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

How hot do they get when been worked hard,like on a beach????
You may find that the high thermostat temp is for emmisions control whilst not working(no engine load).Is there plenty of reserve capacity in the cooling system to maintain the 102deg under extreme load???If so I wouldnt be too concerned.
Andrew

The primary purpose of the thermostat is to ensure the engine reaches its optimal operating temperature quickly and ensures the engine doesn't run cold. The engine generates excess heat. The ability to shed that heat depends on a whole lot of factors including the heat transfer coefficient between the block and the coolant, the heat transfer coefficient between the coolant and the radiator, the transfer coefficient between the radiator and the air, the heat capacity (specific heat) of the coolant, the mass flow rate of the coolant and air across the radiator and, most importantly, the difference between the temperature of the coolant and the air. Clearly with an outside air temperature of 5deg C its easier to shed the excess heat than for temperatures of say 45deg C. The thermostat is not a precision instrument and has a lag in its operation. The coolant temperature will vary across a range (which I don't know for the various engines).

Whilst the glycol may well decrease the specfic heat of water, it allows it to operate at a high enough temperature to operate in hot conditions to allow the radiator to shed the excess heat, without boiling, at which point the coolant becomes ineffective. This temperature is likely to be in excess of 100deg C.

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.

Too true. This is a common mistake most people make.
The problem is that although glycol can absorb the heat, it has an issue transferring it out. It's main primary function is as an antifreeze due to it's ability to store the heat.
The antiboil properties are really nothing more than a side effect of it's chemistry.
Unless your expecting a big freeze, anything more than 40% mix is not required and anything less than about 30% your corrosion protection will start to suffer.

With cooler thermostats, you could use a slightly cooler one but when it comes to late model V8 and TD5's there really isn't too many options available if any at all being a 3port unit.
With the older 3.9 and 4.6 with STD type thermostats, you need to be mindful of the enrichment switching temp. Running rich will obviously use more fuel but can also have detrimental effects on engine life, oil service intervals etc etc.

As Dave said, lazy mechanics, use of cheap quality aftermarket parts NOT meeting original design specs are usually causes for failures.
As for leaks and OAT being "thinner", if you have a leak, your gaskets are not doing what it's intended to do which is generally due to a lack of or just plain bad maintenance. I find it hard to believe this an excuse.



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Originally Posted by LandyAndy

How hot do they get when been worked hard,like on a beach????

Look at where mine peaked at 106 the other day up that sand track! Wasn't particularly hard going but with the A/C going and the EGT gauge sitting on 550-600, it didn't take very long to get there...



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They are talkin D2 V8s at the moment man.
Andrew

Yep D2 V8. Dont forget too that alloy should transfer out the heat quicker than cast (ie dissipate or radiate it out) and heat up quicker under load.

When I tow my 2 tonns in the middle of summer (last summer) it would not exceed 105 but I will see how it goes soon.

I only use genuine for the cooling system - genuine clutch fan hug, stat' and hoses.

Cheers

I just replaced my viscous hub,I can now hear the fan pulling air when the temp is over 90degC.
Andrew

Originally Posted by ozscott

Yep D2 V8. Dont forget too that alloy should transfer out the heat quicker than cast (ie dissipate or radiate it out) and heat up quicker under load.

When I tow my 2 tonns in the middle of summer (last summer) it would not exceed 105 but I will see how it goes soon.

I only use genuine for the cooling system - genuine clutch fan hug, stat' and hoses.

Cheers

Problem with aluminum is that it's less stable under high heat (slipped liners) and it's ability to transfer heat is only as good as the radiator that removes it.
There is a lot to be said for larger core and higher volume radiators but really not a lot of options.....


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