temperature gauge shows cold, normal, hot

aldo · Post by **aldo** » Sun Sep 07, 2008 2:16 pm

My temperature gauge is one of those replacements that shows cold, normal and hot. The few times that I've overheated the dexta, it went slightly into the hot range for a minute or two before I noticed. I thought that was really serious, but had no idea what the the temp was really.

So today when I had the gauge out to remove the tank, I thought I'd test it. I put the bulb in an old electric kettle and turned it on.
When the temp was about 60*C (just hot to touch), the gauge was in the lower part of the normal range. At about 80*C, (which I think is roughly when the the thermostat is fully open), the gauge was right in the middle of the normal range. When the water was at full boil (100*C), the gauge was exactly on the line between normal and hot.

So my temp gauge does gives a useful reading, and the few times I've overheated the dexta, the water was probably at only about 110*C (under pressure and with some antiboil in it). So I don't think that's very serious at all. Once I've fixed this coolant leak, and get some fresh antiboil in there, that will raise the boiling point to about 120*C, which would be off the gauge.

Mervyn Spencer · Post by **Mervyn Spencer** » Sun Sep 07, 2008 5:35 pm

Hello Aldo

Here in South Africa we use celcius to measure our temperature and 100*c is boiling point. I take it you may be getting a little confused with *f and *c.

If my memory serves me correctly the Dexta runs normally at about 85 - 90*c. I may be slightly out. 110 - 120* to me sounds a little hot, unless there is a difference between northern hemisphere and southern hemisphere temps.

Kind regards
Mervyn

Meanderer · Post by **Meanderer** » Mon Sep 08, 2008 1:37 am

G'day Mervyn,
Aldo is correct with his estimations and temp scales. He has a good grasp of "Pressure/Temp" relationship. (No comment though on the recommended operating temp though). I think we went through this not too long ago with you having an incorrect Radiator Cap? The difference is that in UK they seemed not to use Pressure Caps but export did? (Can't remember for sure).
Anyway, here in Australia we do use pressure caps on everything.
In the old days, (as some of us on here will remember), we used to have to use "Steam Tables" in booklet form, and Logarithem Tables and Slide Rules etc (Oh my god), to calculate all this stuff.

. Now you young "whiper snappers"

can just punch in "Steam Tables" into google and then use the on-line calculators available! Ha! Where's the fun in life gone to I ask?

Just note that when calculating, pressure has to be absolute pressure (i.e. add atmospheric pressure to gauge pressure.)
Radiator caps can be for different pressures. Lets say 10 psi. Then you have to input 15 psi (rounded off) so input 25 psi into the calculator and you'll get around 115 deg C as the temp. That temp is for pure water without the addition of Coolant Additive.

Cheers,
Rick

Mervyn Spencer · Post by **Mervyn Spencer** » Mon Sep 08, 2008 7:34 am

Hi Rick

Thanks for coming to our assistance. I must admit that when it comes to all that other physics with additives etc i'm lost.

With regards the whiper snappers if wasnt for you old timers who pioneered the computers where would we be?

Post by **Brian** » Mon Sep 08, 2008 7:39 am

The pentagan and Rhunes still works for me!

aldo · Post by **aldo** » Mon Sep 08, 2008 8:32 am

Mervyn Spencer wrote:Hello Aldo
If my memory serves me correctly the Dexta runs normally at about 85 - 90*c. I may be slightly out. 110 - 120* to me sounds a little hot, unless there is a difference between northern hemisphere and southern hemisphere temps.
Kind regards
Mervyn

Operating temp of 85-90*C sounds goods to me, full open thermostat (I think there usually marked 87*C, or thereabouts), which would put it right in the middle of the normal range of my temp gauge. 110-120*C is very hot, but the idea is that if your coolant can get to that temp without boiling it out, then you're safe on the rare occasion when you slightly overheat the engine - -no coolant loss, just stop working it and let it cool down.

Meanderer · Post by **Meanderer** » Mon Sep 08, 2008 12:45 pm

aldo wrote: when you slightly overheat the engine - -no coolant loss, just stop working it and let it cool down.

Just adding to that aldo, I recommend that "to cool the engine down" I'd leave it running without load at lower revs where the coolant can keep circulating through the entire engine to allow uniform cooling. If you turn the engine off when in the high temp range, the water in upper reaches of the engine will get trapped there and get hotter and your engine will suffer unnecessary stresses as it cools down unevenly.
Even a small air cooled engine as in a chainsaw or lawn mower should be allowed a couple of minutes to cool down under no-load idle speed to allow even cooling.

Mervyn Spencer · Post by **Mervyn Spencer** » Mon Sep 08, 2008 7:54 pm

Hello Brian

Excuse my ignorance, please explain what the pentagan and rhunes is all about

.Heard of the pentagon in the US. I've always been told we must learn from our elders.

King regards
Mervyn

Mike Kuscher · Post by **Mike Kuscher** » Mon Sep 08, 2008 8:34 pm

Mervyn,

'The Pentagon' are 'magic' markings on the ground and the 'Rhunes' are 'magic' stones, used by the Druids to 'forcast' many things of importance.
I'm afraid that's all they use in Norfolk

You think Brian 'logs on' with a PC or Laptop - He actually throws pebbles into the pool and 'looks through the ripples'.

Actually, I correct myself, it's 'Runes', because 'Rhunes' are the name given to the 24 characters of the 'Futhark' alphabet.

What's the Futhark alphabet? It's the alphabet the druids used.
Amazing what you can Google these days - Maybe it can tell me how to stop this rain

Mervyn Spencer · Post by **Mervyn Spencer** » Tue Sep 09, 2008 7:38 am

Hello Mike

Thank you for the explanation, and yes I did roll on the floor when I read what Brian and the folk in Norfolk use

With regards the rain, you are welcome to send it down to us, very bad time of the year with hot and dry weather together with raging fires all over the country. Our temp for Pietermaritburg today is predicted to reach 38*c.

Kind regards
Mervyn

aldo · Post by **aldo** » Tue Sep 09, 2008 11:22 am

Meanderer wrote: Just adding to that aldo, I recommend that "to cool the engine down" I'd leave it running without load at lower revs where the coolant can keep circulating through the entire engine to allow uniform cooling. If you turn the engine off when in the high temp range, the water in upper reaches of the engine will get trapped there and get hotter and your engine will suffer unnecessary stresses as it cools down unevenly.
Even a small air cooled engine as in a chainsaw or lawn mower should be allowed a couple of minutes to cool down under no-load idle speed to allow even cooling.

Agreed. And here's what I've done a hundred times with no adverse effect, on cars and tractors. If I've overheated it, and maybe lost some coolant, or otherwise no chance of cooling down just by idling it for a while, and can't turn it off for the reason you gave above, then I pour water all over the radiator, slow steady stream, while the engine is still running. Works wonders.