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TR2/3/3A bypass hose

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BobbyO

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I'm confused! Happens often now-a-days. Anyway, what is bypassed by the "bypass hose"? Seems like the water pump but how is this bad after the thermostat opens? Seems like it's there to send warmer water to the thermostat to cause it to open earlier. Is the water pump there to pump water into the block? Could someone give me a simple (possibly stick diagram) of the water flow and how the bypass hose works? I've seen posts where the bypass hose flow is restricted. What advantage is this? Thanks!
 
With the thermostat closed that hose permits coolant to still circulate through the block even though flow to (and thus from) the radiator cannot occur.

Once the coolant is hot, such bypassing of the radiator is undesirable - you want all coolant to go through the radiator.

When the original style thermostat opens it blocks that hose to prevent the bypass.

If you use a modern commonly available thermostat the hose does not get blocked and some hot coolant is returned to the block w/o the benefit of radiator cooling.

Even Triumph seemed to recognize this as the later (TR4) housing has a smaller opening for the little hose.
 
Good question; so as one who runs an original bellows thermostat, to replace what was in there originally, do I need to add an insert to the bypass hose? Using an infrared thermometer, I don"t seem to go much above 190*
 
Does the thermostat sold by Moss close off the bypass hose? I don't think so. It seems to be just open with no blocking.
 
The sleeved thermostat they sell is as original and does, but it is pricey. There is an original on eBay for 170.00
 
mrv8q said:
...as one who runs an original bellows thermostat, to replace what was in there originally, do I need to add an insert to the bypass hose?
Click to expand...

I wouldn't presume to tell someone what they need to do - but what I do is use a partial blockage in that hose.

Where I live ( and to some degree where you live) hot summers and stop & go traffic are the norm. I still have a stock radiator with the hand crank hole in the TR3 so I try for any cooling advantage I can find.
 
Please, to finish: the manual says the 'stat should start to open at 160 degrees. To me this makes sense, if it runs cold, use a hotter 'stat (180) so if it runs hot, use a colder one (160). My measures show a 180 starts to open about 190.:playful: Le
 
2liter4cyl said:
...My measures show a 180 starts to open about 190...
Click to expand...

That would be too hot for my comfort -- I use (if I recall correctly) a 74°C thermostat which is about 165° in old money.

The usual operating temp (measured at the tstat housing) with that in place is 185°.
 
Geo Hahn said:
I wouldn't presume to tell someone what they need to do - but what I do is use a partial blockage in that hose.

Where I live ( and to some degree where you live) hot summers and stop & go traffic are the norm. I still have a stock radiator with the hand crank hole in the TR3 so I try for any cooling advantage I can find.
Click to expand...

Thanks, Geo, for the advice. I've been meaning to pull my apron after 10 years and go through the radiator, et al. Redoing the hoses is on the list, perhaps over winter.
 
Geo Hahn said:
That would be too hot for my comfort -- I use (if I recall correctly) a 74°C thermostat which is about 165° in old money.

The usual operating temp (measured at the tstat housing) with that in place is 185°.
Click to expand...

I installed Moss's aftermarket temperature gauge in my TR3 and it reads around 160 while driving and around 150 measured at the thermostat housing. Is the normal operating temperature supposed to be 185? Better too cool than too hot I suppose but it seems odd that it is so low. What do other TR3 drivers get for there temperature readings on a day that is not overly hot? The rad has been cleaned out,bypass blocked,TR6 fan,mixture of 50% antifreeze/33%distilled water/17% water wetter.
 
Years ago I 100% blocked my bypass hose and installed a GT6 meal fan and cured all over heating. Runs steady at 185 degrees.
 
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