what does the voltmeter tell you?

[tdafforn]

Hi Guys,
A couple of weekends ago I drove the +2 on a pilgrimage to the Goodwood Revival meeting (550miles). The long trip (a fair amount on motorways) gave me ample opportunity to look around the car as it was running.
One of the things I ended up wathcing was the Voltmeter. I have never quite understood what it told me except that when running needle to the RHS of the line was good.
Anyhow heres somehting I notices. Running at 80MPH the guage would switch from 14V ish to 11V ish every 5 minutes or so and then back again. I also noticed that at the same time the temp guage moved. 11V on the guage, temp guage up a little, 14V temp gauge back to normal.
What is happening?
One thought was that the cooling system isn't handling 80MPH for long periods and the movement was linked to the fan going on and off.
Does this seem likely?
If so I guess I need to recore the rad (I back flushed it last winter).
Also if 11V ish is bad, how long can the car run like this before the battery runs out? does the volts keep droping?
Anyhow interesting observation, and great meeting at goodwood, if a little wet!
cheers
Tim

[lotuselan2]

It does sound like the fan is calling the low voltage, but it could also be a bad volatage regulator. The voltage regulator could be checked by diconnecting the fan before you overheat.

I won't comment about the need for the new radiator.

The 11V is a bad sign. It depends on where your voltmeter is connected. The load of the fan should not drop your voltage from 14 to 11 unless you have a real wimpy alternator (generator?). the voltmeter could just be showing the no so unusual drop in voltage in the wiring harness. Many Elans only get 9V to the headlamps. (Then owner buys more powerfull lamps and gets 7V and less light!) Check voltage at battery with and without fan running or better yet up front at the solenoid or fuse block.

I would not drive too far in traffic with 11V's unless you like showing how easy your car is to push home.
Ken