more boring pressure probs
Discussion
HI Jezz,
Not a whole lot of info in that post, do you mean hot or cold oil pressure? What is it fully hot stationary at 800/900rpm(idle), 2500 rpm and at 4000rpm? Are these values different on the move? I am struggling to think of an obvious reason for a drop on pulling away, short of severe oil surge due to very low oil level, but you've topped this up.
Yours is a 500 1996-7 so I assume its got a serpentine front end and therefore the very efficient and high capacity crank driven oil pump, as opposed to the older and much weaker cam driven gear pump. What's the engine mileage, is it making any odd noises.
In all likelyhood, if all else is reasonably normal, it is most probably the sender / wiring / gauge, as this system is notoriously erratic and inaccurate. Mine gave me a big fright on a track day by dropping to zero every time I topped 4000rpm
just noticed the gauge reading ZERO in the middle of a hot lap, was just waiting for the death rattle of big ends to follow. Turned out to be no more than the spade connector to the sender needing pinching up (and it didn't look / feel loose)! Phew! Took the opportiunity to re-calibrate the system (sender)against an indepedent mechanical gauge when i got home and my oil pressures are much more in line with what would be expected now: Fully hot idle; 25-30psi, 2500rpm 50psi, 4000rpm 55-60psi, when cold it will show 50-60psi at idle and just under 70psi max (limited by the relief valve) this is on a 1999 20,000mile 450 - on Mobil 1 motorsport 15w-50. Hope that helps or give us some more details... 
PS: oil pump failure is very unlikely (especially the crank driven type), unless theres been some major issues with the engine, even the gear pump is pretty reliable (if not great in terms of maintaining hot oil pressure in a worn engine). Could - just possibly - be a weak or broken relief valve spring? I wouldnt start tearing the front cover off just yet before investigating this a lot further.
>> Edited by tahiti450 on Thursday 5th January 01:21
>> Edited by tahiti450 on Thursday 5th January 01:23
Not a whole lot of info in that post, do you mean hot or cold oil pressure? What is it fully hot stationary at 800/900rpm(idle), 2500 rpm and at 4000rpm? Are these values different on the move? I am struggling to think of an obvious reason for a drop on pulling away, short of severe oil surge due to very low oil level, but you've topped this up.
Yours is a 500 1996-7 so I assume its got a serpentine front end and therefore the very efficient and high capacity crank driven oil pump, as opposed to the older and much weaker cam driven gear pump. What's the engine mileage, is it making any odd noises.
In all likelyhood, if all else is reasonably normal, it is most probably the sender / wiring / gauge, as this system is notoriously erratic and inaccurate. Mine gave me a big fright on a track day by dropping to zero every time I topped 4000rpm
just noticed the gauge reading ZERO in the middle of a hot lap, was just waiting for the death rattle of big ends to follow. Turned out to be no more than the spade connector to the sender needing pinching up (and it didn't look / feel loose)! Phew! Took the opportiunity to re-calibrate the system (sender)against an indepedent mechanical gauge when i got home and my oil pressures are much more in line with what would be expected now: Fully hot idle; 25-30psi, 2500rpm 50psi, 4000rpm 55-60psi, when cold it will show 50-60psi at idle and just under 70psi max (limited by the relief valve) this is on a 1999 20,000mile 450 - on Mobil 1 motorsport 15w-50. Hope that helps or give us some more details... PS: oil pump failure is very unlikely (especially the crank driven type), unless theres been some major issues with the engine, even the gear pump is pretty reliable (if not great in terms of maintaining hot oil pressure in a worn engine). Could - just possibly - be a weak or broken relief valve spring? I wouldnt start tearing the front cover off just yet before investigating this a lot further.
>> Edited by tahiti450 on Thursday 5th January 01:21
>> Edited by tahiti450 on Thursday 5th January 01:23
tahiti450 said:
HI Jezz,
Not a whole lot of info in that post, do you mean hot or cold oil pressure? What is it fully hot stationary at 800/900rpm(idle), 2500 rpm and at 4000rpm? Are these values different on the move? I am struggling to think of an obvious reason for a drop on pulling away, short of severe oil surge due to very low oil level, but you've topped this up.
Yours is a 500 1996-7 so I assume its got a serpentine front end and therefore the very efficient and high capacity crank driven oil pump, as opposed to the older and much weaker cam driven gear pump. What's the engine mileage, is it making any odd noises.
In all likelyhood, if all else is reasonably normal, it is most probably the sender / wiring / gauge, as this system is notoriously erratic and inaccurate. Mine gave me a big fright on a track day by dropping to zero every time I topped 4000rpm
PS: oil pump failure is very unlikely (especially the crank driven type), unless theres been some major issues with the engine, even the gear pump is pretty reliable (if not great in terms of maintaining hot oil pressure in a worn engine). Could - just possibly - be a weak or broken relief valve spring? I wouldnt start tearing the front cover off just yet before investigating this a lot further.
>> Edited by tahiti450 on Thursday 5th January 01:21
>> Edited by tahiti450 on Thursday 5th January 01:23
Tahiti450!
Just read your response and found it very informative! I too have had problems with erratic readings and am going to get the gauge, sender etc checked when it is in for some work at the end of the month. I have had low readings on the gauge for some time but have had so much work done on the engine that it is practically re-built. Everyone that has worked on it have said it is running great! Hopefully it will be a similar problem as you outline above, so I can get it sorted once and for all!
BTW: am considering a respray in Tahiti Blue....fantastic colour!!!!
Cerby4.5
cerby4.5 said:
Tahiti450!
Just read your response and found it very informative! I too have had problems with erratic readings and am going to get the gauge, sender etc checked when it is in for some work at the end of the month. I have had low readings on the gauge for some time but have had so much work done on the engine that it is practically re-built. Everyone that has worked on it have said it is running great! Hopefully it will be a similar problem as you outline above, so I can get it sorted once and for all!
BTW: am considering a respray in Tahiti Blue....fantastic colour!!!!
Cerby4.5
Thanks Cerby, Tahiti blue has been a real favorite of mine since I first saw it on Rovers and MGs years ago, i think its lush. BTW there are a lot of threads on oil pressure on the site, so It's worth searching these if you need more info, but let me know if you've any specific queries. Alan.little update changed oil and filter to see if that would help
put mobile 1 15/50 in all was ok for an hour or so when cold 45 psi
at 900rvs when hot 20 but will only go up tp 35psi when hot at 4500rvs
then started the same again droped to 10psi doing 70mph
i then take it out of gear give it a few revs then it will slowly crep back up car is 97 500 62000 miles
car is running well the only prob i have is the alternater is load sounds like a milk float wouldnt think this is anything to do with it
cheers for the help guys
put mobile 1 15/50 in all was ok for an hour or so when cold 45 psi
at 900rvs when hot 20 but will only go up tp 35psi when hot at 4500rvs
then started the same again droped to 10psi doing 70mph
i then take it out of gear give it a few revs then it will slowly crep back up car is 97 500 62000 miles
car is running well the only prob i have is the alternater is load sounds like a milk float wouldnt think this is anything to do with it
cheers for the help guys
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