Thermic Sensor

[Rickgt]

Hi all, can anyone please tell me how I test the thermic sensor and heat flap that are situated in the standard air cleaner box
Many thanks. Rick

[StokeyStag]

Have a look in the ROM - section 17 30 01

Mark

[richardthestag]

Reproduced here, don't think that I am breaking an copyright but if I am, sorry bout that

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[Rickgt]

Thanks guys, that’s really helpful, I just need to find out what I can use to deliver a measured vacuum, any ideas? Also if I do need to replace the temperature sensor and or the air flap motor do you know the best place to get them from, if it is still possible that is.
Thanks in advance Rick

[Philip Wardle]

If it helps, a vacuum of 9 inches of mercury is equivalent to 4.4 psi below atmospheric pressure, which is 14.7 psi so this is what you'd set your vacuum pump to. If you google "automotive vacuuum pump" there's quite a few available, I have been looking at this myself but haven't bought one yet so can't recommend one. However, I should think a cheap one would do the job as long as it doesn't need to develop a very high vacuum.

[Goldstar]

Never seen one connected tbh. Not really sure what problem they solve but willing to be educated

[Simon Rivers]

Hi Rick, you probably already know, but the thermic sensor is no longer available, should you need to replace it. I got one from Tony White.

[Philip Wardle]

Never seen one connected tbh. Not really sure what problem they solve but willing to be educated

I think we're generally agreed that they are part of the arrangement that gets the engine to working temperature asap, particularly in cold ambient temperatures. My theory as to why Triumph would bother is that, depending on the methodology for compliance testing against emission requirements, it may be vital to minimise emissions during startup as I should imagine these contribute a large proportion of the total measured over the full engine temperature cycle.

[APS]

Importantly you do not want the flap in the air filter box stuck in a position of providing just warm air, especially if you have the exhaust manifold to air filter box hose in position. Even without the hose, you will be depriving the engine of forced cool air. Not good.

Though without vacuum the flap is in the horizontal position and it is more likely if stuck to be in this position. Which is not a major issue except for delaying warm up.

After 50+ years, either the thermic sensor or the flap or both could quite easily be faulty.

You do not need a vacuum pump to check if the sensor and flap are working. The engine is providing the vacuum to do the test.

Firstly if you have all the vacuum hoses in position, ie from manifold to sensor and from here to the flap device.

Remove the flexible rubber gaitor at front of the air box. Putting your fingers in the front of the air box you should be able to feel the flap in the horizontal position.

With the temperature reasonably cold, start the engine and feel the flap in the air box. Being careful of the engine fan. The flap should move so as to direct air from the warm air connector.

If whilst the engine is warming up you should be able to feel the flap begin to revert to the horizontal position. If this happens all is good.

If you get no movement of the flap then you need to test if the sensor or the flap is faulty.

First test that the flap moves with vacuum. With a longer vacuum hose connect the flap directly to the inlet manifold. This bypasses the sensor and the flap should move to the warm air position, regardless of temperature.

If the flap moves, then the problem is most likely with the sensor.

The sensor allows vacuum to the flap when cold and turns off vacuum once a certain temperature has been reached.

Hope this makes sense.

Ok some will feel this is of little consequence, but it will delay warm up and theoretically cause more engine wear when cold.

I can imagine a lot of stags not having this working, I see stags for sale without the warmup hose from the exhaust manifold.

If you are one of these then it is not a major issue. But it is important that you have all the vacuum hoses in place or your introducing a major air leak into the inlet manifold which can contribute to poor running as well as being able to properly tune the carbs.

[Lingen]

There is another reason for diverting hot air in to the carburettors, and that is to stop icing at the jets. Most cars of the period had a system of some sort to provide this- not always automatic- until fuel injection became universal. This was usually a hand operated lever on the air filter to be used in cold weather. I remember forgetting to use the one on my Fiat 1300 (!) one winter, and on a very cold day the engine slowly died. I felt it was a fuel problem, so took the top off the air filter pan to peer in to the carburettor. The venturi was almost completely blocked with ice, made from frozen damp air. It thawed pretty quickly from the warmth of the engine, and with the "Winter" setting adopted, I had no further trouble.
It is fact of science that when a liquid, in this case petrol, becomes vapourised, it needs heat to make the change. (That is how a fridge works). This will further lower the temperature of the already cold incoming air. It will soon get below freezing, and if the air is moist, it will form frost and ice..
However, unless you are proposing to take you Stag on a a ski-ing holiday, there is no real need to get the system working. I think it looks better to have it in place though.
Mike.

[nigele]

I fitted a new Thermic sensor for a Metro, part number PHT10001. It’s virtually identical to the original, apart from the size of one of the holes drilled in the connection ports. It’s working perfectly, and definitely helps with running during warmup. Rimmers currently list this part number, although I didn’t buy it from them.
More info here in attached link.

Nigel

[Philip Wardle]

Useful info, thanks Nigel - I have made a note of PHT10001 in my parts book.

[Rickgt]

Hi guys thanks for all your great advice, Also Simon thanks for the recommendation to contact Tony for a replacement sensor