On my bone stock long-block L98 motor with ~90K miles on it.

Loses oil pressure on quick stops, or pulling into a parking space quickly.
Also around hard corners it dips.
Also dips on constant accelleration with revs above 4000.

Yes, the oil level is correct.

Seems very consistant under these conditions.

Any possible way this could be the sender?

Seems the classic signs of a pickup that is too high in the pan, or has cracked or come loose from the pump.

Just wondering if I should bother trying a new sender before dropping the pan.
And can the pan come off w/o jacking up the motor??? Hope so...

Fun fun fun. Need to get the car in shape for track use no later than Feb this year...

Scott

 

I had pretty low oil pressure at idle (around 10-15psi) ... turns out it was a rod bearing... :( .. engine is in the shop right now. Hope yours isn't something similar!

 

No, don't think it's bearings. Plenty of pressure at idle - in the 40-50psi range when warm. Mobil1 10w30 in there. Makes plenty of pressure at all times except for when motion causes the pick-up to uncover, or at least that's how the symtoms present. I've had similar issues many many years ago with a hot rodded 327 with the wrong pick-up for the pan.

I'm quite confident it's either the pickup or the pump with an outside possibility of the sending unit going out, but it seems too consistant for a sending unit.. Presents itself very consistantly.

 

Sounds like you will have to drop the pan and find out what's going on. After you fix the problem, you may want to install an AccuSump for racing.

 

I plan to add an accusump when I plumb up the oil cooler. I have an integrated cooler water to oil in the radiator, done by Ron Davis. Nice unit.
Not cheap...

:(

 

Mine does that right when I'm ready for an oil change. :)

 

meaning your engine burns or leaks out and you are low when you change it?

I checked and the level is normal.

Dude, btw - 21 thousand posts? Thousand???

:eek:

 

heheh.. yup.. he spends more than twice as much time on the forum as i do....

 

oooohhh you got me a bit worried now.... mine's doing around 20-25 psi at idle (500 rpm) it rises to around 50 - 60 psi during highway. is this okay??? :eek: :confused:

 

If you see it drop below 15psi, be warned.

 

Mine idles at 800, and is probably close to 40psi. Could explain the difference, 500 vs. 800.

Scott

 

Idle pressure seems rather high. I am trying to remember if there is a relief in the pump. If the pressure is high due to a pump problem, you may be filling the valve covers and emptying the pan. Although the sender might be another area of suspicion, I think I would drop the pan to be on the safe side.

One other thought, some of the aftermarket heads had problems with oil flow back to the sump and the valve cover would fill with oil. Wondering if you flow back holes are clogged at all? Long shot I guess.


[Modified by vettenuts, 7:23 PM 12/14/2001]

 

Put an extra quart of oil in it and try again. (1 qt. over full)

This might help give you some idea of what you're looking for.
If the symptons diminish or go away with the extra quart then it's probably not pump or bearings. Then you might pull the pan and look for a pick-up problem.

Probably not applicable but I'll ask anyway: Could it be the wrong dip-stick for the engine thereby causing the sump to be a little under-filled?

Just FYI and maybe a point of interest: I have a 350 I built for my truck a few years ago. Plugged the oil filter bypass valve so as to have a full flow filter.
It would start to drop oil pressure at times out towards the oil change time because the filter would start getting clogged up. (Didn't do it with the cheaper paper only filters)

I know, I know .. it sounds stupid but you might try a new oil filter just for grins. Your engine should have the filter bypass valve operable but some old race engine builder like me could have disabled the bypass before you got the car.


As a rule of thumb 10 PSI per thousand is adequate oil pressure on the SBC.
Oil PUMP pressure relief valve limits upper pressure but the bearing clearances
(rod/main/cam) normally dictate idle/low rpm oil pressure.

I've built a lot of small block Chevy's but typically they don't seem to have a lot of idle oil pressure after they get up to operating temp.:nonod:

Generally, a spun rod bearing or two won't show on the oil pressure gauge.

Hope this helps the "thought" process. :seeya

 

It does, I thought about trying 1 more qt then changing oil before dropping the pan just to see the effect.

Motor is bone stock, I seriously doubt the oiling system was modded in any way. Pickup is an L98 pick-up as well.

Stock TPI motors (at least the 2 I've had) seem to have very high pressure at idle. Close to 40psi anyway. Similar story with our brand new suburban. I've built many sbc motors as well and typically end up with 20-25psi at idle, which is plenty. But stock motors tend to have tighter bearing clearances I guess.
The TBI motor in our '94 burb didn't, however - by the gauge it showed only 15 at idle, but who knows how accurate the gauge was - it had 99K miles on it when I sold it and still ran like a champ.

Scott