The Stovebolt Site Forums The Shop Area Engine Shop Converting a 216/235 thermostat housing to a bypass system

Jerry 'Hotrod Lincoln' Herbison and I put our heads together to see if we could figure out a way to convert a stock 216/235 thermostat housing to a bypass system. A recent string of posts about the stock 261 bypass system and the extinct thermostat that fits it is what gave us the challenge.

We have a fairly simple to build solution that we would like to share. It will only work on a 261 or a newer model ('55-'62) 235 with a low water pump. It will not fit a 216 or an early model ('53-'54) 235 with a high water pump.

Testing in my '57 with a 235 has shown the following:

The engine temperature gauge shows the engine warming up quicker. This makes sense because the bypass allows coolant to circulate through the engine, so warm coolant will reach the temperature gauge sensor faster.

The engine runs cooler. The temperature gauge used to run at about 1/3 of the way toward hot. With the bypass, it runs about 1/4.

The temperature gauge does not fluctuate. Before the bypass, I would get some fluctuation. With they bypass, there is no fluctuation. This makes sense because coolant is always circulating even with a closed or partially open thermostat, thereby normalizing the temperature instead of the non-bypass system simply cycling between an open or closed thermostat.

I have submitted a Tech Tip so that Jerry and I can share the idea with others. I also scanned the draft of the Tech Tip into Photobucket, so instructions and pictures can be found at this link--

http://s844.photobucket.com/user/ma...20PM_zpsc5sif7vb.png.html?sort=2&o=0

Jerry and I continue to work on a version that will fit a 216 or a high water pump 235.

The conversion is relatively easy. After seeing the performance...and after getting educated on the why's and how's of the 261 bypass system from the recent string of posts...I'd put this high on the 'gotta do' list for a Saturday morning.

Matt

Thanks for the update, Matt- - - -I'm working on a modification to the original design for the high water pump thermostat housing, moving the extra port from the front of the housing to about 45 degrees off to one side. That should solve the fan clearance problem with the other one. I should have another prototype for you to to test soon.
Jerry

A private post asked me for more of an explanation, so I am adding it here in case others are interested. I will also add it to the submitted Tech Tip and the draft posted on Photobucket. Feel free to correct if I have stated anything in error.

Matt
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Coolant will flow from the water pump through the block to the thermostat housing. Without a bypass, it just stalls there until the thermostat opens. The thermostat acts like a flood gate. The exception is that the coolant will flow through the heater feed line in the lower housing if the heat control is turned toward hot. If not, the heater valve also acts like a flood gate. 

By adding the bypass to the lower housing, the coolant will flow back to the water pump and through the engine block in a constant loop even when the thermostat is closed. In the modified lower housing, it flows through the 3/8" nipple inserted through the bottom of the housing. It 'bypasses' the thermostat, hence the name. Since coolant is always in circulation, it eliminates hot spots and steam pockets in the water jacket caused by relatively stagnant coolant waiting to heat up.

When the coolant in the bypass loop gets warm enough, the thermostat will open. The coolant is circulating past the thermostat through the lower housing as part of the bypass loop. Without the bypass, the coolant surrounding the thermostat is more stagnant and relies more on convection for enough hot coolant to reach it to cause it to open. The circulation of the bypass causes the thermostat to be more efficient because it operates based on the temperature of the coolant circulating through the system, not just the temperature of the relatively stagnant coolant against the thermostat. In a non-bypass system, coolant in the engine block is much hotter than coolant adjacent to the thermostat in a running engine with a closed thermostat.

When the thermostat opens, the coolant in the loop has reached the thermostat temperature and now needs the radiator to cool it. The flow of the cooling circuit needs to change. Two things need to happen. First, the path of the of the coolant now needs to be past the thermostat (flood gate opens) to the radiator for cooling back to the engine via the water pump. Second, the path through the bypass circuit needs to be closed so that the radiator can do its job. This is accomplished by the disk at the bottom of the bypass thermostat sealing off the fitting that was added to the lower thermostat housing.

In a situation in which the thermostat is partially open, a hybrid loop needs to happen. Some of the coolant needs to flow to the radiator and some can continue through the bypass. That is accomplished by having both gates partially open. As the thermostat opens part way, the flow to the bypass becomes restricted as the base disk of the thermostat moves toward the new fitting. The thermostat acts like a mixing valve. This normalizes the flow better than with just a cycled open/closed thermostat in a non-bypass system.

The heater is mentioned in the first paragraph because the heater circuit can also act as a bypass. The heater control must be on hot or the heater valve will be close off the bypass loop. Moving the heater valve toward cold acts the same way as having the base disk on the bypass thermostat close off some or all of the flow to the bypass as the thermostat opens. The heater loop will function as a bypass regardless if the thermostat is open or closed. The heater core will also act to lower the temperature of the coolant. The bypass system does this all automatically. Plus, do you really want the heater on full blast in the middle of summer?

Did you ever hear that if your temperature gauge is getting too hot that you should turn your heater and fan on full blast? The reason is twofold. One is to get some coolant circulating just in case the thermostat is stuck. The second is to get the additional cooling effect of the heater core. It is not an old wive’s tale᠁it is true.

Was this tech tip not published? I can't find it. Photobucket doesn't work very well, but I was able to get the screenshot linked above and have posted it below.

The temp gauge on my truck goes to HOT when the engine is working and drops very quickly when going downhill (esp. if you put it in neutral!). I have the 261 thermostat housing. The thermostat I have is a Stant 13928 (the one with the rubber ring). Still thinking about what to do about this...