Thread: Coolant Temp and Low alarm

Originally Posted by martnH

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Is the coolant temp as useful? Like what is the consequences of coolant temp being 110 C?
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I find that knowing the coolant temp(or engine/head temp) is more important than low levels of coolant.
But also that a fast reacting gauge is important.
Press the loud pedal in hot conditions, and my coolant readout climbs quite fast in some situations(not all, but some).
I like that. As it approaches a set temp, I then react according to the conditions.
eg. if more uphill loading of the engine .. I'll slow right down, back off, or even pull over before damage may be done.

As for 110°C for prolonged periods .. no idea.
I just know that engine life won't be harmed with lower operating temps.
I used to run a 72°C thermostat in my RRC(carb). In really cold(sub zero) ambients I did struggle to provide heat for the interior tho .. and small made up blanket over the grille was an easy fix for that tho.
Ran it like that for about 13 or 15 years or so for most of it's life that I had it ('79 model bought in '88) .. of it's 600K klms I'd done a bit over 450 of those, in my time with it, and still on it's original engine(other than many seals changed) .. and still went OK(not ideal, just OK).

I'm sure I've read that under 15Psi of pressure, the cooling system boils at 120(-ish) or so degrees. Maybe just a bit more due to the addition of various doses of coolant additive too tho.

I like mine to tun in the low 80's, but don't mind it up in the mid to high 90's .. 100°C is my panic point tho! Not where I stop or keel over and call ofr assistance type panic .. more like I need to keep an eye on it, work out how much further I to go under those load conditions and get ready to react if it gets worse.

Other thing I've noted many times now with my A/C on heating up issue is: somewhere at about the mid 90°C mark .. the poor underpowered Tdi loses power (if that is even a possibility .. hasn't got any to lose in the first place! )
Compared to how responsive it feel at it's normal 80-ish operating range .. at 100 it feels much more 'gutless' even with turbo under pressure.

"I'm sure I've read that under 15Psi of pressure, the cooling system boils at 120(-ish) or so degrees. Maybe just a bit more due to the addition of various doses of coolant additive too tho."


Arthur, the following is from the White Trucks Sales Engineering handbook. Converted from Fahrenheit to Centigrade.

Boiling point of water at sea level using various radiator pressure caps.

0 psi 100
4 psi 106.7
7 psi 111.6
10 psi 115.6
15 psi 121.1

Knowing engine temperature is LESS important than knowing the cooling system is full and pressurised.

Nucleate boiling is far worse for the head / engine than running at an elevated temperature.

Nothing helps though if the system depressurises and the cooling media boils.

Originally Posted by Bigbjorn

"I'm sure I've read that under 15Psi of pressure, the cooling system boils at 120(-ish) or so degrees. Maybe just a bit more due to the addition of various doses of coolant additive too tho."


Arthur, the following is from the White Trucks Sales Engineering handbook. Converted from Fahrenheit to Centigrade.

Boiling point of water at sea level using various radiator pressure caps.

0 psi 100
4 psi 106.7
7 psi 111.6
10 psi 115.6
15 psi 121.1

Correct,, that is for straight water..
Now add Glycol

I just looked up the label on a bottle of Penrite OAT red coolant concentrate which is said to meet LR specifications and it says at 50% dilution it has a boiling point of 109 degrees Centigrade. Would that be at sea level?

Originally Posted by DiscoMick

I just looked up the label on a bottle of Penrite OAT red coolant concentrate which is said to meet LR specifications and it says at 50% dilution it has a boiling point of 109 degrees Centigrade. Would that be at sea level?

Yep STP (standard temp and pressure)
Add a pressurised cooling system and we increase the boiling point significantly.

The downside is that glycol reduces the heat transfer of water.

For those who want to DIY, when trying to solve the same problem on my Disco1 I found a cheap optical sensor that works well:
Optical Infrared Water Liquid Level Sensor Switch, High Sensitivity 1.8m cable | eBay

You need to built a simple circuit for it and mount the alarm somewhere sensible. ( Mine worked a treat, just couldn't see the Red light from the driving position.)

Originally Posted by LateAgain

You need to built a simple circuit for it and mount the alarm somewhere sensible. ( Mine worked a treat, just couldn't see the Red light from the driving position.)

My low coolant light is also difficult to see from the driving position. The previous owner had it installed.