Losing oil pressure?
07-08-2009, 09:37 AM
#1
Losing oil pressure? Engine starts up and oil pressure is 25psi. Rev engine up to 3500rpm and goes to 55psi. Make a run down the track and it will be 20psi. or lower, let off the throttle and it will come back. The engine is a ls1 chevy. Main clearance is .0028 on all but but #5 that is .0029 It has a Katech oil pump and a c5 oil pan. I started the engine on mobil 1 5w30 then went to 20w50 valvoline, gained 3 psi. I have had this engine out of the car 3 times. It is NOT the pick-up "o" ring. Thanks fellas for any suggestions. JC
09-15-2009, 10:31 PM
#5
LSxGuy widda 9sec Mustang
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The mains are on the looser side for an aluminum block, I like them around .002" myself due to the aluminum expanding when warmed up to temperature. You could run a higher volume oil pump with the stiffer spring and probably pick up some pressure as an easy fix, of course that would also require a single roller chain if you use the GM high volume (L92 style) pump.
As mentioned above, it could also be attributed to looser than normal cam bearings, I believe the clevite spec range is .002-.006", if they are all close to .006" (aftermarkets are commonly looser than GM) and your main bearings are .028-.029" cold, then it is just a matter of having up to 10 internal oiling system leaks, the more clearance and more potential internal leaks, the less pressure. Tightening up one or the other or both would lead to an increase in pressure.
It is like trying to fill up a 5 gallon bucket with water, if the bucket had a bunch of holes drilled in it. The more "holes"; the less available quantity stays in the oiling system and you consequently pump it back into the oil pan.
As mentioned above, it could also be attributed to looser than normal cam bearings, I believe the clevite spec range is .002-.006", if they are all close to .006" (aftermarkets are commonly looser than GM) and your main bearings are .028-.029" cold, then it is just a matter of having up to 10 internal oiling system leaks, the more clearance and more potential internal leaks, the less pressure. Tightening up one or the other or both would lead to an increase in pressure.
It is like trying to fill up a 5 gallon bucket with water, if the bucket had a bunch of holes drilled in it. The more "holes"; the less available quantity stays in the oiling system and you consequently pump it back into the oil pan.
09-16-2009, 12:15 PM
#7
Everything is spot on clean! I have cut ever filter apart. i have also replaced the mains to move the clearances to .0023 If I drive down the road and mat the throttle the oil pressure will just keep dropping. It is in a chevy II pro street car. It has a mechanical cam. I do not think oil is getting away from the pick-up, because I have added 2 more quarts and it is still the same. I know that if the oil is foaming that you will not make pressure. Anything will help. thanks JC
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09-16-2009, 01:10 PM
#8
FormerVendor
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Stupid question but I haven't seen it addressed yet, have you checked the oil pressure sender? Any way to run a mechanical gauge to get a more accurate reading on it?
09-16-2009, 01:21 PM
#9
Staging Lane
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Not sure if this is the culprit but i know in a 6.0 i had was doing the same thing and mine turned out to be the barbell plug in the back of the block that deverts the oil had popped out just a bit. Its a pain in the *** to get to but might be worth your while to check. I also heard that the plug from ls2's work better simply because they are longer.
09-16-2009, 07:49 PM
#11
Not sure if this is the culprit but i know in a 6.0 i had was doing the same thing and mine turned out to be the barbell plug in the back of the block that deverts the oil had popped out just a bit. Its a pain in the *** to get to but might be worth your while to check. I also heard that the plug from ls2's work better simply because they are longer.
09-17-2009, 08:15 AM
#16
FormerVendor
You need 8956-16 as the ones you have (8950-16s) are moving way too much oil up the pushrods and into the cylinder heads. The 8950-16 is discontinued and does not work on most engines and base circles. You might be able to get by with restricted pushrods but I would probably change the lifters and all your issues will be gone. Basically you are directly venting your oil pressure up all 16 pushrods since the pushrod oil hole is into the main oil galleys and the pushrods are seeing direct oil pressure.
