Highlander944

Being a complete rookie to automobile / Porsche mechanics, I have noticed a trend in my car which feels abnormal.

This is most noticed in the summer, however we had a day above freezing today, and I felt it again.

If my car is let get hot... sitting idle for say 15 -25 minutes so that the temp gauge in the car reads right around 1/2 I find that when I begin driving the car does not have as much power as it did when the temp gauge was closer to 1/3.

My estimation would be that the computer senses the increased temp and reduces fuel flow, is this even remotely correct? If so, what is this temp set point? I mean, is the temp sensor sending falsely high readings OR does the coolant temp switch/sensor need turned down?

How does this vehicle regulate its engine temp? How do I check this? What should it be? Could this be a root cause for the decrease in power when the car is 'hot'.

Thanks,

Peter.

fast951

To warm up the car properly you shouldn't let it idle for a long time. Let it idle for 1-3 minutes if very cold outside, then drive it without load and keeping RPM below 4000. You need to get the fluid in your transaxle warm as well, which can't be done when idling.

Now to your question... If the car is idling, more than likely you are getting heat soak. The intake manifold is getting hotter, your intercooler will not dissipate the heat (after a boosted run then sitting idle)..

Do you know if the fans are on when you notice the degraded power? Maybe a voltage drop (if fans are on)?

The change in performance is much more pronounced in change of outside temp. The hotter it is the less power the car will make... Got to love cold days, even though traction will be limited...
The engine temp at mid-range (assuming sensor and gauge are accurate) should not affect the performance.. Start noticing other factors that there is no gauge for ....

Highlander944

fast,

I know the fans 'work' and I don't notice any appreciable voltage drop when they come on. If I let the car idle in the garage (with the door slightly open so I don't kill myself ) once the temp gauge gets just above 1/2 way I can hear BOTH fans kick on. The temp drops rapidly at this point.

I have never noticed the power loss come on when the vehicle is moving. Typically I don't warm the car up by letting idle for hard driving... it's more so I don't freeze when I get in.

The way this problem manifest itself is most evident on a hot summer day. After driving pretty hard (and at full power) if you stop the car for maybe 15minutes or so, when you come back out and get on your way the power is WAY down. After cruising a bit, it seems to come back but sometimes I feel like I have to pull over, turn the car off then back on to 'reset' the power. I'm not 100% certain if the turning off then turning back on 'resets' something of if it is my imagination.... I'll have to wait till summer to increase my certainty.

Does this sound about normal?

Thanks.

fast951

It sounds like Heat Soak!

BoostSciences

I too think it could be heat soak, but would the effect be so noticeable. In cold weather, the same effect was seen, just driving for a few minutes or so after that 15 min idle (which is way too long by the way) , the engine bay should cool down rather quickly. I wonder is the heat buildup is affecting some of your sensors which may be going south. Also, some cheap ignition coils have been known to cause problems in high heat conditions. Either way I'm with fast951 on this, heat soak is probably the root of the problem.

adrial

Do you have the stock intake?

fast951

Heat soak causes it.. However under the hood temp affects some sensors, so it's not just a mechanical ot thermal effect. The temps are being measured as well. Be it by the Intake Air Temp inside the stock AFM, be it by water temp... The computer compensates for such variables...
Too much heat will induce knock, the KLR pulls back timing which hurts performance...

Of course a bad coil could do it, but I would expect to see more of a change under load...

As you have noticed by now, there are many factors involved...

jimbo1111

I remember reading something on rennlist a while back. I think it stated that there is a temp sensor on the block that when its going south will retard timing by 3 to 6 deg. Not sure but I think it was Danno who stated it . Maybe do a search under engine temp sensor.

fast951

If sensor is bad, it's bad even after driving few minutes... A bad sensor will affect overall performance. Unless it's intermittent, which will be an interesting find and not likely.