Issues using "cooler" thermo fan switch?
06-19-2006, 01:25 PM
#31
Nordschleife Master
Originally Posted by Mark944na86
Perhaps if you could explain why having the thermo fan switch cool the radiator down a bit more is going to be different from driving down the highway on a cool day, I'd understand your point a bit more clearly.
I expect that wearing out the fan and using a bit of extra gas to do it doesn't have much traction with most of this crowd.
On the using gas issue, those of us who live in variable climates and track gas mileage will report that summer mileage is much better than winter mileage. This goes beyond not running the heater and warm-up times to that the engine is more efficient when running hotter. I can verify this personally having run the experiment while in engineering school where we varied the operating temperature of an engine while measuring the BSFC (brake-specific fuel economy): you get more power from the gas when running the engine hotter. This is to a point , of course, but that point is beyond ~220F.
06-19-2006, 01:26 PM
#32
Rennlist Member
AR10 is right. If you study thermodynamics, a hotter engine is more efficient than a cooler one. However thermodynamic efficiency is not the concern here. Getting your engine to operate at the designed temperature is.
Just because humans are uncomfortable at 83C doesn't mean your engine is uncomfortable. The engine was designed to run at this temperature for various reasons, including bearing clearances. So if you put in a lower temp thermostat, it may psychologically make you feel better by seeing the gauge lower, but the engine may not be as happy. It's possible you could be causing more wear on it.
Putting in a lower temp thermo switch will just wear out your fan motors. I do mostly highway driving and they never come on. I could probably count on my hand the number of times they came on in the last two years.
____________________________________
1986 944 NA - Guards Red - 90k miles
1983 944 NA - Platinum metallic - beginning a new life
1985.1 944 NA - Guards Red - donor car
1984 911 Carrera Coupe - Guards Red (gone, but not forgotten)
"If you're not living on the edge, you're not living"
Just because humans are uncomfortable at 83C doesn't mean your engine is uncomfortable. The engine was designed to run at this temperature for various reasons, including bearing clearances. So if you put in a lower temp thermostat, it may psychologically make you feel better by seeing the gauge lower, but the engine may not be as happy. It's possible you could be causing more wear on it.
Putting in a lower temp thermo switch will just wear out your fan motors. I do mostly highway driving and they never come on. I could probably count on my hand the number of times they came on in the last two years.
____________________________________
1986 944 NA - Guards Red - 90k miles
1983 944 NA - Platinum metallic - beginning a new life
1985.1 944 NA - Guards Red - donor car
1984 911 Carrera Coupe - Guards Red (gone, but not forgotten)
"If you're not living on the edge, you're not living"
06-19-2006, 01:39 PM
#33
Rennlist Member
I have to disagree with you guys, the fans as previously mentioned will only run during stop and go traffic. While you are moving the fans are not running, also the low temp. thermostat is sold by Porsche so I think if they thought that it would do harm than they would not make it available. The lower temp is not significant enough to make engine wear an issue and another thing is that the coolant temp. is not always directly connected to oil temps. There is my speel and disagree as you may. The fact is I run both and my car runs perfectly fine and is in the normal temperature range.
06-20-2006, 05:29 PM
#34
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Originally Posted by black944 turbo
I have to disagree with you guys, the fans as previously mentioned will only run during stop and go traffic. While you are moving the fans are not running, also the low temp. thermostat is sold by Porsche so I think if they thought that it would do harm than they would not make it available. The lower temp is not significant enough to make engine wear an issue and another thing is that the coolant temp. is not always directly connected to oil temps. There is my speel and disagree as you may. The fact is I run both and my car runs perfectly fine and is in the normal temperature range.
going up the hill from work or driving flat/level/60 mph, the fans are on by the middle mark and stay on unless i'm on a long downhill stretch.
87951
06-20-2006, 07:14 PM
#35
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You guys, you are all talking about COOLANT tempreatures.....no-one mentioned OIL tempreatures....THAT's where it counts the most (remember those air cooled 911's?) oil temp matters most for the 'efficient' range......
During winter months (low 50'sF during the night), my coolant is runing at 75-80C all the time at highway speeds when fully warm, i rarely heard the high spped fans kick in, even in traffic. The oil temp. was different, it was always in the 175-190 range, maybe 200F in traffic. Manual called for normal operating temp for oil is 80C (176F), which is well in the 'normal' range, and that is with both lower thermostat and switch.
In summer (now), coolant reads 85C or so, but oil temps are in the 190-200F during highway, and reach 220 in traffic. Even then, the coolant reads 85-90C.....which matters the most? oil or water emps?
My NA overheated (went midway in the red zone) and the coolant was not boiling under the pressurized system, release the pressure, and watch it overflow like mad.
During winter months (low 50'sF during the night), my coolant is runing at 75-80C all the time at highway speeds when fully warm, i rarely heard the high spped fans kick in, even in traffic. The oil temp. was different, it was always in the 175-190 range, maybe 200F in traffic. Manual called for normal operating temp for oil is 80C (176F), which is well in the 'normal' range, and that is with both lower thermostat and switch.
In summer (now), coolant reads 85C or so, but oil temps are in the 190-200F during highway, and reach 220 in traffic. Even then, the coolant reads 85-90C.....which matters the most? oil or water emps?
Originally Posted by AR10
I repeat; if the coolant is not boiling the engine is not overheating.
06-20-2006, 08:29 PM
#37
Nordschleife Master
Originally Posted by hosrom_951
You guys, you are all talking about COOLANT tempreatures.....no-one mentioned OIL tempreatures....THAT's where it counts the most (remember those air cooled 911's?) oil temp matters most for the 'efficient' range......
Oil temp is what matters for crank and rod wear protection.
This is why engine management systems look at water temps and racers want oil temps.
06-20-2006, 09:30 PM
#38
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Originally Posted by AR10
I repeat; if the coolant is not boiling the engine is not overheating.
I'm not trying to be rude or pick a fight or anything, but I don't understand your reasoning....
06-20-2006, 11:13 PM
#39
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Well, I`m just a cranky old fart who`s been around these things for a lifetime
and I know that the manufacturers require antifreeze and pressure caps so they can run more efficient temps. I also own an aircooled car (Corvair) and the cyl. temps. typically run around 240F Same thing for my aircooled 1946 airplane.
and I know that the manufacturers require antifreeze and pressure caps so they can run more efficient temps. I also own an aircooled car (Corvair) and the cyl. temps. typically run around 240F Same thing for my aircooled 1946 airplane.
06-21-2006, 09:50 AM
#42
Race Director
Originally Posted by AR10
Temp. guages are not very accurate. In your case it was telling you the temp.
was at the upper limit, but if it was not boiling it was still safe.
was at the upper limit, but if it was not boiling it was still safe.
I lost my H2O pump at Watkins Glen on the track. The temp guage went into the red - car overheated - coolant spewed out of the coolant over-flow valve.
I managed to drive it home (cool October day), but it did overheat once more on the ride home.
About a year later, my head developed a crack.
My car had about 130k miles on it at the time, and I bought it used, so I don't know if any other over-heating issues occurred.
For me, the bottom line is: I don't want to overheat my motor again. It may be the most powerful if you get it up to those temperatures, but it's also the most expensive way to run a motor, since you'll likely cause damage.
-Z.
PS: Lots of racing orgs require cars to run with straight water instead of coolant on the racetrack. Why? water evaporates - coolant turns into a slippery substance on the track.