Brief, mysterious loss of oil pressure (1 Viewer)

[SiestaTom]

Two weeks ago, took a leisurely, low speed drive for about 20 minutes. After making a slow speed U-turn, both myself and passenger noticed a very subtle change in the engine sound - very mild tapping. I looked at the oil pressure guage and it showed none! I immediately shut her down and checked the dipstick - it was full. Waited a couple of minutes and started it up, and got totally normal oil pressure - tapping sound was gone. Have driven it several times since and oil pressure, engine sound, and everything else has been normal. There is nothing to suggest the guage is faulty or erratic, and the tapping sound we heard seems to confirm that we did indeed suffer a momentary loss of oil pressure. I'm a bit freaked and have no idea what to do - if anything, other than keep my eyes glued on the guage.

Rig is 1974 40 that's been in the family for decades. No recent work on it other than installing a Pertronix ignition about 6 weeks ago - but I didn't pull the distributor or even remove the clamp. Truck has about 130,000 miles and nothing like this has ever happened. Oil pressure on this rig seems to run pretty high. At idle the gauge is mid position, and at any running speed the needle is at least 3/4 toward the high mark. This rig is only driven 1000-2000 miles each summer and it sits garaged all winter. Oil and filter are changed regularly and oil is sparkling clean now. My dad thinks we should run some type of oil cleaner / additive through it. If anyone agress, what product would you suggest? Any thoughts greatly appreciated.

 

[sggoat]

What you describe almost sounds like there might be something floating around in the oil pan that got into the oil pump suction for a brief time, shutting down oil flow. Anything in the smaller oil passages up top would not cause this. It has to be in the pump discharge--there is only a short distance from the pump output to the oil pressure sending unit. The dip in pressure plus the rattling indicates it's not a gauge issue either. I would drop the pan and check.

 

[vtgbeemer]

I agree with sggoat assuming that u-turn was on level ground and not terrain that would allow the pump to suck air.

 

[SiestaTom]

The turn-around was relatively flat and slow, so there's no way the oil sump intake went dry, even for a moment. 3 weeks ago I did some relatively steep trails and had no issues that were apparent. Then again I wonder if I could have missed a similar, brief pause in oil flow given my focus on the trail. hp Have to admit your assessment sounds logical, though with my long time ownership and regular oil changes it's hard to imagine something large enough floating around, blocking the flow. Given my work schedule, dropping the pan may take awhile to get to. In the mean time, I'll welcome all other thoughts - and I'll keep my eyes glued to the gauge.


Thanks guys

 

[Augusts96]

Hi there! Did you figure out what it was?

 

[shelfboy1]

did you check the dipstick ? sounds like there was low oil level in the engine