hi all
i am new to the JEC having just got a XK8. but i have had a x-type now for some years which i use as daily transport. not that i go anywhere on a daily basis. however i digress.....
The problem i get has happened for some time and there seems to be no reason for it. the headlights on the X-type will dim for a time and the get brighter again. other times they will get very bright for a while and then dull down. this does not seem to have any reason or connection with anything else coming on or turning off. this can last from just a few seconds to 2-3 minutes.
i have had the battery replaced as it was getting on a bit but no change. they also checked the alternator and the voltage regulator or something and all was well with that . grange jaguar say they are unable to find a fault. the headlight bulbs have gone a couple of times over the years and I have change them but it still happens (i change both at the same time)
has anyone had a similar problem. or could shed some light in it (sorry for the pun). if so is there a fix or on the other hand is it detrimental to the cars running.
it not a major problem but i would like to get to the bottom of it if possible.
just like to say that I love the magazine. quite the best club MAG I've seem
and this BB is very well arranged.
i should have joined years ago.
Headlights dimming for no reason
Moderators:Dave Eynon, steveisleofwight
Dim then very bright? This sounds to like a lack of regulation in the charging system.
My suspect is the altenator. Very bright lights imply an overcharge situation. There can really only be one way that can occur. The altenator loosing the plot!
You could try to make the scenario occur again with a voltmeter across the battery terminals. If you were to see more than 14.4 volts, you would know something is adrift. For that voltage to occur normaly, you would have to have a well discharged battery. Such voltage would not otherwise occur. Expect to see 12.8 - 13.4v max, engine switched off.
Much higher that that and the battery has been overcharged. Again indicative of a duff altenator. Altenator voltage should fall as battery voltage rises. That is the regulator working correctly. The altenator should then maintain the battery voltage at an acceptable 13.4 volts max.
Similarly voltage readings with the engine running of below than around 12.3v volts would also imply voltage regulator problems within the altenator.
Altenators are generally reliable. Most problems occur within the diode pack. At night, in a darkened car at idle speed, this can usualy be detected by a slowly flashing dim red dash charging light which extiguishes as revs are raised. Does your car exibit that fault?
I`d go back to the garage again with the car if you cannot satisfy yourself that charging is being well managed.
Mike Kennedy
My suspect is the altenator. Very bright lights imply an overcharge situation. There can really only be one way that can occur. The altenator loosing the plot!
You could try to make the scenario occur again with a voltmeter across the battery terminals. If you were to see more than 14.4 volts, you would know something is adrift. For that voltage to occur normaly, you would have to have a well discharged battery. Such voltage would not otherwise occur. Expect to see 12.8 - 13.4v max, engine switched off.
Much higher that that and the battery has been overcharged. Again indicative of a duff altenator. Altenator voltage should fall as battery voltage rises. That is the regulator working correctly. The altenator should then maintain the battery voltage at an acceptable 13.4 volts max.
Similarly voltage readings with the engine running of below than around 12.3v volts would also imply voltage regulator problems within the altenator.
Altenators are generally reliable. Most problems occur within the diode pack. At night, in a darkened car at idle speed, this can usualy be detected by a slowly flashing dim red dash charging light which extiguishes as revs are raised. Does your car exibit that fault?
I`d go back to the garage again with the car if you cannot satisfy yourself that charging is being well managed.
Mike Kennedy
tried the volt meter thing. battery was at 12.54v then when the car stared up the reading went up to 15.09 to 15.01 this stayed like that for about 10 minutes. then dropped down to 13.25 - 13.30v.
i put on the lights heater and anything to use power and it dropped to 13.08 - 13.25v. i ran the car with the light on for an hour but at no time did the voltage change.
later i tried again with the same results.
also there is no indication on the dash of low voltage( which of course there is to much if anything).
i will try it again and see if i can rig up the volt meter so as to be able to read it when driving.
would it be possible to fit the voltmeter to the headlight power to see if the voltage is changing there?
any ideas would help. thanks
i put on the lights heater and anything to use power and it dropped to 13.08 - 13.25v. i ran the car with the light on for an hour but at no time did the voltage change.
later i tried again with the same results.
also there is no indication on the dash of low voltage( which of course there is to much if anything).
i will try it again and see if i can rig up the volt meter so as to be able to read it when driving.
would it be possible to fit the voltmeter to the headlight power to see if the voltage is changing there?
any ideas would help. thanks
That start up voltage does seem a little high to me Fungus.
As I said earlier, it is indicative of a partly discharged battery state. Even after a burst of high current engine starting, I would`nt expect to see such a high recharge voltage.
You could certainly rig a cable for your meter from the headlight circuit to read what is happening when the lights are on. Me thinks however, that battery terminal voltage is likely to be a more interesting point to read from.
I assume you have had a good look at all earth points on the car and checked for corrosion issues. Low voltage, high current applications do not like corrosion or resistance hot spots.
You might also have a drop test performed by a garage on your battery. Even new batteries can sometimes go duff under load.
Hope this helps,
Mike
As I said earlier, it is indicative of a partly discharged battery state. Even after a burst of high current engine starting, I would`nt expect to see such a high recharge voltage.
You could certainly rig a cable for your meter from the headlight circuit to read what is happening when the lights are on. Me thinks however, that battery terminal voltage is likely to be a more interesting point to read from.
I assume you have had a good look at all earth points on the car and checked for corrosion issues. Low voltage, high current applications do not like corrosion or resistance hot spots.
You might also have a drop test performed by a garage on your battery. Even new batteries can sometimes go duff under load.
Hope this helps,
Mike
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