Engine knocking noise

[simon-g]

Hi all, hope you are well. I have a "noise" which can only be described as a metallic rattle noise which is coming from the engine. The noise gets worse when the car gets hotter, I have the car booked in with a BMW specialist at the moment, and he thinks the noise was coming from beneath the cam cover. So he started by stripping off the cam cover, and he has checked the timing, vanos, tensioners, and said the engine looks prestine, which is should be as it has only covered 36k miles. Now he thinks the noise is more evident over cylinder 1, and he want to start stripping the engine down, by first removing the cams, and if the problem is not evident there, then removing the head.

The car drives perfectly, with no hesitation whatsover, its just this "noise" coming from the engine. I have not had the car long, just over 1 month, and I am worried that this noise could lead to a more serious problem that is only just beginning to surface. The garage I bought it from provided an initial 3 month warranty, which they want this to be done through, the only problem is that if we strip the head off etc, which will cost in excess of £700 labour alone, and the fault still isnt found they nor I want to pay the bill, and the warranty sure as hell wont cover just the labour without a problem being found.

Im unsure what to do from here, but I would be grateful for any advise and if anyone else has experienced such a noise as this. Its not the water pump, and he has also removed the fan belt. Any ideas please chaps?

[Mike Fishwick]

IF you want sensible repies, it would be wise to tell us what engine you have, mileage etc.

I assume yo have a double-VANOS M52TU engine - in this case, and if the noise is a rattle at idle and low speeds, a BMW Service Instruction lists either a hydraulic tappet or oil pump problem, and possibly a noisey oil pressure relief valve.

Problems withthe pump or relief valve mean dropping the front cross member to get the sump off - better not to think about that unless you have to!

I would bet it is a hydraulic tappet nopise, which can sometimes be cured by an oil change, particularly if it has not been changed for ages - irrespective of how many green SI lights you have. SI systems are the curse of modern cars, and simlpy mean officially-condoned neglect.

What oil is in the engine? I bet you don't know, in which case a change to a thin oil such as SAE 0-30 may be the answer, particularly an oil whichis suitable for diesel as well as petrol engines, with a high level of detergency to clean out the engine in general, and the tappets in particular.

Avoid expensive 'Long Life' oils in favour of a semi-synthetic 0-30 for this purpose. Even synthetics should not be left in the engine for more than a year or 10,000 miles if you intend to keep the car for a long time.

Most garages change the oil after it had cooled own, which causes a build-up of sludge - another prime cause of tappet problems. The use of a 0-30 high detergency oil for a few thousand miles - drained while hot - will clean out the engine and can only do good.

So - my advice is to give your car a proper oil change while hot, use a 0-30 high detergent oil for 3 or 4,000 miles, and see what happens.

[simon-g]

IF you want sensible repies, it would be wise to tell us what engine you have, mileage etc.

I assume yo have a double-VANOS M52TU engine - in this case, and if the noise is a rattle at idle and low speeds, a BMW Service Instruction lists either a hydraulic tappet or oil pump problem, and possibly a noisey oil pressure relief valve.

Problems withthe pump or relief valve mean dropping the front cross member to get the sump off - better not to think about that unless you have to!

I would bet it is a hydraulic tappet nopise, which can sometimes be cured by an oil change, particularly if it has not been changed for ages - irrespective of how many green SI lights you have. SI systems are the curse of modern cars, and simlpy mean officially-condoned neglect.

What oil is in the engine? I bet you don't know, in which case a change to a thin oil such as SAE 0-30 may be the answer, particularly an oil whichis suitable for diesel as well as petrol engines, with a high level of detergency to clean out the engine in general, and the tappets in particular.

Avoid expensive 'Long Life' oils in favour of a semi-synthetic 0-30 for this purpose. Even synthetics should not be left in the engine for more than a year or 10,000 miles if you intend to keep the car for a long time.

Most garages change the oil after it had cooled own, which causes a build-up of sludge - another prime cause of tappet problems. The use of a 0-30 high detergency oil for a few thousand miles - drained while hot - will clean out the engine and can only do good.

So - my advice is to give your car a proper oil change while hot, use a 0-30 high detergent oil for 3 or 4,000 miles, and see what happens.

Mileage is 36k as above, but it is the single vanos 2.8. Oil was changed recently by myself using Mobil Synt S 5W-40, and it didnt seem to make any difference to the noise.

[Mike Fishwick]

How many miles have you covered since the noise became apparent, and how many since the oil change? What kind of running has the engine done - maybe short journeys?

A failed tappet is usually easy enough to find - if pressed down by a force of about 2 lbs it should move, and then may move further still if the force is increased to about 5 or 6 lbs. Even so, they often correct themselves with a bit of clean oil and plenty of use.

But if you have not covered many miles since the oil change, my reaction would be to simply drive the car and see what happens, particularly as you have a 3 month warranty to fall back on. Spending you own money - perhaps for nothing - is not a sensible option.

[OXO]

The garage I bought it from provided an initial 3 month warranty, which they want this to be done through, the only problem is that if we strip the head off etc, which will cost in excess of £700 labour alone, and the fault still isnt found they nor I want to pay the bill, and the warranty sure as hell wont cover just the labour without a problem being found.

Why not? It's a warranty isn't it?

I'm sure a lot of garages would like the unsuspecting buyer to share warranty costs, but that's not the law. Just demand they fix it, and if they can't, then either get them to take the car back, or provide an extended warranty (like 12 months). If it's a serious fault, something should break by then and they can fix that under their warranty.

[simon-g]

Thanks guys, we came to basically the same conclusion with the garage, im just going to continue using it, and see if it gets any worse, as they cant find anything wrong with it.

There is 2 months left on the warranty, and I have the option to extend it to 12 months. To be honest I have only done a couple of hundred miles since the oil change and the car has been used for very short journeys for the past 8 years, of about 3 miles a day. So I shall see what happens, thank you for your help.

[Mike Fishwick]

There was an interesting bit in the BMWCC magazine this month, by an American garage owner, who had repeatedly found that use of Mobil 1 was guaranteed to make the tappets noisey, a change to (in his case) Castrol curing the problem.

It also showed the effect of extended oil changes - in tihs case every 15000 miles, by a BMW dealership using an unknown synthetic oil, which had produced so much sludge in the cam box that the only parts one could see were the cam lobes!

Like I have been telling people for years - extended oil change intervals will kill an engine in the long term.

Maybe your Mobil oil is having the same effect. I know someone with an M Coupe who swears by Mobil 1 (maybe he likes the colour of the tin) but who had a new VANOS unit at 20,000 miles . . . draw your own conclusions.

[simon-g]

There was an interesting bit in the BMWCC magazine this month, by an American garage owner, who had repeatedly found that use of Mobil 1 was guaranteed to make the tappets noisey, a change to (in his case) Castrol curing the problem.

It also showed the effect of extended oil changes - in tihs case every 15000 miles, by a BMW dealership using an unknown synthetic oil, which had produced so much sludge in the cam box that the only parts one could see were the cam lobes!

Like I have been telling people for years - extended oil change intervals will kill an engine in the long term.

Maybe your Mobil oil is having the same effect. I know someone with an M Coupe who swears by Mobil 1 (maybe he likes the colour of the tin) but who had a new VANOS unit at 20,000 miles . . . draw your own conclusions.

Thats interesting, although the cams etc are perfectly clean, chap at the garage said the engine was immaculate, so I dont think it is a case of neglect, but who knows.. Im just going to use it more and see where it goes from there.

[Mike Fishwick]

Perhaps Mobil does not have very high detergency levels, and so cannot break down the sludge formation in the tappets caused by so many short runs - anyway, you really should get your poor old Z3 out and treat it to some long runs - it's what they are for!