More Thermostat data

[Bob Johnson]

I have collected temperature data after installing a brand new 160 degree thermostat. I did not drill any bypass holes in the new thermostat. I wanted to collect data without the bypass hole first. I will drill a bypass hole and collect more data.

The attachment shows the data for 3 different tests. The blue line is without a thermostat. The pink (magenta) line is with an old thermostat which I thought was a 160 degree thermostat (maybe it was not a 160). The yellow line is for the new 160 degree thermostat. The temperature probe is located at the top of the radiator inside the neck between the thermostat and the radiator. Thus the temperature does not rise too fast at first until the thermostat opens. The yellow data shows the temperature rising slower then the pink data. This is due to the lack of a bypass hole in the yellow data.

Bob

 

[Glen in Hillman MI]

The yellow and pink lines explain why you need a weep hole in the thermostat.

 

[steve s]

Thanks for doing this, Bob. Nice job with the graphing presentation. Was the motor just running at idle?

I was interested to see how much time with the new one your coolant spends betweeen 170 and 180. I recently installed a temperature gauge in my car, along with the Vintage Precision thermostat housing. With the temp sensor on the motor side of the thermostat, my system (also a 160 stat) pretty much duplicates yours. I was surprised how much time it spends pushing 180, and actually gets there on hills or really hauling. Sort of makes me wonder because others report a steady 160. Also, I have a brand new Brassworks radiator.

Neither of our setups really let us know whether there is localized, spot overheating going on somewhere back in the head or block. That is why you really want some sort of bypass hole, to keep some flow going in there during warmup.

Don't know if you saw them in earlier post, so here's picture of the new housing. You can see the two dished-out bypass holes they've machined in. Sort of goofy looking when mounted, but a good design otherwise and I can't resist that sort of thing.

Steve

 

[marc hildebrant]

Bob,

Thanks for the information.

Marc

 

[AL in NY]

Bob, great data. I have always used a thermostat, but have been thinking of going to the Vintage Precision unit. Where is your thermostat located?

 

[Bob Johnson]

Steve,

The data is from approximately 12 mile trips. The first 3.5 minutes are in town. After that the trips are on the highway going about 55 mph. There are a couple of hills which show up in the data. The first hill is at about the 8:00 mark and the second is just after 12:00 (the X axis is minutes). The blue and the yellow lines show the temperature going up as the car climbs the hills. Then drops as it goes down the hill. The pink line data is too erratic to make out the hills.

Bob

 

[Bob Johnson]

The thermostat is located just above the water pump at the bottom of the hose that connects the head to the top of the radiator.

Bob

 

[Frank Miller]

Bob this is a great data collection. I work in process control and look at this stuff all the time but it is getting collected by computers. The first thing I noticed was all the spikes. I am thinking that when the thermostat opens the water trapped in the block is significantly warmer which is why you get the upward spike and then down when the cold water rushes through. As the water warms up the thermostat finds a spot that will maintain a steady temperature.

I do not think the bypass hole will have a significant effect on the operation. What it will do is allow you to drain the water out of the upper hose when you need to repair something. I put holes in the ones in my 8BA as I ran into that exact problem.

 

[Jim/GA]

If you are going to use a thermostat, consider doing what is done on a more modern car (say, from the 50s to the present) and include some form of bypass from between the waterpump outlet (before the thermostat) and right back into the engine inlet. This way, when the thermostat is closed during engine warm up, this bypass volume will promote uniform temperatures within the block and head. Once the thermostat opens, the majority of flow will go through the radiator, as desired.

You don't want all the coolant backed up and trapped in the block and head with the thermostat closed. Until the thermostat opens, things will be locally very hot. One or two small holes in the thermostat will help to get the hot water up to the heat sensitive wax pellet to open the thermostat in a timely manner, but they do not circulate water for uniform warm up like a bypass hose would.

I have seen hot water outlets and inlets on Model As and at swap meets, intended to be used with hot water heaters in the cars. You can skip the heater core and just run a 5/8" heater hose from outlet to inlet and call it good.

Bob, if you did this on your car, you would want to put your temperature probe right at the same spot where the bypass hose comes out of the waterpump outlet, before the thermostat. Then you would see the temp of the block climb slowly, even before the thermostat opens. Better data than temperatures after the thermostat, more representative of the engine temperature.


Jim
(yes, I am an engineer)

 

[AL in NY]

Jim/TX - would a piece of 3/8" steel tubing routed from a point below the thermostat to the block water inlet work as a bypass, or is something larger needed.

 

[steve s]

Jim/TX - would a piece of 3/8" steel tubing routed from a point below the thermostat to the block water inlet work as a bypass, or is something larger needed.

The problem with a constant bypass is that, once the motor warms up, whatever portion of coolant is passing through it doesn't have the opportunity to cool down in the radiator. That's not such a deal if the bypass loop includes an actual heater, since the heater core is a little radiator. Since the time might come when you want every little bit of cooling possible, I would sacrifice efficiency at the warmup end and just go with the 1/8" hole(s) drilled in the thermostat flange. Simple, prettier, nothing to leak.

Steve

 

[Richard Lorenz]

I have a heater hose bypass on my '29 Tudor, but I never got around to including the heater. The hose is "crimped" unintentionally. The hose gets warm, so I know that some flow exists. I also have a 160 deg. thermostat with some small bypass holes in it. My thermometer say that it all works fine, both in cool and hot outdoor temperatures.

 

[Jim/GA]

Jim/TX - would a piece of 3/8" steel tubing routed from a point below the thermostat to the block water inlet work as a bypass, or is something larger needed.

Yes, that would work. It does not need to be larger. But heater hose is so easy to work with.

 

[Special Coupe Frank]

Just due to fluid mechanics, the majority of the coolant is going to favor the large radiator hoses over the small by-pass, once the stat is open.

Hudson used a 1/2" steel tube for the bypass on its flatheads.

Chrysler Corp began using thermostats mounted in the cylinder head / outlet somewhere around 1934, and incorporated a by-pass circuit for block circulation during warm-up. There was an "external bypass" in the form of a short 1" diameter hose from the water outlet neck to the back of the water pump (pump is located on the "cold return" side of the radiator). Heater connections were "supply" at the back of the head, "return" as a tapping on the water pump.
Around 1950 or so, Chrysler Corp revised the water-pump plumbing to an internal bypass circuit.

Believe the Chevy Stovebolt also had an internal bypass...

Whether it's bleed holes or a small bypass tube, I think some sort of bypass is a must when using a "water thottling type" thermostat...

The earliest "warm-up" devices were winter-fronts and shutter fronts, which restricted air flow through the radiator, not water flow through the engine; therefore by-pass circuits were not necessary.