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Appreciate the member suggestions responding to my post regarding the best choice of radiator cap pressure ratings and thermostats for my BN7. I am running without a thermostat, and one worthy suggestion was to purchase a thermostat with a blanking sleeve to block off the bypass port to insure that more coolant gets sent through the radiator--mine was just recored. Moss now asks about $100 for a thermostat with sleeve (I didn't find British Car Specialists price for this item). That's a bit pricey to me. However, the latest on-line offering from Moss includes a blanking sleeve that the company said serves to block off the bypass port priced at $15.95. Thats a lot for just a sleeve with no thermostat function, I must say. Moss says this bit is intended for race engines. I would appreciate thoughts on using the sleeve rather than getting the very expensive thermostat, keeping in mind that I'm in northern Florida. I definitely don't like the idea of running without a thermostat, which is the way my car arrived.
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Thermostat revist
- Thread starter RDKeysor
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DerekJ
Luke Skywalker
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$100 dollars for a thermostat!!!!! AH Spares sell the correct thermostat for ÂŁ2.95 plus VAT. You should always run a thermostat. It is there to ensure that your engine achieves a minimum operating temperature before it circulates water to the radiator. Without it, in certain conditions the engine will never reach optimum temperature. A thermostat, contrary to what a lot of people think, does not control an engines maximum temperature. That is dependent on many things but not the thermostat. The higher the pressure of the radiator cap the higher the boiling point of the water. However this is only controlling a symptom of an overheating engine.
As the originator of this thread, I want it known that I do think I should be running a thermostat. Regards the Austin Healey Spares thermostat suggested by Derek, I just visited that site and did not find the sleeved thermostat that seems to be recommended. The one pictured for later Healeys at 2.85 British pounds appears to be the conventional design. I suspected that suggestion was too good to be true. But maybe someone . . . .
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I use that sleeve with a modern style thermostat. I had to remove a little metal from the groove in the thermostat housing to get it to sit down flush with both the sleeve and thermostat in place. My car runs at 165F up to 75F outside temperature, and then 90F higher than outside above that.
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With a modern thermostat, it closes off flow to the radiator until the opening temperature is reached. Until then, there is only minor flow (~5%) to the radiator and the bypass.
Lotuswins
Jedi Trainee
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Hi Derek,
Perhaps I can help since I just had a few things clarified to me by the guy at Brass Works who designs impellers. Apparently the thermostat provides a flow restriction even when full open. What that does is keep a higher pressure in the cylinder head, which in turn helps keep steam pockets from forming there. Does that make sense? It also helps keep the pressure differential across the pump such that the pump won't tend to cavitate. This will vary depending on the coolant system design, of course, but is a general rule. Racers will put an oriface into the thermostat area to retain the pressures, but eliminate the potential of thermostat malfunction. He also stated that most pumps max out at 35 gpm, due to the restriction of the thermostat, and the pump intake restrictions. Idle flow should be about 7 to 9 gpm.
I just disassembled my BJ8 pump, and the bypass at the thermostat goes directly to the pump intake, right at the impeller intake, so it must suck a fair quantity. You can block that off easily by making a new gasket for the pump without the hole, cheaper that the sleeve and more effective, though it eliminates the original design theory of a minor flow to keep water circulating during warm up incase of localized hot spots forming steam pockets.
I do have the bellows with sleeve (original Moss repo) type thermostat in mine, and noticed when the temps get hot, it seems to climb faster the higher it is. That could be the bellows contracting due to pressure building due to the temp increase. I have a 7 lb. cap, so I can imagine a 10 lb. cap would exasperate things with this type of thermostat.
I purchased a wax type that was sleeved, Moss sells them, but when installing I measured the depth of the bypass in my cylinder head, and the sleeve position and found that it blocked if off when installed, and when fully open it opened the bypass. Kind of defeating the purpose. So I returned it for a refund.
So, if you install a standard thermostat, with a small hole in it to bypass it with a small flow during warm up, and put in a blanking sleeve, it should be a fairly robust system? It will take a little longer to warm up, but then our cars don't see the extreme use as the original's saw, so it shouldn't be an issue?
Perhaps I can help since I just had a few things clarified to me by the guy at Brass Works who designs impellers. Apparently the thermostat provides a flow restriction even when full open. What that does is keep a higher pressure in the cylinder head, which in turn helps keep steam pockets from forming there. Does that make sense? It also helps keep the pressure differential across the pump such that the pump won't tend to cavitate. This will vary depending on the coolant system design, of course, but is a general rule. Racers will put an oriface into the thermostat area to retain the pressures, but eliminate the potential of thermostat malfunction. He also stated that most pumps max out at 35 gpm, due to the restriction of the thermostat, and the pump intake restrictions. Idle flow should be about 7 to 9 gpm.
I just disassembled my BJ8 pump, and the bypass at the thermostat goes directly to the pump intake, right at the impeller intake, so it must suck a fair quantity. You can block that off easily by making a new gasket for the pump without the hole, cheaper that the sleeve and more effective, though it eliminates the original design theory of a minor flow to keep water circulating during warm up incase of localized hot spots forming steam pockets.
I do have the bellows with sleeve (original Moss repo) type thermostat in mine, and noticed when the temps get hot, it seems to climb faster the higher it is. That could be the bellows contracting due to pressure building due to the temp increase. I have a 7 lb. cap, so I can imagine a 10 lb. cap would exasperate things with this type of thermostat.
I purchased a wax type that was sleeved, Moss sells them, but when installing I measured the depth of the bypass in my cylinder head, and the sleeve position and found that it blocked if off when installed, and when fully open it opened the bypass. Kind of defeating the purpose. So I returned it for a refund.
So, if you install a standard thermostat, with a small hole in it to bypass it with a small flow during warm up, and put in a blanking sleeve, it should be a fairly robust system? It will take a little longer to warm up, but then our cars don't see the extreme use as the original's saw, so it shouldn't be an issue?
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The fixed sleeve has a couple of small holes in it, probably to allow the system to fill. With the sleeve and a modern thermostat in place, when the engine is cold, there is very little flow in any direction. As the engine warms, the thermostat opens and flow goes to the radiator. Hot or cold, the bypass flow is very low.
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If you absolutely determine that the bypass goes directly to the pump intake and nowhere else, you could use a gasket without a hole, but I would have a ~2mm diameter hole so flow isn't completely stagnant. The blanking sleeve has a couple of holes that size. The typical modern thermostat has a small hole in it anyway, so another should not be required. Also, that big lump of iron under the hood takes a long time to warm up anyway.
