TR2/3/3A TR3A - measuring operating temperature w/o gauge?

[lbcs_r_fun]

We have been sorting out minor timing and mixture issues with our son's 3A. We haven't been able to check temperature because all of the gauges are out for r&r. Can we get a reasonably reliable reading of engine temperature with a non-contact, infrared thermometer? Where would be the best place/places to point the laser?

Thanks,

T

 

[Geo Hahn]

When I point my IR thermometer at the thermostat housing (where the sensor or cap tube attaches) I get about the same temp as the gauge indicates.

I guess you have plugged the hole where the cap tube would go... if you plugged with an old sensor you could read the temp with an ohmmeter (assuming you know what sensor you used).

 

[CJD]

I would think the closest to the head temp would be to point it right at the thermostat housing, as that's where the hotest water is exiting the block. But, unless you are overheating, it will likely only read the thermostat rated temp.

For combustion temps, go to the exhaust manifold or downpipe right next to it. The manifold temp at idle or just revving the engine unloaded is not likely to give much good info, as it's the cruise and full throttle temps that matter for mixture. I can't think of a way to take those temps, though, unless someone sits on the wing while you drive.

John

 

[TR3driver]

My IR thermometer gives wildly varying readings from the thermostat housing, apparently because old, oxidized aluminum has a widely varying emissivity. So stick a piece of tape, or a spot of paint, and shoot that.

Or you could probably shoot whatever you used to close off the temperature bulb hole.

Yet another idea is to just pick up a cheap aftermarket temperature gauge. They're only about $20-$25, and it may come in useful at other times.

https://www.amazon.com/Sunpro-CP8062-Mechanical-Water-Temperature/dp/B00029K0UY

 

[karls59tr]

Randall Does that 1/2 NPT fitting on the capillary tube for the SunPro gauge fit in the housing or do you have to modify it to fit? Karl

 

[TR3driver]

Oops, sorry, wrong link. The one I got is actually a CP7975
https://www.amazon.com/Sunpro-CP7975-Mech...0217&sr=1-1
or
https://cgi.ebay.com/ebaymotors/CP7975-SU...sQ5fAccessories

The card that came with it says the threads are 1/2" NPT, but they aren't. They are actually 5/8-18 straight threads, and just like the original gauge, the seal is actually between the sensor bulb and the smooth tapered seat in the housing; the nut only clamps the sensor bulb into the hole. The gauge also fits right into the dash panel.

The only change from original is that it includes its own bulb for illumination, which you can wire into the dash light circuit. I was in a hurry, so I actually wired mine into the ignition circuit instead (just temporarily until I get the electric Smiths gauge sorted out).

Sunpro's (Actron's) website is even more confused, it calls the threads 5/8" NPT!
https://www.sunpro.com/product_detail.php?pid=16324

 

[lbcs_r_fun]

Oops, sorry, wrong link. The one I got is actually a CP7975
https://www.amazon.com/Sunpro-CP7975-Mech...0217&sr=1-1
or
https://cgi.ebay.com/ebaymotors/CP7975-SU...sQ5fAccessories

The card that came with it says the threads are 1/2" NPT, but they aren't. They are actually 5/8-18 straight threads, and just like the original gauge, the seal is actually between the sensor bulb and the smooth tapered seat in the housing; the nut only clamps the sensor bulb into the hole. The gauge also fits right into the dash panel.

The only change from original is that it includes its own bulb for illumination, which you can wire into the dash light circuit. I was in a hurry, so I actually wired mine into the ignition circuit instead (just temporarily until I get the electric Smiths gauge sorted out).

Sunpro's (Actron's) website is even more confused, it calls the threads 5/8" NPT!
https://www.sunpro.com/product_detail.php?pid=16324

Curious, when Triumph started to use electric temp gauges (TR4A ?), did they modify the connection at/into the thermal well? In other words will a capillary bulb for a TR3A screw into the well on a TR4A/250/6? Would the electrical temp sensor from a TR4A/250/TR6 screw into a TR3A well? I assume that we would need a voltage stabilizer for the required 10 VDC. BTW, does Sun have a capillary tube temp gauge with a capillary bulb that would screw into a TR6?

Thanks,

T

 

[TR3driver]

The electric gauge was introduced with the TR4, and the TR3 capillary bulb will fit directly into the TR4/4A housing with no modification. The TR4 sender will also fit into the TR3 housing (and in fact my eventual plan is to use an early "convex glass" TR4 gauge in my TR3 as it looks almost identical to the original TR3 gauge). A VS is required.

However, the 6 cylinder TRs (and Spitfires) take a different sender and the opening into the housing is different. I don't know if one of the adapters supplied with the Sun gauge would fit or not, but surely there is one somewhere that would work.

 

[karls59tr]

I see that SunPro also sells a fuel gauge and sending unit. I wonder if I would be able to use this fuel gauge with the stock TR3 sending unit until I get my original gauge sorted out?

 

[Geo Hahn]

50/50 I'd say since fuel gauges seem to come in 2 basic configurations -- those where zero ohms = full and those where zero ohms = empty. Also variations in scale.

Before my fuel gauge was sorted out I just used a yard stick. 1" = 1 gallon is close enough to keep you from getting stranded.

 

[TR3driver]

I found a Sunpro fuel sender on Amazon that quotes resistance as 33 ohm to 240 ohms; which is quite a bit different than the stock TR3 sender.

Even a plain stick will work, if you don't have a yardstick.

 

[rlich8]

Go on ebay adn get one of the $20 infrared thermometers, you can't go wrong.

 

[TR3driver]

Go on ebay adn get one of the $20 infrared thermometers, you can't go wrong.

But people will definitely look at you funny with the hood open in traffic so you can use it!
:laugh:

Besides, you can easily go wrong. I can get readings that differ by 20F or more, just by moving the dot by 1/4" on the thermostat housing. Somehow, I don't think it's telling the truth, especially when it says the radiator is hotter than the housing!