I've been trying to locate a 180 bypass thermostat for a 59 2 ton 261 . The one I have that seems to operate ok in a pot on the stove as it opens and almost closes as designed but when in the vehicle I can barley get the temp. to 170 and in colder weather it will drop enough to get the green cold lite to come on at idle . I've found a few on line but they don't specifically say they are bypass units . Has anyone bought one that they were satisfied with ??
The "bypass" thermostat for the 261 hasn't been manufactured in many years. It had a flapper built into the moving part of the stat that closed off a big recirculating hose that allowed coolant to circulate inside the block and cylinder head while the engine was warming up. That system was only used on medium and heavy duty applications, IMHO. Any thermostat you can buy today will not have the bypass feature built in, no matter what the advertising copy has to say. Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
I have the appropriate water pump with dual 1/2 in outlets , the bottom one returning from the heater and the upper one leading to the lower thermostat housing fixed to the block . The 1/2 in fitting on the top part runs to the heater as well , does this seem about right ??
Originally, there was a big bypass hose, something like 3/4", which connected the thermostat housing to the water pump. With the no longer available stat installed, that hose got blocked off as the stat opened, routing the bypass coolant to the radiator. Your current hose routing allows flow through the heater core all the time, engine hot or cold. Without the proper t-stat, one of the ports at the water pump, and the one in the lower stat housing should be plugged. Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
The 503 in my GMC had a bypass housing also, however there was a piece of fence wire stuck in the original thermostat, so I used a cardboard thermostat on the way home from Jerry’s part of the country. Since those thermostats are no longer made, I put a small block GMC(Chevy ones are smaller, won’t fit) one in line of the upper radiator hose, works fine.
Ed
'37 GMC T-18 w/ DD 4-53T, RTO-610, 6231 aux., '95 GMC running gear, full disc brakes, power steering, 22.5 wheels and tires. '47 GMC 1 ton w/ 302, NP-540, 4wd, full width Blazer front axle. '54 GMC 630 w/ 503 gasser, 5 speed, ex fire truck, shortened WB 4', install 8' bed. '55 GMC 370 w/270, 420 4 speed, grain, dump bed truck from ND. Works OK.
I’m surprised that the reproduction parts guys haven’t come up with a bypass thermostat yet. What does it take to entice them to make a particular part?
I've ordered the Stant 13958 thermostat which I will pick up on Tuesday and install it and see how that works . I think my current stat is a 160 deg. as that I've read was typical of the heavier trucks in the late 50 's . and that's all the temp I can get out of it without a cardboard helper . When closed it still allows about 10% flow as it doesn't close all the way which I guess was a type of bypass , but I look forward to getting it up to 180 for the chillier nights up north here .
I’m surprised that the reproduction parts guys haven’t come up with a bypass thermostat yet. What does it take to entice them to make a particular part?
Tooling up to produce a complex part to service the few remaining medium and heavy duty truck engines that mostly went out of service 40 years ago doesn't make good nonsense, investment-wise. If someone did choose to make a limited run of that type of thermostat, each one would probably cost a hundred dollars or more just to break even on production costs. Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
Where is your other heater hose connected? If it's at the water pump, there will be very little or no flow through the heater core. If it's at the cylinder head, using the port in the upper thermostat housing will create a huge volume of coolant which bypasses the thermostat, resulting in slow engine warmup. Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
Right Gord&Fran I've seen them advertised with 21/4 , 21/2 and even a 3in. flange with the same product no. , by tonight I'll know which one I got . And yes Jerry it does take a long time to warm up , I still have the temp light that stays green until the motor starts to warm up as well as temp gage and when driving in temps around the freezing point the green light will come back on at idle . It would probably be simpler to just mount a 21/4 housing of which I have a few and run with that but my logical side never entered into the picture when buying this truck and it seems to stay outside when I enter the garage to work on the truck . I appreciate all the input and have learned some stuff with it and I thank you all .
It's teed into the hose that runs from the lower thermostat housing to the water pump.
In that case, the only time you'll get much flow through the heater core is when the thermostat is closed. You'll get lots of coolant circulation during warmup, however. Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
Well I picked up and installed my stant # 13928 thermostat and as it turns out it comes in three pieces . A regular sized 180 deg as used in a 235 , a brass adapter that mounts into the base housing to accept the thermostat and a rubber like spacer that fits between the top of the thermostat and the and the top housing which I guess is to keep the thermostat from popping out of place when the coolant is flowing . The thermostat does not fit wholly into the brass adapter when closed allowing coolant to bypass a bit while warming up . I had to open up the hole on the top housing to allow for the brass adapter , but the motor now runs closer to the 180 mark . I haven't tried the heater yet but I suspect it should perform better now with the engine running warmer .
Thanks for the update. Interesting that your new thermostat comes in three pieces; I'm pretty sure that the one I bought was assembled as a single unit, ready for installation.
Now for my update. Jerry is correct. I switched the hoses around and my heater now works as it should and the engine temp is steady.
