Thermostat Housing Water Restrictor?
#220987
02/11/09 09:02 AM
02/11/09 09:02 AM
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Dads426
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Well, its been about 30 years since I've built an engine that is race-only (not street driven), but have built a lot of street driven engines in-between. On the 493 that we just picked up (Bounty Hunter Clone Car), the water outlet did not have a thermostat (not surprised). Back in the old days the thought was to run a restrictor in the thermostat housing (sold by Moroso) to slow the flow of water down through the engine so that proper heat exchange would take place (in both the radiator and from the heads to the coolant). The car has a Moroso motor driven water pump so I don't know if this thing would flow enough water to even need a restrictor. What is the general consensus today?
Also, on engines that don't use a thermostat, a good friend suggested that I plug the by-pass hole in the water pump housing (just below the water outlet) as this will force all water through the radiator instead of recirculating hot water back in the block. This trick is supposed to help the engine run cooler. Thoughts?
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Re: Thermostat Housing Water Restrictor?
[Re: wildcargo]
#220989
02/11/09 10:21 AM
02/11/09 10:21 AM
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Joined: Oct 2004
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BobR
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Quote:
That is how I run mine, no restrictor, plug the bypass. I do put a small hole in the plug to let air out, allso don't tap to deep as some of the holes are oversize for the thread. the easyest way I have found to turn the tap is to use a 1/2" extention up sidedown and put the tap handel on the male end. 
Plug yes, restrictor no.
Restrictors are good for nothing other than quicker warm up-which may be beneficial for drag racing only applications. They do not help cooling AT ALL. This is cut and pasted from Stewart components website.
Tech Tip #3 - Thermostats & Restrictors
Thermostats & Restrictors
We strongly recommend NEVER using a restrictor: they decrease coolant flow and ultimately inhibit cooling.
For applications requiring a thermostat to keep the engine at operating temperature, we recommend using a Stewart/Robertshaw high flow thermostat. This thermostat does not restrict flow when open. The Stewart/ Robertshaw thermostat enhances the performance of the cooling system, using any style of water pump. However, the Stewart Stage 1 high-flow water pump may require this thermostat to operate properly, and Stewart Stage 2, 3, and 4 water pumps simply will NOT operate with a regular thermostat because these pumps have no internal bypasses.
Stewart further modifies its thermostat by machining three 3/16" bypass holes directly in the poppet valve, which allows some coolant to bypass the thermostat even when closed. This modification does result in the engine taking slightly longer to reach operating temperature in cold weather, but it allows the thermostat to function properly when using a high flow water pump at high engine RPM.
A common misconception is that if coolant flows too quickly through the system, that it will not have time to cool properly. However the cooling system is a closed loop, so if you are keeping the coolant in the radiator longer to allow it to cool, you are also allowing it to stay in the engine longer, which increases coolant temperatures. Coolant in the engine will actually boil away from critical heat areas within the cooling system if not forced through the cooling system at a sufficiently high velocity. This situation is a common cause of so-called "hot spots", which can lead to failures.
Years ago, cars used low pressure radiator caps with upright-style radiators. At high RPM, the water pump pressure would overcome the radiator cap's rating and force coolant out, resulting in an overheated engine. Many enthusiasts mistakenly believed that these situations were caused because the coolant was flowing through the radiator so quickly, that it did not have time to cool. Using restrictors or slowing water pump speed prevented the coolant from being forced out, and allowed the engine to run cooler. However, cars built in the past thirty years have used cross flow radiators that position the radiator cap on the low pressure (suction) side of the system. This type of system does not subject the radiator cap to pressure from the water pump, so it benefits from maximizing coolant flow, not restricting it.
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Re: Thermostat Housing Water Restrictor?
[Re: BobR]
#220990
02/11/09 11:15 AM
02/11/09 11:15 AM
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Joined: May 2007
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Dads426
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Great thread. Thanks for the info.  I did put the plug in the housing and I was careful not to tap it too deeply. I'll drill an air hole in the plug to bleed the system (I used to do that on thermostats in street cars).
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Re: Thermostat Housing Water Restrictor?
[Re: Dads426]
#220991
02/11/09 10:10 PM
02/11/09 10:10 PM
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May be different on a big block, but I just cut the center out of a factory thermostat and use the rest for a restrictor. Then I thought I'd plug the bypass, but it forced too much water through the radiator on my small block. No time for heat exchange, so I took it out.
Yeah, it's got a smallblock.
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