Oil Pressure. Is This Normal?

Question

I drive a 1997 Firebird Formula with the 5.7L big-block LT1 engine. Once the engine has warmed up, and I'm driving 45mph, the oil pressure gauge indicates 40psi. When I brake for a red light, the oil pressure drops to 20psi. As I accelerate, the oil pressure returns to about 40psi. Is this normal?

I understand that oil pressure fluctuates with RPM. However a drop of 50% seems excessive to me. I have consulted with several mechanics and car experts but no one seems to agree.

The oil was recently changed from regular 10W-30 to synthetic 5W-30 Mobil 1. There are no leaks. I replaced the new oil filter as a precaution. The filler cap is on and fine.

Thanks for any help regarding this matter.

Answer 1

Perfectly normal. I have a 98 S-10 with the 4.3 liter 262 cubic inch motor which has done the exact same thing sense it was new 30,000 miles ago.



Incidentally a 5.7 (350 cubic inch) motor is a small block motor. Big blocks started life as a 366 Tall Block, 396, 402, 427@ 427 Tall block, 430, 454, 488, 502 and 572 cubic inch motors.

Answer 2

As a general rule, Electrical oil pressure gauges are very inaccurate.



20psi with a hot engine in drive at a stop is really pretty good.

The oil warning lights don't come on until you get below 4 psi.



The thinner oil is what is causing the wild fluctuations. If your engine is in good condition (20 psi hot indicates good condition), I recommend staying with the 5w30 synthetic. You will see better gas mileage.

Answer 3

i have seen a lot of cars do this especially gm cars,but its not totally normal for this to happen,i had one that did this and i replaced the oil pump,it should go up past 40 at driving speeds,and on idle it can drop as low as 20 but usually they will run around 25 at the lowest,if its not dropping below 20 that's enough to run it but it should run a little more than that,everyone will have different opinions on it,but i owned one for a while and after changing the oil pump i ran 25-28 at idle and about 45-50 driving,i get them in the shop like this though and the customers say they have no problems from them,but to me that's a little scary to have one drop to 20 ,my truck has a 4.3 in it and it idles at 30+ idling,driving around 50-55,to me that's normal,good luck

Answer 4

Okay, you can stop worrying about your oil pressure. It is perfect if it operating like you say and the change to mobil 1 is an improvement too. You're doing it right..,.

Answer 5

too thin of oil, use 10w-40, normal for oil pressure to do that, if you don't think, take valve covers off and start it up, if oit shoots out the push rods you have plenty of oil pressure, you might have to rev it up a little bit, but change oil first

Answer 6

Sounds like the pickup tube on the oil pump is partailly blocked. when you stop the oil runs away from the pickup, causing temporary starvation...take of the pan, clean the pickup screen..



does it have the original dipstick? Maybe there is not enough oil in the pan....

Answer 7

It's a GM...I've seen them as low as 7 psi at idle, and if memory serves me right, 7 or 8 is within OEM specs (barely)..

Answer 8

It is normal, and an LT1 is not a big block. Everybody knows that.