Wacky oil pressure loss

Since my rebuild 2k miles ago, my autometer gauge (electric) now shows that while cruising on the highway at a set speed I will have about 65lbs of pressure. This is great you say, however, the slightest touch of the gas peddle to increase speed causes the oil pressure to drop off instead of rise. We are talking as much as 15-20lbs! On the flip side, I am always showing 10lbs/1k RPM. Any takers on WTF is going on here? I have a new sending unit on the way just in case and am looking for a mechanical gauge to verify my readings before I get deep into this.

Paul

Seems strange Paul. At warm idle, my autometer electric gauge shows 25psi exactly. And a warm drive it never goes past 55psi with 2k and greater. My guess, which could be wrong, is the bypass in the timing cover. That little spring/button thing is designed to let off excess pressure over 65psi i think. If that button is faulty, then it might be letting pressure out at the wrong times. This is just a guess. I believe the pump rebuild kits come with those, at least they do at my work (car-quest).

Loose tolerances. When you load the engine the oil is getting wiped off the bearings.

Of course it could just be a glitch. This is why I always use mechanical gauges.

On a good motor you should be seeing 65psi under all driving conditions above 2000rpm and a hot idle should show at least 30psi. Less than that and you have issues I think.

What oil do you use?

Mobil One 15/40 during the winter and 20/50 in the summer. Strange part of this is I didnt have any pressure issues before the rebuild (during which I found the crank wiped out, bearings pounded and a leaking headgasket) and the current setup has a freshly cut crank and brand new bearings throughout. The oil pump and front cover were in good shape with no significant scoring or scratches. I used to see 35-40 at idle fully warmed up and around 70-75 WOT at the top of the gear with 65 during cruise before the rebuild

Paul

The thicker viscosity oil is actually wearing out your main bearings. Switch to a 5W-30 synthetic oil like AMSOIL's XL-7500 Synthetic Motor Oil.

discipled1

I run 15/50 Mobile one in the XR7 and have the kind of oil pressure you describe prior to your rebuild. 20/50 is too heavy, but I still suspect a clearance issue somewhere. The 10psi/1000 rule is a good one, but if the oil pump is known to be capable of more, then you are spraying a lot of oil around which can't be good and if you have one bad bearing whereas the others are good, then rule doesn't apply there either. I'd verify with a mechanical gauge and if it still does it I'd start getting concerned.

My Dodge 318 does that also. It will drop slightly under load particularily if the oil needs changing.

discipled1 said:

The thicker viscosity oil is actually wearing out your main bearings. Switch to a 5W-30 synthetic oil like AMSOIL's XL-7500 Synthetic Motor Oil.

discipled1

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The thicker oil is actually needed for this mill. I only run the 20 weight when temps remain at 85-90* and above during the day. Regardless, the thicker oil is not wearing out the bearings and it certainly wont starve them either. If we were talking straight 50 weight, I could see the potential. With the kind of abuse this thing sees, at times, it needs every bit it can get.

Anyway, I didn't get to look at it last night, tornado warnings and ridiculous winds and thunderstorms put a damper on any activity. Hopefully I will know more today.

Paul