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Auto cooling systems

Auto cooling systems

Auto cooling systems

Are today's auto cooling systems able to function with straight water as coolant under all conditions including full load at full output? Or are they designed so as to require chemical additives to prevent boil over?
I'm hoping to hear from an auto engineer thats intimately familiar regarding this. I have heard opinions on this subject but am needing factual data. Thank You in advance!

RE: Auto cooling systems

In terms of cooling capacity in the short term? Sure. In terms of corrosion resistance or water pump seal durability? Straight water is not a good idea. If "all conditions" includes engine not running in foreseeable below-freezing temperatures, obviously not.

What are you attempting to do?

My hobby/passion is motorcycle roadracing. It is a technical requirement in the rulebook that glycol coolants are not permissible (because they're really slippery if and when they escape the bike and get out on the track surface - and yes, I fully realise that oil is also slippery when it gets out, but the presence of oil inside an engine is unavoidable, whereas the presence of glycol is avoidable by using straight water instead). Straight water plus an anti-corrosion and lubricity additive (e.g. Motul MoCool) is standard practice. No issue with it.

RE: Auto cooling systems

Pure water has greater heat capacity and cools better than the coolant mixes. Supposedly "water wetter" in small concentration is even better. All the road racing organizations require pure water, I've never heard of that being a problem. Of course, there will be corrosion issues with 100% water. I typically run 25% coolant in my motorcycles at that gives adequate corrosion protection and I have no concern about low temperatures. It doesn't get very cold here and I don't ride below about 50F.


The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

RE: Auto cooling systems

Thank You. This pertains to current production cars. Not trying to "do" anything other than to understand if the systems are sized with enough capacity to permit straight water to provide adequate heat transfer. Or is coolant needed to raise boiling point.

RE: Auto cooling systems

You don't need to run anti-freeze but you do need the corrosion inhibitors in anti-freeze. These are available to be purchased separately as concentrates and get blended with water. Caterpillar sells them as SCA or ELI depending on whether you want to go with a conventional or organic acid technology route. Penool 2000 or 3000, Nalcool 2000 or 3000 are comparable products. Chevron XLI is another.

On the industrial side, I have seen a few engines that require glycol, Cat C32. I guess it prevents cavitation in the water pump. I also see engines that forbid glycol in the aftercooling circuit due to the capacity reduction, Cat 3500 tier 3.

RE: Auto cooling systems

The pressure cap on the radiator becomes more important. But there is no reduction in cooling capacity due to using pure water.

RE: Auto cooling systems

I have to point out the specifics of my question.
1. No part of my question involves corrosion and the side effects of using plain water.
2. No part of my question concerns freeze protection.

Yes, the pressure cap does raise the boiling point. Good point.
BUT are the cooling systems currently installed on current model cars capable of cooling the engine at full throttle- full load conditions with plain water in the system? Or are the systems designed marginally (say on a pickup truck towing AT Capacity) that without coolant to raise the boiling point, the water will boil, lift the cap, and be lost (failure of cooling system IE "overheat" condition)?

I realize this is a very pointed and specific question,and because of that, I was hoping to hear from an automotive engineer directly involved in this area of vehicle design. However, appreciate all comments.

RE: Auto cooling systems

Modern cooling systems are pressurised and thus boiling over will occur at a somewhat higher temperature. The boiling temperature however changes only say 5 degrees C maximum - and thus it will not change the difference between the coolant temperature at the inlet of the radiator and the ambient air that much. The reason for pressurising is to prevent leakage and the need for frequent top up, not increasing cooling capacity. The latter is no doubt a useful feature, but not specifically designed in.

Coolant design for ordinary vehicles can be quite complex. Not only must the system be able to cool the engine sufficiently under full power, but it must be able to do so at nearly any speed - and thus over a gigantic range of airflow. Thus, modern systems can have complicated ventilators mounted on the radiator, that can be driven at high or low speed, together or just one etc. Driving in slow traffic uphill in warm weather usually will pose more problems then driving on the highway at decent speeds....

All that can be achieved with water - with a few drawbacks. Water will freeze at relatively high temperature and it will promote corrosion. Therefore antifreeze is used, together with a suitable anti-corrosion additive. Apart from that the water quality itself is important: hardness, chlorides and other electrolytes need to be kept below certain limits, and likewise pH.

For racing purposes some of these requirements may be overruled for safety reasons - thus the ban for the use of glycol because it can be slippery when spilled and thus be dangerous to competitors. From the engine designers view however a fully formulated coolant will be the preferred choice.

RE: Auto cooling systems

A 50% solution of ethylene glycol and water has a boiling temperature of 107 C at atmospheric pressure (versus 100 C for straight water).

A radiator cap with a release pressure of 1 bar (most of them are +/- that range) on top of atmospheric pressure of approximately 1 bar thus gives an absolute pressure of 2 bar, at which point the boiling temperature of straight water is about 120 C. Glycol will be higher but I don't have information on the simultaneous effects of both pressure and glycol concentration.

In other words, in terms of resisting boil-over, having a functioning radiator cap is a bigger factor than the use of glycol or not.

I know of no vehicle manufacturer that sets their thermostat opening temperature or their cooling-fan switch-on temperature much beyond 100 C. No one cuts it that close in terms of approaching the boiling temperature.

At least in the motorcycle world, for production bikes, which have very constrained radiator sizes and airflow, idling or puttering along in slow traffic in hot weather is usually more of a limiting case than high-power-output operation. Having said that, at Superbike levels of performance (and usage), they often have radiators bigger than standard because they have to cope with full power output in Qatar, or southern Spain, under racing conditions. Some manufacturers have tried using very high-pressure cooling systems in MotoGP in the interest of being able to reduce the amount of airflow through the radiator for aerodynamic reasons.

Cars and trucks these days have huge radiators. There's lots of headroom to accommodate sitting in traffic in hot weather with the air conditioning on full blast ... or for having off-spec coolant mixtures (i.e. water). It's rare to see someone pulled over at the side of the road with the hood up and steam coming out - nothing like how it was 40 or 50 years ago.

RE: Auto cooling systems

Higher boiling point has nothing to do with cooling capacity. It does however reduce the possibility of localised boiling or cavitation at hot-spots in the water jacket and at high velocity locations. Either event can be catastrophic because reduced heat transfer at that location is the start of a death spiral.

je suis charlie

RE: Auto cooling systems

Straight water is better for "cooling capacity". It has about double the specific heat capacity of glycol, and a lower viscosity, so it's easier to pump.

RE: Auto cooling systems

Gruntguru - A question on your statement of a 'higher boiling point has nothing to do with cooling capacity'. I'm not sure I fully agree with that. My logic/thought experiment is provided below. Would you mind pointing out where you disagree or offering clarity?

A radiator/fan is designed to remove heat from the working fluid (we'll assume that the coolant needs to stay in liquid form) to the ambient air. Fix the ambient air variables (temperature, speed, etc.) then increasing the boiling point of the working fluid allows for a greater inlet temperature and more heat exchange. Am I correct on this or do I need to hit the books again?

Practically I agree with your assessment. In a normal vehicle if you're relying on the minor increase in boiling temperature to up the cooling capacity of the radiator then you've already built up steam-coolant pockets in the motor. In non-normal (Brian brought up high-presssure cooling in superbikes) vehicles the pressure difference would allow for greater operating temperature in the radiator.

RE: Auto cooling systems

The temperature of the cooling medium in the engine (and at the radiator inlet) is an engine design parameter. It would be unusual to change this temperature and compromise the engine design for the sake of increased heat rejection from the radiator. The engine design temperature is usually lower than the boiling point of the coolant.

je suis charlie

RE: Auto cooling systems

For industrial engines the use of a water - glycol mix results in two problems: the reduced heat capacity vs 'straight' water means that the cooling devices (radiator etc) are some 30% larger. Then glycol is not good for the environment.

For continuous running, base load sets, the anti freeze properties of glycol are n
Rarely used. We had a heater and pump to keep the system warm when stopped.

We did some generation projects with inhibited water as the coolant. We had a low temperature operated dump valve to put the coolant water down the foul drain in the unlikely event of freezing conditions and no heater. Remember on a large plant, it can take hours for the set to cool to ambient temperature.

RE: Auto cooling systems

Hoxton, it is amazing how cold water can get without freezing if it is circulated. I have seen systems get away with pumping slush.

Rogue, suppressing localized boiling is the challenge. After all in terms of thermodynamics the cooling system is more efficient when hotter (bigger delta T helps heat transfer), but engines have limits.

One issue with using straight water with not even adding corrosion inhibitors is that water quality can very and initial scale formation and corrosion can happen very quickly. If you use very clean water to prevent scaling you are likely to aggravate corrosion issues.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

RE: Auto cooling systems

See the "Glycol Or Water - Which Is The Better Coolant?" article from Hot Rod magazine which walks through the specific heat capacities and concludes "A large-tube aluminum radiator filled with pure water and using at least a 20-psi cap is by far the best heat-transfer setup, provided the vehicle is not subject to freezing conditions. Be sure to add a corrosion inhibitor when running pure water."

RE: Auto cooling systems

California West coast here, we don't run glycol in our marine engines. It's costly to buy and costly to dispose of in an environment that has zero risk of freezing. Caterpillar SCA and ELI (and equivalents) blended with utility water is our choice of coolant. Some systems such as the separately cooled aftercoolers forbid the use of glycol. Some engines such as the C32 require it (we operate none of these).

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