Hi,
Hope the summer is allowing you to enjoy your 944.

Have an issue that is rather odd and confusing me. My alternator gauge reads differently depending on the weather. A bit of background -- when I bought the car (I am third owner) the previous owner told me the alternator was replaced with a used part. And for the past three plus years has not been an issue. The battery is less than four years old and does not seem to be the issue. The starter does not seem to be dragging or turning hard. This leaves the alternator as the issue. Here are my observations:

When the ambient temperature is 75-80 (or less), the alternator gauge shows 13.8V or higher.
When the ambient temperature is 85-90, the alternator gauge shows 13.2V to 13.6v.
When the ambient temperature is 90 plus, the alternator gauge struggles to hit 13.2V.

Temperature drops below 80 after the 90 degree days - the alt outputs more. I have had the system checked on a 94degree day and the output from the alternator was as the gauge showed - low, about 12.7v. So, I think the issue is the alternator. I have read in the rennlist archives that 944 alternators do not like heat over time. With that thought in mind, when I rebuilt the engine's top end three years ago I installed a new connecting hose from the alternator to the air duct so it had access to cooler air. All good there.

My question is: does this sound like the voltage regulator needs replaced, or is this more like the alternator is bad. Your experience and opinions are welcome.

Thanks in advance.

 

It may just be that when it's hot the cooling fans run more, drawing more current. Would be useful to know amperage draw and voltage.

Could also be connections or wiring, generally resistance increases with temp so any excessive resistance will be made worse as things get hot.

Overall as long as it's charging at or above resiting battery voltage there's not really a problem.

 

Possibly a ground issue with the gauge?

 

Agreed. I ran a separate ground from the back of the instrument cluster to the ground point under the dash above drivers left knee. Mike

 

Along the same lines, my temperature gauge will show a 2 needle width higher temp when the car starts running than with the key in the #2 position. Come home with the engine hot, turn off engine and return key and temp will be lower. Start the car and the needle pops up. Souldn't it be the same either way?

 

Hmmmm.... Interesting, I'll have to check that finding in my 944.
Welcome to the Forum!
Mike

 

I've had a similar alternator issue where I can start my car, regardless of temp, and the voltage be around 13v. I'm not sure what I do afterwards while I drive, but at some point it will drop to the first mark (or just slightly higher) and stay there. Sometimes when I restart the car it's at the same place, or it will return to the middle of the range. However it will quickly drop away.

I think I have a bad brush or an intermittent ground issue. Figured I'd go ahead and chime in with my own issues.

 

I see this, I think I would not worry - some alternators include temperature compensation in the regulator to adjust for the different charging requirements as a function of temperature - so long as it seems like a reasonable voltage I wouldn't worry - if you think it's a problem, turn on headlights and see what the color of the lights are and see what the gauge says.