Checking Refurbished water temp gauge

[oldelanman]

Hi John

Without any water a kettle element will run a lot hotter than 100 degrees C.

If the instrument bulb were to make direct contact with the heater element in the kettle then that part of the bulb would not have the insulating effect of the water and so could be subjected to the full metal temperature of the element, that could possibly damage the instrument (and maybe also the kettle). I agree chances of it happening are slim but maybe that is what the repairers are covering themselves against. The same thing could also happen if the bulb were to be placed in a pan of water on a stove and it were allowed to touch the bottom.

Andy

Just got a reply to this question from the people who repaired my gauge - Andy is spot-on. Contact with the element will exceed the range of the gauge and damage the bourdon tube within it.

Regards,

[bill308]

I don't think Andy's reply is quite right.

Assuming the temperature blulb is covered with water in a pan, on the stove, the bulbs temperature will reflect the water temperature to a very large degree. Even if the bulb were in hard contact with the bottom of the pan, the actual contact surface would approach that of a point. This is a very inefficient mechanism for heat transfer due to the small conduction area and the effect of a contact conductance at the interface. The surface area exposed to water is relatively large in comparison and as long as there is liquid, the liquid will remain at the boiling point of roughly 100 C (212 F), assuming sea level atmospheric conditions and pure water, which is well below the 116 C (240 F)that a cooling system might see under worst case conditions. Water soluable contaminants like salt or sugar generally increase the boiling temperature a tiny bit while increasing pressure can raise the boiling point significantly (ex. sealed pressure cooker, closed coolant system).

The bottom line is that this is a very good test that is easily done with almost no possibility of hurting the instrument. For best accuracy, use distilled water.

[tcsoar]

"kettle testing can cause damage to the gauge"

Think someone may have put the whole lot including gauge into a kettle to test in the past

[oldelanman]

I don't think Andy's reply is quite right.

Assuming the temperature blulb is covered with water in a pan, on the stove, the bulbs temperature will reflect the water temperature to a very large degree. Even if the bulb were in hard contact with the bottom of the pan, the actual contact surface would approach that of a point. This is a very inefficient mechanism for heat transfer due to the small conduction area and the effect of a contact conductance at the interface. The surface area exposed to water is relatively large in comparison and as long as there is liquid, the liquid will remain at the boiling point of roughly 100 C (212 F), assuming sea level atmospheric conditions and pure water, which is well below the 116 C (240 F)that a cooling system might see under worst case conditions. Water soluable contaminants like salt or sugar generally increase the boiling temperature a tiny bit while increasing pressure can raise the boiling point significantly (ex. sealed pressure cooker, closed coolant system).

The bottom line is that this is a very good test that is easily done with almost no possibility of hurting the instrument. For best accuracy, use distilled water.

Well??here?s my assessment.

Clearly there is a risk of damaging the gauge or the repairer would not take the trouble to provide the warning ? presumably based on their experience of repairing damage sustained in this way. I think that despite the theoretical assessment of how small the risk may be, it is sensible to take note of their advice, and ensure the sensing bulb does not directly contact the heat source when testing in a water bath. Why take the risk, however small, if you know it exists ?

Just my view of course.

Regards,

[GrUmPyBoDgEr]

I don't think Andy's reply is quite right.

Assuming the temperature blulb is covered with water in a pan, on the stove, the bulbs temperature will reflect the water temperature to a very large degree. Even if the bulb were in hard contact with the bottom of the pan, the actual contact surface would approach that of a point. This is a very inefficient mechanism for heat transfer due to the small conduction area and the effect of a contact conductance at the interface. The surface area exposed to water is relatively large in comparison and as long as there is liquid, the liquid will remain at the boiling point of roughly 100 C (212 F), assuming sea level atmospheric conditions and pure water, which is well below the 116 C (240 F)that a cooling system might see under worst case conditions. Water soluable contaminants like salt or sugar generally increase the boiling temperature a tiny bit while increasing pressure can raise the boiling point significantly (ex. sealed pressure cooker, closed coolant system).

The bottom line is that this is a very good test that is easily done with almost no possibility of hurting the instrument. For best accuracy, use distilled water.

I'm pleased that you took the trouble to write that reply.
At least there are two of us that are singing from the same Hymn sheet
John

[cliveyboy]

Everyone seems enthusiastic about the accuracy of the instrument used to measure the gauge. But no one seems to have mentioned that the gauge its self is likely to be the most inaccurate item .
I would be interested to know what accuracy your gauge was calibrated to as any gauge with a needle and mechanical movement will have a fair amount of inaccuracy. A good quality needle gauge could still only be +/- 2% and that is its accuracy in ideal laboratory conditions.
Double checking an item before fitting is always a good idea but when you are then fitting it to a 40 year old car with fluctuating voltage, bad earths and vibration it means we also have to be realistic and accept the gauge can only ever be a very general indication of temperature.
Clive

[collins_dan]

What I'm wondering is if the gauge is reading the temperature of the water that flows by it or the temperature of the housing it is screwed into as I'm not sure that the two are the same. Based on my readings from the infrared gun, it seems like the temperature of the water going into the radiator is about 190F/88C and the temp of the housing is 235F/113C and the gauge is reading 225F/107C. The install was straightforward enough. I just screwed it into the housing and tightened it. The bulb seemed to be centered in the space, but could it be contacting the side of the housing, causing it to give a false reading?

Dan

[billwill]

Double checking an item before fitting is always a good idea but when you are then fitting it to a 40 year old car with fluctuating voltage, bad earths and vibration it means we also have to be realistic and accept the gauge can only ever be a very general indication of temperature.
Clive

Electricity is not involved in this particular instrument. It is a bulb containing a mystery fluid or wax, and a pressure pipe leading to a Bowden gauge instrument.

[rgh0]

Dan

The surface temperatures measured by your infrared gun will vary in accuracy depending on the emissivity of the surface as previously said and also the temperature drop from the flowing water on the inside to the outer surface, the rubber hose for example is quite a good insulator and the outer surface will be a little cooler than the inner. The impact of the hot exhaust gases in the exhaust ports will also influence the surface temperature of the head around the ports to be potentially higher than water inside the cooling jacket. The reverse applies for the inlets ports which are cooled by the cold incoming air and fuel vaporisation so on the inlet side it will probably be cooler than the water in the cooling jackets.

None of you measurements surprise me greately and if you are not loosing water then not much to worry about i would beleive. The high reading of the guage itself needs to be checked by putting it in a pot of boiling water as previously said or checking it with an independent temperature guage stuck in the radiator top tank through the filler cap opening.

This should confrim if they car is really running warmer than it should or if its a guage accuracy issue.

If it is truely running where the guage says it is then I would change the thermostat and flush and refill the system and ensure the radiator is clean on the outside also.

If still running hot then it is unlikely to be a porous or cracked head if it been running fine and no mechanical damage like a nut going through the engine. The fire rings in the head gasket can crack with age and thermal cycles and let leakage through which results in hot running and ultimately water loss as the leakage increases.

Ignition timing and the cams as indicated should not be a significant contributor. Personally i dont like L2 cams and for a road car the standard sprint cams are a better option I believe but this should not be contributing to an overheating problem


regards
Rohan

[collins_dan]

Thanks. I will check the gauge as described. I had checked the thermostat this winter, but will replace it. Also will do a hot flush, if someone will tell me what a hot flush is.

The radiator is a fairly new aluminum one and is clean, both in and out.

Thanks. Dan

[rgh0]

If it is truely running where the guage says it is then I would change the thermostat and flush and refill the system and ensure the radiator is clean on the outside also.

If still running hot then it is unlikely to be a porous or cracked head if it been running fine and no mechanical damage like a nut going through the engine. The fire rings in the head gasket can crack with age and thermal cycles and let leakage through which results in hot running and ultimately water loss as the leakage increases.

Sorry Dan for the typo - the "hot" got misplaced while editing from 3 lines down while I was typing and I did not notice. If you have a new aluminium radiator then it unlikely to be a radiator problem contributing to overheating but a system flush with one of the proprietary flushing additives and refill ensuring all the air is out of the system will not hurt.

Do you have a coolant recovery cap and catch bottle system? Do you see significant quantities of coolnt pushed into the ctach bottle when hot and sucked back when cold?

cheers
Rohan

[JJDraper]

If the temps from the infrared are right, then why would the coolant temperature and the carb side of the head be much lower temp than the header side. Is this any indication of exhaust gases temp being really high and heating up this side of the head? The frustrating thing is that the car is running great. Thanks, Dan

Having gone over my engine with a Thermal camera, I can confirm that the carb side runs cooler than the exhaust side, probably because of the cooling effect of the intake charge. The webers run cold and pools of condensation collect on the outsides, initially making me think I had a petrol leak, until I tested it (with a finger!). See attached pic of the webers - dark blue is cool, hotter is red with hottest yellow/white.

Jeremy

[collins_dan]

Thanks for all the advice. Looks like the gauge is telling me what I didn't want to hear, that I continue to have a cooling issue. Dan