Loss of performance after warming up?

[dtsol]

Hey All,

First-time Porsche owner, and am loving my 2005 Boxster S. As I'm getting used to the car, I'm starting to wish it accelerated faster, and am wondering whether my car is typical or if something needs to be addressed on it.

What I notice is that it is seems more responsive to the throttle when it is cold than after it has been up to temperature for a while--maybe after driving 15 minutes or more with the temp gauge at dead middle. I also notice a change in the engine sound once I've been driving at temperature for a while--it sounds less "tight," if that makes sense.

(I know my engine is a replacement engine based on the "AT" in the engine number: M96/26AT62665012, and I think this number means it's an '06 engine.)

Just wondering if anyone else has experienced this type of performance change once the car is up to temperature, and if so, how did you address it? Also wondering what would be the least complex way to improve acceleration.

Thanks!

Edited March 31, 2013 by dtsol

[logray]

Nice looking car.

I've experienced the same thing.

When the engine heats up the DME retards fuel and spark, and eventually when it gets too hot it will do enough of this to noticeably impact performance. You can see this on a dyno where on successive runs, by the 3rd, 4th, 5th runs when the engine heats up enough, the power will be down versus the runs when it was in the "goldi locks" zone earlier.

I've found the best way to combat this is to keep the car in that zone. A few inexpensive ways to ensure the car stays cool are to:

• Drive faster. Below about 50mph the radiators don't perform as well.
• Clean your radiators.
• Install a high speed fan switch. When it does start to heat up, don't wait for the DME to "realize" the oil is at 230F before switching on, and turn them on proactively.
• If you drive in hot climates use a heavier weight oil, say perhaps a 5w50.
• Install a 160 degree thermostat

Somewhat imprecisely I've noticed my car performs best when looking at the temp gauge: the needle is at the line below the 180 to roughly straight up and down (oil/coolant between 170-200). Above that HP starts to drop. Below that zone you should drive conservatively until it is warmed up to within that zone.

Of course, I am focusing on one aspect assuming there are no problems and all components are working as designed.

It is also possible there is an actual problem with your car and once the O2 sensors heat up and the DME is adjusting accordingly, the settings it is using would otherwise make a perfectly working car run sub-optimally.

A scan tool such as Durametric and a trained mechanic can interpret various readings and determine if there is a real problem that needs to be addressed.

Some simple tune up tips that keep the car running well.

• Use a bottle of fuel system cleaner once in a while.
• Use a quality fuel such as Chevron or Shell.
• Clean the throttle body periodically.
• Ensure the air filter is clean.
• Understand that working on the car without knowing what you're doing can introduce more problems.

Edited March 31, 2013 by logray

[dtsol]

Logray, thanks for all the great input. It's helpful to know that I'm not imagining things and that you've experienced the same thing I am. I'm taking the car into RMG for an oil change next week, so I'll have the shop check the radiators, air filter, and throttle body. From what I've been reading, maybe I should ask them to check the MAF and the air/oil separator as well?

[logray]

If the MAF is good then don't replace it. MAFs can be tested using a multimeter.

http://www.renntech.org/forums/topic/40768-possible-maf-issue-wiats-reading-high/?hl=%2Bmaf+%2Bvoltage+%2Bohm#entry216461

Generally speaking you also don't replace the AOS unless it is failing, or you track the car and are doing preventative maintenance. There is a definitive test you can perform to determine if the AOS is failing or failed, by testing crankcase pressure:

http://www.renntech.org/forums/tutorials/article/255-an-inexpensive-way-to-test-for-a-bad-aos

If the shop is checking the radiators they should just clean them, that should be done regularly on these cars since they tend to scoop up and accumulate junk.

If they are checking the throttle body they should just clean it, it only takes a few minutes, and is as easy as changing and air filter.

[dtsol]

Great to know--thanks so much!