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[tunnie]

Finally got around to oil pressure testing my 3.2, looks like its suffering from low oil pressure when very hot.

From cold its fine, but when is up to temp, the idle pressure dropped as low as 17-19 Psi, although it would hover around 20 Psi.

Popped the gauge on TB's 3.2 & it stayed noticeably higher, never dropped below 25 Psi, his appeared to hover around 30 Psi.

Book of 'dangle berries' says it should never go lower than 21, so that suggests a problem.

I understand the oil pressure relief valve is inside the oil pump? Guess if you have to strip down that far, might as well change the pump too?

Would thicker oil help 

Oh and thanks to TB today for his helpful advice as always 

[adey2]

proves that the shell garage upsetting him by never having fuel causing him to bury his right foot into the pile works wonders for his engine, on a lighter note hope you get sorted as never a good feeling knowing it not working right

[tgm147]

How many miles has it done and what grade of oil is in it now? I'd try a slightly thicker oil first and see if that helps as long as it's not too thick when its cold. Failing that I'd say oil pump. Is the pressure when it's cold the same as TB's too?

[tunnie]

Its done 138k & its got standard GM 10/40 Semi Synth in it, along with lifter treatment at the moment.

Sadly did not check it when cold, but it sounds fine started cold, no tapping at-all.

Think like oil pressure drops too low, not giving enough to fill some of the lifters. 

[cem_devecioglu]

some good info there
http://www.international-auto.com/fiat-lancia-tips-on-reading-gauges/tips-on-reading-gauges-oil-pressure-gauges.cfm

[tgm147]

Its done 138k & its got standard GM 10/40 Semi Synth in it, along with lifter treatment at the moment.

Sadly did not check it when cold, but it sounds fine started cold, no tapping at-all.

Think like oil pressure drops too low, not giving enough to fill some of the lifters. 

I'd read the pressure on both cars when it's cold too. If the oil pump is on the way out then the pressure will still be down, just might not sound like it with the oil being thicker when cold. If you have lifter treatment in, I'd give it another oil change and see from there. If a bit of crap has come from the lifters and is blocking something, fresh oil might flush it out. Might be worth trying an engine flush too.

[albitz]

Worth droppping the sump to check the pick up strainer isnt blocked with crud before replacing pump ?
Afaik,changin the oil pump on the V6 is a major operation.

[cem_devecioglu]

"Certainly engines that have experienced significant ring and liner wear benefit from thicker oils. Thicker oil use results in compression increases, performance improvements and reduced oil consumption."
http://www.machinerylubrication.com/Read/518/motor-oils

[tunnie]

Its done 138k & its got standard GM 10/40 Semi Synth in it, along with lifter treatment at the moment.

Sadly did not check it when cold, but it sounds fine started cold, no tapping at-all.

Think like oil pressure drops too low, not giving enough to fill some of the lifters. 

I'd read the pressure on both cars when it's cold too. If the oil pump is on the way out then the pressure will still be down, just might not sound like it with the oil being thicker when cold. If you have lifter treatment in, I'd give it another oil change and see from there. If a bit of crap has come from the lifters and is blocking something, fresh oil might flush it out. Might be worth trying an engine flush too.

Its already had 4 oil changes inside 1,500 miles, so doubt another change would help.

Worth droppping the sump to check the pick up strainer isnt blocked with crud before replacing pump ?
Afaik,changin the oil pump on the V6 is a major operation.

Sump dropped, strainer checked all clear 

[Entwood]

Thicker oil might improve the pressure at the guage .. but will probably do more harm in the long term. Oil pressure is a mixture of 2 factors, the output flow from the pump - no pump EVER produces pressure, a pump produces flow .... nowt else - and the resistance to that flow provided by the various pipes and galleries within the engine .. pressure being resistance to flow.

SO, the low pressure you are seeing is caused by one of 2 things ... either the pump flow is reduced - blocked pickup strainer, knackered pump .....  or the resistance to flow is wrong ... this can be interrnal wear ...  big ends known to cause such, or some other  internal "leak".

Now ....  once oil pressure is lower than normal it cannot make its way to all the remote parts of the engine that need lubricating ... so they suffer from loss of oil especially if there is an internal "leak" of some sort as the oil takes the easiest path and the flow rate through the "bigger" holes increases..... using thicker oil will make this WORSE as that oil will take the easier path even more readily than the thinner stuff.

The same ideas apply to high oil pressure as it happens ... high pressure is too much resistance so the oil is not circulating correctly, something is not getting lubricated, the flow rate is now too low ... use a "thinner" oil or "turn down" the pressure at the pump and the remote parts get even less oil.

It is for these reasons that engines have an oil specification and maximum and minimum stated oil pressures, go outside those parameters and you ask for trouble.

[tunnie]

SO, the low pressure you are seeing is caused by one of 2 things ... either the pump flow is reduced - blocked pickup strainer, knackered pump .....  or the resistance to flow is wrong ... this can be interrnal wear ...  big ends known to cause such, or some other  internal "leak".

It is for these reasons that engines have an oil specification and maximum and minimum stated oil pressures, go outside those parameters and you ask for trouble.

Thanks Entwood, very much appreciated.   

Certainly learning a few things here about how oil pressure in an engine and how it works.

Pickup strainer has been checked, number of people confirmed while it was up in the air that although there were a few deposits in it, nothing to worry about. Its since had that oil dropped & changed. The oil does stay clean too, which i think is a good sign.

I've heard big end knock on a V6 before, this 3.2 does not have it.... yet! Driving about it goes like a 3.2 should & sounds like it should from the cabin. Its only once you open window and stick you head out can you notice it. Its not burning any oil either, level staying good.

I did once, briefly, shut it up. Parked with engine running at MrsT flat, traffic warden approached. I may have left some rubber on the tarmac leaving him, letting my frustration be known    It had been idle for a few mins, then almost straight to red line, spun around, came back, stopped again. Got out, silent! 

But soon came back, think that hard blast perhaps forced some oil into one of the lifters which is suffering at low pressure? 

I guess without stripped down to the oil pump, not a lot else to check?

With the amount of effort involved to reach the pump, I assume its best just to replace it with a known working one?

Thanks for everyones help and advice so far 

[TheBoy]

SO, the low pressure you are seeing is caused by one of 2 things ... either the pump flow is reduced - blocked pickup strainer, knackered pump .....  or the resistance to flow is wrong ... this can be interrnal wear ...  big ends known to cause such, or some other  internal "leak".

Pressure relief valve being one mooted previously.... ?

[cem_devecioglu]

Thicker oil might improve the pressure at the guage .. but will probably do more harm in the long term. Oil pressure is a mixture of 2 factors, the output flow from the pump - 1.no pump EVER produces pressure, a pump produces flow .... nowt else - and 2.the resistance to that flow provided by the various pipes and galleries within the engine .. pressure being resistance to flow.

SO, the low pressure you are seeing is caused by one of 2 things ... either the pump flow is reduced - blocked pickup strainer, knackered pump .....  or the resistance to flow is wrong ... this can be interrnal wear ...  big ends known to cause such, or some other  internal "leak".

Now ....  once oil pressure is lower than normal it cannot make its way to all the remote parts of the engine that need lubricating ... so they suffer from loss of oil especially if there is an internal "leak" of some sort as the oil takes the easiest path and the flow rate through the "bigger" holes increases..... using thicker oil will make this WORSE as that oil will take the easier path even more readily than the thinner stuff.

The same ideas apply to high oil pressure as it happens ... high pressure is too much resistance so the oil is not circulating correctly, something is not getting lubricated, the flow rate is now too low ... use a "thinner" oil or "turn down" the pressure at the pump and the remote parts get even less oil.

It is for these reasons that engines have an oil specification and maximum and minimum stated oil pressures, go outside those parameters and you ask for trouble.

as its my subject, just wanted to correct a few definitions  
 
1. every turning pump creates pressure so flow can be established..
 
2. before everything, the fluid itself has a resistance to flow defined by viscosity units which also changes by temperature and pressure.. and also the resistance of those pipes and galleries is a function of the fluid viscosity ( and also their diameter, length etc )

[Omegatoy]

its the main bearings on the crank that carry the pressure Mark, if they are worn the engine will have low oil pressure when hot,its possible to change them with the engine in the car , problem is knowing which size vxhall used when building the lump!! many had production tolerance problems and were resized at the factory!!
the only really difficult one is the gearbox end as access to the main bearing is not possible without dropping the gearbox although you can change the bottom half!!
it will probably run for years like it if its only on tickover its pressure is low, whats the pressure reading at 2.5k rpm?

[TheBoy]

its the main bearings on the crank that carry the pressure Mark, if they are worn the engine will have low oil pressure when hot,its possible to change them with the engine in the car , problem is knowing which size vxhall used when building the lump!! many had production tolerance problems and were resized at the factory!!
the only really difficult one is the gearbox end as access to the main bearing is not possible without dropping the gearbox although you can change the bottom half!!
it will probably run for years like it if its only on tickover its pressure is low, whats the pressure reading at 2.5k rpm?

More than 1k, its way up 50/60 psi, rising further with revs.