7tea1

My cold idle oil pressure reads 40Lbs, and climbs to 70(max) while first starting out (engine cold). The engine is the base 350/270.

After warmup, my readings are 40Lbs cruising at 50MPH, BUT at hot idle, only about 5lbs. of pressure. (These reading are with the stock, mechanical gauge)
I am using Pennzoil 30 and a AC/Delco 25 filter.

My question is....Why is the pressure so high at cold idle, and so low at hot idle???? Is this a sign of a high volume or high pressure oil pump being installed at one time, or worse, a sign of worn bearings???

What would you do---- replace the pump (if so, tell me a good one :yesnod: )
Also, does the pump have a bypass in it for pressure, or is it in the filter?

As always, thanks for you advice!!!!!
:cheers:

Twin_Turbo

When cold the oil is thicker and more viscuous fluids have a higher resistance to being forced through restrictions, thus a higher pressure. 10psi for every 1000rpm is sufficient oil pressure.

The pressure bypass is in the pump, it's a spring loaded plunger in the bottom lid.

Check your reading with a hand held presure gauge.

Marck




[Modified by Twin_Turbo, 5:14 PM 11/12/2002]

7tea1

TTT............
Any other thoughts????

SprintCarDriver

I am no expert but I would check your pressure with a different guage to eliminating that the guage is in error. There are two pressure valves, one in the pump and one in the oil filter mounting flange. You can check both for sticking...

wallyknoch

Until the oil heats up the pressure will be higher. 40 is fine but 5 is low. Plug a guage into the engine and see if it changes to a higher reading when warm. The only other reason for low pressure is increased bearing clearances or merely low oil in the pan. :cheers:

shoptek

I would stick with a stock pump too if you replace it. I don't think you have a need for a hi vol pump. My .02

7Bob3

Marck is right on. 10 #'s a grand, any more and you are using HP to push oil in a SBC.

wallyknoch

A new oil pump would not be the answer. And never use a high pressure or high volumn. It`s almost certian that nothing is really wrong with your pump. The two previously mentioned ones would require at least 25% more oil and requiring a larger oil pan. A used oil pump with a broken rotor would still pass nearly 100% of it`s capacity. I get calls for oil pumps every day from customers thinking that low oil pressure is pump related. It`s probably from fuel pump ideas. Now they will quit. As long as an engine runs the oil pump is turning and passing oil. Every time I broke the Black from Fuel Injection hydraulic, I cleaned the old pump and put it back in. It pegs on startup and runs at 60 with straight 30 racing oil. I do want to try the synthetic oil however. :D :cheers:


[Modified by wallyknoch, 11:21 AM 11/13/2002]

fauxrs

My old camaro was much the same except my hot idle was 10-15 psi - I pulled that motor and found 2 wiped bearings - if your gauge is even remotely accurate - 5 psi is WAY TOO LOW!! :eek:

I would first do as the others suggest and get another gauge to verify the accuracy of the installed one - If the new gauge duplicates those readings I would stop driving the car and pull the motor post haste.

Your pump is not the problem as mentioned earlier - they are quite possibly the most durable part in your engine - even normal wear would only reduce its ability a few percent probably. You do not need a high pressure or high volumn pump for anything less than a very high performance motor. Even the Vaunted LT-1 ran the same pump - it just had a higher tension bypass spring (hence it was a higher pressure pump).

Good luck and let us know what you find.