High oil pressure

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Discussion

CrutyRammers

Original Poster:

13,735 posts

197 months

Sunday 15th September 2013
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Hi all, hoping someone's seen this before.
I finally lit the blue touch paper on the Alfa v6 I've been rebuilding over the last several years, and it worked woohoo
But there is something odd going on with the oil pressure; basically it seems very high. The symptoms are:

- On start, the oil pressure light goes out very quickly. If I stop the engine, with the ignition on , the light stays off for some time, i.e. it seems to be "holding" pressure.

- The oil pressure gauge is off the scale, reading over 100psi.

- During the initial 20 minutes/2-3000 rpm cam running in period, the pressure settled down to around 70psi @3000rpm, and dropped to around 50 at idle. So I thought that all had settled down.

- However, since then, it remains off the scale each time I start it. (i've been chasing leaks so I haven't run it for any more long periods)

Other pertinent information:
- The oil pressure switch and sender unit are on a remote mounting, taken off the original pressure switch port.
- I've checked the pressure relief valve today and it seems fine - the piston moves up and down easily with no binding, and the spring is, well, springy. I rebuilt it all along with the engine so that's as expected.
- The filter is remote-mounted as well, via a take-off plate. There's an oil cooler which is taken off from the original fittings.
- Oil is Miller's running in oil, 10-40 (same grade as the recommended oil for this engine)
- I had the cam covers off after the run-in and there was plenty of oil in the top of the engine, and there didn't seem to be any great wear on the cams.

I'm at a loss to really work out what's going on here. Presumably it's to do with the oil being cold, but given that it's the same grade as the standard oil, that doesn't seem right really. Any help/ideas/things to check much appreciated.


ETA more information

Edited by CrutyRammers on Sunday 15th September 19:42

Mikey G

4,723 posts

239 months

Sunday 15th September 2013
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Double check the pressure sender and gauge with another known set.

Steve_D

13,737 posts

257 months

Sunday 15th September 2013
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Make sure the remote oil filter is pumbed to flow in the right direction. Many filters have a valve in them so you could be flowing the wrong way against the valve.

Steve

CrutyRammers

Original Poster:

13,735 posts

197 months

Monday 16th September 2013
quotequote all
I wondered about that, Steve. It all seems fine though - the OUT port from the take off plate (outside) goes to the IN port of the remote housing (outside) and vice-versa. Filters all work the same way don't they? (flowing in around the outside, and out via the centre)

Mikey - I do have the old sender so I can try that - the new one is a brand new Stack unit. The switch is old but was working before, it seems unlikely that both would be wrong though.

I guess I can remove all the remote stuff and try everything back in the stock positions and see if that changes anything. Man I am fed up of taking oil unions on and off!

CrutyRammers

Original Poster:

13,735 posts

197 months

Monday 16th September 2013
quotequote all
Ok, more tests.
I refitted the original switch and sender in their stock positions (deleting the remote sensor housing). Same results, which should rule out bad earths or sender units.

Running the engine, then turning it off and watching the gauge - initially, the pressure drops to zero over 30-40s. The warning light comes on as the pressure drops below an indicated 5-10psi, exactly as you'd expect.

After a few runs of 20-30s each, the pressure while running has dropped, although is still high (70psi @ idle, 100psi @ 3500 rpm). But interestingly, when the ignition is turned off, the pressure drops to zero and the light comes on in 1 or 2s. So that looks a bit like the oil warming up maybe?

I've ordered a mechanical test gauge so I'll see what that says, but I don't suppose that both sender units and the pressure switch are wrong, somehow.

The stock sender position is high up on one of the heads (arrowed). Surely it couldn't be a blockage causing the high reading so far from the pump, as the galleries have alreay split into several different ones by then?



I don't really want to run the thing too much after reading dire warnings on here about getting load on the engine asap to bed the rings in. But I can't afford to do that if the oil system isn't right.

CrutyRammers

Original Poster:

13,735 posts

197 months

Tuesday 17th September 2013
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I'm probably talking to myself but whatever hehe
Maybe something to do with the engine assembly lube I slathered everything in whilst building it, and the vaseline used to pack the pump with dissolving in the oil and upping the viscosity. The assembly lube in particular is like treacle.

Pumaracing

2,089 posts

206 months

Tuesday 17th September 2013
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The pressure relief valve should discharge into a port which returns the excess oil to the sump. Is that clear? Otherwise it can only really be the gauge or the relief valve. A bit of engine building lube won't be hurting anything.

CrutyRammers

Original Poster:

13,735 posts

197 months

Tuesday 17th September 2013
quotequote all
It's rather hard to get at but I shall have a look. I guess I can stick a hose over it and blow to see if it's clear.
I've found a few examples of this on the internets in different engines, but nobody ever updates their threads to say what it was/what happened.

CrutyRammers

Original Poster:

13,735 posts

197 months

Tuesday 17th September 2013
quotequote all
OK. I took the relief valve piston and spring out, and ran the engine up for 2-3s. I'd have expected that to give me very low or zero pressure (as it should be dumping the oil straight back in the sump), correct? But in fact it shot up to 100psi again.
So I guess that's pointing to the bypass port being blocked somehow?

Pumaracing

2,089 posts

206 months

Tuesday 17th September 2013
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Or maybe the pump doesn't even have a bypass port due to a production cock up. Time to strip it down and see.

CrutyRammers

Original Poster:

13,735 posts

197 months

Tuesday 17th September 2013
quotequote all
Well it had done 150,000 miles before I rebuilt it, so if there's no port it probably doesn't need one smile
I'll see what else I can find out with it in place first - this all forms part of the engine mount and I don't think I can get it off without taking the whole lot out frown

Edit - think I'm being dense here.
The thing I removed is a spring loaded piston in the oil filter housing. Looking back through my photos, there's also a spring loaded plunger in the pump body itself. So I guess the thing I removed is to bypass the filter in case that gets blocked, whereas the thing in the pump will be the one which actually regulates the pressure?


Edited by CrutyRammers on Tuesday 17th September 22:31

PaulKemp

979 posts

144 months

Wednesday 18th September 2013
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Yes the spring in the pump is the pressure relief
What pressure are you trying to achieve?

Evoluzione

10,345 posts

242 months

Wednesday 18th September 2013
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CrustyRammers said:
Well it had done 150,000 miles before I rebuilt it, so if there's no port it probably doesn't need one smile
I'll see what else I can find out with it in place first - this all forms part of the engine mount and I don't think I can get it off without taking the whole lot out frown

Edit - think I'm being dense here.
The thing I removed is a spring loaded piston in the oil filter housing. Looking back through my photos, there's also a spring loaded plunger in the pump body itself. So I guess the thing I removed is to bypass the filter in case that gets blocked, whereas the thing in the pump will be the one which actually regulates the pressure?


Edited by CrustyRammers on Tuesday 17th September 22:31
Some pictures posted up would help a lot, you're asking us to advise blind while you look at the pics....

Look at the diagram you posted up, you can clearly see bypass valve inside oil filter (as it normally is).
What you may have been fiddling with is the thermostat, you may well have put some part of that (and part of the actual pressure relief valve) back incorrectly or it has dirt on it and has stuck.

CrutyRammers

Original Poster:

13,735 posts

197 months

Wednesday 18th September 2013
quotequote all
PaulKemp said:
Yes the spring in the pump is the pressure relief
What pressure are you trying to achieve?
Nothing clever or unusual - normal figures given for this engine are as low as 15psi for warm idle, topping out at 50-60 when revved. Pretty standard stuff. The fact that it was off the scale seemed odd, is all. And even when warm it's 50 at idle, 70-80 at rpm. I want to make sure it's not a problem before I go any further.

CrutyRammers

Original Poster:

13,735 posts

197 months

Wednesday 18th September 2013
quotequote all
Evoluzione said:
Some pictures posted up would help a lot, you're asking us to advise blind while you look at the pics....

Look at the diagram you posted up, you can clearly see bypass valve inside oil filter (as it normally is).
What you may have been fiddling with is the thermostat, you may well have put some part of that (and part of the actual pressure relief valve) back incorrectly or it has dirt on it and has stuck.
Yeah sorry!
It's not the thermostat, I know what bit that is smile. But I think the manual was misleading me - the key to the diagram above says that number 6 ("oil pressure limiting valve") "controls system pressure". But really it's a bypass valve to allow flow around the oil filter if it's blocked? In which case, removing it wouldn't have affected the pressure, which fits with what I saw.

Then I remembered that the oil pump also has a spring loaded valve in it - it's in the housing circled:

As I recall there's a plunger and spring, held into the housing by a split pin. I guess that it's this which actually regulates the pressure, and which I need to look at.


oakdale

1,786 posts

201 months

Wednesday 18th September 2013
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What do you think is wrong with having oil pressure that is over 100psi with cold oil?

As long as the pressure is within the correct range when at working temp I wouldn't worry about it.

On an engine in good condition, the pressure will go high with cold oil even when the pressure relief valve of its seat.

rev-erend

21,404 posts

283 months

Wednesday 18th September 2013
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I have something similar ..

One sender sent the guage - right to left and another type Left to right.

Evoluzione

10,345 posts

242 months

Wednesday 18th September 2013
quotequote all
oakdale said:
What do you think is wrong with having oil pressure that is over 100psi with cold oil?

As long as the pressure is within the correct range when at working temp I wouldn't worry about it.

On an engine in good condition, the pressure will go high with cold oil even when the pressure relief valve of its seat.
That figure and beyond is way too high, it should be 6 bar cold, around 1 bar hot (circa 100'c) any more and you risk damage. He's right to be concerned.

PaulKemp

979 posts

144 months

Wednesday 18th September 2013
quotequote all
1 bar hot??
14 psi??
I like 25psi as a lower figure and at least 7psi per 1000rpm
Currently have 5 bar hot to the red line
I get twitchy when its not good pressure

oakdale

1,786 posts

201 months

Wednesday 18th September 2013
quotequote all
Oil pressure figures quoted by car makers are the usually lowest acceptable value and are often given as quite low to cover them from people complaining under warranty.

Oil pressure is the result of the pump pushing a virtually incomressible fluid against the resistance of the oilways and is greatly effected by the temperature and viscosity of the oil.

I can't see a problem if the oil pressure is within limits when the engine oil is up to temperature.

One of the main reasons that an engine should not be revved too hard from cold is because of the excessive oil pressure this causes.