How old is the oil & what is its viscosity?
Should be NEW
and 20W50 mineral oil.
Quite important. Synthetics aren't the greatest for common oiled engines. Or something like that
I'd be checking that first
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| Oil Pressure problem When Hot https://www.ausmini.com/forums/viewtopic.php?f=2&t=58272 |
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| Author: | goodie [ Tue Oct 27, 2009 5:37 pm ] |
| Post subject: | Oil Pressure problem When Hot |
G'day All , hopfully somebody can help, I've got a mate that has a Mini K , brand new 1100 motor ,basically standard , has done no more than 1000 klm's, Oil pressure was fine until recently ie: Cold = 50 -60 psi , on startup, ---- 40 - 50 psi hot running temp. 25 @ idle-hot, Now ; Cold =Approx 50 psi - on startup, 40 psi hot running, next to no oil pressure @ idle when hot, he tells me that he can see it dropping off the hotter it gets. It appeared the oil wasn't holding under heat so we changed it to Castrol Edge 25-50. We also changed the coolant , the engine isn't running hot , so what i'm asking does anyone have any suggestions on what could possibly be happenning with his engine. Thanks Colin. |
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| Author: | willy [ Tue Oct 27, 2009 5:40 pm ] |
| Post subject: | |
How old is the oil & what is its viscosity? Should be NEW and 20W50 mineral oil.
Quite important. Synthetics aren't the greatest for common oiled engines. Or something like that
I'd be checking that first |
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| Author: | goodie [ Tue Oct 27, 2009 5:54 pm ] |
| Post subject: | |
G'day willy ,thanks mate, yeah oil is brand new Castrol Edge Sport 25W - 50, same as i use in my '" S "( non synthetic ) i recommended he change to that oil as i thought his oil wasn't holding up under running conditions, car goes well doesn't blow smoke, everthing seems fine unless it has some sort of underlying problem. |
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| Author: | willy [ Tue Oct 27, 2009 5:56 pm ] |
| Post subject: | |
Ok oil could be thinning down enough to run some crap thru the oil pressure relief valve. check whether this is the case. very easy to do... if there's any form of scoring (bad) on the valve, replace with spring & ball. |
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| Author: | Mick [ Tue Oct 27, 2009 6:05 pm ] |
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Check your guage as well, it may be playing up although they're pretty good usually. Swap it out with a known guage before you pull the engine apart..just another tact to try. |
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| Author: | sgc [ Tue Oct 27, 2009 6:27 pm ] |
| Post subject: | |
Does it have a mechanical fuel pump? Could the diaphragm be leaking fuel into the oil, thinning it down? Does the oil smell like petrol? |
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| Author: | wallygog [ Tue Oct 27, 2009 6:39 pm ] |
| Post subject: | |
Easy. the oil pressure relief valve is stuck open like willy said. when the oil is cold and thick the valve opens up further, when it gets hot it doesn't return back far enough to give oil pressure at idle because it has a bit of gearbox wedged in it. Quote: Ok oil could be thinning down enough to run some crap thru the oil pressure relief valve. check whether this is the case. very easy to do...
easy to do unless it's a rover with front mount air con 
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| Author: | goodie [ Tue Oct 27, 2009 6:40 pm ] |
| Post subject: | |
Yeah guys, forgot to mention two of the things we tried were , got the car up to temp and then checked the oil pressure with a Master gauge, ( it read pretty much the same as the gauge in the car ) then we changed the oil pressure relief valve and spring with a new spring and ball that the other mate has in his 1275. which didn't make any difference. |
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| Author: | BALLISTIC [ Tue Oct 27, 2009 6:44 pm ] |
| Post subject: | |
If you have changed the oil and the symptoms havent changed its not the oil. Check the oil pressure relief valve as previously mentioned by willy and get another known working gauge and check as Mick said.  Is the engine temp when running a little hotter now  (is the temp gauge in degrees C or F?)
Before the engine was built was the crank crack tested and straightend (if required) also was it balanced (im guessing that the big ends and mains were machined as well not that it is overly important at this time)
Is the engine running a harmonic balancer/damper
Was the oil that was drained checked while it was coming out or when it was in the drain tin If so did it have a silver slick or trace as it was draining out If so im gunna say that it has probably hurt the centre main and the crankshaft may have a slight bow in it.......I could be wrong/mistaken and hope I am 
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| Author: | wallygog [ Tue Oct 27, 2009 6:45 pm ] |
| Post subject: | |
then the motor is knackered or built with too larger bearing clearence |
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| Author: | drmini in aust [ Tue Oct 27, 2009 6:49 pm ] |
| Post subject: | |
The spring and ball can give problems unless you put a bit of 5/16" rod (40mm long) inside the spring. Read this- http://www.ausmini.com/forums/viewtopic.php?t=58088 |
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| Author: | jester99 [ Tue Oct 27, 2009 7:01 pm ] |
| Post subject: | |
I am also experiencing a similar problem. When the engine is cold, up until about 140 degrees farenheit oil pressure is good at idle. about 20-30 psi. after the engine warms up and i have driven the car for a few minutes or so, the oil pressure drops at idle to below 20psi. i recently did an oil change using penrite HPR50 20W50 and this made a big improvment in idle oil pressure even when hot. for about a week, then it came back to where it has always been. i have only had the car for about 4 months now and have tried a few things to no result. i have been told by a few specialists and some engine builders that this may well be related to bearing clearances, being either the engine is to worn or the bearings are worn. it is unknown how old the engine is in my vehicle, probably very, but it blows no smoke and has excellent compression on all cylinders. i am going to try a few different oils and fit an oil cooler to help the issue. it worries me that the engine is getting such little oil pressure at idle. but i suppose as long as you are not idling to long it isnt to much of an issue. |
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| Author: | drmini in aust [ Tue Oct 27, 2009 7:05 pm ] |
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jester, Check if you have a ball in there, or the original plunger. The ball gives problems (moves sideways) if the spring bends on it, then it unseats. But if you put a rod inside it, the ball seals better at idle than the plunger ever did, so you will get more idle pressure when hot. 
see my link above. |
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| Author: | goodie [ Tue Oct 27, 2009 7:34 pm ] |
| Post subject: | |
Ok, Doc ,yes the relief spring did have the 5/16 rod inside it, Simon , yes i'm sure it has a mechanical fuel pump but i did check the oil on Sunday when we took it for a run up to a mates place, i did the old finger test and it still felt okay, still felt tacky. Ballistic,gauges are standard K, Cooper S , engine is not showing signs of running too hot,i can't answer the crank question, harmonic balancer , i'm sure it has . as to your next question the one thing that did concern me was that when we changed the oil in it the magnetic sump plug did have a lot of filings ( fur ) on it. I'm starting to think that is something deeper , maybe we should drop the oil again and check the sump plug for metal. Keep the thoughts coming guys you all have been a great help |
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| Author: | AEG163job [ Tue Oct 27, 2009 9:25 pm ] |
| Post subject: | |
wallygog wrote: then the motor is knackered or built with too larger bearing clearence
And maybe also the oil pump was not replaced. Mandatory for any A series rebuild. Unfortunately, I suspect a shoddy rebuild and rapidly deteriorating bearing clearances. Sorry pal. 
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