300tdi belt failure

Last night, while doing 66mph on a Motorway, I suddenly heard a frantic tapping noise from the engine, but not a metallic noise, more like a flapping, slapping noise. I immediately lifted off the power and the noise reduced, I put a little power back on to double check it was definitely coming from me, and the slapping came back. I decided it could be something serious and didn't want to do any further damage, so quickly pulled over to the verge.

I noticed as I stopped, that the engine temp was high, and climbing with the engine off.

A lift of the bonnet revealed a tiny bit of steam, a small splatter of coolant on the underside of the bonnet, and wetness around the water pump area. I'd say I lost no more than a teacup of fluid from somewhere.

I then noticed the cause... My belt (serpentine) was missing!!

So, rewind 2 days ago, I decided to solve the mystery of why for the 2nd time this year I had a noisy tensioner bearing, and replaced the whole tensioner this time rather than the bearing. I also changed the belt while I was at it as it was pretty old.

I'd been driving it about nicely since then, happy that the work was good. Yesterday when the belt failed, I was coming to the end of a long 6 hour, 236 mile, round trip, of a mixture of motorway and b road driving. All was perfectly fine until that point.

I found the belt, on the floor under the landy, so it only actually came off as I came to a stop. It's in one piece but has a piece split off, hanging off but still attached. Like someone has gone at it with a Stanley knife. I think the slapping noise was this piece hitting things as it rotated.

By the time I was recovered 2 hours later, there had been no further leaking from what had been spat out when I'd first pulled over.

So the landy is home, the AA kindly loaded her up and drive us home. And now it's time to get her running again. Quickly.

The 2 main questions, as I've only been learning basic mechanics for the last 2 years I've had it, are:

1) What would have caused the belt to get cut/shredded like that? Is it something I did wrong when replacing the tensioner, or is this just a faulty belt?

2) what am I likely going to have to fix that would have been damaged in the process of pulling over? I'm assuming I can't just put my original belt back on and be back in business.

Thanks for any help and advice guys.

Update:

I've discovered a leak this morning still, and, the likely cause... The water pump is moving, the pulley is leaning forwards and loose. I'm thinking it failed for whatever reason, and that movement pulled the belt forwards, resulting in it cutting the belt. I think this also then created slack and worked the belt off as we pulled over.

I'm pretty confident it's a coincidence that it happened after replacing the belt and tensioner, or that the new tensioner and belt at the very least exposed a weakness in my pump/pulley.

I also suspect that there will be no engine damage as technically the belt stayed on until I turned the engine off.

Fingers crossed a water pump and pulley replacement will do it.

Please shout if you think otherwise.

HeywoodFloyd said:

Update:

I've discovered a leak this morning still, and, the likely cause... The water pump is moving, the pulley is leaning forwards and loose. I'm thinking it failed for whatever reason, and that movement pulled the belt forwards, resulting in it cutting the belt. I think this also then created slack and worked the belt off as we pulled over.

I'm pretty confident it's a coincidence that it happened after replacing the belt and tensioner, or that the new tensioner and belt at the very least exposed a weakness in my pump/pulley.

I also suspect that there will be no engine damage as technically the belt stayed on until I turned the engine off.

Fingers crossed a water pump and pulley replacement will do it.

Please shout if you think otherwise.

Click to expand...

Did you change the tensioner or did a garage do it? If you tighten the belt too much it will put a lot of strain on the water pump bearing and the result will, be what you have now. Change the pump and belt, top up the coolant and see how it goes, should be ok but keep you eye on the coolant and oil for the next few weeks.

Col

Colthebrummie said:

Did you change the tensioner or did a garage do it? If you tighten the belt too much it will put a lot of strain on the water pump bearing and the result will, be what you have now. Change the pump and belt, top up the coolant and see how it goes, should be ok but keep you eye on the coolant and oil for the next few weeks.

Col

Click to expand...

I did it. I've been trying to do everything on this old girl myself, learning as I go.

I think there is advice in the Haynes manual about how much tension the belt should be under. There should be some lateral movement on the longest run of the belt. In other words you should be able to pull the belt out by 3 or 4 centimetres. It's better if its too lose rather than too tight. In my opinion.

Col

Ok.. I just need to work out how to achieve that or find a video on how to adjust it.

First up, new pump.

HeywoodFloyd said:

Update:

I've discovered a leak this morning still, and, the likely cause... The water pump is moving, the pulley is leaning forwards and loose. I'm thinking it failed for whatever reason, and that movement pulled the belt forwards, resulting in it cutting the belt. I think this also then created slack and worked the belt off as we pulled over.

I'm pretty confident it's a coincidence that it happened after replacing the belt and tensioner, or that the new tensioner and belt at the very least exposed a weakness in my pump/pulley.

I also suspect that there will be no engine damage as technically the belt stayed on until I turned the engine off.

Fingers crossed a water pump and pulley replacement will do it.

Please shout if you think otherwise.

Click to expand...

that sounds very likely,water pumps a common failure with age,belt failure wouldnt damage the engine, over heating due to water pump then not been driven could,but it sounds you caught it before that

HeywoodFloyd said:

Ok.. I just need to work out how to achieve that or find a video on how to adjust it.

First up, new pump.

Click to expand...

theres no adjustment, tensioner is pre set, a new one is likely to exert more pressure than an old one as spring wears with age

jamesmartin said:

theres no adjustment, tensioner is pre set, a new one is likely to exert more pressure than an old one as spring wears with age

Click to expand...

That's what I thought. Hence me wondering how to adjust it. So yeah I think a new tensioner and a nice new belt, and a few hundred miles of driving was probably too much for the old pump.

Pump would likley would have gone anyway,perhaps made a few more miles. When checking under the bonnet a push/pull on a water pump pully can give early warning of failure if movement is found. Not possible with all vehicles but if you can.

tottot said:

Pump would likley would have gone anyway,perhaps made a few more miles. When checking under the bonnet a push/pull on a water pump pully can give early warning of failure if movement is found. Not possible with all vehicles but if you can.

Click to expand...

Indeed - I will now be adding this to my "before a longer journey" checks.

HeywoodFloyd said:

Update:

I've discovered a leak this morning still, and, the likely cause... The water pump is moving, the pulley is leaning forwards and loose. I'm thinking it failed for whatever reason, and that movement pulled the belt forwards, resulting in it cutting the belt. I think this also then created slack and worked the belt off as we pulled over.

I'm pretty confident it's a coincidence that it happened after replacing the belt and tensioner, or that the new tensioner and belt at the very least exposed a weakness in my pump/pulley.

I also suspect that there will be no engine damage as technically the belt stayed on until I turned the engine off.

Fingers crossed a water pump and pulley replacement will do it.

Please shout if you think otherwise.

Click to expand...

No such thing as coincidence I say - I suspect the new tensioner with it's new spring was able to tension the system a bit higher, the pump bearing was on it's way out and the extra tension was enough to kill it.

Also note, there are 2 belt lengths for the 300tdi, 1580mm & 1595mm - the latter being for the larger alt. pulley - 61mm.

Yes the same tensioner is used on both variants however using the shorter belt on the larger pulley will lead to less deflection and reduce the dampening effect so the tensions will not be the same and the smaller belt on the larger pulley will subject components (i.e. the pump which is directly next to the tensioner) to increased stress as the belt has less room to deflect. Just watch a tensioner when the engine runs, it doesn't sit still, it moves about all the time as it helps to dampen the combustion cycle knocks and the alternator grab just after a firing stroke.

discomania said:

No such thing as coincidence I say - I suspect the new tensioner with it's new spring was able to tension the system a bit higher, the pump bearing was on it's way out and the extra tension was enough to kill it.

Also note, there are 2 belt lengths for the 300tdi, 1580mm & 1595mm - the latter being for the larger alt. pulley - 61mm.

Yes the same tensioner is used on both variants however using the shorter belt on the larger pulley will lead to less deflection and reduce the dampening effect so the tensions will not be the same and the smaller belt on the larger pulley will subject components (i.e. the pump which is directly next to the tensioner) to increased stress as the belt has less room to deflect. Just watch a tensioner when the engine runs, it doesn't sit still, it moves about all the time as it helps to dampen the combustion cycle knocks and the alternator grab just after a firing stroke.

Click to expand...

I replaced the belt with the same one that was on there, using the dayco numbering on the belt. I guess if it's the wrong length belt, then it has always been the wrong length.

I think you're right that this is just a case of a nice new tight belt and new tensioner, exposing a pre-existing issue on the pump.

On a related note, I'm going to try and fix her up on Friday with a new pump, etc. When I take the pump off, will I need to do a full coolant change, or will I just lose a bit, that needs topping up?

My garage did the last coolant change for me last year, so I've no idea what they've put in it. I'll have to purely go on colour, or I guess I can give them a ring and hope they can remember.

I'd drain the lot and replace it, you know exactly whats in it in that case.

HeywoodFloyd said:

On a related note, I'm going to try and fix her up on Friday with a new pump, etc. When I take the pump off, will I need to do a full coolant change, or will I just lose a bit, that needs topping up?

My garage did the last coolant change for me last year, so I've no idea what they've put in it. I'll have to purely go on colour, or I guess I can give them a ring and hope they can remember.

Click to expand...

For the price of a gallon of coolant, dump it and add new good old fashioned ethylene glycol blue/green.

It should be blue/green in which case any other blue green would mix anyway.

I would not waste my time trying to re-balance the mix. You will need to buy about 2/3 litres anyway so you are as well to buy a gallon so no saving in cost.

I had a similar issue not long after I inherited my 90....
Local garage wanted £600 to change the water pump so I posted on here and gained the usual helpful advice and did it myself. It is not a difficult job and apart from getting the belt back on the tensioner I had no major issues. Agree the advice to start fresh with coolant, best be safe and happy! Total cost with new pump, belt and coolant was less than £80.....

Yep, thanks guys, I did it on the weekend, was one of the easiest jobs so far on this old girl.

Musicman said:

It is not a difficult job and apart from getting the belt back on the tensioner...

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Use a longer ratchet or 2' bar and swing it further out of the way, belt will slip on no problem.

discomania said:

Use a longer ratchet or 2' bar and swing it further out of the way, belt will slip on no problem.

Click to expand...

Yeah I have never really had an issue getting the belt back on - not sure why people have trouble with that.

The biggest issue I had was undoing, and doing back up, the pulley bolts, especially the idle pulley with the way the pulley's face is inset rather than flush. I'm sure there's an appropriate tool out there to do it easily, I just used a bent screwdriver wedged in between 2 bolts - and a lot of swearing - and some knuckle skin loss.