BrianH
10th Aug 2006, 17:49
Hi everyone,
Last week the Land Rover started making a quiet whirring noise which would increase in pitch with the speed of the engine. I thought at the time that maybe one of the belts or pulleys were starting to go noisy, and thought no more of it.
The noise has since got much louder, and a few days ago I noticed that intermittently, the rev counter would drop to zero and then shoot back up again. I thought to myself, uh-ohhh... that looks like a problem with the alternator!
I popped the bonnet, and sure enough the noise does seem to be coming from the alternator, and it's got quite a bit louder. I've since noticed that while driving along, the alternator supplies current with no problems until the engine speed reaches just over 3000RPM. At this point the alternator gives up completely. The rev counter falls to zero and the battery warning light comes on. If I continue to push through this barrier, the alternator will wake up again at about 3600RPM and it's fine after that (not that I tend to rev much further than this normally - I've just been experiementing with the problem).
It seems strange to me that the alternator would behave in this manner. I've taken a voltage reading across the battery terminals while increasing the engine speed, and the alternator is providing 14.6V to the battery at idle, all the way up to 3000RPM. Then it supplies nothing (the meter shows 13.2V, decreasing to 12V) and if I continue increasing engine speed she suddenly starts working again, providing 14.6V across the battery terminals. Meanwhile, it's making quite a loud whirring noise.
I can't understand why an alternator would only show a failure when it's subjected to a particular rotation speed. If it's faulty I'd expect it to show a problem regardless of engine speed, although it may show a tendancy to fail when different loads are placed upon it such as turning on all the lights or something. My alternator continues to work perfectly with all the lights on, main beams on, spot lights on, interior fan at full, rear window heater on, and fog lights on. It only shows a failure at that particular window of engine speed!
Can anyone offer an explanation for this? I assume the problem is related to the noise it's now making, which at first I thought might be dry bearings or something - but then I'd expect the alternator to continue working (just more noisily).
Either way it looks like I'll be needing a new alternator very soon, and we're going away on holiday at the end of the month so I'll try and deal with it before then. I had it repaired about a 12 month ago for a different problem (completely dead) so this time I think I'll just replace it.
Is it the 100A model fitted as standard to 300tdi Discoverys?
Thanks for any advice,
Brian
Last week the Land Rover started making a quiet whirring noise which would increase in pitch with the speed of the engine. I thought at the time that maybe one of the belts or pulleys were starting to go noisy, and thought no more of it.
The noise has since got much louder, and a few days ago I noticed that intermittently, the rev counter would drop to zero and then shoot back up again. I thought to myself, uh-ohhh... that looks like a problem with the alternator!
I popped the bonnet, and sure enough the noise does seem to be coming from the alternator, and it's got quite a bit louder. I've since noticed that while driving along, the alternator supplies current with no problems until the engine speed reaches just over 3000RPM. At this point the alternator gives up completely. The rev counter falls to zero and the battery warning light comes on. If I continue to push through this barrier, the alternator will wake up again at about 3600RPM and it's fine after that (not that I tend to rev much further than this normally - I've just been experiementing with the problem).
It seems strange to me that the alternator would behave in this manner. I've taken a voltage reading across the battery terminals while increasing the engine speed, and the alternator is providing 14.6V to the battery at idle, all the way up to 3000RPM. Then it supplies nothing (the meter shows 13.2V, decreasing to 12V) and if I continue increasing engine speed she suddenly starts working again, providing 14.6V across the battery terminals. Meanwhile, it's making quite a loud whirring noise.
I can't understand why an alternator would only show a failure when it's subjected to a particular rotation speed. If it's faulty I'd expect it to show a problem regardless of engine speed, although it may show a tendancy to fail when different loads are placed upon it such as turning on all the lights or something. My alternator continues to work perfectly with all the lights on, main beams on, spot lights on, interior fan at full, rear window heater on, and fog lights on. It only shows a failure at that particular window of engine speed!
Can anyone offer an explanation for this? I assume the problem is related to the noise it's now making, which at first I thought might be dry bearings or something - but then I'd expect the alternator to continue working (just more noisily).
Either way it looks like I'll be needing a new alternator very soon, and we're going away on holiday at the end of the month so I'll try and deal with it before then. I had it repaired about a 12 month ago for a different problem (completely dead) so this time I think I'll just replace it.
Is it the 100A model fitted as standard to 300tdi Discoverys?
Thanks for any advice,
Brian