The Stovebolt Site Forums The Shop Area Engine Shop Heater Bypass

I have a simple cable operated on-off valve to shut the water off to the heater core. The problem I have is that the truck will overheat unless the valve is open. This means that I have to run with the heat on at all times which is not pleasant in the Summer.

SO, I could replace the simple valve with a bypass valve of some sort like this:
https://www.amazon.com/dp/B07H5DCS7H/ref=psdc_15723841_t3_B004AF34DQ

OR I could get a pressure operated bypass valve like this:
https://www.amazon.com/dp/B004AF34DQ/ref=psdc_15723841_t3_B07H5DCS7H

I like the looks of the pressure operated bypass valve.

Ideas welcome!

Note that I have the 261 style thermostat housing with a Stant 13928 thermostat. This setup seems to work fine as long as there is coolant flow from the underside of the thermostat, through the heater and back to the water pump. I'm assuming that the heater core does not provide enough cooling to keep the temp gauge needle in the middle!

Im not sure the flow of coolant is in the direction you noted. I think it might be the opposite. But that is really not the point. I would verify that the coolant gauge is working properly especially when the vale is closed. If gauge is operating correctly and the motor has NO other coolant issues, I would use a shut off vale that moves the flow of coolant to the other hose instead of just shutting it off completely. You could probly find one that does exactly that or design it yourself by T-ing both hoses together b4 the shutoff itself. Im not familiar with the pressure type valve u listed but I think the 1st valve would do exactly as I stated.

I just want to understand what you have before asking questions...

You have a 235 engine and head with a 261 By-pass type T-stat housing, is this correct???

Mike B

Yes. It's a 1962 235. Don't know why it has the 261 T-Stat housing - that's how it was when we got the truck. There was no thermostat at all when we got the truck and I found out fast that a regular small 235 thermostat wouldn't fit. The Stant 13928 fits the housing. The bypass hole in the housing has a plug in it, so there is no bypass.

If it was my engine I'd take the 261 t-stat housing off and put the correct 235 housing on. Or connect the by-pass back to the water pump like it was on a 261...

The 261 housing has a by-pass outlet the was connected to the top inlet port on the water pump with a short 90* hose. This allows coolant to circulate through the block while the engine was warming up. After it's warmed up, the t-stat opens to the radiator and closes the by-pass outlet putting full flow to the radiator.

Do a Stovebolt search, there was a good discussion about the 261 t-stats 3-4 years ago, it might help...maybe Tim remembers...

Mike B

Thanks for the replies.

Mike, I did read the discussion you referred to before making my post. The "sink strainer" thermostat for the original 261 bypass from the top thermostat housing to the pump is no longer available, so installing the bypass hose is not an option.

The problem is really my fault; I installed the shut off valve. I have the recirculating heater. According to the old car manuals, there is no flow control on the recirculating heater. Coolant is always circulating through the core. Cabin heat is simply controlled by the electric fan in the heater; the faster the fan turns, the more heat you get. So, my options are:

• Remove the valve
• Disable the valve by setting it to always open
• Implement one of the ideas in my first post

I will set the valve to open for now...

There are thousands of 1954 Chevy trucks driving around that don't have a heater at all. Their water inlet/outlet ports at the head and water pump are plugged and they don't overheat during warm up...

There's something else going on...t-stat installed backwards or not operation correctly (test it in a pot of water on the stove and confirm it opens at 180*).

Mike B

Just because the t-stat you put in there fits does not mean that it is correct for that 261 housing.
It is my understanding that the correct t-stat (hard to find), is dual action. When it opens up to allow the radiator to cool the engine, it closes off flow to the bypass system.
I am guessing that your current t-stat is allowing the coolant to recirculate through the bypass and back to the block, rather than making its way to the radiator.

I think I may have caused some confusion. I did some more searching and found this post.

https://www.stovebolt.com/ubbthreads/ubbthreads.php?ubb=showflat&Number=407854

The t-stat bypass and the heater can share the hose to the water pump by installing a tee.

https://www.stovebolt.com/ubbthreads/ubbthreads.php/topics/1182200/1.html

If interested, this is the long discussion about the 261 t-stat that Mike referred to above.

https://www.stovebolt.com/ubbthreads/ubbthreads.php/topics/1164312/1.html

At this point, it looks like I should forget about my ideas in my original post. I should:

• Replace plug in upper t-stat housing with a hose fitting
• Move heater hose from lower t-stat housing hose fitting to the new hose fitting
• Install tee in heater hose that returns coolant to water pump
• Install hose from lower t-stat housing to new tee

This will provide the bypass and allow me to shut off the heater with the simple valve I have already installed.

Just to finish the thread....

I picked up the tee, hose adapter and some clamps at Home Depot. Installed everything as described in my last post and now all is good! Took the truck on a test drive. Today is one of the hottest days we have had this year (30 C) and no overheating.