Whistling under load

A couple of months ago, I changed the glow plugs on my '99 P38 DSE. I removed the inlet manifold (checked the gaskets but didn't change them) to get decent access. When I put it all back together having checked everything was serviceable and correctly fitted, I took it for a test drive. It now has a whistling noise that goes up and down as the load on the engine increases and decreases. There is no loss of power (didn't have much in the first place!) and it doesn't do it when stationary in neutral. Anybody got any advice please. It started at exactly the same time as I did the job, so it must be something that I have done. Should I have changed the inlet manifold gaskets regardless? If it is boost pressure escaping from a naff gasket, wouldn't it do it all the time and not just under load? Cheers, John

At the least I'd recheck the torque on the manifold bolts again.

My Disco 300tdi gained a whistle when the stud holding the manifold end, nearest the bulkhead, broke, thus not clamping the gaskets properly. This also occurred under load, my reasoning being that when stationary it's not under much load, when it's under load, it is!!!

Paul D said:

At the least I'd recheck the torque on the manifold bolts again.

My Disco 300tdi gained a whistle when the stud holding the manifold end, nearest the bulkhead, broke, thus not clamping the gaskets properly. This also occurred under load, my reasoning being that when stationary it's not under much load, when it's under load, it is!!!

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Thanks, makes perfect sense, I will go and check that now.

Unlikely to be manifold unless you have something trapped under it, although not impossible. The rubber seals are pretty bullet proof. You may like to check the turbo pipes for a split or loose connection though.

I have just finished checking the manifold nuts and the 2 nearest the bulkhead, whilst not loose, were nowhere near as tight as the others. Once I had tightened them, I took it out for a quick drive. The whistle is still there but it is less pronounced and a different tone so I know I am on the right track. I will order some new gaskets and get them fitted. I checked the turbo pipes for splits while I had them off and they all appear to be split-free. Thanks all, John

Nipper4761 said:

I have just finished checking the manifold nuts and the 2 nearest the bulkhead, whilst not loose, were nowhere near as tight as the others. Once I had tightened them, I took it out for a quick drive. The whistle is still there but it is less pronounced and a different tone so I know I am on the right track. I will order some new gaskets and get them fitted. I checked the turbo pipes for splits while I had them off and they all appear to be split-free. Thanks all, John

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There should not be gaskets as such just rubber rings. Like this. https://rimmerbros.com/Item--i-LKJ000070 Flick them out and turn them round.

Nipper4761 said:

I have just finished checking the manifold nuts and the 2 nearest the bulkhead, whilst not loose, were nowhere near as tight as the others. Once I had tightened them, I took it out for a quick drive. The whistle is still there but it is less pronounced and a different tone so I know I am on the right track. I will order some new gaskets and get them fitted. I checked the turbo pipes for splits while I had them off and they all appear to be split-free. Thanks all, John

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That far end by the bulkhead has a bracket. You've not trapped the bracket in there?

They are prone to warping manifolds Check if any black residue around exhaust manifold.

wammers said:

There should not be gaskets as such just rubber rings. Like this. https://rimmerbros.com/Item--i-LKJ000070 Flick them out and turn them round.

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Wammers,, mine definitely has gaskets cos I checked them when I took the manifold off, I have just ordered some off the net and they look exactly like mine?

Does the non egr ally manifold use the same `o` rings ? just a thought.

Nipper4761 said:

Wammers,, mine definitely has gaskets cos I checked them when I took the manifold off, I have just ordered some off the net and they look exactly like mine?

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Your engine should have a plastic manifold and EGR. That uses the O'rings. Only the pre EGR (1997 back) alloy manifold uses gaskets.

If you ordered stc2203, those are for alloy inlet manifold.
The alloy and plastic manifold use different sealing method.

kds said:

Does the non egr ally manifold use the same `o` rings ? just a thought.

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No. If it has an alloy manifold it is either not a 1999 engine or the head has been changed for a pre EGR unit from 1997 or earlier. It is not possible to fit a plastic manifold on early heads but later heads could be modified to take one and either manifold could be used.
https://www.ebay.co.uk/itm/BMW-525-...447112?hash=item3fa5ca6f88:g:2a4AAOSwQFNbBoCc
In the head photo above you will note that the first three inlets have spare positions for studs bottom left and top right on each port. At the moment it will take an alloy manifold, if the other stud positions were drilled and tapped you could fit a plastic manifold. Early heads did not have the cast in spare positions. Hope that is clear.

Nipper4761 said:

Wammers,, mine definitely has gaskets cos I checked them when I took the manifold off, I have just ordered some off the net and they look exactly like mine?

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Just because they were there when you took it off, doesn't mean it's correct.

make sure you have not trapped the wire to number 4 injector under manifold ( easilly done )

eldescans said:

make sure you have not trapped the wire to number 4 injector under manifold ( easilly done )

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I would double "DOUBLE" check all the turbo pipes for splits, even though they may look ok when ticking over, the pressure from the turbo will open up any tiny holes that you can't see normally. Also make sure the hose clips are on tight and sealing.

wammers said:

No. If it has an alloy manifold it is either not a 1999 engine or the head has been changed for a pre EGR unit from 1997 or earlier. It is not possible to fit a plastic manifold on early heads but later heads could be modified to take one and either manifold could be used.
https://www.ebay.co.uk/itm/BMW-525-...447112?hash=item3fa5ca6f88:g:2a4AAOSwQFNbBoCc
In the head photo above you will note that the first three inlets have spare positions for studs bottom left and top right on each port. At the moment it will take an alloy manifold, if the other stud positions were drilled and tapped you could fit a plastic manifold. Early heads did not have the cast in spare positions. Hope that is clear.

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Well, that's interesting. Mine is definitely an alloy inlet manifold and is non-EGR. I guess at some point in its long life someone has either changed the engine or the head. You live and learn!

Bagshot said:

I would double "DOUBLE" check all the turbo pipes for splits, even though they may look ok when ticking over, the pressure from the turbo will open up any tiny holes that you can't see normally. Also make sure the hose clips are on tight and sealing.

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Thanks, I'll do that.

Nipper4761 said:

Well, that's interesting. Mine is definitely an alloy inlet manifold and is non-EGR. I guess at some point in its long life someone has either changed the engine or the head. You live and learn!

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Same as mine. Should have 6 cardboard gaskets. The breather bracket should be attached at the far end of the inlet manifold.

Grrrrrr said:

Same as mine. Should have 6 cardboard gaskets. The breather bracket should be attached at the far end of the inlet manifold.

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Gaskets have just arrived...I'll be changing them tomorrow and properly checking the turbo trunking for holes.