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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
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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