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Test for thermostat stuck open


daverclasper
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If you run the engine with the cap on, the top of the radiator will remain cool then suddenly get hot when the engine is up to temperature and thermostat opens.  That is what I have observed with my cooling system.  If the temperature of the top of the radiator gradually gets warmer, that would indicate that the thermostat is stuck open.

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run at idle with the rad cap off    you will see the coolant rush over the top tubes and ebb and flow as the stat modulates the flow 

there will be no flow while its closed  but the stat opens and closes or partially closes every few seconds  its not   just open or closed 

and if removed for testing you are not boiling an egg  they are a very sensitive little unit , we had a test tank for them which circulated the water and raised it in 0,1C 

increments and plotted the opening it all gets quite techy so if in doubt  testing at home wont prove much  just replace it  make sure it has a jiggle pin air bleed in the rim to aid refilling .

Pete

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Think i would just buy a new one with gasket and change. For 10 pounds or less and half an hours work , which includes going to and from the garage. If in doubt rule out. If it is sticking open you run cool but if it fails closed you overheat. Change it , if you still have the problem your 95 percent sure its not that. If it goes away job done.

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On 17/04/2021 at 08:20, Mathew said:

Think i would just buy a new one with gasket and change. For 10 pounds or less and half an hours work , which includes going to and from the garage. If in doubt rule out. If it is sticking open you run cool but if it fails closed you overheat. Change it , if you still have the problem your 95 percent sure its not that. If it goes away job done.

+1

That's exactly what I would do.  Thermostats don't last forever, they're almost a service item. 

Nigel

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a hotter engine can run on weaker mixtures 

most 70/80s cars on carbs raised the temperature to 88c  to help   get "lean burn" as they called it 

who remembers Avengers with a near white exhaust pipe ,

as for triumphs there are 3    there is no winter /summer but  but based on countries climate ( in most parts lists ) 

74 C hot climates ( not just hot uk summers)

82C std   uk/ European spec 

88C colds climates  ( not a smidge of UK snow)  and later models like 1500 spit  < onwards with leaner running and more emission controls 

or there abouts 

and if you fit a 88c to a 82c car the temp gauge will be  nearer the red  than mid way ...and many are paranoid about that anyway

supposed overheating is a common trend on here 

Pete

 

 

 

 

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1 hour ago, Pete Lewis said:

 

and if you fit a 88c to a 82c car the temp gauge will be  nearer the red  than mid way ...and many are paranoid about that anyway

supposed overheating is a common trend on here 

Pete

 

 

 

 

Guilty as charged

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2 hours ago, daverclasper said:

Thanks folks

Interested in why, as no info given.

Cheers, Dave

Hi Dave,

 My reasoning is better in the winter as cabin is warmer & in the summer the heat rejection is greater as the delta/difference across the radiator is greater.
Once its open it is open. 

Cheers.

Iain.

 

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13 hours ago, Pete Lewis said:

as for triumphs there are 3    there is no winter /summer but  but based on countries climate ( in most parts lists ) 

74 C hot climates ( not just hot uk summers)

82C std   uk/ European spec 

88C colds climates  ( not a smidge of UK snow)  and later models like 1500 spit  < onwards with leaner running and more emission controls 

or there abouts 

and if you fit a 88c to a 82c car the temp gauge will be  nearer the red  than mid way ...and many are paranoid about that anyway

Temperature gauge? What's that?

It's a sign of how things have changed; back in the day drivers worried about how warm the car was running... now they worry about how cold the driver is. You were meant to change the thermostat for Summer / Winter but these days, with a lot of our cars being Summer use only, fit an 82 and just leave it all year round. Now I'm going to have to go and check mine...

 

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Temp gauges on modern cars (90s onwards?) are not like our cars. They are controlled by teh ecu, and will read "normal" over a wide range of temps to avoid panicking drivers, and reassure them their car is not overheating. On our cars drivers have a meltdown if the gauge goes much over normal.

I like modern cars with simple warning light for overheating, less to worry about.

My spitfire temp sensor got nudged and the terminals broke. It sat at 1/4 for normal driving, and the rad fan came on when it read 1/2, 92 degrees. The first new sender, supposedly "oem equivalent" read 1/4 before the engine went on , and went full scale in minutes. Bin and refunded. Found another after a recommendation, it reads 1/3rd normal driving and 2/3 when the fan comes on, so a tad more accurate. But is meant for a rover SDI. I may investigate other senders if I see them cheap....

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2 hours ago, Mathew said:

No worry guages, like the glasses that turn black when there is danger in the hitch hikers guide to the galaxy?

'Joo Janta 200 Super-Chromatic Peril Sensitive Sunglasses' ...wonderful things. I wonder if you can get a windscreen made using the same technology?

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Just listen for hissing and watch for steam at junctions.

I've been out looking for a thermostat for the Herald in my stash of parts... and seem to have everything but 82. Quite a few 88s, one 70, one 72, one quite rusty 82 and the highest so far has been 94. I know I bought the 70 as an early thermostat advertised for a Herald - yes it fits but the vendor never mentioned the temperature! - but no idea where the others came from over the years.

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