rumble from below!

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Mark Piercy

Mark Piercy

Well fumbled member....
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Sud ouest France !
Ok then,
P38, 2.5td auto.
189,000mls.
The box functions brilliantly. No issues there.
Oil and filter recently changed.
Light waste in the sump.
Once the engine and gearbox are warm if you rev the engine in neutral to 2000rpm then shut it off there is a rumbling from the gearbox immediately after the engine stops.
As if the internals of the torque converter are slowing to a stop with a rumbling sound!
Any thoughts please?
 
Ah hah! First time I heard the sound was by accident, I had pulled up at home revving the engine and shut it off, (like the old carb filling trick), that's when I heard it rumbling after the engine had stopped. Ta da!
 
Mark Piercy said:
Ah hah! First time I heard the sound was by accident, I had pulled up at home revving the engine and shut it off, (like the old carb filling trick), that's when I heard it rumbling after the engine had stopped. Ta da!
Click to expand...

Don't know, never come across that. Stop it from idle.
 
As above, IMHO, do NOT cut the fuel at anything other than idle RPM, not only is it bad for the turbo "bearings" - because they actually don't exist - the shaft actually floats in a film of oil - thus no oil = no bearings. You can guess how this will end. The other contender is the TQ, which might be draining of oil due to being still spinning without the pump being driven - this is also a bad idea.
One other point I would make is that the FIP itself might not like this - and I have some experience of this on older pumps. ( but almost none on electronic **** - as I steer clear of it )

Allow the engine to idle for a short period, and then cut the fuel. Much better all round, and no rumbling noise for you to worry about.
 
Mark Piercy said:
Ok then,
P38, 2.5td auto.
189,000mls.
The box functions brilliantly. No issues there.
Oil and filter recently changed.
Light waste in the sump.
Once the engine and gearbox are warm if you rev the engine in neutral to 2000rpm then shut it off there is a rumbling from the gearbox immediately after the engine stops.
As if the internals of the torque converter are slowing to a stop with a rumbling sound!
Any thoughts please?
Click to expand...
allot of them jump in with both feet and explain not to rev the engine ..and shut down
if I have read correctly you are only reving the engine and shutting down for test purposes as you noticed a noise and trying to find it

since you said it sounds like gearbox area / torque convertor remove the inspection plate and check the flex plate

since the oil and filter has just been changed re check oil level (correct procedure )
 
ozzyboydeano said:
allot of them jump in with both feet and explain not to rev the engine ..and shut down
if I have read correctly you are only reving the engine and shutting down for test purposes as you noticed a noise and trying to find it

since you said it sounds like gearbox area / torque convertor remove the inspection plate and check the flex plate

since the oil and filter has just been changed re check oil level (correct procedure )
Click to expand...

You didn't read it properly.
 
ozzyboydeano said:
I will let the MARK PIERCY be the judge of that
Click to expand...

I do find it helps if people that don't have clue what they are on about keep quiet. Cutting the oil supply to a turbo doing several thousand RPM is not a good idea. How can a TC that is not being driven is disengaged and is stopped rattle?
 
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wammers said:
I do find it helps if people that don't have clue what they are on about keep quiet. Cutting the oil supply to a turbo doing several thousand RPM is not a good idea. How can a TC that is not being driven is disengaged and is stopped rattle?
Click to expand...

its funny because part of my job I rebuild turbos ,,if this turbo was rumbling it would be already far to gone

as for reving an engine and shutting down is safe but only for diagnosing issues
I reved my TD5 today to 2000 rpm in neutral i barley made 2 psi boost pressure so this indicates the turbo is not under full boost and no engine load means no HEAT


I wont go into to much detail why we idle down turbos but a google search will help you out

as for the rumble noise the OP already stated it sounds like transmission area and the title of the OP is rumble down below
he also stated this only happens when the engine and gearbox is warm

 
ozzyboydeano said:
its funny because part of my job I rebuild turbos ,,if this turbo was rumbling it would be already far to gone

as for reving an engine and shutting down is safe but only for diagnosing issues
I reved my TD5 today to 2000 rpm in neutral i barley made 2 psi boost pressure so this indicates the turbo is not under full boost and no engine load means no HEAT


I wont go into to much detail why we idle down turbos but a google search will help you out

as for the rumble noise the OP already stated it sounds like transmission area and the title of the OP is rumble down below
he also stated this only happens when the engine and gearbox is warm
Click to expand...

So in your expert opinion what do you think is still moving in the gearbox when the engine is stopped. Boost pressures cannot be properly measured when the engine is not under load you should know that, but spinning a turbo up then stopping the engine is stupidity.
 
wammers said:
So in your expert opinion what do you think is still moving in the gearbox when the engine is stopped. Boost pressures cannot be properly measured when the engine is not under load you should know that, but spinning a turbo up then stopping the engine is stupidity.
Click to expand...

there is nothing moving or spinning ..but seems like something could be warming up and expanding... and when the engine shuts down it has movement ie a clunk clunk but depending on the rumble sound of original post we are both in limbo ....up to now he said gearbox area so yes more info is needed

how ever even if the rumble sound came from the turbo area why does this rumble sound only appear when up to operating temps ?

I also once had a rumble sound near the turbo area the frequency of the rumble would hum inside the cab and only did when the engine was warm... reason was the oil thermostat does no kick in to the centrifuge until oil reaches a curtain temp .... resulting in idle shut down my oil spinner was out of balance due to accumulation of carbon (so i could imagine this humming sound i heard would be worse if i was to rev the engine and shut it down

as for measuring boost levels this is why we purchase boost gauges this monitors all boost levels to different loads
and if you have a scan gauge ..go into live data you will see a low percentage figure of engine load at idle

did you also know using the air con puts your engine under a load
you will be very surprised how much power a viscose fan can rob power from an engine when its locked up

besides all that my gauge gets a reading from the inlet manifold when i revved my engine to 2000rpm are you saying my steady 2 psi reading is wrong ...just saying
 
Last edited:
Disco1BFG said:
As above, IMHO, do NOT cut the fuel at anything other than idle RPM, not only is it bad for the turbo "bearings" - because they actually don't exist
Click to expand...
there are ball bearing turbos on the market they run more efficiently

but the turbo in question runs a bearing bush ..some thing like you find in the bottom end of an engine like main and big end bearing shells journals
but the one in the turbo is one piece bearing bush these type of bearing the oil is the bearing

regardless if you turn off an engine at idle the turbo shaft will spin for a few seconds ..

high boost levels means heat ..so shutting an engine down straight away is a no no

the turbo bearing bush or bearing does not like to sit in one place while cooling down from high heat ..if it does the bearing starts to warp as well as the turbo housing.... just like a brake disk rotor would from hard braking and if heat is left in one spot for a period of time it will warp
this takes out the bearing out and balance of the turbo
 
Last edited:
ozzyboydeano said:
there is nothing moving or spinning ..but seems like something could be warming up and expanding... and when the engine shuts down it has movement ie a clunk clunk but depending on the rumble sound of original post we are both in limbo ....up to now he said gearbox area so yes more info is needed

how ever even if the rumble sound came from the turbo area why does this rumble sound only appear when up to operating temps ?

I also once had a rumble sound near the turbo area the frequency of the rumble would hum inside the cab and only did when the engine was warm... reason was the oil thermostat does no kick in to the centrifuge until oil reaches a curtain temp .... resulting in idle shut down my oil spinner was out of balance due to accumulation of carbon (so i could imagine this humming sound i heard would be worse if i was to rev the engine and shut it down

as for measuring boost levels this is why we purchase boost gauges this monitors all boost levels to different loads
and if you have a scan gauge ..go into live data you will see a low percentage figure of engine load at idle

did you also know using the air con puts your engine under a load
you will be very surprised how much power a viscose fan can rob power from an engine when its locked up

besides all that my gauge gets a reading from the inlet manifold when i revved my engine to 2000rpm are you saying my steady 2 psi reading is wrong ...just saying
Click to expand...

P38s don't have centrifugal oil filters. When the engine stops there is nothing turning other than the turbo or maybe the viscous fan for a few RPMs. If the Torque converter drive plate had cracked was becoming detached he would know about it without having to rev the engine and switch it off believe me. In neutral there is nothing being driven other than the gearbox oil pump and the disengaged first motion shaft. He can check the flex plate by removing the inspection plate under the bell housing and turning the engine to reveal each attachment point. Boost gauges are to all intents and purposes just another toy people fit to look at. You will never get the full boost capability of the turbo indicated unless you follow specific test procedures.
 
38s don't have centrifugal oil filters. When the engine stops there is nothing turning other than the turbo or maybe the viscous fan for a few RPMs. If the Torque converter drive plate had cracked was becoming detached he would know about it without having to rev the engine and switch it off believe me. In neutral there is nothing being driven other than the gearbox oil pump and the disengaged first motion shaft. He can check the flex plate by removing the inspection plate under the bell housing and turning the engine to reveal each attachment point. Boost gauges are to all intents and purposes just another toy people fit to look at. You will never get the full boost capability of the turbo indicated unless you follow specific test procedures.[/QUOTE said:
I never said the centrifuge was the issue I was using this as an example of the sound coming from the turbo area

your words
the gearbox oil pump and the disengaged first motion shaft
could it be possible if some thing is warming up and playing up in that area

as for your boost gauge comment I guess you never played around with remaps ..adding in a LPG conversion bigger intercooler as well as EGTs and exhaust mods
the reason I have a boost gauge
Click to expand...
 
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