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MG Midget and Sprite Technical - Blanking Sleeve Problem
|The car has been running hot so after reading some of previous threads I decided to install a blanking sleeve and drill a couple of holes in the thermostat flange. The problem I have is the temperature sensor does not allow the sleeve to go all the way down. Do I notch or try an angled hole thru the sleeve? |
This is a replacement sender from Moss, are the originals shorter? The local auto parts store had no threaded fittings to push the sender further out from the housing.
|Are you talking about that round collar that fits in the hole for the stat? |
I never understood the concept behind that...except for all out race cars ...I didnt think you where supposed to use a stat with it
just drill an 1/8th inch hole in the stat face flange, maybe 2 if its a brutly hot engine...no sleeve needed
|Is this what you have?|
|Yes Prop, that's it. I solved my problem. Being the pack rat that I am I went thru a box of old parts and found the original sender. Sure enough it is a half inch shorter. Put it in, reassembled everything and no leaks. Time to take it for a ride and see what kind of a difference it makes.|
DID you have to use an electric heater to help warm up the engine with all that cooling going on.
8 ^ P
The only advantage to the sole use of a blanking plate in lieu of a thermostat is that there is no thermostat to stick in the closed position and thus cause the engine to overheat. However, it should be understood that a blanking plate is normally intended for racing use. On a street machine, installing a blanking plate without including a thermostat while leaving the pulleys the original diameter usually results in hotter running, as well as much longer warm up periods. This is due to the fact that without the flow restriction caused by the presence of a thermostat, the coolant circulates so rapidly that it does not have time to absorb heat from the engine, nor does it have time to release heat into the cooling matrix of the radiator. Thus, if you have chosen a camshaft which causes the engine to be normally operated at a higher average engine speed (such as a Piper BP285), then it would be wise to install a larger-diameter pulley wheel onto the coolant pump in order to reduce the pumping speed of its impeller. This will assure that the coolant has sufficient time to absorb heat from the engine and release it into the radiator matrix.
The function of the thermostat is to maintain a stable engine temperature, thus keeping the running tolerances of the engine constant, and by doing so, prolong the lifespan of the engine. Too much coolant flow can force the coolant through the coolant passages too quickly, causing it to not accomplish maximum heat transfer. This condition can also prevent the coolant from having enough time inside of the radiator in order to allow efficient heat transfer. On the other hand, inadequate coolant flow can overheat the coolant before it gets a chance to release the heat energy that is stored in its mass into the radiator. If coolant flows too rapidly, as in the case of no thermostat being present, the coolant can leave air pockets inside of the coolant passages of the cylinder head, thereby “superheating” the trapped air into an expanding gas, which forces water out of the overflow even though the water leaving the engine appears to be well below its boiling point. This is a dangerous situation that leads to serious engine damage resulting from cracked heads and cylinder blocks, often without warning. Tests have proven that by simply opening the thermostat precisely at the same temperature over and over again, the average temperature of the engine remains cooler. Engines can warm up faster to normal operating temperature, and cool down quicker once the engine exceeds the set point. This results in slower cylinder wear, and consequently longer engine life. By opening the thermostat “on time”, every time, the temperature swing is reduced, allowing for more consistent cooling. Opening the thermostat as quickly and as far as possible allows the warm coolant to exit quickly, thereby delivering it to the radiator to begin its cooling cycle as quickly as possible. As a result, getting the coolant into the engine and holding it there extracts as much heat from the engine as efficiently possible, therefore enabling to radiator to work at its maximum potential as well.
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, a 1650 Fahrenheit (73.9 degrees Celsius) thermostat will start to open at 165 degrees Fahrenheit (73.9 degrees Celsius) but will not be fully open until the coolant temperature reaches 185 degrees Fahrenheit (85 degrees Celsius). A winter thermostat such as the 1950 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 (101.70 Celsius), which is 30 Fahrenheit (1.61 degrees Celsius) more than the boiling point of pure water. It should be noted that the thermostatic sensor that is incorporated into its fan control switch (BMC Part# URP 1126, Moss Motors 542-215) inside of the radiator header tank of the Rubber Bumper MGBs is calibrated at 194 degrees Fahrenheit (90.0 degrees Celsius) / 180 degrees Fahrenheit (82.2 degrees Celsius). Consequently, the fan switch will close when the temperature of the coolant that is entering the radiator is measured as being 194 degrees Fahrenheit (90.0 degrees Celsius), and open when the temperature decreases to about 180 degrees Fahrenheit (82.2 degrees Celsius). The popular aftermarket Hayden fan has a thermostatic sensor that is incorporated into its fan control switch that is calibrated to open at 185 degrees Fahrenheit (85 degrees Celsius). This being the case, a either a 185 degrees Fahrenheit (85 degrees Celsius) or a 195 degrees Fahrenheit (90.6 degrees Celsius) thermostat will cause either of these electric fans to run almost continuously.
It is a widely known fact that that at atmospheric pressure at sea level, pure water will boil at a temperature of 212 degrees Fahrenheit (100 degrees Celsius). Ascend to a higher altitude and the boiling point will occur at a lower temperature (approximately 4.5 degrees Fahrenheit (15.3 degrees Celsius)lower for each 1,000 feet in altitude). Fortunately, the boiling point of the coolant is raised by both the addition of antifreeze and by the radiator cap of the radiator, which raises the boiling point by 3 degrees Fahrenheit (1.61 degrees Celsius) for every PSI of pressure. You would be well advised to use the “fail-safe” type of thermostat that locks in the full-open position should it fail in order to preclude overheating in the middle of nowhere. Moss Motors sells a 180 degrees Fahrenheit (82.2 degrees Celsius) “fail-safe” type general-purpose thermostat (Moss Motors Part # 434-205).
Be aware that a thermostat cannot prevent overheating. It can only prevent overcooling. A thermostat can only be the cause of overheating if it is defective and does not open as it should. In selecting a thermostat, be aware that the B Series engine tolerates high operating temperatures quite well. Whenever a thermostat is changed for one with a different operating temperature, it will be necessary to adjust the fuel / air mixture of the carburetion, richer for a cooler thermostat and leaner for a hotter one. This is due to the fact that the hotter the intake ports become, the increased heat is transferred into the incoming fuel / air charge, expanding the air and thus effecting the fuel / ratio. 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 coolant system that should be used in order 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 from 2 to 3%.
Decades ago when control of air pollution was not a priority for engine designers, engines typically employed cooler 180 degrees Fahrenheit (82.2 degrees Celsius) or even 165 degrees Fahrenheit (73.9 degrees Celsius) thermostats not for the purpose of keeping the engine’s operating temperatures lower, but rather for the purpose of allowing the oil to run cooler in order to prevent it from breaking down. The oils of that era would break down at relatively low temperatures, so engines were run at as low an operating temperature as possible in order to preclude this problem. However, today’s modern oil formulas are designed to withstand much higher operating temperatures. Also, before the days of today’s ethylene glycol antifreeze with its boiling point of 386 degrees Fahrenheit (197 degrees Celsius), the antifreeze most commonly employed was ethyl alcohol. Ethyl alcohol has a much lower boiling point of 172.4 degrees Fahrenheit (79 degrees Celsius) than that of water at 212 degrees Fahrenheit (100 degrees Celsius), so by keeping the coolant temperature as low as possible, the alcohol was not driven out of the system as quickly. This was more important during the winter, obviously, so cars typically had winter thermostats that were, while warmer than their summer thermostats, still colder than those used in the modern cars of today.
The Original Equipment Smiths bellows-type thermostat originally developed for use in the B Series engine 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, resulting in hot-spots and possible localized boiling. However, such thermostats are unavailable new, often being regarded when encountered as quaint curiosities from a bygone day. When the Original Equipment Smiths bellows-type thermostats ceased to be produced, the wax pellet type becoming its substitute, a key feature was lost : the sleeve which controlled the bypass passage in the head.
The modern wax pellet style thermostats of today, lacking the reciprocating sleeve, have no provision for exclusive recirculation. As a result, hot coolant can not only move off into the radiator via the opening in the thermostat, but a certain amount can also recirculate back into the head, diluting and warming the coolant that was returning from the radiator, thus causing the head to run hotter than was originally intended. In addition, because of the routing of the coolant through the system, this also increased the amount of heat retained in the system in general. This can lead to overheating under the most adverse running conditions of ambient heat and heavy loadings, resulting in preignition. The most practical way to deal with these problems when they arise is to install a blanking sleeve in addition to a modern balanced-type thermostat. The only drawback is that this will result in a somewhat slower temperature rise during the warm-up period.
Although the modern wax pellet type thermostat is a non-rebuildable item, it can be helpful to understand how it works. 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 poppet valve that seats against a valve seat that is formed by a canelure in the upper bridge section. A coil sealing spring surrounds the copper cup in order to maintain the sealing pressure against the valve seat. Attached to the bridge section is a rod that projects down into the copper cup, attached to which 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 away from the valve seat, thus opening the valve. Over time, the sealing edges of the piston and the inner wall of the copper cup wear to the point that the wax compound leaks out and the thermostat ceases to function. Fortunately, this is an item that is easy and inexpensive to replace.
However, you do not have to resign yourself to the use of a conventional wax pellet thermostat. Prestone markets an updated version of what is called the “balanced” thermostat that was originally designed and marketed by Robert Shaw Controls (Prestone Part# 330-195 for 195 degrees Fahrenheit, Prestone Part# 330-180 for 180 degrees Fahrenheit). 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”. In a cooling system that is equipped with a conventional thermostat, there is always a relatively high pressure difference between the intake and the outlet of the coolant pump, especially when the thermostat is partially closed. This is due to the fact that the coolant pump struggles to draw the coolant through its intake while at the engine outlet the conventional thermostat reduces the outgoing coolant flow. As the purpose of the coolant pump should be to supply flow and not pressure, some of its work, and thus power, is wasted. In addition, due to the thermal inertia of the thermostat bulb, every time that there is a quick variation in temperature of the coolant that is returning from the radiator, a relevant part of this variation is increased by the loading on the pump. When a conventional thermostat is either closed or partially open, the coolant flow inside of the engine is low and its pressure is high. This also leads to a gradient between the pump and the engine outlet. Also, when the speed of the coolant pump increases, its output pressure then increases. However, a pressure release thermostat, in addition to opening in response to temperature, will also open in a manner that is related to the pressure within the engine that is created by the coolant pump. This opening of the pressure release thermostat is accomplished by a simple comparison of these pressures, which is achieved mechanically by its pressure balancing spring which is designed to operate at a trigger pressure drop that is determined by the aforementioned pressure balancing spring. This allows the thermostat to open effortlessly and accurately no matter what the rate of coolant flow or the speed of the coolant pump happens to be at that particular time. The inherently inefficient hydrodynamic shape of the poppet-type valve of the non-balanced designs is prone to being forced closed when the pressure resulting from increased coolant flow abruptly increases, such as during sudden increases in coolant pump speed after downshifting. 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 simple wax pellet type thermostats. While its effectiveness is not immediately obvious when first installed, its superiority does become more obvious while driving at sustained high speeds (70+ MPH) with a power-enhanced engine. A balanced thermostat maintains the temperature of the coolant to within +/- 2 degrees Fahrenheit (.67 degrees Celsius) compared with temperature fluctuations of up to 20 degrees Fahrenheit (6.7 degrees Celsius) with a conventional wax pellet 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. In conventional wax pellet thermostats, the small area of the poppet valve requires that the piston must make a long stroke in order to open the thermostat far enough for adequate coolant flow. Unfortunately, the long stroke compromises durability. In the case of the balanced thermostat, the triangulated strut design, being inherently stronger and more stable than the single-span bridge design of conventional wax pellet thermostats, provides superior strength, thus permitting a larger aperture area for coolant flow. This in turn allowed the achievement of a shorter stroke by means of a uniquely-designed flange and a larger-diameter sleeve-type valve. This design feature 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 stem of the bypass valve is welded on. The weld tends to fail under stress. In order to eliminate this problem, in the Robert Shaw design the entire copper cup and the bypass stem are manufactured from a single piece of metal. Fabricating the triangulated strut assembly from brass instead of steel provides another benefit: brass, being more malleable than steel, can be precisely formed in into a more efficient hydrodynamic profile in order to maximize coolant flow. Most manufacturers use a one-piece rubber diaphragm in order to seal the charge and drive the piston. Should the rubber seal rupture, the thermostat then fails. 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 the unique requirements of each part. Consequently, wear or minor damage to the stem seat will still permit the thermostat to operate in a satisfactory manner. The piston itself is activated by a temperature-sensitive mixture of metallic powder and wax. Some wax pellet thermostats use an all-wax charge which reacts 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 its rapid response to temperature changes will not deteriorate over time and so that the thermostat will not “stick-open”, thus causing the engine to run cool. Happily, it is also a “fail-safe” design that will remain open should it ever fail, thus preventing overheating.
But you REALLY need to be more detailed in your responces, just never enough info.
|<< The car has been running hot >>|
Bud, can't help with the blanking sleeve, but as to runs hot: the NA 1500 midget:
1: Set your timing to 10 btdc, not 2 atdc,
2: feed the air filter/carb with air from outside, i.e. not air from under the hood,
3: install an oil cooler
4: if the 3 items above don't cure what ails you, replace the catalytic converter with the alternative straight-through pipe from Moss/Vic Brit.
Removing your thermostat is typically not the most sound way to correct for "The car has been running hot".
Just my 2 cents worth. Been there.
|Stephen - thanks for all the info and the time you put into it. Here's where I'm at now - I installed the blanking sleeve with the thermostat but drilled 2 small holes thru the flange of the thermostat as shown here;|
Prior to doing this water temp was approx. 245 degrees farenheit and oil temp was almost the same. Took the car for a nice ride and water temp stayed right around 210 and oil temp around the same.
1. Will check timing
2. Running dual HS4's with K&N filters and have wanted to do something for more air. possibly a scoop or louver of some sort.
3. Oil cooler will be installed this week.
4. Already running a straight-through pipe.
|Bud, I am not sure that your lower water temperature reading truly means that your engine is now running cooler. Careful re-reading of Stephen's post reveals that the loss of the thermostat can lead to the coolant circulating too fast, preventing it from properly picking up the heat in the engine. This will lower the coolant temperature, only to leave the heat where you don't want it.|
Very good information!
You're right about the balanced thermostat...I had one on the shelf (P/N 330-180) that I bought for my Chevy truck awhile back, but never got around to installing.
I installed it in my Midget this morning after reading your post & went for a blast down the freeway. The temperature guage rose & then stayed constant, even at traffic lights, unlike the poppet style thermostat I replaced.
I'd forgotten I had it & the reason why I'd bought it.
It appears to work as advertised.
|Dave Rhine ('78 1500)|
|Just ordered one - thanks for the advice.|
What kind of fan are you running?
Are you running the stock fan with clutch?
If so, you may want to check the clutch to make sure it's operating properly. I had an overheating problem last summer & it turned out to be the clutch...I replaced the pump, fan & belt with one for a '74 Spitfire (it's clutchless), all for the cost of a new clutch alone.
Just a thought...
|Dave Rhine ('78 1500)|
210F seems a bit hot to mee
My A-series never goes over 195/200 even in traffic on verry hot days
Might be a good idea to flush the cooling system and thourgly clean the radiator
Running fan with clutch. Didn't know about the spitfire set-up, never liked fans with clutches, maybe worth a try if it turns out to be the clutch.
Here's another info source you might want to consider, alot of 1500 owners there:
|Dave Rhine ('78 1500)|
You state above that: ‘On a street machine, installing a blanking plate without including a thermostat while leaving the pulleys the original diameter usually results in hotter running, as well as much longer warm up periods.’
My experience on a street Sprite on back to back testing that replacing the thermostat with a blanking sleeve and ADDITIONALLY blanking off the bypass outlets on both the water pump and cylinder head did not result in hotter running but cooler running. Subsequent testing with a larger water pump pulley produced marginally hotter temperatures in some circumstances but mostly resulted in cooler running temperatures.
Additionally you state that: ‘Thus, if you have chosen a camshaft which causes the engine to be normally operated at a higher average engine speed (such as a Piper BP285), then it would be wise to install a larger-diameter pulley wheel onto the coolant pump in order to reduce the pumping speed of its impeller. This will assure that the coolant has sufficient time to absorb heat from the engine and release it into the radiator matrix.’
My understanding is that the use of a larger diameter water pump pulley on an A-series engine is to reduce cavitation of the water while the pump is attempting to pump it.
Further, you state that: ‘Decades ago when control of air pollution was not a priority for engine designers, engines typically employed cooler 180 degrees Fahrenheit (82.2 degrees Celsius) or even 165 degrees Fahrenheit (73.9 degrees Celsius) thermostats not for the purpose of keeping the engine’s operating temperatures lower, but rather for the purpose of allowing the oil to run cooler in order to prevent it from breaking down. The oils of that era would break down at relatively low temperatures, so engines were run at as low an operating temperature as possible in order to preclude this problem’. Your statement may be correct and if this is the case the engine designers were mistaken because with an A-series engine there is rarely any correlation between engine coolant and engine oil temperatures. The coolant temperature can move from 70C to 100C and the oil temperature will not vary. However, if the engine rpm is increased to in excess of 6000rpm while being driven in top gear, for more than a few minutes the oil temperature will rapidly rise anything from 10 to 30 degrees while the coolant temperature will remain largely constant.
|Re: fan clutch failure:|
Last time mine failed it was associated with a brief high hum heard only at shutdown, also felt as brief vibration with hand on gearshift, again, only at shutdown.
|My fan barely turned at idle, then made a screeching noise when I revved the engine.|
|Dave Rhine ('78 1500)|
This thread was discussed between 04/09/2010 and 07/09/2010
This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.