TEMP Alarm Sensor Position

[The Great Pretender]

My carer says it is time for bed................

[cheffy34]

My carer says it is time for bed................

sack her n get a new one be a rebel

did that gauge come with the thermosistor


Dar

[Aethelric]

TGP, would you expect the coolant to get hotter and register a problem if the the overheating problem was caused by air trapped in the head (due to poor bleeding)?

Yes because the coolant is there to react to the heat produced by the engine, if the head is half full of air there is only 50% coolant that needs to try and remove all the heat so the temp will rise most at the outlet of the head.

Hmm.

But a small amount of air trapped in the head should not effect the volume of coolant circulating around the engine. The engine is generating the usual amount of heat. So why should the coolant be hotter if there was a small air pocket?
In fact those parts where the coolant reaches should be running slightly cooler as they have an increased flow of coolant at the expense of those parts which are in contact with non circulating air (causing nasty differential temperatures)

BUT if the air pocket is big enough it will restrict the effective cross section of the coolant flow, and then the volume IS reduced and the temperature WILL go up at the engine outlet. But it will spend longer going around the radiators and will be back to normal when it reaches the engine inlet. This must have a bearing on the best position of a block sensor.

I agree that there is a design weakness that any air that gets into the engine cannot purge by itself. Now air dissolves in water (thats how fish breath) and cold water holds more than hot water. So if someone is continually topping up the cooling due to a small leak somewhere, then they are introducing air into the system too, which will accumulate in the head. Perhaps a regular cold bleed, say when the oil is changed, may be a good idea to purge the head.

Dave

[mikeonb4c]

Isn't the point that coolant needs to be in direct contact with the metal in order to conduct heat away from it? Air is a very poor conductor of heat compared to the coolant so wherever there is an air pocket there is likely to be local heat build up. That's how I imagined it anyway

[Aethelric]

Isn't the point that coolant needs to be in direct contact with the metal in order to conduct heat away from it? Air is a very poor conductor of heat compared to the coolant so wherever there is an air pocket there is likely to be local heat build up. That's how I imagined it anyway

Absolutely right Mike. A gas pocket in the system will cause local heat build up. If you have air in the system then the gas pocket is always there. If the cooling is insufficient (due to reduced circulation or not losing sufficient heat outside of the engine) then gas pockets will form due to boiling coolant. I'm not convinced that the sensor on the inlet side would catch the increase in time to stop "an incident"

If the main reason for the sensor is to compare bongos then the coolant pipe seems a simpler solution.

I would also think that the position of the standard temperature guage sensor will be optimum. It was designed by the engine designers. The instrumentation engineers and marketing bods then got their input.

[The Great Pretender]

Hmm.

But a small amount of air trapped in the head should not effect the volume of coolant circulating around the engine. The engine is generating the usual amount of heat. So why should the coolant be hotter if there was a small air pocket?

What is small? You need to look at the size of the waterways through the head.

In fact those parts where the coolant reaches should be running slightly cooler as they have an increased flow of coolant at the expense of those parts which are in contact with non circulating air (causing nasty differential temperatures)

Sorry that is wrong, the faster a fluid moves its pressure reduces, the lower the pressure the lower the temp that it boils compounding the issue.




Dave[/quote]

Agree with your last post as the inlet is the furthest point from the problem.

[lindeelu]

Below is the original quote from Haydn's post

"To date we have been advising a position for the Temp Alarm Sensors on the exaust side in one of the threaded holes in the cylinder head ...as below


Thanks to some feedback and my own observations whilst towing ...we are getting temps close to the max the alarms can regiester....125C

One of the forum members who has just fitted one has found a really good place to locate the sender and I have now moved mine to this new position...I would advise members to do the same....allow 30 mins and you need a 10mm & 13mm socket.....pull the carpet away from the rear of the engine cover and remove the metal inspection cover......right next to a core plug you will see 2 threaded holes...go for the bottom one....
this is very close to the coolant and well out of any airflow or other heat sources.
I have routed the cables around under the passenger seat well away from the exaust and anything else that could damage them. (you will only have one cable...the 2nd one in the photo is a new ESTC combo unit under test) (see web shop below for details)

You will find the gauge now reads quite a bit lower and be more consistant.

You may find you can locate the threaded hole and fit the sensor and bolt from under one of the seats and not need to remove the above mentioned inspection cover. Might be quicker even if a bit fiddley."

So forgive me if I am just a backward Ozzie, but just where has all the debate come from?

From experience, not theory, a better position for the heat sensor has been identified.
Haydn as a matter of course has passed this information on to owners of the heat sensor he sells.

The actual temperature recorded from vehicle to vehicle is immaterial.
It is just a relative reading, relative to each individual vehicles normal running temperature.
If the normal running temperature moves out of the monitors set window, the alarm activates.

The reason for the change of sensor location was simply because the Tm-2's top reading is 127 degrees.
With the sensor above the exhaust manifold, radiated heat can move the apparent temperature being monitored
outside the devices operational monitoring window.

I have just had word that in the new position, the recorded temperature was as follows:
"92 C top recorded and it is a hot day"

I hope users of Haydn's temperature monitoring devices find this helpful

[Aethelric]

Hmm.

But a small amount of air trapped in the head should not effect the volume of coolant circulating around the engine. The engine is generating the usual amount of heat. So why should the coolant be hotter if there was a small air pocket?

What is small? You need to look at the size of the waterways through the head.

In fact those parts where the coolant reaches should be running slightly cooler as they have an increased flow of coolant at the expense of those parts which are in contact with non circulating air (causing nasty differential temperatures)

Sorry that is wrong, the faster a fluid moves its pressure reduces, the lower the pressure the lower the temp that it boils compounding the issue.

Interesting discussion, and I'd like to know how big the waterways are in the head, (fortunately I have not had to remove the head) and why the pressure on a fluid has anything to do with its speed. But I really don't want to hijack the thread from the Temp alarm sensor.

Dave


Dave

Agree with your last post as the inlet is the furthest point from the problem.[/quote]

[mikeonb4c]

So forgive me if I am just a backward Ozzie, but just where has all the debate come from?

You are forgiven . Bongo owners have a long tradititon I'm afraid, of wandering off thread - and long may it continue. In this case I'm not they did actually wander off thread (certainly not as much as they/I often do). The thread was entitled TEMP Alarm Sensor Position and there was input from those who thought that the position need not be confined to various engine block surface positions.

I used to do a lot of work with clients, getting their views, working with them in groups etc. and found it was sometimes better done in 'closed session'. Have the commercial interests for TM2 considered buying a domain like www.tm2.co.au or somesuch and starting a forum on there for focussed discussion. The only downside I could see might be that it might not be so good for getting the views of prospective customers ('prospects', as the marketeers like to call them). These views can be valuable to product development provided of course that they are welcomed.

[Lewy]

I went to do this - got to the holes but I don't have a bolt to fit - I'm assuming its a 13mm? The only spares I had are 10mm so will look to do this when I get a suitable bolt.

[haydn callow]

I have hundreds of the correct bolt....send me your address and I'll put one in the post.

[The Great Pretender]

Goodday Mate from a backward Pom.

So forgive me if I am just a backward Ozzie, but just where has all the debate come from?

Mine came from the third post on the first page of this thread.

From experience, not theory, a better position for the heat sensor has been identified.

Better for the sensor not for reading what is happening, see my first post.

The actual temperature recorded from vehicle to vehicle is immaterial.
It is just a relative reading, relative to each individual vehicles normal running temperature.
If the normal running temperature moves out of the monitors set window, the alarm activates.

Can't agree, again see my first post.
If you fit the sensor where it is reading coolant returning to the engine unless the rest of the system isn't working correctly you wont see the problem.
The Bongo cooling system when working properly is more than capable of coping with our climate. So, lets have an imaginary problem with the head, the temp rises 10c more than normal. This raises the temp high enough to bring the radiator fans on to bring the temp down to normal. It then enters the block and your new sensor position then reads the temp before it gets back to the problem area. How will that help?
This information is provided from hands on experience after understanding the theory and dismising some of it as it dosn't comply with reality in the workshop.
This is just expanding on my first post, hope it helps mate.

[The Great Pretender]

Dave this may explain.

http://theory.uwinnipeg.ca/mod_tech/node68.html