Hey all, I recently built a 5.3 motor and replaced all bearings (cam, crank, rod). I also put on a new melling oil pump, Holley 302-2 oil pan, and pickup tube. Upon first crank to see if oil pressure was good, it took longer than I expected for it to build up. It eventually built 20 or so cranking, so I fired it up. When running it sat at 45psi and then when warm will widdle its way down to 30psi. I didnt think too much of it until the next moring I went to start it and it took about 4 seconds to build pressure. Then, as the car warmed up, it would drop again. After research, a lot of people say bearings or the oil pickup tube are usually the culprit of this. With all the new bearings, I find it hard to believe that they are the cause, so then I took the windage tray nuts off that were holding the pickup tube steady. With them loose, but the oil pump girdle bolts tight, it seemed loose. Is that normal? That is a new oring and it's the larger one (Black,) so the green one has even more wiggle.

 

The Green one is larger than the Black one. This has been the case on EVERY Genuine Melling LS pump I have purchased.

No It shouldn't be that loose.


-

 

The correct O-ring to use goes with the style of pickup tube you have.

Look closely at the end of it where it plugs into the oil pump. There are 3 styles: stepped, angled, and straight. The step is maybe 1mm deep; the angle dips in about that same amount right at the bolt flange; and the straight one is ... straight. AFAIK there's no way to know which one you have other than by looking; it's not like LS1 uses this and LM7 uses that, or 19xx - 20xx is this and 20yy-up uses that, or any such. Just gotta look at the part in your hand. If you can't tell whether yours is angled or straight, use your calipers; the straight one will be the same OD all the way from the end to the bolt flange, the angled will be quite a bit narrower at the flange.

The straight one takes the thin O-ring. The other 2 take the thick one.

Don't try to use the color as the guide. In addition to green and black, I've also seen read and blue ones. Can't recall what thicknesses any of em were. In any case, the color is irrelevant; what matters is the thickness. Use your calipers on the new ones to be sure which is thicker.

The right one should make it somewhat difficult - not "hard", butt not exactly "drop in" either - to assemble. If it fits loose, it won't seal, and it WILL suck air in along with the oil, and the oil pressure will be low esp when hot; and air bubbles do not lubricate.

Did I forget to mention, USE YOUR CALIPERS, and MEASURE. Don't "assume" anything.

 

Thanks gents. I went ahead and ordered a new pickup tube along with the correct oring to fit it. Will be here tomorrow and will let you know what the oil pressure does.

 

what oil filter are you running? i put a cheap carquest red filter on mine one day as thats all that was locally available at the time and thought id hurt something as the first time it warmed up the oil psi was significantly lower than normal, bought a wix from the next town over the next day and all was back to normal

 

I’ve had quite a few oil and filter combos on it. Stp was this last one. Going with nicer brands now as I realize it matters more.

 

What pickup tube was that? Looks aftermarket?

 

I got it with the 302-2 oil pan. If you’re wanting that exact one you’ll have to call Holley and order from one of their techs