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85_Ciera_Rebuild
09-30-2007, 12:52 AM
I have run some tests on a new stock Melling Pump installed in my 88 Beretta (2.8). On my digital dash, oil pressure is given in number of bars seen...I determined via shop-air hook direct to oil-sender that

5 Bars = 30 psi...and
9 Bars = 60 psi

Hot Idle:

a. 10-40 - 3 Bars
b. 5w-30 - 2 Bars

Cold Idle

a. 10-40 - 9 Bars
b. 5w-30 - 8 Bars (but just after oil change with warm engine)

After 2100 RPM, 5w-30 (Quaker) stays pegged at 7 bars (42 + psi)
10-40 has similar results...

Conclusions -

A. With Cold Idle, bypass is kicking in

B. With Hot Idle, bypass is not kicking in

C. After 2100 RPM (Hot), by-pass is kicking in.

D. By-pass spring tension is temperature dependent; as temp increases, your by-pass pressure decreases.

> 150,000 miles of wear on this 2.8 motor

Rod - 0.0015 clearance

Footnote:

Engine Oil Pressure (http://users.spec.net/home/emxjc/rebuild.html)

Oil Pressure should be 25-40psi at 1000rpm and 45-55psi at 2000rpm. Minimum oil pressure should be 15psi at 1000rpm and 30psi at 2000rpm. If this is not the case clearances betwen the bearings and crankshaft journals are excessive. Pressure should be checked only when the engine is warmed-up."
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At 1,000 RPM Hot...the 25 psi may be a valid number...I have not checked this RPM...but off idle, my oil pressure does pick up quickly.

>45-55psi at 2000rpm

This is within the range I am seeing (*45*) at 2100 RPM HOT...but I feel this new Milling pump's bypass circuit is kicking in...since even if you take it up to 4,000+ RPM...it's still *45* psi.

85_Ciera_Rebuild
10-04-2007, 02:35 AM
Melling Tech notes:

Pumps are not temp sensitive as to when the bypass opens. It opens when the resistance in the engine becomes great enough to
move the valve open.

The temp. affects the viscosity of the oil and that in turn that affects oil pressure .