engine temps in Southern Cal?

[CJ_Boxster]

Ok Jim,

Heres what i learned...

My radiator fans will not turn on at 96 celcius, They turn on at 103, and stay on until the coolant temp reaches 100. If it matters, the Ambeint outside Temp was at 61 degrees.

Why would the fans turn on so late? i checked them twice, during idle they will turn on only at 103 celcius until temp goes down to 100 celcius. Can the dealer program it to trigger at 96.75?

[MNBoxster]

Originally Posted by CJ_Boxster

Ok Jim,

Heres what i learned...

My radiator fans will not turn on at 96 celcius, They turn on at 103, and stay on until the coolant temp reaches 100. If it matters, the Ambeint outside Temp was at 61 degrees.

Why would the fans turn on so late? i checked them twice, during idle they will turn on only at 103 celcius until temp goes down to 100 celcius. Can the dealer program it to trigger at 96.75?

Hi,

If I had to guess, and this is essentially what I'm doing, I'd say that either your Coolant Temperature Sensor or your Cooling Fan relays are showing their age and not operating at 100%. The Software in the DME didn't suddenly start looking for 103°C instead of 96.75°C. Ambient Temp would have nothing to do with the Default Parameters, though it would with normal operating ones (1 component the DME uses).

We're only talking about 6°C here and that could well be within any innacuracies of the Temp Sender or the Gauge or Climate Display. It's not affecting anything. I doubt the MAPs are affected, nothings going to melt, you're not creating appreciably more emissions or suffering any reduced performance. I think you're just obsessing. But, if it bugs you that much, start by cleaning the radiators, replacing the Fan Relays, and changing the Coolant, and see what effect that has on the readings. Hope this helps...

Happy Motoring!... Jim'99

[David N.]

I actually had a problem with the engine compartment fan not coming on when expected, and indeed it seemed to be a worn out relay, so such things are certainly possible (this was on a 2000S with 48k miles).

But concerning the radiator fans...is there any mode in the AC diag that accurately tells you radiator fan speed? I tried the line item 'fan speed' but hasn't budged from 0 even tho I know the radiator fans are on.

Also, for what it's worth, my car in Los Angeles goes from 90-92 coolant temp at 80mph on the freeway to 100-103 idling in traffic. I need to clean the radiators still, but I'll bet it only buys you a few degrees at the most. Still, I'm getting over the fact that 103 isn't that hot, I probably wouldn't worry -too- much..


One more for Jim, where did you get that 60% engine-cooling-from-oil number? Are you referring to just Boxster engines?


-David
Ocean Blue 2000 S

[MNBoxster]

Originally Posted by David N.

I actually had a problem with the engine compartment fan not coming on when expected, and indeed it seemed to be a worn out relay, so such things are certainly possible (this was on a 2000S with 48k miles).

But concerning the radiator fans...is there any mode in the AC diag that accurately tells you radiator fan speed? I tried the line item 'fan speed' but hasn't budged from 0 even tho I know the radiator fans are on.

Also, for what it's worth, my car in Los Angeles goes from 90-92 coolant temp at 80mph on the freeway to 100-103 idling in traffic. I need to clean the radiators still, but I'll bet it only buys you a few degrees at the most. Still, I'm getting over the fact that 103 isn't that hot, I probably wouldn't worry -too- much..


One more for Jim, where did you get that 60% engine-cooling-from-oil number? Are you referring to just Boxster engines?


-David
Ocean Blue 2000 S

Hi,

No, I am not referring to Boxster engines, that's the Rule-of-Thumb for any auto engine. The fact that the Boxster has an Oil Cooler (which most cars do not), this figure may favor the Oil even more. That it is a mid-engine and thus not able to take as much advantage of direct air cooling as a front-engine car does, it may cancel out the Oil cooler to some degree. But, don't forget, you want to manage the heat, not eliminate it. Too cool is also not good because the engine cannot operate as efficiently. You want to live in a narrow band of say 100°C-117°C for maximum efficiency.

Think about it, aside from the heat from the combustion chamber, most of the heat occurs at the Crank and Big Ends. There are no water jackets here, which only leaves the Oil to carry off the heat.

One more consideration, there is a distinct difference between the temperature of the Coolant and the temperature of the engine. To put it another way, who cares if the Coolant is 1,000 degrees so long as it's carrying the heat away from the engine?

Also, remember that most of the combustion heat is carried away from the Combustion Chamber by the Spark Plugs. Look at a Spark Plug. Why is it designed like a Giant Heatsink? Because it carries most of the Combustion heat away and transfers it to the Head where the Coolant picks up this heat and releases it to Atmoshere.

103°C isn't really that hot in a system pressurized to 13PSI. At 13 PSI, water doesn't turn to steam until approx. 128°C (262.4° F) and this is really the key. If the Coolant were to boil, the water galleries in the Head, and the Water Jackets in the Block would not have liquid Coolant to carry away the heat - Very BAD. Also, the Coolant Pump naturally produces bubbles (gas), but the system pressure reduces the formation of these bubbles as well.

So far as cleaning the radiators, I think you are waaaay pesimistic about it's effects. The Heat transfer can incease (or conversely decrease) by as much as 40%, or as much as 10-15° depending upon how restricted they are. It is definitely worth it to insure that the Radiators are operating optimally...

Happy Motoring!... Jim'99

[CJ_Boxster]

Originally Posted by MNBoxster

Hi,

If I had to guess, and this is essentially what I'm doing, I'd say that either your Coolant Temperature Sensor or your Cooling Fan relays are showing their age and not operating at 100%. The Software in the DME didn't suddenly start looking for 103°C instead of 96.75°C. Ambient Temp would have nothing to do with the Default Parameters, though it would with normal operating ones (1 component the DME uses).

We're only talking about 6°C here and that could well be within any innacuracies of the Temp Sender or the Gauge or Climate Display. It's not affecting anything. I doubt the MAPs are affected, nothings going to melt, you're not creating appreciably more emissions or suffering any reduced performance. I think you're just obsessing. But, if it bugs you that much, start by cleaning the radiators, replacing the Fan Relays, and changing the Coolant, and see what effect that has on the readings. Hope this helps...

Happy Motoring!... Jim'99

Thanks Jim, Ill probably first replace the relays,... are those the thin tube looking thing with a wire coming out of it directly below the fans?

[MNBoxster]

Originally Posted by CJ_Boxster

Thanks Jim, Ill probably first replace the relays,... are those the thin tube looking thing with a wire coming out of it directly below the fans?

Hi,

No, those are the Ballast Resistors, which come to think of it may actually be the problem. They are PN# 996.616.101.00 - $25 (Sunset). These Ballast Resistors control the Fan Speed by varying the amount of current to the Fans. You can test them by connecting a test lead from an Ohm meter (or Multimeter with Ohm function - always a digital). It doesn't matter which lead goes where. But, you should see some resistance, most likely in the 0.75Ω-1.50Ω Range.
What you do not want to see is an 'Open Value' or Infinity (sometimes the display will show - ∞) If you see this, the Resistor is bad.

You also have 4 relays. 1 for each Fan and Fan Speed. They are located in the Relay Block which lives above and behind the left side Footwell Panel above the Fuse Box. The 4 relays are in the 2nd to bottom row and are the 4 immediately in-line of the right side. Their numbers are (in R-L reverse order):

• #22 - Right Engine Cooling Fan, High Speed
  
  #21 - Left Engine Cooling Fan, High Speed
  
  #20 - Right Engine Cooling Fan, Low Speed
  
  #19 - Left Engine Cooling Fan, Low Speed

These are the same part, so you can interchange them to see if they make a difference between the Fans. The PN# for these Relays is: 141.951.253.B - $10 (Sunset). Hope this helps...

Happy Motoring!... Jim'99

[David N.]

The coolant system is pressurized to 13 PSI? Isn't 1 atm ~15 PSI, where water boils at 100 degrees C? Seems like 13 would have it boil even lower.

[MNBoxster]

Originally Posted by David N.

The coolant system is pressurized to 13 PSI? Isn't 1 atm ~15 PSI, where water boils at 100 degrees C? Seems like 13 would have it boil even lower.

Hi,

Well, you're both right and wrong. 1 ATM is equal to 14.5 PSI (standard) at Sea Level, and pure water does indeed boil at 100°C. But we're not boiling water here, we're talking about a 50/50 mix of Anti-Freeze and Water which boils at 106°C at 1 ATM.

All pressure measurements are made using 1 ATM as the starting point (because you have no pressure until you exceed this), so technically, the system pressure is 13PSI above atmospheric pressure, or 27.5 PSI above a vacuum - 0PSI, but again, only at Sea Level.

The Cooling System uses pressure to further raise the boiling point of the Coolant. Just as the boiling temperature of water is higher in a pressure cooker, the boiling temperature of Coolant is higher if you pressurize the system. If the system is pressurized to 13PSI, this adds about another 25°C to the boiling point totalling 131°C or 267.8°F.

There is one more reason to pressurize the system. As the Coolant Pump Impeller turns, it creates bubbles by adding energy into the Coolant and causing dissolved gasses to precipitate. You do not want Air Pockets (bubbles) collecting around Water Jackets because little or no heat transfer will take place. By pressurizing the system, you decrease the ability of the dissolved gasses in the Coolant to form bubbles. Hope this helps...

Happy Motoring!... Jim'99