Its the coolant that exceeds 100c - technically the water doesn't exceed 100c We don't use straight coolant for a reason either...the water is there too assist with keeping a thermal exchange relationship with the coolant, but they still maintain their own boiling points regardless of whether being mixed in %. 101 is above boiling point and is a guide that something is wrong whether the system can handle peaks up to 120c or not, as now your relying on the coolant only to absorb and dissipate the heat - the water wants to vaporise at 100c but is only held in by pressure......Ideally you should not exceed 99c for this reason unless your under extreme conditions It's really too hot...... I would be checking my coolant system with temps constantly above 100c Hope that explains the context better.......
Ummm anti-freeze/anti-boil may raise the boiling point of water a few degrees but what you guys are missing here is what happens to the boiling point of water under pressure hmmm? IIRC the system blowoff pressure is 13psi so why dont you go off and google what that means to the boiling point of water. Not to mention a token improvement from the anti-boil properties of coolant. Once armed with this knowledge, freely available on the internet, you might not be so paranoid about seeing water temps of 100C or higher. Go forth and research ladies!!!!! Its possible you may be surprised! E
Rated boiling point for a recommended mix glycol/water at 1bar is about 130*C, 110*C with no pressure. 90-100C is standard operating water temp for most cars when you take them to a track day. Outlet temperature isn't the only tell of system health, if the engine is taking in 20*C water and putting out 100*C then you're probably producing a lot of heat but you're also removing it very quickly, if your outlet is 100-110*C because you're taking in 90*C water then your system is struggling to keep up and probably not pulling much heat out of the engine. Edit: Oh, and don't forget mass flow/flux.
Tas is correct. the pressure of the coolant system raises the boiling point of the liquid. this is why steam shoots out when the cap is cracked and the pressure is released the drop in pressure reduces the boiling point instantly which vaporises the coolant creating a blast of steam. also rated boiling points of X deg @ 1 bar is most likely at 1 bar above atmospheric pressure which happens to be around 1 bar at sea level depending on the weather conditions at the time
Being a firey for many years... I know a little about water.....lol Water cannot go past 100c in a natural state - its impossible. (It can go higher in temp but only under pressure - this is agreed but you should still never get to this temperature and so yes ............I'm paranoid past 100c). The relevant point here is in regards to the latent heat of vaporisation of water itself and its purpose in coolant systems, not whether water can be held at higher temps under pressure in such a system: But you say................ There is virtually no difference in getting the temperature of water from 100c to 101c (using pressure as pointed out) but there is a huge difference between the extra energy required to get water from 27c to 28c or let's say 99c to 100c, based on the fact that the specific heat of water is 1 calorie/gram °C = 4.186 joule/gram °C but only up to 100c! - after that its almost negligable! Why........This is because the physical state bonds that hold water together have been completely broken and so no more energy can be absorbed by the water without resorting to pressure. The heat energy to break the bonds is 100c and so the energy absorption is considerably less once it's all past 100c. ( i.e. it's all just steam and vapour being held in by pressure after 100c regardless of whether its 100c or 120c!) Water has one of the best thermal latent heat absorption rates and that's why we don't just use coolant alone. Coolant has a lower specific heat value than water, so coolant compounds cannot thermally exchange heat better than water at temperatures up to 100c, thus the only purpose of coolant is to absorb spikes of temps up past 100c - when water can no longer absorb the heat itself without significant pressure. As stated earlier.... the engine can withstand spikes up to 120c (max temp danger level) but anything above 100c should still be considered as not normal as you no longer have the thermal energy buffer protection of water but only the coolant now at 30% of the thermal volume (on average) protecting the engine which actually causes heat soak or hot spots. If you use the guide ROB260 provided (for the mix specs of coolant figures) /or Fists rather accurate figures! you are no longer protected after 109c / 110c by coolant as there is no more absorption capability (of the mixtures ability to transfer thermal energy as a mass only), so technically speaking at 109c / 110c+ you have thermal hotspots developing in your engine starting. If your say going up a steep hill under labour or doing some high boost laps around Mt Panorama, it would be a concern being above 100c but not necessarily abnormal nor imply disaster, so your right in that 101c+ doesn?t mean disaster. But once your over 109c / 110c your in potential hot spot temps and past 120 is possible disaster Back to pressurised coolant systems: The fact the system has pressure indicates it is designed to handle temps consistently above 100c but these should only be thermal spikes and not considered as normal conditions based on the fact we largely use water as part of the mixture for its own unique latent heat properties. If your running above 100c constantly ..... you should consider running 100% coolant because the water is no longer useful in your coolant system! Personally I would be checking for a problem. As a guide everyone here is right but if we are going to be technical then: Optimally you should have between the thermostat temperature (76c) and ECU compensating temp (90c) This is the Nissan VG30DETT engineers specifications for an optimal temp at light to normal load for this Motor to prevent minimal heat sink into any parts. If your running between 90 c (cruise) and 99c (foot down) that's o.k. but the closer to 90c the better! Your engine should be labouring above 100c -109c ... this should not be normal ! A good temp for labouring is between 92-95c based on averages but 100c is the critical figure here - it means your system has now exhausted the thermal protection of water in energy terms Your engine should only be under temporary extreme conditions for figures above 109/C -110C! 110C - 120C is dangerously high and should ideally never be encountered Let the water do its job and only rely on the coolant for sudden thermal surges or spikes only - it is not normal operating conditions even if under pressure My car never gets to 100c at the sensors even on hot day under max load with Air Con on....otherwise I would be testing for a faulty system or racing at Mt Panorama .........I don't advise others to run that as normal temp either. The water variation temp should not be a great deal from the engine proper (say 2c-3c from block to block ends) Regards JC :zlove:
Just to clarify re: breaking of the bonds- water can't go past 100c in a natural state so to push water to 101c for the same amount of energy as 99c to 100c - your relying on your cap pressure which in turn reduces the thermal efficiency of the waters ability to transfer thermal energy to the coolant itself proportionate to the volume thermal efficiency of both. 100c is a critical temp, the next being 110c when the coolant can only dissipate heat on average to the block or to the water by using pressure. (Coolant has a much higher specific boiling point but it would wreck your engine at those temps and so you mix a % of coolant to a % of water to get the average thermal maximum temp of around 109c / 110C which is around 30-50% coolant depending on the product used. Less reliance on max spring cap pressure.....means less likely to potentially generate thermal hot spots/ heat soaking
Hee hee haa hee. Not like you tass to miss a detail like that. Whoops. My 2c. Kitty is NA manual, pod filter, Std fan, shroud (missing the bottom strip). Fully flushed system (thermostat out). New thermostat. techally 90+ (supercheap) Idling any period 73 degree (EcuTalk) general driving 75-85 mid summer, raises to 95-98 when climbing up the warrumbungle mountains, quickly dropping back to 85 on the downhill run. The grey car. NA auto, std airbox, std fan, broken shroud. no flush, existing therostat. coolant (unknown) Idling 85 degree, general driving 85-88 late summer raises to 95 -98 climbing driving, dropping back to 88-89. If the car is in fair mechanicl condition and the cooling system has had a full flush and service (replacing the thermostat) there should be minimal problems. Key would be plenumm pull and bypass the under plenumm hoses, and replace old coolant hoses.
OK . All of that theory and dazzling science is wonderful...in theory. And a lot of that dissertation might be very relevant in stationary water...but water travels mighty fast around and engine and trades heat and relative cool quite liberally. Now, explain to me why an circle track race car producing circa 800 Hp runs around flat out for at least 500 miles at circa 8500rpm in addition to qualifying and practice at coolant temperatures up around 130 degrees C and doesnt go bang.... hmmm? Hint.........radiator cap. E
I think your firefighting physics teacher was doing a bit of hand waving there, when you're spraying water onto a fire that is burning at hundreds of degrees then yes the water is going to vaporise basically instantly but heating water in a vessel is going to work a bit differently. Water absolutely can, and does, continue to absorb heat very well right up until it actually vaporises, the water in your electric jug regularly sees peak liquid water temperatures over 100*C as it requires time and nucleation points to actually boil. You'll notice that even after the jug switches off it continues to boil for a few seconds as there is extra energy stored in there above the temperature required to boil, so long as it stays liquid for whatever reason it continues to absorb energy at the same rate. I'm not aware of any car designed in the last 50 years that had an unpressurised coolant system, they don't just do it for fun, it actually works. If water didn't take in energy over 100*C there would be no benefit to the pressure.
You will overheat your engine if you use 100% concentrated coolant, it's the water that absorbs the heat from the engine. That is why you don't see water/coolant concentrations above 50/50.
Re boiling point. A standard TT radiator cap is 1.2 bar. The boiling point of water at 1.2 bar (32psi absolute pressure) is 123*C (http://www.engineeringtoolbox.com/boiling-point-water-d_926.html). The boiling point of a 50/50 mixture of ethylene-glycol and water is 130*C at 1.2 bar (https://durathermfluids.com/pdf/techpapers/pressure-boiling-point.pdf) The heat capacity of an ethyl-glycol/water mixture increases with water content, and decreases as the mixture approaches boiling point. A 50/50 mixture has nil capacity at boiling point, and roughly 6% reduced capacity at 86% of boiling point (http://www.engineeringtoolbox.com/ethylene-glycol-d_146.html) compared to capacity at "normal" 80*C operating temperature. This reduction in capacity must be offset by an increase in flow. Considering our theoretical boiling point 130*C I can't see any reason to believe that coolant stops absorbing heat at 100*C.
I've always found it fascinating that the zed is the only car I've owned which wanted to run at 83 as standard operating temp. All my other cars run 90-95 standard, even ones with a hell of a lot more engine than the zed. So much to the point that when I went thermofan I increased the cut in and cut out temps so that I'd maintain 90 to see the results. Power was still good, economy was slightly better, no harm no foul. She got to about 105 on the track days, again, no problems. 2nd fascination was back in the day that when I did this, so many shouted I was overheating, and my car was a timebomb. I still maintain that 83 is too chilly.
Here you go, so long as there's the pressure to suppress boiling water keeps absorbing heat. (it actually gets better as it heats up) http://www.engineeringtoolbox.com/water-properties-d_1258.html Interestingly the pressure has a slight negative effect on heat capacity.
It doesn't get better -bigger number means more heat required to effect a change in the water molecule
What effect does running at 90 have on the fuel and timing maps? It's hot enough for the ECU to notice and start to push the idle higher -if it retards timing as well... My Golf runs at 90 but that's a diesel. Don't forget too you have different expansion rates between the head and the block which I assume have some effect on optimum running temp
Not sure whether you're think more energy per degree is a bad thing or if you didn't notice temps listed are in Farrenheit so take one of these replies. More BTUs per degree means more energy is being removed, that's a good thing. It does mean that at the radiator you have slightly diminishing returns but that's probably covered by the fact that higher radiator temps (or larger water-air differences) improve heat transfer rate. There is a trough at about 100*F (~40*C) but after that it gets better so at running temps heat capacity increases as temperature does. It's a small difference though, you'd struggle to measure the 0.5% improvement.
From memory, the temp correction tables on stock ecu are flatlined from about 75degs right through to about 100.
Hmm I read their article http://www.engineeringtoolbox.com/specific-heat-capacity-d_339.html and understood it to mean that more BTUs per degree meant that the capacity for the coolant to absorb heat was decreasing. If what you're suggesting is correct then you have more heat transfer as the water or coolant approaches boiling point, which I don't think is right.
I couldnt agree more TBH. Ive often wondered myself why the VG was specified to run at lower outlet temps than most engines. Im wondering if it was a way to increase water flow thru the system at lower temps to help reduce any potential "hotspots" in the cooling system that require additional flow. The efficiency % of the radiator (heat transfer rate of the metal) and its surface area and ambient temp (combined result in an efficiency in percentage) are fixed so the only way to increase heat loss is to increase heat transfer delta at the radiator. As the entire system heats up, but with more or less fixed water flow as the thermosts is well open, the heat transfer delta at the radiator increases so adding additional heat loss at the radiator = gives off more heat energy for the same water flow. Kind of self regulating. Reminds me in a way of very early watercooled MX bikes that employed purely a thermosyphon circulation and no thermostat. Anyway. E
Well the ideal temperature (within a window) for an engine to run at will generally be dictated by the materials used and their expansion at the "operating temperature" to give the tolerances that the engine was designed for. This really becomes moot when the engine is 25 years old worn past any exact temperature v tolerance debate. Also moot when you build an engine on after market parts. I'm fairly certain outside of competitive motorsport, engine builders aren't building tolerances based on a specific temperature. Combustion is more efficient in the 90 degree range and also running too cold will keep your oil too cold. You need it above 100 degrees to burn off any moisture that makes it's way into the oil. Remember, water is a significant by-product of the combustion process.
