18 replies to this topic

[robminibcy]

hi ive had a problem recently with the oil pressure my 998. its runs at 50 at idle, and about 70 a 60 mph in 4th. however after a long run at constant high speed it starts to dop and goes down to 60. then when at idle it drops to just below 40 but does very slowly start to come up again. Today i fitted a ball bearing and uprated spring pressure relief valve however when started the gauge went up over 100 and then sat at just below 100! i did not wnt drive it like this as i wasnt sure if it would be damaged so i put the old alloy relief valve in with the new spring. this brings it to about 80 at cold idle and 50 at hot idle. It does however go up to 90 when cruising. I took it for a fast run to see if it would still drop off and it did not seem to at speed although it did drop a bit at idle straight after. Therefore: is there any damage going to be caused by the high pressure? What coud be causing the drop in pressure after high speed distance drives (or is this normal). and what is going to be te best pressure relief valve/ spring to use. The engine has done 90K and is a pre a plus with 20 50 halfords classic motor oil about 1000 miles old. Cheers Rob

[bully]

the figures you refered to with the standard valve are fine, the oil pressure goes down when the engine is hot and should return to normal when the oil cools down. you dont need high oil pressure just constant. as long as when your driving along the oil pressure is stable and doesnt drop alot when idleing then it will be ok.
the drop in oil pressure will be due to quailty of oil or the valve spring is weak.
when fitting the stronger spring with ball the oil pressure will go up to 100 but will start to drop of when the engine warms up which is what i use in my race engine but after a long period the seat where the ball sits will become damaged
do not use the strong spring with the plunger as this will cause you problems.
you best bet is the buy a new standard spring and plunger and put some good quailty 20/50 oil in there.
to increase the pressure on the standard setup you can but a adjustable cap which will increase or decrease oil pressure to a correct limit
very high oil pressure wont cause damage to you engine but will cause it to leak oil.
hope this helps.

[bmcecosse]

If your gauge was pushed over 100 psi - the readings can no longer be relied on. When using a ball - the spring must be shortened. I would source another gauge that you can trust....

[Cooperman]

There are many cases when going to a ball valve have caused some strange results and for consistency it seems that a plunger is more consistant.
As oil warms up it gets thinner, so when an engine is hot the oil pressure at given revs will naturally be lower.
as a guide, a good condityion engine will have 75 psi to 90 psi cold at 4000 rpm. When warm this will drop to 60 psi to 70 psi at 4000 rpm. At tickover of 800 rpm it is not unusual for a hot engine to drop to under 20 psi. All those figures are approximate and are fort a good quality 20w50 oil.

[carbon]

Running with the ball bearing & unshortened spring can have consequences... I think what may be happening is that the spring gets coil-bound at over a certain relief flow rate then it all get a bit frantic.

I had ball & spring installed, like you oil pressure on start-up was approaching 100psi on the gauge. Until one very cold morning when it suddenly dropped to zero - luckily I had warning light as well as gauge fitted, and switched off motor right away.

The high pressure had blown one of the main oil gallery brass plugs completely out. Needed to take engine out, split gearbox to recover and replace.

Since then I have always used standard oil pressure relief valve.

[robminibcy]

ok cheers for that. will order a new valve and spring now then!

[tiger99]

I think there is a clue insofar as you mentioned an alloy relief valve. All of mine have been steel. But in any case a new valve and spring ought to fix it, unless the seating is damaged.

[Cooperman]

When fitting, just make sure the plunger slides in the housing smoothly and with no sticking.

[robminibcy]

my mistake, then probably is steel, its the same as on minispares. and will make sure it is smooth, seemed ok when i took it out and came out easy as was not stuck at all which was nice for a change!

[mailman]

Question. Is it better to run the standard relief valve or, better to run the ball bearing set up with a coil taken off??

And if it is the latter, how many coils should be removed?

Thanks.

If the ball is not better why did they bother making it?

[robminibcy]

What he said ^. and also does the spring have to be shortened in all applications. If so why are minispares selling it as a straight swap with claims to a constant 75 psi?

[Spitz]

From your original post there wasn't really a problem with your numbers. Many are happy with numbers lower than that. Dropping to 15-20lb at idle is no problem.

[robminibcy]

ok cheers. i just want her to be running 100% which is abit much to ask really from nearly 100k milage 33 year old daily driver! the pressure never used to drop so much and id rather get a second opinion if there was likley to be engine problems developing. but if the numbers seem good im happy! had a new valve today so will see how it goes

Edited by robminibcy, 31 January 2013 - 11:56 PM.

[Cooperman]

Several people on here and elsewhere have claimed to have experienced fluctuation pressure when using the ball instead of the plunger.

[Goacher65]

I have also just put my fresh 1380 engine build in, and cranking with the plugs out over the weekend, the oil pressure gauge happily showed a reading, but continued to rise to 100psi just cranking. From reading posts above, I think I shall clean and return the original spring and follower instead of the 'cooper s' ball bearing type. Maybe try refitting at a later date when the engine has been run in a bit, and see what difference it makes then. When building the engine, I was on the lower or near the lower limit of all tolerances so it's all pretty snug in there at the moment!

Edited by Goacher65, 07 April 2014 - 08:53 PM.