P38A P38 rattle at idle

ar1g3 · Oct 16, 2024

So my P38 developed some engine noise today..

It makes this noise at idle, regardless of the gear selected (P, N R, D,...). Seems to change frequency with revving however to me it sounds not like it is following the engine revs proportionally. If I set off driving it's there until about 20 to 30 kph if I am gentle on the throttle. It seems as when I put some load on the engine the noise disappears. Oil and coolant level are okay, they've also not dropped. All lubricants where changed earlier this year, gearbox oil level was checked about 2000km ago and I didn't see any signs of the gearbox leaking. Also gearbox oil was replaced 4000km ago and between then and the last check there was no drop in level.

I'm on a roadtrip through Ireland and in any case about 1500km away from home.

Any ideas what this sound may be?

Oh and it's a 4.0 auto from 1999.

kermit_rr · Oct 16, 2024

not sure tbh.. doesnt sound like piston slap or liner knock (but this tends to quieten under load).. doesnt sound like the timing chain either

@Henry_b any ideas?

Mark Piercy · Oct 16, 2024

See if you can get a bar in-between the engine crank pulley and the engine casing behind to check for movement, the rubber breaks down inside the pulley and it can rattle in the same manner.

Datatek · Oct 16, 2024

Also check the heat shields have not come adrift.

DanClarke · Oct 16, 2024

It couldn't be that counterbalance malarky thingy gone loose could it?

ar1g3 · Oct 16, 2024

kermit_rr said:
not sure tbh.. doesnt sound like piston slap or liner knock (but this tends to quieten under load).. doesnt sound like the timing chain either

@Henry_b any ideas?

Yeah that was my first idea but then I gather that this usually starts occuring after overheating and she didn't overheat, at least not in the last 2 yrs.

Mark Piercy said:
See if you can get a bar in-between the engine crank pulley and the engine casing behind to check for movement, the rubber breaks down inside the pulley and it can rattle in the same manner.

Datatek said:
Also check the heat shields have not come adrift.

I'll try to fins somewhere to crawl underneath tomorrow thanks!

DanClarke said:
It couldn't be that counterbalance malarky thingy gone loose could it?

I think that's just for the diff no?

Anyway in the meantime I noticed that the noise is only there when the engine is at operating temperature. If the needle is only halfway between cold and normal temp then there's no noise.

kermit_rr · Oct 16, 2024

I had an engine with a loose liner and it was very much an isolated, distinct knock. I read somewhere they can just let go one day, didn't have to be linked to overheating and you don't need a cracked block (coolant loss) either.. I'll try and find the vid itook of the liner noise.. that only occurred at operating temperature too

kermit_rr · Oct 16, 2024

kermit_rr said:
I had an engine with a loose liner and it was very much an isolated, distinct knock. I read somewhere they can just let go one day, didn't have to be linked to overheating and you don't need a cracked block (coolant loss) either.. I'll try and find the vid itook of the liner noise.. that only occurred at operating temperature too

Hear you go

ar1g3 · Oct 16, 2024

kermit_rr said:
Hear you go

Thanks! That sounds a lot more high pitched than what I have, but same kind of frequency.

ar1g3 · Oct 17, 2024

Okay on startup this morning she makes the noise when cold so has nothing to do with temperature apparently

ar1g3 · Oct 17, 2024

Went to a LR specialist in Galway today and he had a look. Didn't think it would be anything major, rather something like a bracket come loose on the exhaust. Didn't put it on a lift as he had another car on there, and he understandably didn't dare crawling underneath to have a proper look as my car is still on air. But he managed to recreate the rattle by tapping on the exhaust.

I was thinking, could it be the cats failing? Kinda would fit in with the conditions where the rattle occurs. But I've never had one fail yet so don't know how they sound when they rattle..

norseman · Oct 17, 2024

Doesn't sound like a liner, that is more of a distinct 'tap' commensurate with engine revs.

For reference such a noise would start quite suddenly as the engine starts to warm up & is at piston speed, rather than valve gear which is half of that.
Out of interest, is the car running on LPG?

Henry_b · Oct 17, 2024

ar1g3 said:
Went to a LR specialist in Galway today and he had a look. Didn't think it would be anything major, rather something like a bracket come loose on the exhaust. Didn't put it on a lift as he had another car on there, and he understandably didn't dare crawling underneath to have a proper look as my car is still on air. But he managed to recreate the rattle by tapping on the exhaust.

I was thinking, could it be the cats failing? Kinda would fit in with the conditions where the rattle occurs. But I've never had one fail yet so don't know how they sound when they rattle..

cats breaking up do rattle.

Manifold leak too can sound like an mechanical tapping.

Henry_b · Oct 17, 2024

I'd drop the inspection plate off of the bottom of the bell housing and look at the flexplate..

ar1g3 · Oct 17, 2024

norseman said:
Doesn't sound like a liner, that is more of a distinct 'tap' commensurate with engine revs.

For reference such a noise would start quite suddenly as the engine starts to warm up & is at piston speed, rather than valve gear which is half of that.
Out of interest, is the car running on LPG?

Well the noise is there even on an ice cold engine so I guess I'm good with regards to the liners.
The car has run on LPG before but that system has been completely removed.

Henry_b said:
I'd drop the inspection plate off of the bottom of the bell housing and look at the flexplate..

What does the flexplate do? Never heard of it.. BUT the sound does remind me of a broken dual mass flywheel, which the p38 does not have. Is the flexplate a similar device? And if it is broken, am I good to drive another 1500km? (About 1000 miles

)

Henry_b · Oct 17, 2024

ar1g3 said:
Well the noise is there even on an ice cold engine so I guess I'm good with regards to the liners.
The car has run on LPG before but that system has been completely removed.

What does the flexplate do? Never heard of it.. BUT the sound does remind me of a broken dual mass flywheel, which the p38 does not have. Is the flexplate a similar device? And if it is broken, am I good to drive another 1500km? (About 1000 miles )

In short The flexplate is bolted to the flywheel the flexplate is what connects the engine to the torque converter, its known for them to crack/breakup.

If it is broken don't drive it.

ar1g3 · Oct 17, 2024

Henry_b said:
In short The flexplate is bolted to the flywheel the flexplate is what connects the engine to the torque converter, its known for them to crack/breakup.

If it is broken don't drive it.

Hmm okay thanks! And it is visible if its broken through the bell housing inspection hole?

Henry_b · Oct 17, 2024

ar1g3 said:
Hmm okay thanks! And it is visible if its broken through the bell housing inspection hole?

you might see a crack or several yes

ar1g3 · Oct 17, 2024

Alright thanks, I'll find a rock to crawl onto tomorrow and have a look.

Datatek · Oct 18, 2024

I assume that you have done the easy checks of crank pully, exhaust mounts and heat shields?

P38A P38 rattle at idle

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