oil pump

[gilbertmonchat]

hello,
i think i have oil pump failed, but i want to change for a better's one than the 1995, is it possible to change for the one on a 1998, i agreed it was better. and where i can find a good dealer. thanks

[john8662]

Uh oh...

Whats the symptoms?

There have been some good discussions about oil pump failure here on the forum, a quick "search" will grant you what you're looking for, and also search for the oil pump part number.

There are Two sources for the oil pump, the dealer and an aftermarket Melling Oil pump.

You will be able to physically see the difference between the old style pump and the higher volume pump.

[gilbertmonchat]

no trouble at cool, but when is hot the gauge are really low indication (at idle) and when i accelerate it's coming at normal level....sorry for my english !!!!! ;)

[john8662]

What kind of pressure did you have?

Cold Idle?
Cold @ 2K RPM ?

Hot Idle?
Hot @ 2K RPM?

When my oil pump failed, it didn't fail completly, just all of a sudden read about 15-20psi less in all situations than the rig normally ran. So I had an engine that normally idled at 45psi down to about 25, and that usually ran 55-60psi at 2K RPM, now couldn't make it to 45 psi hot or cold. The pressure relief valve had failed in my pump.

[gilbertmonchat]

my pressure was not in PSi, is in KPa

cold idle 250kpa to 275kpa
hot idle 100kpa to 150kpa
cold (2000rpm) 275 kpa
hot (2000rpm) 225kpa
is it possible it was only the relief valve and how check it, and change it

[JohnC]

First thing to do is verify the accuracy of the gauge. You should see about 300 kpa minimum at normal operating temperature at 2000 RPM. According to GM, if it's not in the red, it's OK...

[ 08-31-2005, 11:54 AM: Message edited by: JohnC ]

[john8662]

here is what I got for the conversion:

cold idle 36 to 39psi
hot idle 14.5 to 21.7psi
cold 2000 39psi
hot 2000 32psi

Those numbers are on the lower side, but still render the engine useable.

Your cold 2K RPM number is what bothers me, you really should see 50psi (344Kpa) with a bone cold engine, then level off when warmed up.

The oil pressure relief valve isn't really serviceable, you just replace the whole oil pump, it's an integrated part of the pump. I couldn't physically see mine that had failed, but it did, the pump was clean, as well as the rest of the oil system.

The part number for the HV oil pump (98+) is 12564768 which comes with the screen, which is different from your current pump and screen.

I also agree on using a known reliable gauge for a second opinion. Also you might consider swapping out the oil pressure sender/switch to make sure it's not giving a false reading.

[Kennedy]

Personally, I don't think a higher volume oil pump is worth the effort. Once you verify the pressure with a known accurate mechanical gauge, you'll know if indeed it is low. If the pressure is actually low, it is generally because of excessive clearances in the bearings or a mechanical failure elsewhere.

[gilbertmonchat]

i anderstand but the pressure is low only when is hot, and a mechanic failure or bearings clearance result of low pressure at all time!non???

[JohnC]

The pump puts out a particular volume at a particular speed. The pressure is determined by how fast that volume bleeds out past all the bearings and other lubricated parts. When the oil is thick, it bleeds more slowly. The pressure relief valve allows excess oil to flow back to the sump to limit the pressure. If the valve is fully open, the oil pressure will rise with RPM, as you see with the cold oil pressure readings. As the oil warms and thins, the relief valve closes more and more, maaintaining a fairly constant pressure. If it closes all the way, then the oil pressure begins to fall. This is usually due to excess clearances within the engine, although it can also be caused by a faulty relief valve (won't close tightly) or a worn pump.

Installing a high output pump in a healthy engine only increases the amount of oil bypassed by the relief valve. The later engines use the higher output pump to accomodate the piston oil spray nozzles.

[gilbertmonchat]

ok but how to know witch parts are the problem, can i make some test? or only change parts until i find the problem!!!!!!!!

[JohnC]

First verify that you have a problem, not a faulty gauge. If you have a problem, did it come all of a sudden, or gradually? Eventually you'll probably have to drop the oil pan and look at the pump and bearings.