Thread: What is wrong with using O.A.T. coolant?

Originally Posted by Traco

What I said was that if your cooling system is working effectively you shouldn't be running at, or getting near to, 100C+.

Anything that enhances the effectiveness of the system on a LR - and helps prevent it approaching boiling point - is a good thing in my book. Especially on a LR in fact where the dreaded porous block syndrome may result if the system is not up to the mark (V8s).

Correct me if I'm wrong, but my understanding is water on its own is generally regarded to be more effective at removing heat than water mixed with glycol. Water mixed with Redline Water Wetter is claimed to be even better than pure water alone because it breaks down the internal surface adhesion, but still provides protection against corrosion etc.

Traco,
You are confusing a couple of different issues, temperature and heat content. Generally speaking, the heat content capacity in a fluid is greater at greater temperature. However, two different fluids can have very different heat capacities at a given temperature.

I'm not sure if the heat capacity of water with glycol has greater heat capacity at a given temperature than water alone but it raises the boiling point of water to allow the coolant mixture to increase its heat content capacity. Water's ability as a coolant only works if it isn't boiling, which normally occurs at 100deg C at 1 atmosphere pressure. The pressurised system and the coolant added to the water raise the boiling point, increasing its ability to take away excess engine heat without boiling. I'm not sure what the designed operating temperature of the engine is but I would guess that at its peak operating temperature range it would be above 100deg C.

Mal

The specific heat of water is 4.2 kJ (approx) per kg per degree C temp difference. Adding glycol lowers this figure but raises the boiling point at a given pressure. A glycol/water mix will contain more heat at its boiling point, which being higher that water alone will have a bigger risk of block cracking. That is why I won't run large percentage glycol mixes, it will run hotter. By the time its boiling you are at risk.

so BU(just to get this clear in my head,,)
a lower concentrate will boil at a lower temp but not (do as much?)damage (to) the engine?

I suppose that begs the question, at what temp does damage occur?


The main problem with the D2 V8 is its operating temp,, its sooooo close to boiling anyway,,

Originally Posted by bee utey

The specific heat of water is 4.2 kJ (approx) per kg per degree C temp difference. Adding glycol lowers this figure but raises the boiling point at a given pressure. A glycol/water mix will contain more heat at its boiling point, which being higher that water alone will have a bigger risk of block cracking. That is why I won't run large percentage glycol mixes, it will run hotter. By the time its boiling you are at risk.

Correct, I use 25 to 30% concentration. Any higher and you are throwing $$ away.

And DON'T use OAT.





JC

Originally Posted by Pedro_The_Swift

so BU(just to get this clear in my head,,)
a lower concentrate will boil at a lower temp but not (do as much?)damage (to) the engine?

I suppose that begs the question, at what temp does damage occur?


The main problem with the D2 V8 is its operating temp,, its sooooo close to boiling anyway,,

If you choose to operate right up to the boiling point but not beyond, then the risk is higher with glycol mix.

It's a curse operating so close to the danger zone. Not saying that having any specific engine operate at boiling point will kill it, but boiling it dry certainly will. The thing is fatigue cracking is statistical, some will fail, some won't. Over 10 000 engines the effect becomes clear. Adding stress/temperature increases the odds of failure noticeably. Let's face it, top hatting a 3.9/4.6 is the only method available to reduce failure to a practical level. Personally unless its a life-or-death situation, stopping before overheating is best.

I knew an old bloke with a P76, he used to swear by 50% glycol, he said he could safely operate it in the red zone that way. Sadly for him it dropped a liner, which is relatively rare on one of those. So after re-blocking the engine, he still trotted out this mantra until I pointed out how much it had cost him. So thanks but not for me.

Originally Posted by justinc

Correct, I use 25 to 30% concentration. Any higher and you are throwing $$ away.

And DON'T use OAT.





JC

From this link:

Ethylene Glycol Heat-Transfer Fluid

a 25% glycol solution at 93C will have 95.3% of the specific heat of water alone. Puts a number on it anyway.

Like you mentioned, clean water is best, but only if you are monitoring and maintaining it. Most people think red rusty water is sufficient from what I have seen over the years so I'll keep filling there systems with Glycol based coolant and ensuring the rest of the system is in good working order. It was interesting to see the chart showing flow requirements, a good perspective.

JC

Originally Posted by Pedro_The_Swift

so BU(just to get this clear in my head,,)
a lower concentrate will boil at a lower temp but not (do as much?)damage (to) the engine?

I suppose that begs the question, at what temp does damage occur?


The main problem with the D2 V8 is its operating temp,, its sooooo close to boiling anyway,,

Pedro - I agree. I have done the fan hub, full flush, new thermostat and hoses and mine is happy again around 94-96 cruising along, but at lights will go to 99 and if going into a building car park after stop start at lights will go to 102 degrees sometimes, 100 at other times. They just run hot and thats with the Red conditioner in it.

Cheers