Loud generator-like noise

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paulfromperu

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Hello, I had the strangest thing happen about a week ago: I parked my 97 TDI Discovery after a 15-20 minute drive and turned it off; after about 5-10 minutes I turned it back on for a quick park-job and noticed a loud generator-like sound over the normal engine noise. It sounded kind of like an electric lawn trimmer in the distance, so I didn't really pay much attention to it, but when I rolled down my window and got out of the truck to have a better listen, I realized It was coming from the engine room.

The truck had never made that noise until then and it sounded kind of loud, so after taking a very quick look at the engine I decided to turn it off for fear that something might burst. To my surprise, the noise did not stop when I shut down the engine and even removed the key.

It was really dark and my flashlight had died on me, so I wasn't able to get a great look at where the noise was coming from. Initially I thought it had something to do with the turbo, since I the noise seemed louder in that general area and I had recently had work done on the turbo, but then I realized that the turbo, as far as I know, does not have any electrical components and only works with the engine's exhaust, so I ruled it out. I did notice, however, that the crankcase ventilation hose was blowing out exhaust gas as if the engine were running. I tried turning the engine back on, but it wouldn't start or do anything (as if the battery was completely dead). Again, the sound was very loud and I din't want something to burst, so I decided to disconnect the battery to see if that would stop it, and it did. With the sound gone, I reconnected the battery and started the engine as if nothing had happened; I've been driving the truck for about a week now and haven't had the problem again.

I'm definitely a newbie as far as technical knowledge regarding the Disco, but my family has owned the truck for 12 years and we've never seen this happen before. Also, I live in Peru, South America, so it's really hard to come by mechanics who know about this particular vehicle; any insight would be greatly appreciated. It seems to me like a pump (maybe the vacuum pump?), fan or something electrical got stuck in the on position when it shouldn't have. The Disco is a 97 TDI with 100,000km on it; let me know you need more specifics.
 
sure the starter motor solinoid didn't get stuck in???......................

And carried on turning the engine???
 
I bet a pound to a penny it's the centrifugal oil fiter can spinning down from about 15,000 rpm.

Read the handbook - it tells you about these noises that may go on for a minute or more after you switch the engine off.

If that is what it is, you know it's working!

CharlesY
 
CharlesY said:
I bet a pound to a penny it's the centrifugal oil fiter can spinning down from about 15,000 rpm.

Read the handbook - it tells you about these noises that may go on for a minute or more after you switch the engine off.

If that is what it is, you know it's working!

CharlesY
Click to expand...

It's a 300tdi CharlseY;):doh::p

To add to that it was blowing out crank case pressure out the breather hose and the ignition went dead.

My money is still on the starter motor running on.
 
MartinBird said:
sure the starter motor solinoid didn't get stuck in???......................

And carried on turning the engine???
Click to expand...

It wouldn't do that if the engine fired up, as the starter pinion is on a free-wheel which means as soon as the engine fires up to more than starter speed (about 120 rpm at most) the starter is free-running but NOT fast enough to be "driving" the engine which at tickover will be doing about 750 - 800 rpm.

CharlesY
 
I have witnessed this on many cars where the ignition sticks on or more likely the starter motor solenoid, it will not actually be driving the engine but tens to either a) starter jammed in flywheel so starter being taken for a ride or b) the solenoid drops back far enough to disengage teeth but the contact are welded together so the starter is still attempting to crank.

In theory this cannot happen as the teeth should engage just a moment befor ethe contacts 'make' however, often the contacts pit and bits of contact metal start pitting and building up on the contact faces eventually leading to this welded scenario.

My money is still on the starter,

regards

Dave
 
I would be taking the starter off and giving it a good inspection and clean - just to be sure it's not going to do it again, and the starter last longer.
 
Thanks everybody for your insight. What you guys say about the starter solenoid getting stuck makes sense, however, I have a question: Would a stuck tarter solenoid or ignition switch cause the crankcase ventilation hose to blow out exhaust?
I will be getting the truck checked out by a mechanic tomorrow morning; other than the starter solenoid and ignition switch, is there anything else I should have them check? Again, thank you so much for taking the time to answer; I actually posted on a US-based forum and didn't get a single reply... ha! probably because they don't have the TDI version there, but still... I mean, I don't want to sound like a jerk or anything (I'm actually American), just wanted to note that UK-tians rock.
 
If it was blowing out (and not just coming out after as it does once it heats up) I suspect that the starter may have engaged - then stayed engaged even after the engine was running (it was only a short while while you were parking it wasn't it) and when you then switched the engine off the starter then continued to run and turned the engine over - that would explain the generator noise when the engine was running because the starter would have been spinning REALLY fast. Also I doubt you would hear the starter motor just spinning when not engaged over the engine noise - it's just a powerful electric motor and when not turning an engine over would just make a gentle whirring noise.

So, it could the the solenoide stuck/welded itself OR the switch kept the starter running. I would get the mech to check the switch and then if it's OK take the starter off and strip it down for a full inspection and clean up at least - solenoide anyway.

If that happened and you drove on it the starter would probably catch fire after a while.
 
Last edited:
Hi

bear with me with the following story / possible explanation to your problem:

I had a TD5 that when turning off the engine you could hear the turbo still spinning down and would go on for ages - made a similar sound. At the time I thought nothing of it as was a brand new car, however the first time I took the car on a fast motorway run the turbo went phut. This was with about 5k on the clock. Evidently the oil seals burnt out and the turbo seized with resultant smoke screen and loss of power :mad:

The root cause of the problem was a kinked oil return pipe from the turbo, which restricted the oil flow through the bearing, which caused it to overheat and size.

Now the fact is that normally when you feel the impeller of the turbo it' should be kind of sticky and snug and not carry on spinning for long and certainly not make a noise when you turn the engine off, unless you really gun the engine and then kill the engine. This is because normally there is sufficient drag of the oil in the bearings to slow the impellor down quite quickly.

In hindsight, my TD5 turbo had already been suffering damage prior to my motorway run, the bearings were probably worn with excessive clearance coupled with little oil allowed the impellor to carry on free wheeling for a conciderable time after turning off the engine.

Therefore, my prognosis is that your turbo is excessivly worn and what you are feeling from the crankacse breather is the pressure output from the turbo impellor coupled with the noise of the worn impellor spinning at several thousand RPM.

Another possible explanation is the fact that there is no 'back pressure' or rather resistance to the output of the turbo when switching off the engine - because you have a leak in the crankcase breather pipe ? this would then allow the impellor to freewheel as it spins down as there is no resistance/load.

Sorry for the long ramble, but hopfully it makes sence.

Try plugging up the leaky crancase breather pipes and make sure teh output of the turbo truning is all sealed correctly first.

Good luck
 
discomania said:
Why did it stop when he disconnected the battery then??
Click to expand...

Good point and to be honest I don't know other than co-incidence perhaps.

I may have missed something but I didn't get the impression from the OP that the engine was being turned over by the starter motor after switching it off. Although surely that would be pretty obvious if that was the case and therefore problem solved.

If the starter motor is spinning but not turning the engine over that would certainly explain the noise and sounds like a very plausible explanation, although the expelled air coming out of the crankcase breather is a strange one, but of course that could be a red herring and it maybe just vapour.

All in all quite intriguing, but not helped by the lack of clear info from the OP.

Cheer
 
DiscoTDi said:
Therefore, my prognosis is that your turbo is excessivly worn and what you are feeling from the crankacse breather is the pressure output from the turbo impellor coupled with the noise of the worn impellor spinning at several thousand RPM.
Click to expand...

A freewheeling turbo (engine off) IMHO would not have enough pressure/volume to fill any cylinder which has an open intake valve AND force pressure past the piston rings and then pressurise the crankcase before the turbo came to rest.

Further, the owner decided to disconnect the battery which would have taken a few minutes to find a spanner and disconnect the termianls and THEN the noise stopped. All in all I would guess that the turbo would have been slowing from engine off to battery disconnect for a time of about 5 or 6 minutes......... unlikely.

I'll stick with the sticky starter solenoid theory for the moment.

regards

Dave

regards

Dave
 
Last edited:
starter solenoid is where i'd put my money.

Had it happen on my 200tdi engined 90. The starter was old and by the time i came out of the shop smoke was filling the engine bay. but the starter gear didn't engage on the flywheel so the engine wasn't turning over just the starter spinning. hitting it with a hammer got it to stop
 
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