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Kitch

Sky-High Oil Pressure On Tu5 8V

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Kitch

Hi all,

 

I'm currently building a Hillman Imp with a Saxo VR 8v lump in the back. The oil pressure when fast idling or revving the engine has suddenly become excessive.

 

The engine is a 98 blacktop, came from a Saxo VTR. The car ran well, showed good compression and made 95bhp on our dyno (I popped it on to assess the health of the engine).

 

Before fitting it to the Imp, I replaced the headgasket as a matter of course. I also fitted a Newmans PH3 camshaft. We made an adapter and fitted an oil pressure sender to go with the original switch, so it could operate a gauge. The engine's also running bike carbs and I fitted a trap door sump insert kit before putting the engine in (had concerns about oil surge on launch or braking!)

 

When we fitted it and got it running, the oil pressure was fine. We've had a couple of leaks, but the gauge always showed between 30psi on idle, and 60psi at max revs. The gauge tops out at 80psi. The engine is running Evans Waterless Coolant, and if anything the cooling system is too efficient! It struggles to warm up at times.

 

Now I have an issue where at idle, the oil pressure is at 40psi, and on fast idle it goes full-scale, in excess of 80psi. It's blowing oil back out of the dipstick. The breather vent from the crankcase seems to be venting steam more than anything else, which is very weird given that it has no water in the cooling system! The oil level had dropped, and when I dropped the oil to check it the other day, I found it had used about a litre in 20miles. It doesn't blow smoke from the exhaust at all, of any colour.

Compression readings were 189psi, 190psi, 193psi, 189psi. Leak down test is planned next, but the engine seemed in great health up until last week, especially in the donor Saxo.

Trying to figure out what could have gone wrong, other than assuming it's rings or HG related. It's a customers car, so I don't want to go ripping it apart on his time without really being confident of what the issue is. Every time I land on something like a the piston rings, I then manage to counter the theory (no smoke, good compression etc).

 

I'm not sure how the oil pumps work on these engines, and whether there might be some kind of relief valve that could be jammed? That's certainly more plausible than sudden and unexplained ring failure!

 

Any ideas?

 

Thanks

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welshpug

yep, there's an oil pressure relief valve in the oil pump.

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RossD

As Welshpug says, either the pressure relief valve is stuck, or a possible failure of the headgasket between cylinder 4 and the main oil feed from the block to the head. However, I doubt the latter and expect its the former!

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Kitch

Cheers chaps, new oil pump ordered. Will try that before condemning the rest!

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welshpug

I'd only use o.e pumps, there haven't been many stories of success with aftermarket units.

 

They aren't known to cause much issues so I'd strip it apart first of all, you can replace the spring and plunger separately just like an XU.

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Anthony

Just musing, but given that idle oil pressure has also jumped from 30 to 40psi, surely that suggests that the issue is unrelated to the oil pump PRV?

 

After all, 40psi is below the point where the PRV should be open, so even if the PRV was stuck closed it wouldn't explain the oil pressure jump at idle?

 

Not only that, but excess oil pressure =/= excess crankcase pressure, which is presumably what's causing the oil to be forced out of the dipstick?

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Kitch

I'd only use o.e pumps, there haven't been many stories of success with aftermarket units.

 

They aren't known to cause much issues so I'd strip it apart first of all, you can replace the spring and plunger separately just like an XU.

 

Ideally an OE pump would have been better, but I didn't want to go throwing big money parts at it based purely on a hunch. It won't get a hard life, so if it does the job for a year while an OE one is sourced it'd be a result!

Did wonder about stripping and inspecting, but my worry is that if the valve was jamming under certain conditions that I couldn't replicate with my fingers, I'd never know. Changing the whole thing will prove it one way or the other, and for £97.

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Kitch

Just musing, but given that idle oil pressure has also jumped from 30 to 40psi, surely that suggests that the issue is unrelated to the oil pump PRV?

 

After all, 40psi is below the point where the PRV should be open, so even if the PRV was stuck closed it wouldn't explain the oil pressure jump at idle?

 

Not only that, but excess oil pressure =/= excess crankcase pressure, which is presumably what's causing the oil to be forced out of the dipstick?

 

This is my only concern....why is it affecting crankcase pressure? Before I pull any pumps out, I'm going to do another leak down test only ramp the pressure up to 60psi or so, and see if the oil pressure moves at all. That'd prove the head gasket is or isn't ok at least, but there are a lot of unanswered questions at the moment.

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And

The pumps do 2 things one the gears wear into the end part but that gives low pressure, but two the one that could be your issue is the cap /valve that fits on the pressure relief Spring wears the oil pump casing that can give low or high pressure depending were it alows the valve to stick, they are easy to rebuild just fiddly closing back up with the spring trying to push both parts apart, getting parts tho is the hard part although I used a xu 6bar Spring in mine, my tu runs 6bar cold dropping to 2bar hot at idle and 4bar hot at fast idle. don't forget oil will steam when hot as the engine heats up and cools down it will condensate very slightly so it's just the moisture evaporating back off nothing to really worry about. that oil consumption is a bit worrying tho just a bit excessive.

Edited by And
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Kitch

Ok, so had more of a play just now, and things aren't as clear cut as they seem. In fact, the waters are well and truly muddied!

 

Leak down test was the first thing I did. I ramped up the pressure to 80psi with each piston at TDC to see if the oil gauge budged - it didn't on any of them. I did here varying degrees of hissing from the crankcase, but then I'd expect to hear something. The results were a bit muddled as well (I'm beginning to think the leak down tester isn't up to much! First test I did on all four showed a 3% leak on #4, 6% on #3, 25% on #2 and 8% on #1. I immediately think "Ello, looks like a problem with no.2 cylinder" before hooking no.4 up again and finding it at 20% at TDC! My colleague then said he always gets wild results from it too, and has stopped using it for measuring and now uses it purely as a listening device!

 

On one hand I'm wondering if the rings are leaking, but that makes no sense as why would they suddenly fail? The only potential factor in that theory is that we're running the car on bike carbs, and though Bogg Bros advised the customer they were set up for a 1600cc TU engine, we've found they're running massively lean and require tuning. The car hasn't done any real hard work in that time, but I'm wondering if the cylinder temps have gotten too high and done something to the rings.

The crankcase pressure is excessive, and the only point I'm wondering on that is the ventilation - it just goes to atmosphere, as there is no easy way to plumb in a balanced vacuum. I never thought this would be an issue when we built it, as I see so many TU's just running the main breather vent straight into a plastic bottle, with no issues.

.

The ring suggestion doesn't explain the high oil pressure though. The only theory I've popped up with is that could the crankcase pressure have force-fed the oil pump pickup as it looked for a way out? Could that have jammed a relief valve operation in a slightly worn-pump casing? Could the two problems be related, but not the same problem?

 

Add to this the fact that the car is a customers who I'm desperately trying to save from spending s*itloads of cash, and the fact the engine is running inline now in the back of an Imp - could running inline have done something? I'm pretty sure Imps have been used in competition with TU engines fitted, and as it covered 20-30miles before with no issues, it seems weird it's just gone now.

The ring issue caused by high cylinder temps caused by lean running are a possibility I came to as I was trying to think of something that could have caused a failure between now and when we fitted the engine. But that only works if it is possible that an oil pump can be 'supercharged'!

 

It's got to be two related issues, rather than the same issue, surely? If the crankcase pressure was force-feeding the oil pump, surely the relief valve would deal with it?

 

 

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Kitch

So following on from the above, I've just been out for a few hours playing with it. I recorded the behaviour of the oil pressure gauge relative to the revs, and some of the numbers I got before seem to have changed. We'll have to assume my previous readings are wrong, as I never wrote them down.

 

So, when it reaches full operating temperature, these are the readings:

 

Idle (around 1k revs) - 30PSI (indicated)

2000rpm - 40PSI

3000rpm - 50PSI

3500rpm - 55PSI

3800rpm(ish) - full scale deflection!

 

Does this with the breather hose on, or off. The crankcase pressure from the breather hose doesn't increase as the revs climb, which I would expect it to if the rings were suspect.

 

I took this quick video of the gauge so you can see the way it suddenly bounces off:

 

https://youtu.be/Hsct7RF0L5I

 

Takes a while for it to return down to normal readings too. I even managed to take the car for a quick spin, and it behaves the same under load.

 

We've got a new theory (and one I'd LOVE to be true) where the gauge is lying, and the pressure from the crankcase is because our breather hoses are too restrictive. We're going to try a different gauge on it, and plumb in larger-bore breather hoses, as we have no vacuum extraction for them, and see where that gets us.

 

Does the behaviour of the gauge tie in with a jammed relief valve at all, do you think?

 

Cheers

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welshpug

has it had a recent oil change?

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Kitch

has it had a recent oil change?

 

Yes, but the problem was there before and after. Wasn't left empty for any length of time either, it was all done in one hit.,

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Anthony

The way that gauge is behaving looks somewhat suspicious to me - you shouldn't really have oil pressure jumping massively like that in the space of a couple of hundred rpm, even if the relief valve was jammed.

 

I'd check this first and foremost with another (mechanical) oil pressure gauge and go from there, but gut feeling is that it's a false alarm and the actual oil pressure is fine.

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RossD

Agree with Anthony. In your earlier posts I simply presumed you were using a decent mechanical oil pressure gauge and not relying on a dodgy looking in dash one :P

 

Get a decent mechanical (i.e. doesn't use an electronic sender) in there and check again. The Stack one I use was only 20 or so quid!

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And

May sound stupid but the sender has a good earth? as it needs a earth right through back into the engine block if it's a single (oil pressure) wire one,

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And

On another note I have seen a photo of a inlet mainfold by said company and well he is lucky the engine is still running and not got holes/melted Pistons on 2 cylinders I havent heard any thing good about them.

Edited by And

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idoari

i didn't read the whole post but it can be also a oil restriction inside the engine (like sludge from not changing oil for a long time)

OR

i'm not exactly sure if this engine has oil breather pipe/valve but if it cloge than it can lead to this symptom.

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Kitch

Thanks everyone.

 

I think I've nailed the issue, or rather two separate issues. The crankcase pressure issue is, I think, caused by the breather system we've designed simply being too restrictive. Obviously originally it's under vacuum, but it just vents to atmosphere here, and we haven't just plonked a breather filter on the rocker cover because we've trying to direct all the gases away from the engine bay, as they're having an irritating desire to leak their way into the cabin and give the driver a headache! But the system we came up with, including using a catch tank, isn't allowing the gases to escape and I believe that's the cause of the problem with the dipstick and front crank seal.

The oil pressure, having read some of the comments here, leads me to think is a fault with the gauge. The other gauges are a bit erratic too, but sadly I have no mechanical gauge here to plumb in and test it. We may well buy one in and fit it permanently on the engine, but having carried out lots of revving and a fair bit of test driving, I don't actually think it is running that high at the moment. No evidence of it doing so anyway.

 

Got other issues with it misfiring and cutting out, but I hope the oil ones were a bit of a red herring.

 

Cheers to all that helped.


On another note I have seen a photo of a inlet mainfold by said company and well he is lucky the engine is still running and not got holes/melted Pistons on 2 cylinders I havent heard any thing good about them.

 

Care to elaborate? I've had mixed opinions based on what I've found on these carbs too.

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