Propylene Glycol vs. Ethylene Glycol/water 3

[curtis74]

I'm trying to do some math, but would settle for some real-world simplicity since engines don't run on math.

I'm trying to verify some empirical claims from a well-known coolant manufacturer that sells non-aqueous propylene glycol coolant. I'm thinking about using it in my own personal tow vehicle (a 99 E350 Powerstroke) but I'm a bit concerned.

Is the higher boiling point of greater benefit than the loss of the heat capacity associated with not having water mixed with it? I'm hoping to open a dialogue of the benefits/drawbacks based on safe engine alloy temperatures, engine oil temperatures, and hopefully emerge with a better understanding of whether or not I should use the stuff.

 

[IRstuff]

At 230°F, water's thermal conductivity is almost 4x that of 100% PG. So, yeah, if you were using 100% PG, you'd need the higher boiling point, because you wouldn't be able to get as much heat out. Which means that your engine interior would be running hotter. Conversely, with water, you wouldn't need the higher BP, since the engine would be running cooler, all else being the equal.

TTFN

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[curtis74]

So, is there a benefit, a drawback, or is it a wash?

Here is what I'm looking at:

Benefits: reduced corrosion from lack of water, reduced nucleate boiling, reduced (or eliminated) diesel-induced cavitation.

Drawbacks: potential for increasing internal engine temps (oil, iron, etc) to the point of damage or reduced fatigue life

 

[MikeHalloran]

The lower conductivity suggests that the thermal gradients will be greater than those the engine was engineered for, or more likely, evolved for.



Mike Halloran
Pembroke Pines, FL, USA

 

[IRstuff]

I don't know how you read any benefits into that. Unless your engine was specificallu designed to operate at higher temperatures, higher operating temperatures will be detrimental.

TTFN

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[curtis74]

I politely disagree. Higher engine temps can have big benefits - reduced friction, better MPG, greater thermal efficiency.

The traditional thinking is that engines overheat and get damaged at 240F, but we know that its the boiling that allows superheating of areas of an engine causing damage. If there is no boiling, what would be the drawbacks to the coolant being, say, 300F? As long as I don't cook the engine oil or tranny fluid, wouldn't that be just fine?

 

[patprimmer]

A coolant temp of 300F will actually allow a lot of oils to cook or at very least put a lot of extra load onto the oil cooling system.

When it runs out of piston to wall clearance and ring end gap that will certainly introduce enough friction to more than negate any TE gains.

If you are prepared to do enough trials to determine the optimum piston to wall and ring end gap to operate at 300F, they will be less suitable during warm up than current settings and when operating under the control of your current thermostat, unless you can get a say 270F thermostat.

Regards
Pat
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[BrianPetersen]

It depends on the choice of materials throughout the engine. Aluminum weakens at elevated temperatures. Seals will likely only take so much, too. Higher coolant temperatures would be expected to raise piston temperature - by how much, is anyone's guess. If the engine has an oil cooler whose temperature is regulated by the engine coolant (or no oil cooler), it could send oil temperature into an unsafe range. This could result in the viscosity being in an undesirable range. It might result in the oil partially breaking down, which is never good.

No doubt someone has tried it, and credible "actual field results" from someone independent of the manufacturer might be obtainable. I'd for sure be keeping an eye on the engine oil temperature if it's proposed to run the coolant temperature up that high, and maybe think about running an auxiliary oil-to-air supplementary oil cooler.

 

[patprimmer]

Also, what are you going to use for coolant hoses. I know with EG, 100% vs a recommendation of 30% can damage many OEM hoses and water pump seals and thermostats. PG being a larger heavier molecule should be a little less aggressive at lower temperatures, but the higher temperatures possible will also increase the potential to attack any elastomers or plastics in the system. Nylon radiator header tanks might also suffer. Nylon valve covers and timing chain tensioners if present might also suffer.

Regards
Pat
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[curtis74]

Most people who have tried PG have reported about a 10 degree increase in their overall coolant temps, but what we don't know is how its measured or how accurate they are... nor can we know the weakest point of each individual cooling system to see where these numbers are coming from.

I used the 300 degree number as a rather high exaggeration on a what-if proposition.

My biggest concern is heavy towing. Normal driving, these Powerstrokes seem to be very temp-stable. I'm worried that (with the reduced heat capacity of a non-aqueous liquid) heat soak will become an issue; i.e. more heat going in than coming out. Towing 10k lbs uphill in the desert with the A/C blasting kinda thing. Right now that isn't an issue, but I'd hate for it to become one with PG.

I appreciate all the objective data. Thanks folks.

 

[IRstuff]

If it's hot desert, there's absolutely no reason to not use pure water. The main reason to use EG or PG is to keep the coolant from freezing. THAT's the primary rationale, and THAT's the reason you'd find 60/40 EG mixes, so that you can get to < -40°C operations.

TTFN

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[Tmoose]

Is that the stuff that claims it allows running zero pressure and thus is kinder to hoses, etc?
I think I stumbled on some info that the vapor pressure of PG was simply real low, and I was thinking the zero system pressure might be a result of that low VP, rather than a condition that is acceptable due to the high boiling point.

I'm not prepared to try it quite yet.

 

[Compositepro]

PG is also non-toxic. EG and PG are important not only as an antifreeze but for increasing the boiling point to prevent boil-over in hot weather.

Running 100% EG or PG is a bad idea. The heat transfer is not nearly as good as a 50-50 mix, so not only will the engine run hotter but also be less uniform in temperature. It is the hot spots that will increase in temperature the most.

 

[ivymike]

If you want to achieve lower friction, you don't have to get the engine parts extra hot to do it. Just use a lower viscosity oil.

With respect to thermal efficiency, I'm not sure you can count on a benefit.

A big drawback of running hotter will be reduced combustion seal life and head cracking. In diesel engine heads it seems pretty common that the head life is limited by low-cycle fatigue of the flame deck (perhaps on the inside by the coolant passages). The larger the magnitude of your thermal cycles, the shorter the life. The thermal cycles in question are the startup/shutdown variety, not usually the low-to-high load cycles in operation.

 

[drwebb]

I recall my grandfather had an antique bottle of methanol in his garage with label describing it's application as a freeze-point depressant for engine coolants. It should exceed the low temperature performance of glycol/water blends, and it could be produced from renewable resources. But of course its toxicity is now perceived as unduly dangerous, and it is not as popular as a coolant hop-up as PG or surfactant blends.

 

[patprimmer]

I think alcohol also lowers the boiling point as well as the freezing point whereas glycol lowers freezing while raising boiling points giving an all year round advantage.

Regards
Pat
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[rmw]

I work with a non-automotive industrial heat exchange process which is sold and guaranteed to -40F (-40C) and our standard coolant is 60/40 PG so I deal with it regularly.

Frankly (and it would beneifit us to have it) the boiling point elevation is worthless. Yes, it is a few degrees, but from where we start, it is worthless. What we use it for is the freeze protection.

That said, our customers won't freeze and burst their piping, but the viscosity/density relationships at the very low temperatures are such that the stuff can't be readily pummped with the pumps we have for normal temperatures. We have applications of the process where (plain) water is used, so I have to be able to calculate it both ways.

That said:

First, some respected Automotive Engineers with expertise vastly superior to mine have weighed in on the engine internal aspects of this (bad in my opinion) idea. I'll leave that to them.

Second, for my part, think about the heat transfer on the heat rejection end of the cycle. Unless you do something to accommodate the heat transfer penalty of that concentration of PG in your radiator, the same problem you have getting heat into your coolant will plague you in reverse when you need to get the heat out.

Third, if you realistically need the PG for freeze protection, do some calculations (Dow has technical data available on the net) regarding the flow characteristics of the stuff at low temperatures. I suspect - using some overstatement - that you could burn up an engine in very low temps before you got the fluid throughout your system warm enough to be able to have a complete flow loop unless you had some type of heat tracing system or radiator heater version of a block heater to keep the stuff warm enough to serve its function.

That is our experience. We require that our customers maintain the fluid somewhere well north of 0F in order to start the system up. Below that the stuff just won't flow easily enough to permit the pumps in the system to pump it around fast enough to do the heat transfer duty. I had to go to top Management at Dow to get the properties of 60/40 at -40F and assure them that I didn't intend to try to pump it at that temperature, just to be able to calculate to prove that I couldn't. It has the consistency of soft butter at that temp. It has the consistency of 90w gear lube oil at some of the temps that I do need to pump it.

Anecdotally, I had a personal friend who thought that if 50/50 EG was good, then 100/0 EG was better and that was what he ran in his vehicles. However we lived in an environment where our low temps weren't very low (the low record was +6F) and the highs weren't very high - 100F was a real scorcher, so he got away with it and... he was the type who knew everything and couldn't be confused by the facts so I didn't try.

I think that the best statement made in this thread above was the one that said if you intended to do some heavy hauling in desert environment temperatures, use pure water. From a heat transfer point of view, you can't get any better than that.

rmw

 

[Metalguy]

Big problem running "pure" water is corrosion. You need silicates, phosphates or something else for protection.

"You see, wire telegraph is like a very long cat. You pull his tail in New York and his head is meowing in Los Angeles. Do you understand this? Radio operates the same way: You send signals here, they receive them there. The only difference is there is no cat." A. Einstein

 

[rmw]

Isn't "pure water" an oxymoron?

rmw

 

[jmw]

Pure water is corrosive stuff.

JMW

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