21 replies to this topic

[smurfomatic]

Driving my Mini Marcos (998 engine) to work this morning, got about two miles from work and the car got really sluggish at low revs. Practically stalled in the middle of a roundabout, had to dip the clutch and rev hard to get it going again. Once the revs built up it ran fine, but slowing down to turn into work it did the same again. Judders and almost stalls until you "nurse it" a bit.

The alternator belt has squealed a bit over the last few days, changed it at the weekend, checked the tension and it's fine but still squealed a bit when there was load on the alternator (like running with headlights, heater and wipers going...) and squeals when the problem happens - not that you can really hear it over the other horrible noises from under the bonnet.

Alternator's only 18 months old, but the water pump is older. Alternator seems to be working fine, charges to about 14V on the gauge, drops off a bit with the electrics going but goes up again with less load. Could the bearings have gone in the water pump, meaning it's struggling to turn the alternator belt? It ran a bit hotter than usual, but then again it's so cold in the mornings it was never going to overheat.

I need to try and get it home this afternoon, but don't want to drive it too far (20 miles to get back) if it's going to go bang. I have AA cover and there's a Mini garage round the corner from me, so I could get towed if something catastrophic happens.

Then again, I managed to recover the same distance with a cracked cylinder head a few months ago, including about five "water stops". I'm hoping it's just the water pump because that will at least be cheap and quick to fix!

[charie t]

Loosen the belt and see how easy it is to turn. If there is any play in the bearings. Alternator belts can go hard or dry and cause squealing even though they appear to be in good condition. How old is the belt?

[smurfomatic]

The belt I fitted at the weekend is brand new, only bought a few weeks ago. Will try the pump with the belt off and see how easy the pump moves.

[smurfomatic]

Hectic day at work so no chance to check the pump myself. Left it with the local Mini garage so hopefully will be sorted tomorrow. Got me home fine, no major problems like this morning, just a bit more noise when pulling away at traffic lights etc. It was running a lot hotter though, so possibly the water pump causing the noise...

[charie t]

Possible seized alternator too but without diagnosing the issue, its guess work

[smurfomatic]

Right, water pump changed at the weekend - wasn't bad but thought it wouldn't matter too much. Belt still squealing just as bad this morning, when alternator under load. Next stop - try a different belt (this one's new but a no brand one) then if that doesn't work, spend more cash on a new alternator...

[charie t]

spend more cash on a new alternator...

Don't just go pointlessly throwing money at it, did you check the waterpump before you changed it?
What about the alternator did you check it was spinning free while the belt was off?
Back to the belt, why did you change it in the first place?

[Cooperman]

Sounds like the belt is not tensioned enough.

[smurfomatic]

Charie: the pump was worn (not that surprised, it's one of the few things not looked at on the car since I bought it) and certainly seemed to be the likely cause of the problem.

The alternator seemed to be spinning fine when it was all apart, and has been charging fine, but the squealing only happens when it's "under load" - like having the lights and wipers going, then stopping at traffic lights and the revs drop off. It is only a 36 amp one though, and it could probably do with at least a 45A version instead - for the winter months at least.

I changed the belt because (a) I assumed that was why it was squealing, (b) it was old and worn and © I'd tried re-tensioning it a couple of days before to stop the squealing.

Cooperman - there's plenty of tension in the belt, only about 10mm of play when you push it down between pump and alternator. Previous attempts tightened it even further and no change.

[Vonski]

Smurfomatic, no point in changing the alternator if you don't need to.
If the pulley can be freely spun by hand with the belt off then its not seized, If the pulley rotates cleanly by hand with no roughness, and there is no up\down or side to side play then the bearings are ok.
When checking that the alternator is charging - first check voltage with engine running and everything electrical turned off, anything between 13.8v to 14.3 is perfect.
Then check voltage with engine running and everything electrical turned ON, including all lights, hazards, wipers, stereo, blower fan. Anything between 13.5v to 14.3v is perfect. If the voltage drops below about 13.5v or ever rises much above 14.5v then you have a fault with the regulator in the alternator. If you see a high voltage then check the cells of your battery (if it has removable filler plugs on the top) as it may be boiling the battery.

However, your original problem of the car nearly stalling at low revs but being ok with more revs on sounds to me like a fuelling problem. This is a classic symptom of a blocked fuel filter. The engine struggles to pull fuel through at idle, but with the increased flow at higher revs then it is able to cope. Although if it is a blocked filter then it will only get worse. Of course any point in the fuel system that is gunked up or blocked will cause the same problem, wether it is the pick up in the tank or a dirty carb jet.

Edited by Vonski, 26 November 2012 - 11:33 PM.

[smurfomatic]

Vonski - the voltage is about 14V (dashboard voltage gauge) with nothing running, however when idling at traffic lights with headlights & wipers on, it dips down to about 10v. This is when the squealing (also now accompanied by a regular clunking noise) kicks in.

Battery should be fine, it's a four months old Bosch silver bought after the previous one, a cheapie, packed up. Only had these issues for the last ten days or so, as it's undercharging rather than overcharging shouldn't have done any damage.

I think the car cutting out/stalling (which only happened on that one day by the way) may have been a temporary blockage somewhere, no problems like that since so it seems like a red herring.

I'm thinking that an alternator is only £50 from Minispares (I take it http://minispares.co...rs/GXE2211.aspx will be a direct replacement for the 36 Amp LRA100?) and not sure what else could produce these symptoms.

[Vonski]

Bingo - you've diagnosed a faulty alternator.
Replace it and all will be happy!

[smurfomatic]

I hope so Voski, at least until the next time something starts making grinding, crunching or banging noises! Ordered from mimispares, hopefully fit the new one over the weekend - fingers crossed for some good weather and the old one holding out until then...

[tiger99]

Just a thought about the squealing. I have known this to be caused by a pulley which has begun to spread or wear, so that instead of driving by friction on the sides of the V, the belt is sitting on the bottom of the groove, which does not give nearly as much grip. It could be any of the 3 pulleys. On one occasion I found that the previous owner had overtightened the belt so much (maybe just a guess, but there was no other explanation) that the excess tension caused the crankshaft pulley to try to spread, with the result that a fatigue fracture developed almost right round the centre, leaving the outboard flange flapping about, held by almost nothing. In a dire emergency, I took it off and welded it back together, and it must have then run another 50k miles or so, but a new pulley would have been preferable.

On the other hand, as your alternator seems to be suspect, I think that it probably has shorted turns in the windings, which will make it waste a lot of energy, needing more from the belt, which could well make it squeal. Worth looking closely at the pulleys though, it only takes a minute, just in case....

[smurfomatic]

Hoping that the new alternator arrives today, as I can probably get away early and fit it before darkness falls...

I'll take a look at the driveshaft pulley tiger, keeping my fingers crossed if any of them are problematic it's the alternator as that's being changed!