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What oil pressure to turbo? by regcheeseman on 17 Jul, 2011 02:23
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I've fitted a pressure gauge to the turbo feed, problem is I don't know what I should see.
The gauge reads just over 20 psi at idle which would seem pretty good, but I have no reference to go by. -
#1 by vdubspeed on 17 Jul, 2011 05:25
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why does it matter. VW ran oil feed from the oil filter housing straight to the turbo. On my car I run it from the head to the turbo. Works fine.
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#2 by regcheeseman on 18 Jul, 2011 04:56
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Why does it matter? well it may not matter to you because you've taken a low pressure feed to your turbo which should have a high pressure feed.
Maybe I'd just like to know that my oil presure is good bad or indifferent, if that's ok with you?
It also matters to me as I've a convoluted oil drain and a non standard feed to a turbo that has been clocked because it's fitted upside down.
Anyone know what pressure the oil pump should deliver? -
#3 by Mark(The Miser)UK on 18 Jul, 2011 05:39
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At the risk of being bitten
Could it be that you don't actually want too much pressure, as the bearings are floating and are just interested in flow rate, and would be happy with a few psi attached to a gallon a minute if that were possible.
The bearings are gravity drained aren't they and so you might get that dreaded 'run away' if the excess is spurting into the intake...
Didn't Landrovers get this problem, or did I dream it. [I dream more and more these days
]
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#4 by regcheeseman on 18 Jul, 2011 09:48
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Could it be that you don't actually want too much pressure
Nope I probably don't want too much pressure, so the questions remains....
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#5 by R.O.R-2.0 on 18 Jul, 2011 10:16
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Why does it matter? well it may not matter to you because you've taken a low pressure feed to your turbo which should have a high pressure feed.
Maybe I'd just like to know that my oil presure is good bad or indifferent, if that's ok with you?
It also matters to me as I've a convoluted oil drain and a non standard feed to a turbo that has been clocked because it's fitted upside down.
Anyone know what pressure the oil pump should deliver?
nah, he used the stock TDI oil line.. most of the TDIs are fed from the side of the head AFAIK.. first gen ones atleast.
*i have no oil squirters, and i run about 35 psi oil pressure at idle when warmed up. but that shouldnt matter, the squirters shouldnt even be spraying at idle* -
#6 by Mark(The Miser)UK on 18 Jul, 2011 10:52
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I've fitted a pressure gauge to the turbo feed, problem is I don't know what I should see.
There seems to be no direct spec, except being as oil is taken from the same flange as the 'filter pressure sensor' then this will be the pressure 1.8 bar for gassers and ... just looked in the VAG service and in the Bentley junk mail; 1.4 bar for Turbodiesels.
The gauge reads just over 20 psi at idle which would seem pretty good, but I have no reference to go by.
I think that is rated at 2000rpm. That's 19.6psi ish so I guess you are fine and on spec.
Oil pumps were enlarged to maintain this pressure with the inclusion of the turbo were they not?
Then as a replacement/upgrade to all 4 cylinder engines IIRC -
#7 by regcheeseman on 18 Jul, 2011 15:00
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nah, he used the stock TDI oil line.. most of the TDIs are fed from the side of the head AFAIK.. first gen ones atleast.
Isn't the head take-off at lower pressure than the filter take-off though - but if as you say the TDI makes do with this then it's all ticketty-boo. -
#8 by rabbitman on 18 Jul, 2011 21:13
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I doubt the pressure between the head and flange is much different, kinda like if you check pressure in a leaky garden hose at several locations I don't think it would be much different.........I've never checked though.
Also if you have good bearings in the turbo they won't let a large enough flow of oil get through into the cavity faster than it can drain, if the bearings were worn very bad the cavity would fill faster than it could drain and would push oil through the seals.......that was a weird sentence.
What I'm trying to say is with good bearings high or low oil pressure would be ok, with bad bearings you'd need high oil pressure but if the oil flow past the bearings exceeded the drains flow capacity you'd have seals leaking and a possible runaway. Hope this helps.
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#9 by Mark(The Miser)UK on 19 Jul, 2011 06:51
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I doubt the pressure between the head and flange is much different, kinda like if you check pressure in a leaky garden hose at several locations I don't think it would be much different.........I've never checked though.
I think you are only correct if the bearings were seals and not 'leaks' by design. If you look again at the perforated garden watering hoses there is a noticable drop in spurt height as you work along the hose. To overcome that the holes need to get bigger the further away from the pressure source.This is never done on a cheap hose.
The diesel head has low pressure compared with source because of the large flowrate out onto the bearings, hence the 4 oil drains in the cam area. Initial high pressure spikes occur due to oil viscosity etc. Head pressure warning is either 0.3 bar or 0.6 bar which is, on the face of it, not very much. It being so low is because of flowrate. A keypoint in the function of a bearing is load distribution, and lubrication. In a shell bearing a tight 'good' fit is a bad bearing as it prevents cooling under load. A relatively loose bearing allows better lubrication. This has to be balanced with the oil pump being large enough to not starve the other bearings
Also if you have good bearings in the turbo they won't let a large enough flow of oil get through into the cavity faster than it can drain, if the bearings were worn very bad the cavity would fill faster than it could drain and would push oil through the seals.......that was a weird sentence.
What I'm trying to say is with good bearings high or low oil pressure would be ok, with bad bearings you'd need high oil pressure but if the oil flow past the bearings exceeded the drains flow capacity you'd have seals leaking and a possible runaway. Hope this helps.
I have never had to strip a turbo, but I thought the bearings are merely bathed in a river of oil to allow them and the rotor to float, and flow was high for cooling purposes. I know that my turbo left overnight does not spin freely with fingertips, but once gorged would spin freely.
The whole oil supply system is balanced, and apart from a bit of leaway, severe wear in one bearing will cause excess flow rate that starves other bearings.
A good personal example is in the case of a gasser vw 1.8 I had, that was perfect until the head seized! It was a major failure of #1 main bearing which then took all the oil the pump [in good condition it turned out] could produce.
Other than the cam belt snapping, releasing the cam by loosening the carrier bolts and smearing the bearings with a little fine pebble polishing abrasive, and rotating cam by hand whilst gradually retightening bolts was sufficient to unbind...