temperature difference - steel pipework to adjacecent rubber

[widdowson2008]

Always knew there was a temperature difference between the steel pipework and adjacent rubber pipes but I didn't think it would be this much.
Jaylee very kindly agreed to do an experiment for me. He recently fitted a temperature gauge with the sensor positioned on the metal stub (top hose) as it leaves the head. He is now in the process of fitting a second sensor on the heater circuit.
http://www.igmaynard.co.uk/bongo/forum/ ... 9&start=15

To see what the difference in temperature readings was between steel and adjacent rubber pipework, I asked him to temporarily place the 2nd sensor on the rubber hose as close to the original sensor (on the steel stub) as he could, and take some readings, and these are the results.
Thanks for the effort Jamie

The sensors are around 100mm apart.
There is a deffinite (and larger than I expected) lag
@ 35C, the difference is 3.6deg (10.17%)
the surprise is that the lag actually got bigger at higher temperatures, so
@85.5C, the difference was 15.79 (15.79%)
These were taken as the temperature was still rising. I suspect that the difference may reduce as the temp increases further, but there will probably still be a lag.
As the stat opens and the C1 value drops, what do you think will happen at C2? will it still lag behind?

Key:
C1 - Blue on graph - 1st sensor on steel stub
C2 - Red on graph - 2nd sensor on rubber hose (100mm from C1)
Black line on graph shows the (increasing) difference between the two (C1 - C2)

[Kincaid]

I've put a sensor in the engine top hose. My temps are pretty much the same as those Jamie is getting from the sensor attached to the rubber hose. My water temp will really struggle to get to 82c (stat opening) during normal running. During normal travel it generally hovers around the 72-75 range and the cylinder head temp stays around 85-90c which I take to be a good operating temp.

If the cylinder head gets higher than 90c the water temp rises quite quickly to stat open temp and then brings the cylinder head temp back down to it's usual range.

[widdowson2008]

I've put a sensor in the engine top hose. My temps are pretty much the same as those Jamie is getting from the sensor attached to the rubber hose. My water temp will really struggle to get to 82c (stat opening) during normal running. During normal travel it generally hovers around the 72-75 range and the cylinder head temp stays around 85-90c which I take to be a good operating temp.

If the cylinder head gets higher than 90c the water temp rises quite quickly to stat open temp and then brings the cylinder head temp back down to it's usual range.

Bit confused with your numbers.
From above, your sensor is IN the top hose and reading 72-75. Is that an in-line sensor actually IN the coolant flow? If so, where are you measuring the head temp (85-90c)?
Apart from that, your stat appears to be doing its job (if I'm reading your numbers right)

[missfixit70]

I've put a sensor in the engine top hose. My temps are pretty much the same as those Jamie is getting from the sensor attached to the rubber hose. My water temp will really struggle to get to 82c (stat opening) during normal running. During normal travel it generally hovers around the 72-75 range and the cylinder head temp stays around 85-90c which I take to be a good operating temp.

If the cylinder head gets higher than 90c the water temp rises quite quickly to stat open temp and then brings the cylinder head temp back down to it's usual range.

Either your gauge isn't very accurate (reading about 10 degrees too low), or there's another issue there such as the wrong stat or it's been drilled or something?

Good work on showing the temp difference between the sensor positions guys

[Poohbear]

Isn't it failry obvious that there would be a temperature difference between a steel part and a rubber part? Steel is a much better conductor than rubber. Try filling a metal cup and a plastic cup with boiling water and then pick them up.

[missfixit70]

Yup, I've been saying it all along, & it's why I fitted my temp sensor where it is, but some people have to be shown numbers to prove it Theory is all very well, but practical demonstration is even better.

[Kincaid]

I've put a sensor in the engine top hose. My temps are pretty much the same as those Jamie is getting from the sensor attached to the rubber hose. My water temp will really struggle to get to 82c (stat opening) during normal running. During normal travel it generally hovers around the 72-75 range and the cylinder head temp stays around 85-90c which I take to be a good operating temp.

If the cylinder head gets higher than 90c the water temp rises quite quickly to stat open temp and then brings the cylinder head temp back down to it's usual range.

Either your gauge isn't very accurate (reading about 10 degrees too low), or there's another issue there such as the wrong stat or it's been drilled or something?

Good work on showing the temp difference between the sensor positions guys

hi - I've got the water temp in the actual top engine hose and the head temp at the back of the head. I rekon my temps are reasonably accurate (say +/- 3c or something) as if I am parked up and idling as soon as the water temp reads 80c you can actually feel the rad bottom hose change temp as the new Mazda thermostat opens up. It's a CUBE alarm that quite a few others are using.

[alant54]

Isn't it failry obvious that there would be a temperature difference between a steel part and a rubber part? Steel is a much better conductor than rubber. Try filling a metal cup and a plastic cup with boiling water and then pick them up.

Tried your suggestion.... I am on my way to A&E with serious burns to my right hand when the plastic cup melted and no fingerprints on my left hand.... ...any more daft suggestions....

[widdowson2008]

I've put a sensor in the engine top hose. My temps are pretty much the same as those Jamie is getting from the sensor attached to the rubber hose. My water temp will really struggle to get to 82c (stat opening) during normal running. During normal travel it generally hovers around the 72-75 range and the cylinder head temp stays around 85-90c which I take to be a good operating temp.

If the cylinder head gets higher than 90c the water temp rises quite quickly to stat open temp and then brings the cylinder head temp back down to it's usual range.

Did some extensive cooling system heat tests with Helen (Bulgaria) using 6 sensors placed in a variety of locations around the system.
In order to ensure uniformity, before the sensors were fixed to the van, they were placed in hot water together and tested (coupled to their respective gauges) alongside a standard thermometer.
All gauges SHOULD have been reading the same, but in fact, a couple were giving low readings. The sensor supplier replaced the duff sensors with synchronised ones.
What I'm saying here is that you have probably got one of the 'low reading' sensors. As Kisrty has pointed out, you appear to be reading 10 degrees too low. No problem - just mentally add 10 degrees to the figure you are getting and you will 'see' the thermostat operating.
Having said that, you are measuring at the absolutely BEST place with the sensor IN the top hose.
The 'back of head' sensor you have is actually nowhere near a waterway - ( but very close to the rear camshaft pedestal bearing). However, it closely simulates the head coolant temperature. This is why I think the 'in hose' sensor is reading low.

[widdowson2008]

Isn't it failry obvious that there would be a temperature difference between a steel part and a rubber part? Steel is a much better conductor than rubber. Try filling a metal cup and a plastic cup with boiling water and then pick them up.

Agree with you. It is obvious. But I prefer to quantify it with factual numbers rather than guestimating - hence the diagram. Like Kirsty said, some folk need pics, some need numbers, others are happy just believing what they are told. I prefer numbers and pics personally.
All I was trying to do with these figures to show there IS a lag and see how much the lag is.

[widdowson2008]

Isn't it failry obvious that there would be a temperature difference between a steel part and a rubber part? Steel is a much better conductor than rubber. Try filling a metal cup and a plastic cup with boiling water and then pick them up.

Tried your suggestion.... I am on my way to A&E with serious burns to my right hand when the plastic cup melted and no fingerprints on my left hand.... ...any more daft suggestions....

Hope the fingers heal soon. Thanks for input.

[Poohbear]

Isn't it failry obvious that there would be a temperature difference between a steel part and a rubber part? Steel is a much better conductor than rubber. Try filling a metal cup and a plastic cup with boiling water and then pick them up.

Tried your suggestion.... I am on my way to A&E with serious burns to my right hand when the plastic cup melted and no fingerprints on my left hand.... ...any more daft suggestions....

Hope the fingers heal soon. Thanks for input.

Perhaps I should have put a warning on my statement so that some daft so and so didn't try it!

[widdowson2008]

Key:
C1 - Blue on graph - 1st sensor on steel stub
C2 - Red on graph - 2nd sensor on rubber hose (100mm from C1)
Black line on graph shows the (increasing) difference between the two (C1 - C2)

In order that these numbers (and graph) do NOT get taken out of context, I would stress the following:
The numbers indicate that there is always a lag. This is not necessarily the case. This data was gathered whilst the engine was in its warming up cycle.
Questions still to be answered are: (further tests to be conducted)
1. If the engine was allowed to settle to its working temperature and the heat in the rubber hose allowed to 'soak' through to the sensor, would the two sets of data converge? (probably )
2. If the engine was to continue to run so that the thermostat began to operate, would the temperature in the rubber pipe again lag behind when the temperature in the steel pipe decreased? (I suspect so)
The answer to these two questions is purely academic, simply because the lag has been detected, suggesting that sensors placed on the rubber hose will not reflect the coolant temperature 'as it happens'.

[haydn callow]

I think the metal stub will always read HOTTER than actual coolant tempreture once up to tempreture. After all the coolant is exaxctly that...Coolant ..and it's job is to cool down the metal bits.....When my coolant is at 65C the metal bits are 75C

[widdowson2008]

I think the metal stub will always read HOTTER than actual coolant tempreture once up to tempreture. After all the coolant is exaxctly that...Coolant ..and it's job is to cool down the metal bits.....When my coolant is at 65C the metal bits are 75C

Good point
Got some new numbers from Jaylee today (head vs heater supply). Sent graph to Jamie to get his opinion. Waiting for his response before posting. Results are not exactly what I expected and need some explanation attaching to the graph. Got me scratching my head