed - further reducing any pressure differential across the thermostat. I have never seen fluctuations in engine temperature at highway speeds - if anything the temperature falls slightly and stabilises compared with town driving. Sorry - but Steve's post seems just to be a cut & paste from Prestone's advertising material - the benefits may be realised in modern vehicles but IMHO a waste of time & money for a B series! |
| Chris at Octarine Services |
| "It is held open by a strong spring and is closed by the wax capsule" Tother way round? Thought the wax capsule expanded with heat to open the stat, and the spring closed it again when the wax cooled and compressed. |
| Paul Hunt |
| Chris- The aformentioned advantages in using a balanced thermostat in a B Series engine have been noted by several people, including our own Bob Munchausen. The engines that I have built for my own MGs are all high performance versions, so they create more heat for their cooling systems to cope with. When using a conventional wax-pellet-type thermostat, running these engines under heavy loads, such as when accelerating hard for a prolonged period up steep grades in the mountans and the long hills of nearby Appalachia, taxes the cooling system to the point that temperature change is always notable. As you have pointed out, cruising at a steady speed on the highway does not produce this effect. However, as with any cooing system, changes of engine speed results in changes of coolant pump speed, and hence changes in coolant flow rate, and hence pressure. I have never bothered to measure the actual amount of pressure change, but when using a conventional wax pellet-type thermostat the temperature change is consistent under these circumstances. The use of a balanced thermostat has essentially eliminated this problem. I am confident that the more stable temperatures are the result of this change, as it is the only change that has been made to the cooling system. Yes, I did mention some of the design advantages that is included in advertising literature, but only because they reflect the superiority of the Robert Shaw design. You said that "There is also a bypass drilling between the head and pump which allows some circulation of water when the thermostat is closed - further reducing any pressure differential across the thermostat." With the thermostat closed, the pressure differential would be irrelevant. The passage that you mention was actually intended not for pressure reduction, but rather to take advantage of the Original Equipment Smiths bellows-type thermostat originally developed for use in the B Series engine, which was a rather interesting design. It not only had an orthodox (for its time) bellows valve for controlling coolant flow, it also had a vertically reciprocating sleeve that surrounded its bellows unit. Whenever the temperature of the engine was below its optimum level, the sleeve remained in its bottom position, leaving a bypass passage in the head open. This bypass passage was intended to allow coolant from the warming engine to recirculate in a closed circuit back through the cylinder head and thence onward to the engine block so that the engine could warm up as quickly as possible prior to the thermostat opening, thus permitting heated coolant so that the cylinder head would warm up more quickly. As the temperature of the engine approached its optimum level, the sleeve rose and blocked off the recirculation port, thus allowing the heated coolant to bypass and circulate exclusively into the radiator matrix instead into the head where it could only contribute to higher temperatures in the head than are considered to be appropriate. However, such thermostats are unavailable new, often being regarded when encountered as quaint curiosities from a bygone day. By the way, you've got the functioning of the conventional wax pellet-type thermostat reversed. Contained inside of a copper cup is a specially-formulated combination of thermosensitive powdered metal and wax that forms a pellet. The upper section of the copper cup forms a valve that seats against a valve seat formed by a canelure in the upper bridge section. A coil sealing spring surrounds the copper cup to maintain sealing pressure against the valve seat. Attached to the bridge section is a rod that projects down into the copper cup. Attached to this rod is a piston that is sealed inside of the copper cup. When the wax pellet is exposed to heat, it melts and expands, overcoming the resistance of the sealing spring and forcing the copper cup and its upper section away from the piston and consequently from the valve seat, thus opening the valve. One other small correction: Technically, a thermo-syphon system, best known to folks as that such as used in the Ford Model T cooling system, uses the principle of heat rising to provide circulation. It does not use a pump at all. |
| Steve S. |
| Steve S. Thanks for the comprehensive explaination of the thermostat. Do you know if the Prestone (Robert Shaw) 330-195 stat and Fel-Pro gaskets 355627 are available at the normal supply houses -Advance Auto, Auto Zone and PEP Boys and etc? Also, is the 330-195 stat suitable for the MGC or just the MGB? Dave Kalp 1969 MGCGT 1980 MGB |
| Dave Kalp |
| Dave- Yes, the Prestone (Robert Shaw) 330-195 thermostat will fit into and is suitable for the MGC, no problem. Prestone and Fel Pro products are widely available. You certainly should be able to order any of their products that you should happen to need from any of the NAPA, Advance Auto, or Autozone stores. I wouldn't bother with Pep Boys, though. They're not worth going into for anything that has to be ordered. |
| Steve S. |
| Yes, the temperature on the gauge does go up a bit on a long climb compared with cruising on the flat, and a long down-hill puts the temperature below a cruise on the flat, but so what? You will also see higher temperatures on the flat on a very hot day than on a cold day. The normal range is anywhere from just above the C to just below the H. If you have an MGB with electric fans you will see more variation on the temp gauge on those in given conditions than you will on a mechanical fan car. And in any case we are told that the hotter they are the more effciently they run. Companies advertise all sorts of products and claim to improve things for the same reason a dog licks its privates - because they can. Doesn't mean it is something we should attempt to emulate. Companies frequently get by with spreading Fear, Uncertainty and Doubt amongst the unwary. I think we have enough miles on enough cars in enough variations of climate to know the factory system works just fine, if kept in good condition. Chris said that the cooling system is a 'pump assisted thermo syphonic' system and that is what it is. Without the engine turning i.e. no pump there is still some thermo syphonic cooling while the coolant is hot enough to keep the thermostat open. While the engine is turning the pump is 'assisting' that. The fact the Model T Ford had a non pump assisted thermo syphonic system is irrelevant. The bypass port allowed for circulation of coolant through the head and block while the engine is still getting up to temperature to prevent hot-spots and possible localised boiling if there is no coolant flowing at all. Without it the coolant by the thermostat would depend on being heated from the castings to 'know' when to open, by that time the coolant closer to the combustion chambers would be much hotter. The bellows type closed it off when open to push all the coolant through the radiator, i.e. prevent localised circulation of hot coolant which reduces the overall effectiveness of the cooling system. There is more than enough cooling available in the MGB physical arrangements under most circumstances, and adequate in desert states without closing it off altogether. |
| Paul Hunt |
| Another question for the thermostat experts. I have seen recommendations before to drill a small hole in thermostats that don't have them to help relieve any chance of trapped air (air blocks). Your thoughts? Thanks, Frank |
| Frank Mooring |
| Steve, Why are you and Bob M. recommending the 195 degree thermostat over the middle of the road 180 degree version? Again would love to hear your thoughts. Thanks, Frank |
| Frank Mooring |
| Some do have a jiggle-valve, or just a small hole or notch on the edge of the main valve, for that purpose, see http://www.mgb-stuff.org.uk/wn_coolingframe.htm and click on 'Thermostats ...'. It's really an aid to filling, shouldn't make any difference in use with a properly functioning cooling system. |
| Paul Hunt |
| For those that are interested Advance Auto sells the Mr Gasket (Prestolite)version of the balanced thermostat MRG-4364 (180 degree) and MRG-4365 (195 degree). Frank |
| Frank Mooring |
| Paul- Strictly speaking, a thermo-syphon system uses the principle of rising heat as the sole means of circulation. To speak of a pump-assisted thermo syphon system is the rough equivalent of an oxymoron, much like saying "a smart dumb person". As I pointed out, a balanced thermostat keeps the coolant temperature within 2 degrees Fahrenheit (.67 degrees Celsius) compared with temperature fluctuations of up to 20 degrees Fahrenheit (6.7 degrees Celsius) with a conventional thermostat. It is not commonly understood that a thermostat starts to open at its rated temperature but does not become fully open until 20 degrees Fahrenheit (6.7 degrees Celsius) later. This being the case, 195 degrees Fahrenheit (90.6 degrees Celsius) thermostat will begin to open at 195 degrees Fahrenheit (90.6 degrees Celsius) but will not be fully open until 215 degrees Fahrenheit (101.7 degrees Celsius), which is 3 degrees Fahrenheit (1.61 degrees Celsius) more than the boiling point of pure water. 20 degrees Fahrenheit plus 215 degrees Fahrenheit equals 235 degrees Fahrenheit (112.8 degrees Celsius), which is higher than the boiling point of water (212 degrees Fahrenheit, 100 degrees Celsius). With a good antifreeze and a pressure cap this may not result in a serious overheating problem, but for some of our cars with old, encrusted radiators, it is not a good thing. Keeping the temperature as stable as possible can only do good. For those with a highly-tuned engine that unsurprisingly produces lots of heat, it's also a good idea. It's also a good idea for sitting in traffic on a hot summer day. H-ll, it's a better mousetrap, so why not use it? Frank- 195 degree thermostat will keep the engine at the temperature where it is at optimum effeciency. At an operating temperature of 190 degrees Fahrenheit (87.8 degrees Celsius) or higher, it will normally run best with a fuel / air ratio of 12:1. Happily, this is the ratio at which both power output and fuel economy are maximized. Unfortunately, some owners go to great lengths in order to keep the engine temperature down to 180 degrees Fahrenheit (82.2 degrees Celsius). Although the engine does not overheat, they do not realize that they are diverting energy in the form of heat into the cooling system that should be used to produce pressure on the piston. Operating the engine at 180 degrees Fahrenheit (82.2 degrees Celsius), will result in a reduction of power by 2% to 3%. By the way, just to supplement Frank's info on part numbers, the Prestone Part#'s are 330-195 for 195 degrees Fahrenheit, and 330-180 for 180 degrees Fahrenheit for those who insist upon using one! |
| Steve S. |
| Pump-assisted thermo-syphonic is no more an oxymoron than 'power-assisted' brakes or steering. Without power assistance you still have brakes and steering, albeit with some difficulty if it's present but notworking, just like a pump-assisted thermo-syphonic system will have difficulty keeping the engine cool if the pump assisted part isn't working as it should, whereas a purely thermo-syphonic system under similar conditions may not. Your stat may well keep the coolant within closer tolerances, I don't dispute that. I'm saying it's irrelevant in an MGB I *do* dispute the statement that it is somehow better than the normal variations in a correctly functioning cooling system with a standard stat. Any of us can fit whatever we like to our cars, but I object to implications that the rest of us are somehow putting our cars if not lives at risk by not buying everything on the shelf. We have enough cars, owners, miles and years between us to know that simply isn't true. |
| Paul Hunt |
| Paul- I doubt that it can be taken to the point that becomes an issue of putting anything thing at risk. We use thermostats instead of blanking sleeves because it's just a better of maintaining proper running clearances inside of our engines. I and others have noticed temperature flucuations in the cooling system with the more conventional thermostats, and a thermostat that makes the operating temperature more stable is better still, thus it is not irrelevant. In terms of greater component longevity resulting from more stable operating clearances, the short-term benefits may not seem to be readily apparent, but in theory they should be there over the long term. For most drivers, that's the idea behind using a balanced thermostat. For performance-oriented drivers like myself who love to build a better mousetrap, they have a very real appeal, much like converting to a louvered-fin, four-row alloy radiator matrix. It's just better, and that's what we love. Better. (Chuckle). |
| Steve S. |
| Steve, The Fel Pro gasket part number you list above comes up on the Advance Auto web site with a version that is for a housing with two rather than three holes like the MGB. Do they have one specifically for the MGB? Also the Felpro gray bolt seal appears to be discontinued from what I can find via the internet. Have any alternatives? Thanks, Frank |
| Frank Mooring |
| Frank- I'm pretty sure that my part number is correct. However, you might check with Fel-Pro and post the results. I've still got some Fel-Pro gray bolt seal in the garage, so I've had no need to find an equivalent. Are you sure that they stopped making it? |
| Steve S. |
| Steve, Did discover via a contact question to Loctite that they have just released a new product called Headbolt and Water Jacket Sealant (1158514). Looks nice but very pricey at approximately $25 a bottle through one of their distributors. With regards to the gasket I know Fel-pro makes one specifically for the MGB without the rubber seal. Will research this some more. Thanks, Frank |
| Frank Mooring |
| Steve, Which one of these is the correct Prestone thermostat - the "Ultralife" or the "Power Performance"? http://www.cadna.com/pages/Prestone/Prestone_Stats.html I'm having trouble locating the part online for order to good ol' NZ, should I feel so inclined, as I've got the thermostat cover off at the moment due to a small leak on the radiator. For the gasket sealant (as an adjunct to the actual gasket), I've got some DynaGrip DynaCopper Hi Temp RTV Silicon. I've also got some loctite 510 flange sealant for rigid assemblies (worked great on chainsaw engine block), and DynaGrip Gasket No 1 (hard setting) and No 2 (flexible) - no idea what's best to use to seat the thermostat and to augment the paper gasket - any ideas? |
| Curtis Walker |
| Cancel the above post - reading Bob's site, I see it's the Power Performance one. Another question then, is the blanking sleeve of any use with or without the balanced thermostat? Last question - I've tried searching - does anyone carry these online? |
| Curtis Walker |
| Hmmmm - some more research shows that these "Mr. Gasket" thermostats are possibly the same item, just repackaged: http://www.partsamerica.com/ProductDetail.aspx?mfrcode=MRG&mfrpartnumber=4364&parttype=133&ptset=A Sources: 1. http://www.mgexperience.net/archive/thermostat_info/840199 2. http://gmcmotorhome.info/engine.html |
| Curtis Walker |
| Must be time for bed - since I've just noticed the above posts with the links to Advance Auto Mr. Gasket. Some more links to vendors in that mgexperience link in my last post too. Zzzzz! |
| Curtis Walker |
| Some 'high-performance' semantics... (i) a high-performance produces just about the same heat under most conditions (eg at idle or in traffic) as a low-performance engine, given that the power required to idle the engine or to drive slowly is pretty much the same. (ii) when you're giving it the beans then the engine is going to be very hot so the thermostat opening temperature is largely irrelevant - it'll be open. Neil |
| Neil |
| (i) will depend on compression ratio. An engine with a high compression ratio is much harder to turn at idle i.e. throttle virtually closed than a low compression, as basically the engine is just acting as a vacuum pump. Because of that to maintain a given idle speed a high compression engine will require more fuel, hence more heat. But since the amount of heat produced by either is negligible in relation to the heat produced at full throttle it is irrelevant anyway. |
| Paul Hunt |
This thread was discussed between 11/01/2009 and 17/01/2009
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