Engine overheating

[woodenewe]

My 1999 – 996 C4 engine was replaced with a factory rebuilt unit about 3000 miles ago; the car now has 90K miles. The engine compartment fan usually comes on after turning the engine off after a moderate drive and runs or about 5 minutes. We just returned from a 2700 miles drive from Washington State to Las Vegas and back. As soon as we reached hot weather, the coolant temperature rose above the normal 180 mark on the gage and the warning light began flashing. We called a dealer in Reno and was advised to check the coolant level and add water if needed. There might have been air trapped in the system when the engine was replaced, and after adding about 20 ounces of distilled water, we drove on. The car was checked out at the Reno dealer and they could not find any problems, other than a few grasshoppers on the radiators.

The farther south we went, the hotter it got. Once the air temps went above 95 or so, the temp gage indication would start to rapidly climb above the next mark above 180 (220?), heading for the redline with the warning light flashing. Not wanting to have a boil-over, I turned off the AC and the temp dropped back to just below the 220 mark (warning light continued to flash). Driving in the late afternoon 112 degree ‘Vegas traffic with the AC off is not fun. We waited until evening to drive home when the temp had dropped (from a reported 117 where we were staying south of ‘Vegas) to 112. Once the outside temp went below 95 or so, we could run the AC without the engine temp climbing.

The Porsche dealer service consultants were mystified by the AC unit’s inability run above 95 and thought that the AC compressor (the only engine accessory moved over from the old engine) could be wearing out. After scanning the Renn files I did not find similar history (I did read one entry stating running AC in ‘Vegas was not a problem).

Sorry for the length of this message, but hopefully the details would be helpful. Two issues; the engine fan running after shutdown even in cool outside temperatures, and the inability to run the AC without danger of overheating when the outside temps go above 95. Would anyone have suggestions as to the cause and fix for this situation?

[Loren]

Dirty radiators or stuck thermostat are likely causes. I would start with them.

The only way you can really clean the radiator debris is to remove the front bumper and then pull the AC condensers out (slightly).

[SH-GT3]

Just to give you some idea of the kind of crap that accumulates, here are a few pictures from a 1999 Boxster. It did not appear the radiators had ever been cleaned out.

Here are a couple from my clean out event on my 04 C4S

After:

[beauar]

I just did this last week with a shop vac. I couldn't believe how many leaves were in there. Your pictures look exactly like mine did. I really don't notice a difference in running temps though

Just to give you some idea of the kind of crap that accumulates, here are a few pictures from a 1999 Boxster. It did not appear the radiators had ever been cleaned out.

Here are a couple from my clean out event on my 04 C4S

After:

[woodenewe]

Tghank you for the advice; where do I find the information to remove the front bumper?

[Loren]

Tghank you for the advice; where do I find the information to remove the front bumper?

How to Remove the Front Bumper

[1999Porsche911]

Verify that both raditor fans are on HIGH speed when AC is running. Not running on high speed will quickly raise the engine temps to those levels.

[wwest]

Verify that both raditor fans are on HIGH speed when AC is running. Not running on high speed will quickly raise the engine temps to those levels.

The description is exactly what I experienced years ago in AR in August in our 99 C2. I quickly discovered that one of the front radiator fans was not working and drove all the way home to Seattle with the A/C working and the engine NOT overheating.

The secret...

Turn the temperature control to MAXIMUM cooling "lo", recirculate mode, and then use the blower speed to control/regulate cabin temperature.

Bypassing the system's reheat/remix temperature regulation path results in lowering the heat loading of the radiator enough that I did not need to replace the fan until I got home.

[1999Porsche911]

Verify that both raditor fans are on HIGH speed when AC is running. Not running on high speed will quickly raise the engine temps to those levels.

The description is exactly what I experienced years ago in AR in August in our 99 C2. I quickly discovered that one of the front radiator fans was not working and drove all the way home to Seattle with the A/C working and the engine NOT overheating.

The secret...

Turn the temperature control to MAXIMUM cooling "lo", recirculate mode, and then use the blower speed to control/regulate cabin temperature.

Bypassing the system's reheat/remix temperature regulation path results in lowering the heat loading of the radiator enough that I did not need to replace the fan until I got home.

Actually, it was your high speed driving and therefore full air flow over the condensers that kept temps down. My fans are always completely off running on the highway and AC running while maintaining <200F engine temps. Just short trips, like from Chicago to Vegas, :notworthy:

[wwest]

Verify that both raditor fans are on HIGH speed when AC is running. Not running on high speed will quickly raise the engine temps to those levels.

The description is exactly what I experienced years ago in AR in August in our 99 C2. I quickly discovered that one of the front radiator fans was not working and drove all the way home to Seattle with the A/C working and the engine NOT overheating.

The secret...

Turn the temperature control to MAXIMUM cooling "lo", recirculate mode, and then use the blower speed to control/regulate cabin temperature.

Bypassing the system's reheat/remix temperature regulation path results in lowering the heat loading of the radiator enough that I did not need to replace the fan until I got home.

Actually, it was your high speed driving and therefore full air flow over the condensers that kept temps down. My fans are always completely off running on the highway and AC running while maintaining <200F engine temps. Just short trips, like from Chicago to Vegas, :notworthy:

No, road construction all across AR was what first brought the problem to my attention. But yes, throughout the remainder of the trip as long as I was able to maintain a decent roadspeed the problem didn't exhibit itself, or wouldn't have were I not using the "procedure".