Climbing temp gauge

[flaps10]

For comparison, I recently replaced my water pump and all the rear hoses.

This past weekend I had to drive a 280 mile road trip (one way) to visit my dad. The outside air temperature went from low 90's at the start of my trip up to 102 degress. It bounced from 100-102 for over 100 miles on my outbound leg.

In heavy stop and go traffic (right where I expect the boxster to start hemorrhaging coolant) the needle would climb to the edge of the "0" in 180. Once moving however it would go down a needle width or two.

On the open road I tested out the theory of spinning the engine faster for improved coolant flow. Quite repeatedly, I was able to lower the temp to the right edge of the "8" by running 6th gear. If I down shifted and ran it that way the temp would increase (around the middle of the "0"). Rinse, repeat, I did it several times.

That was not the expected outcome - for me anyway. I faced similar temperatures on the way home and the car behaved perfectly for the entire road trip (another thing I'm not used to).

More surprisingly, I've found that I can run the A/C and it will run cooler even stuck in traffic (right between the "8" and "0"). Again, not expected by me since the condensers for the A/C are in front of the radiators and therefore add to the heat problem - not to mention requiring more effort from the engine to run the compressor.

Also, (and you'll want to verify this on your own) the way I learned it was that increasing the ratio of coolant/water is the wrong direction. Coolant is good at not freezing, but it's not awesome at carrying heat away. That's done by the water.

[911monty]

Are we taking into account the fact that the oil cooler is dumping BTUs into the water system?
I ask this because Last year I installed new WP, LT stat new hoses AND the larger S oil cooler on my 2.5 base. At the same time I removed both radiators and had boiled out and flushed. Now I have been watching the temp display on the AC panel religiously.
As Rick3000 says below 75 deg ambient the temp gauge at cruise speeds is at the 180 hash mark. Once temps move up the temp also increases. When I get into the hilly twisties the temps rapidly climb and will get to the right 0 edge, approx. 213 deg.
I think the additional BTUs (and ESPECIALLY the larger S cooler) due to work load rapidly heat the water the radiators are trying to get rid of. The LT stat is wide open with full flow to the rads. At this point if the radiators are not 100% you are fighting a losing battle.
My theory is this, it is only a theory. Increasing RPM on say the freeway only increases the BTUs from the coolant and the engine oil. I found that running in 6th with the resultant decrease lowers BTU output and the engine cools.
I also think that part of what stop and go does is lessens the air flow across the sump. If you think about the 100 deg differential between the 200 deg oil in the sump and 100 deg air, a considerable amount of BTUs are being swept away. I think a finned sump cover would be awesome.
I also have concerns about an engine with a LT stat, and S cooler in the winter. This may be due to my old school thinking but If oil in sump never gets above 180 how does it boil off the contaminates? Water boils off at 212 deg. Now at 6"WC vac (sump pressure) water boils at approx 195 deg. Is this why our cars have a 195 deg stat stock?

edit: Randall could your increasing temps be due to the increased humidity you guys have this time of year? Humid air has less effective heat adsorption?

[JFP in PA]

Originally Posted by 911monty

I also have concerns about an engine with a LT stat, and S cooler in the winter. This may be due to my old school thinking but If oil in sump never gets above 180 how does it boil off the contaminates? Water boils off at 212 deg. Now at 6"WC vac (sump pressure) water boils at approx 195 deg. Is this why our cars have a 195 deg stat stock?

You are overlooking the fact that your oil is always hotter than your coolant, otherwise an oil to coolant cooler would not work. Even in the dead of winter, your oil is hotter than 200F, even with a low temp stat and the larger oil cooler. We have customers running low temp stats and using the cars in zero and sub zero F environs; UOA's show no adverse levels of water our fuel contamination whatsoever.

[911monty]

Originally Posted by JFP in PA

You are overlooking the fact that your oil is always hotter than your coolant, otherwise an oil to coolant cooler would not work. Even in the dead of winter, your oil is hotter than 200F, even with a low temp stat and the larger oil cooler. We have customers running low temp stats and using the cars in zero and sub zero F environs; UOA's show no adverse levels of water our fuel contamination whatsoever.

This is good to hear! I upgraded the cooler on your statements that it's the best upgrade to do for your car! I agree with it's a must do upgrade since it can transfer much more heat than the smaller cooler which certainly helps the engine internals. I do believe that it is really an exchanger and can exchange heat in both directions. I would think the coolant heats faster and can help warm the oil on startup. The one piece of this puzzle that I'm unsure of is, does oil temp on the Durametric actually indicate oil temp. I know the level transmitter has an oil temp sensor, but there is conflicting info on if it is actually measured or it is only used to backup oil level.
What I have observed is my oil temp on the Durametric is usually 3-5 deg higher than the oil temp on the AC panel which is extrapolated from water temp. So I have been basing my observations on that. So what I see is water 180 then oil is 183 durametric and so on. i know you have a lot better data since the 996 engines actually read oil temp.

[JFP in PA]

Originally Posted by 911monty

This is good to hear! I upgraded the cooler on your statements that it's the best upgrade to do for your car! I agree with it's a must do upgrade since it can transfer much more heat than the smaller cooler which certainly helps the engine internals. I do believe that it is really an exchanger and can exchange heat in both directions. I would think the coolant heats faster and can help warm the oil on startup. The one piece of this puzzle that I'm unsure of is, does oil temp on the Durametric actually indicate oil temp. I know the level transmitter has an oil temp sensor, but there is conflicting info on if it is actually measured or it is only used to backup oil level.
What I have observed is my oil temp on the Durametric is usually 3-5 deg higher than the oil temp on the AC panel which is extrapolated from water temp. So I have been basing my observations on that. So what I see is water 180 then oil is 183 durametric and so on. i know you have a lot better data since the 996 engines actually read oil temp.

Durametric is reading the oil temperature using the sensor in the oil level unit, and it is accurate. The AC display, on the other hand, is not as accurate.

[911monty]

Originally Posted by JFP in PA

Durametric is reading the oil temperature using the sensor in the oil level unit, and it is accurate. The AC display, on the other hand, is not as accurate.

Thanks for the clarification!

[nieuwhzn]

Originally Posted by flaps10

More surprisingly, I've found that I can run the A/C and it will run cooler even stuck in traffic (right between the "8" and "0"). Again, not expected by me since the condensers for the A/C are in front of the radiators and therefore add to the heat problem - not to mention requiring more effort from the engine to run the compressor.

Running the AC forces the fan on at high speed, that's why the temperature goes down. All points to a broken load resistor preventing the fan to run at low speed.