View Full Version : Idle oil pressure change, is it normal?
07-08-2002, 02:08:00 PM
I know, it sounds like an Engine Topic but its also race related. I really need to know if it is normal for the idle pressure to change so much.
I got a brand new professionally built 540. Until the first run last Friday, the oil pressure was always at 80 in my driveway,
no matter what RPM. Oil is 20W50 as the builder instructed me to use, 7Qt of it with Moroso filter and kickout pan.
Engine temp 180 at the launch, pressure 80 as always. Ran easy 6.6/103 1/8th mile and right after shutdown the pressure goes to about 20 and the kill light starts to flicker. Scared the hell out of me since I never saw it so low. I checked the oil level in pits and it was at the ADD mark.
Check it 30 mins later and it is just above full, as before. What I do not understand at all is that now I get 20PSI at idle when it used to be 70-80. It has a new oil and filter after the break in and dyno.Could there have been some assembly lube or something holding the pressure? Should I get an accumulator to be safe? If so, which one? I have a little screen above the cam (can't remember what the heck is it called), I suppose it could be holding the oil back? How hot should the engine/oil be before the run.
I did not call the builder yet, wanted to have some better understanding of it before I do. You guys know it all, please advise.
07-08-2002, 10:15:00 PM
A 60 psi change in oil pressure sounds bad. Cut a filter open and make sure there isn't any mechanical damage and call the builder. He knows what pump and clearances he built it with and will be able to tell you if it's OK or not. I wouldn't start it again till he gives his blessing.
07-08-2002, 11:15:00 PM
Thanks Marv, this is what I'll do and also it is what he (builder) told me. I was also told that it could be a hung bypass in the pump, colapsed filter, possibly oilpan door stuck open (not sure how that would effect idle while not moving). I sure got some work to do. The filter is a Moroso kind and I am going to get a System 1 next. Also, someone recommended oil restrictors for the top but I thought that a Merlin block is already setup for priority oiling.
07-09-2002, 10:37:00 AM
Kinda sounds like its normal now as opposed to having 80lbs at idle as you did before. In any case. i'd cut the filter and pull the pan to get a visual on things just to make sure. I also ran across your post in Dragraceresults...
maybe there could have been some kind of restriction causing the high idle pressure... then on your first run it came loose?? Something in the gallys?? or maybe you had a "stuck closed" bypass and all is normal now......
Shut up, get in, sit down and hold on... Why are you looking at me like im crazy??
07-09-2002, 02:26:00 PM
What type of oil filter are you using?
If it's a fram get rid of it... I've seen engines go 0 psi with fram filters and a blocked off bypass. Hard to believe yes, but it's the facts.
07-10-2002, 02:31:00 PM
the filter is a Moroso racing kind, not really sure who actually makes it. Yes, I am going to cut it open as soon as my son's 70 is out of the garage hopefully on the weekend and replace it with System 1. I am not excited about pulling the motor to look at the bottom but may have to. Really interested in seeing the trap door.
I also thought that 70-80 PSI at 1100 RPM is somewhat high but TwinTurbo79Z28 is the first one to suggest it.
I'll let you know what I find and if you have any ideas, let me know please.
[This message has been edited by Fast72RS (edited July 10, 2002).]
07-10-2002, 04:01:00 PM
My 540 also has about 80 pounds of oil pressure at idle.When it warms up it runs about 60 with 15w 50w Mobil 1.If it dropped to 20 do as others suggested,start checking before you start it again.
07-10-2002, 05:12:00 PM
Wow Brian.. If thats the case, then im in agreement as well.
07-27-2002, 06:59:00 PM
Thank you all for your advice, I have pulled the engine and disassembled the pump, cut the filter and found no problem at all. Put it back, filled with Kendall 20w50 and got 80 PSI cold again. When hot after a run, it drops to 40 or so but goes well over 80 with RPM, the builder said that Valvoline VR1 oil is known to run like a water when hot and that is the reason for the low pressure. Anyway, the engine runs great now and I do not get the kill light in my face any more.
Thanks again for the great site and people on it!
07-28-2002, 03:00:00 AM
Actually it sounds like your builder did some foolery with the spring pressure in that oil pump. No need really for 80 PSI at idle let alone 40. Unless you are turning truly astonishing RPM with this no need to run over 80 up high as well. Some day ask the builder what color spring he put into the pump and what thickness shims. Then it would be interesting to find out why.
with that oil pressure I WOULD NOT run that motor hard at all until you have AT LEAST 180 degree oil temps. 200-210 is about what I would want for oil temps prior to a run.
70 SS 454 CI 650+HP All Aluminium Fuel Injected Small Block
07-28-2002, 02:24:00 PM
Rick, I had the pump apart and the spring had what seemed to me like a purple color.
I am not sure what shims you mean, I have not seen any. The engine is built by Shafiroff and should go to 7800 RPM with valve float at 8400, according to the spec.
He insists on using 20W50 oil.
Thanks for the temp recommendation, I will follow it. BTW, what kind of a problem would a high pressure typically cause?
07-29-2002, 01:58:00 AM
Is it a Melling pump?
Sometimes folks will shim the springs to give more pressure.
I usually install white springs in my motors. I'll find out the specs on the purples.
I too would, and do, run 20-50 as do all the racers I know. I much prefer Sheaffers racing syn. oil though. I didn't build the engine so I won't and can't say that there is anything wrong running that much pressure just that it seems like a lot(+80). I also don't think 40 at hot idle is low either, sounds more than adequate. But you have to trust your builder. It is a funny, black art, area with engine builders..... this oiling thing. Everybody has their own tricks so I guess that is what Scott wants. He should know what his engines like. My motor idles at 50 when cold and 25-30 when hot. Max pressure is around 65-70.
One thing though based on your initial post your low pressure after the run may have been due to the fact you started draining the oil pan. If the pump is a high pressure and high volume unit and the drain back is not sufficient you just may be sucking too much oil to the top end.
Best thing you can do is warm up that oil prior to any hard throttle abuse. Right after the next easy run check the oil gauge and see what pressure and temps you are running. If temps are normal (200-230) and the pressure is real low try adding an additional quart prior to the next run and see what happens. That would be one way to see if you may need a bigger oil pan sump.
70 SS 454 CI 650+HP All Aluminium Fuel Injected Small Block
08-01-2002, 07:11:00 PM
I appreciate every advice I can get to keep things running longer and better. http://www.nastyz28.com/ubb/smile.gif