Cheap, non-volatile, thermally conductive fluid?

[Ric]

Hello,

My Volvo MD2020 only has a crude on-off overheat alarm, and I'm too disillusioned with Volvo customer service to pay them any money for an analogue gauge.

Out of curiousity I would like to experiment with a digital thermocouple in a couple of external cavities in the casing of my engine (unused bolt-threads etc) to see if I can use this as a warning of overheat problems. I have found one particularly promising hole in the cylinder head into which I can insert the thermocouple. Can anybody suggest a non-volatile, odourless, cheap, thermally conductive liquid which I could use to ensure optimum thermal contact?

 

[dt4134]

Can anybody suggest a non-volatile, odourless, cheap, thermally conductive liquid which I could use to ensure optimum thermal contact?

Water meets those requirements as stated.

 

[VicS]

Oil would do the job!

but I suspect just inserted dry and the top of the hole plugged would be good enough.

The liquid with the highest thermal conductivity that I know of is mercury but I'd not recommend that you use it !

Water would evaporate!

 

[jimmcgee]

maplins , thermal compound .

 

[semisimple]

maplins , thermal compound .

+1

Just pick the cheapest one of these...(but check the temperatures they might get are okay - I can't see why not. Most compounds should cope with temperatures up to a 150C).

http://www.maplin.co.uk/computing/fans-and-cooling/thermal-compound

 

[team OSD]

How about heat conductive paste? It´s a conductive mixture of magnesium/zinc oxide and silicon oil. Widely available are different kinds of paste, some melt at 120C, 150C an the expensive one´s at 165C or more.
a Little package 3 cc; between 2 and 6 euro.

ed; Semisimple beated me by minutes!

 

[savageseadog]

A wax might do it

 

[greenalien]

If you already have some Copaslip on board, it should do the trick.

 

[theoldsalt]

Ric,

Lots of suggestions have been forthcoming but what is the fluid/liquid for/expected to do?

 

[William_H]

Thermocouple

As said the conduction of air in a tight bolt hole should be adequate however the paste used by electronics people to improve conduction of power transistor body to heatsink is what you need. (usually white)

I don't know whether you are aware that piston (air cooled) engine aircraft often have a cylinder head temp gauge in the form of a washer that goes under the spark plug in place of normal copper washer which is a thermocouple. (2 metals) It is quite sensitive to change indeed enough to be used to adjust mixture from CHT. However your diesel engine may not use similar copper washers. The idea however is very applicable to checking cooling as the hot head is exactly what you want to avoid.
This aircrraft type CHT could be ideal for outboard motors. You could buy just the thermocouple or a complete kit with meter from aircraft spares suppliers. olewill

 

[Ruffles]

A hand held infra-red temperature gauge is useful for making comparative measurements.

 

[NickRobinson]

Careful-

Are you screwing in anything behind this liquid (eg a bolt)?

If so, don't create a hydraulic lock and split the casting.

Nick

 

[aquaplane]

Vic gave the right answer in post 3, oil.

It's commonly used in thermocouple pockets.

 

[pappaecho]

You might consider using an organic oil like olive oil or rapeseed oil.

 

[farmer.leo]

Antifreeze.

You don't want if freezing, it conducts temperature away. Oil is also an idea that sounds good. Maybe the manufacturer of a thermocouple could offer a suggestion.