4.6 Loses oil pressure after running high rpms

[seanyb505]

I only noticed it after the initial breakin period, not during. I switched to Brad Penn 10W30 Racing oil at 1100 miles, and am using a mopar oil filter. Ive used the same brand filter ever since the engine first ran, so I dont think its that. I used 30wt breakin oil all during the first 1100 miles, so I dont think the oil is too thin either. I only noticed the drop in oil pressure when Ive sustained higher than grandma rpms (highway cruising at 85ish) and hard acceleration when the temp is a little high. (Stop and go traffic, traffic light to traffic light). The only time it will drop is if I come to a complete stop and the engine has 5 seconds to idle. As soon as I bring the rpms up a little the pressure returns to 10ish psi only to fall again if I let it idle again. If I stop and dont let the engine idle at 750 but keep it at 1000 it will not drop. Im wondering if I should go to a different oil, oil filter, or if i need to replace my standard flowing oil pump for a high volume unit. Any ideas? Ive also heard of shimming the spring in the stock piece, would this help at all?

[Mgardiner1]

I would hook a mechanical gauge to it and get it so you can watch it in the cab. I wouldn't rely purely on the calibration of an electric gauge or sending unit. See if you can "tee" the gauge in so both gauges will work at the same time and see if you notice a difference

[SIXPAK]

Putting on a mechanical gauge is a great idea to start. If the new gauge shows the same thing is it possible that you may have used the wrong pick up for the oil pan that you are running? Short pick up tube could be the culprit?

[seanyb505]

The oil pan and the pickup tube came from the stock engine. Only the pump was changed.

[IH 392]

A new screen is CHEAP! insurance, I NEVER! reuse an pressed in screen, what kind of pump did you use?, it sounds just like what my Jeep was doing with the OE aluminum pump (in the stock 4.0), I switched it for a new MELLING iron pump and a NEW pickup tube and all is SWEET!!! at 134,00.

[6TIME]

Ditto on the mech gauge. I put a T where the factory oil sender is and plugged a 1-1/16" 100psi gauge in so I could observe the oil psi during initial startup and break-in. It made it nice not having to run back and forth to the check the dash gauge. I found that the factory gauge likes to jump around 5 or 10 psi sometimes while the mech gauge is rock steady. Go figure? I also switched from a factory aluminum oil pump to a Sealed Power Iron pump and my psi never drops under 30psi. The motor has 50k on it. The factory pumps with aluminum cases do not fair well if any debris goes through them.

[Heck]

I saw similar problems with my sister's grand cherokee with the 4.0. The engine got overfilled a little bit at an oil change, and the level got into the crank, causing foaming in the oil, which caused a loss of pressure after hard running.
Just something to check.