engine temps in Southern Cal?

[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