Wild oil pressure readings

stina

stina

New Member
Hi all . Sorry i'm back to this again . I've been watching the oil pressure since uprating the pump gears a few months ago ( longer gears in the standard P6 cover ) I fitted a new relief plunger and standard spring at the same time , as advised in the fitting instructions .
On the original pump the oil pressure was running at around 10 psi at hot tick over . Not a problem in itself i know . Occasionally the gauge would read up to 60 psi with the oil warm , not hot with a road speed of 60 ish mph . then drop back to around 30 / 40 psi with normal driving .
Since fitting the uprated gears it has around 15 / 20 psi hot tick over ( which is what i was hoping for ) but the top reading is not consistent .
After driving to Petworth on Sunday ( around 80 miles each way ) i have a better idea of what it's reading . On the way up it Stayed around the 50 psi mark all the way at about 60 mph , dropping to around 30 psi through towns and villages . About what it says it should be in the hand book .
On the way back i was cruising along at 50 with a nice steady 45 / 50 psi no problem . On stopping at a set of lights and sitting at tick over for a minute or so then getting up to back up to 60 mph the needle was right on the 60 psi and on occasion over that even , and with a gentle acceleration seemed to keep climbing . It stayed like that the rest of the way home ( 50 mls or so ) and wouldn't come back down .
When i got back it was the normal 15 / 20 psi on tick over .
I know some of you on here can't see the problem with high oil pressure , but with the uprated gears it puts allot of strain on the distributor / oil pump drive gears . That's not the debate i want to get into . I'm more concerned about weather the high readings are actually high or a gauge / sender fault .
I can't understand why gives different readings in similar situations . And i can't see the relief valve would work one minute and then not ??? As said it's new and slides freely .
It does have the later type of sender bought from Ian last year , i know they're not as reliable as the original type .
Is there a voltage stabiliser or something in there that could cause these symptoms ?
Apart from that it ran lovely , never missed a beat .
All a bit jumbled , but i wanted to give as much info as possible .
Thoughts ???
 
Hi Stina,

For me you have to take these gauge readings with a pinch of salt. Checking them against what is physically possible. So thinking about how the system works and what is the gauge telling you. The oil pump forces a fixed volume of oil per revolution. Oil is an incompressible fluid so that oil must leak out of the system somehow or the system would hydraulically lock-up; it does this largely around the crank shaft bearing shells, but some slips back through the pump, around rocker shafts etc…. The amount of pressure required to force the oil out of the system is what the gauge measures, as the bearings wear the oil leaks out easier so naturally the pressure falls as the engine wears. The ease at which the oil leaves the system is also affected by its viscosity, hot oil having a lower viscosity to cold oil so the pressure for any given RPM is lower when the oil is hot. So given the above it’s easy to see how pressure follows RPM and why fitting a larger volume per revolution pump pushes up the oil pressure for any given RPM.

If there wasn’t a pressure relief valve in the system the pressure would continue to rise as you rev’ed the engine, at best this would just use up energy unnecessarily but at worst it could cause mechanical damage. To stop this happening a pressure relief valve opens at a fixed setting allowing some of volume of oil being pumped to simply return to the sump. So at lower RPMs the valve is completely shut, assuming if functioning correctly, and oil pressure will follow RPM, at some point the set point of the relief valve will be met and the pressure will no longer rise. The pressure value that this happens at is the same hot or cold (it’s just a spring) but again the higher the viscosity of the oil and tighter the clearances in the engine the earlier in the Rev range the valve will start to have an effect.

So you’d really now got to look at the readings you have observed and check if they make sense?
Fitting the higher volume gears, raised the oil pressure at tick over, this makes sense as the leak rate passed bearings etc…. was unaltered. As we are way below the opening point of the relief valve at tick over it has no effect at all, assuming again that it works properly and closes fully. As you rev the engine pressure seems to be largely following RPM. Is what you are saying in your post that for a period of your journey the pressure was above its “normal” max of 50 psi setting and still following RPM? This would suggest that the relief valve has in fact stuck closed. This is probably just temporary and it will free up again, a wee rev when the engine is cold and high pressures are easier to reach might be all it will take to nudge it free again.

Just my thoughts on the mater :idea:

Tim
 
No idea about your symptoms or effects but why don't you rig-up a temporary mechanical oil pressure gauge to the car for a month or two. They're more accurate & reliable than the electric gauges & it's a simple way to check your intrumentation. It's something I did to my 2200TC a few years back.
 
Hi

Sorry to jump in , but what oil pressure did you have on the 2200TC, idle and whilst driving hot and cold. Mine seems to run 55psi all the time The gauge hardly moves up from the centre position at all is this normal ?

Pat
 
The Rovering Member said:
I can't recall now but the four-pots do run with quite high oil pressure, much more so than the V8's.
Click to expand...

Indeed they do, that's why the V8 guage only goes up to 60psi, while the 4 pots go up to 100psi.
 
Hi Tim . Thanks for the input , i understand what your saying . What i don't understand is why it would sit at 50 psi for 80 odd miles ( obviously during those miles the relief valve was doing it's job ) then after coming down to tickover it was running high pressures . The spring is obviously correct otherwise the reading would be consistantly high ??? The relief valve plunger is new and slid freely in the bore when i assembled it . What could make it stick shut ? could i remove it again and polish it ?? Don't know with what though ! You've obviously seen the inside of one , I can't see how it could get wedged and stuck side ways ? It's too long for that .
 
If you make a couple of assumptions, namely that your oil pump is working correctly and the pressure relief valve is working too, then the only thing that can vary the pressure with the same revs is the oil temperature This doesn't necessarily follow the water temperature so you could think the scenarios are the same, ie cruising at 60 then slowing down into a village, but the oil temperature could be different each time.
 
Hi Stina ,at least your oil pressure gauge works :) mine works when it wants to :roll: :LOL: I have read they are a bit "iffy" to say the least :LOL:


Adam
 
Hi Paul i can see your thinking . But the motor was well up to temp having driven about 30 miles . came down to tickover for about a minute , not long enough to cool the oil , if anything it would of got hotter with no air flow . pulled away again then it stayed high for the next 50 miles . I'm begining to to think the gauge is telling the truth and that coming down to tickover lets the valve close and the pressure to follow rpm on low revs then sticks when i press on again . I've been watching it for a few months and this seems the best explanation . Don't know why , or how to deal with it though . Obviously i've not been thrashing it .

Edit , it did a similar thing when i used it for my mates wedding . On the way there it sat at 50 psi . Parked up all day , when my old man drove it back it was over 60 psi all the way home . Think it points to the relief valve sticking under certain circumstances .
Wondering if i could strip it down and polish the bore and plunger ?
 
pat180269 said:
Hi

Sorry to jump in , but what oil pressure did you have on the 2200TC, idle and whilst driving hot and cold. Mine seems to run 55psi all the time The gauge hardly moves up from the centre position at all is this normal ?

Pat
Click to expand...

Pat, this is what my TC does too. It doesn't change between hot and cold. My capillary gauge shows 45-50 psi at idle, 55 psi up to 2800 rpm, 60 psi over 2800 rpm.
I don't think that there is anything to worry about.

Stina, i am with Tim when he said to take the readings with a pinch of salt. More so because this is an electric gauge and any issues that are going to affect the resistance from the sender itself to the gauge (and there are rather a lot!) will show as a change in oil pressure. If this doesn't give you peace of mind, then fit a capillary pressure gauge as Gary suggested, along with an oil temperature gauge in order to monitor correctly what your engine does.
In any case, i wouldn't think that a real temporary change in oil pressure from 50 to 60 psi would cause any harm to the pump driving gears.
 
Hi Demetris . Yes i agree the electric gauges give unreliable readings . And i will fit a capillary type at some point . I was looking at vaultsmans set up at the show . I will find out the fittings needed . I'm not worried about the 60 psi , more so when it goes above that and off the gauge . I may remove the plunger tomorrow , and make sure it's totally clean and free sliding . ( although i'm sure it is )
Thanks for the input .
Stina
 
Hi Stina,

I do think your pressure relief valve is sticking slightly. This isn’t unusual as the oil that goes through it is pre-filter so tends to be a tad dirtier than what goes around the engine. Old A-Series ones used to get terribly scored with the metallic crap that came from the combined engine/gearbox arrangement, the V8 should be nothing like this but still a wee bit of crap can cause issues. The fact that it’s new and tight might be making things worse!!

I wouldn’t panic about it too much, just keep an eye on it, if it doesn’t sort itself you might have to remove the plunger and clean it up a bit.

60psi is high for a Rover V8 but not crazy high and certainly not high compared to other engines.
A good quality mechanical gauge would be a good upgrade, it will give you some extra confidence in the number if nothing else :D

Tim
 
Hi demetris

That's good to know. I think/hope my gauge is a little faulty. last time I drove the car I was sat at some traffic lights and I happened to look down at the gauge and the oil pressure read zero! It freaked me out. However whilst I was watching it the reading slowly recovered to normal then went to zero again. the engine was quiet and the oil light remained off thankfully. it coincided with the engine temperature going a little further over to the right as it was a warm day and I was in traffic for a while just before it happened.

I found a 0w30 top up bottle in the boot from the previous owner so I have changed the oil for 20w50 and also the filter. Interestingly the small filter in the cam chain tensioner oil banjo is missing. I also changed the o ring were the oil pump pipe bolts to the block after reading a post on here by someone with a similar problem.

Pls feel free to reassure

Pat
 
pat180269 said:
I think/hope my gauge is a little faulty. last time I drove the car I was sat at some traffic lights and I happened to look down at the gauge and the oil pressure read zero! It freaked me out. However whilst I was watching it the reading slowly recovered to normal then went to zero again. the engine was quiet and the oil light remained off thankfully.
Click to expand...

Since you have a 2200 TC, the gauges on the late style dash are notorius for not making very good contact with the printed circuit board at the back. If you remove the perspex cover you can try and move the gauge and see if this affects the readings.
 
Kman1600 said:
Hi Stina,

I do think your pressure relief valve is sticking slightly. This isn’t unusual as the oil that goes through it is pre-filter so tends to be a tad dirtier than what goes around the engine. Old A-Series ones used to get terribly scored with the metallic crap that came from the combined engine/gearbox arrangement, the V8 should be nothing like this but still a wee bit of crap can cause issues. The fact that it’s new and tight might be making things worse!!

I wouldn’t panic about it too much, just keep an eye on it, if it doesn’t sort itself you might have to remove the plunger and clean it up a bit.

60psi is high for a Rover V8 but not crazy high and certainly not high compared to other engines.
A good quality mechanical gauge would be a good upgrade, it will give you some extra confidence in the number if nothing else :D

Tim
Click to expand...

Thanks for the input again Tim .
A mechanical gauge is on the list !
I've not been overly worried about it but it's been playing on my mind , and i've been trying to work out what's going on .
Stina
 
I agree with Kman. It is almost certain that your pressure relief valve is sticking shut, but it is just possible that something bizarre is going on with the electrics of the gauge.

Sice the valve is sticking shut, I'd run till next oil change is due. Then I'd have the plunger out looking for debris or any other reason it might stick. Plus, I'd give the engine a good dose of flushing oil - normally inappropriate, but I know your rocker gear is already clean. Then I'd use the K&N HP2003 filter on re-assembly along with the correct oil (ie not any old 20/50 but as recommended in the p6 Club magazine).

Of course, if your pressure relief valve should decide to stick open instead... then it's don't panic Mr Mainwaring time!

Chris
 
Chris , are you suggesting i don't already use anything other than millers 20/50 :D
Gonna remove the plunger in a minute , i'm not too good at waiting :D
 
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