So about 2 weeks ago I made a thread on here that I had no oil pressure. I changed the sensor and it went away.

However, problem is obviously not fixed. It seems to be intermittent. It seems to be worse in the morning when I go to work. It's nvr done it in the afternoon even after letting it sit.


It is indeed no pressure; at least to the top end. Noticed the oil pressure was flat this morning after start up. Shut down and restarted 3 times. The third time I waited about 5 seconds and the pressure suddenly kicked on.

When the pressure finally finally kicked on, I heard a distinct change in the top end (valve train). Previously the valves sounded much louder, and then suddenly sent quiet and normal when the oil pressure kicked on.


What could be going on? This engine had a complete rebuilt about a year ago. Was bored, new pistons/pumps, timings etc. Pretty much only reused the valves...and I think the oil pick up tube.

 

Have you changed then sending unit or is that what you meant by sensor? Oil Pump and pickup tube are another two things it could be. I don't have nearly as much experience with Ford gas engines or DOHC Motors but the oil pump, pickup tube, and sending unit are a few. Maybe cam bearings but not sure on DOHC motor what else could cause it.

 

What are you using for an oil filter? If it's not a motorcraft, it may not have a backflow valve. Some of the cheap aftermarkets don't have it and will cause the no oil pressure upon start up. If I remember right, you didn't replace the oil pump, right? All your descriptions and ideas seem to go to the oil not being up where it is suppose to be when started. A bad oil pump will let the oil pressure disappear when cold or sitting for a while. If the oil pump has excessive clearance, it can not hold the pressure where it is necessary, causing no oil pressure upon start up. I really think you need a new oil pump.

 

Another possibility would be the oil pump pick up screen holes. These tend to get blocked with carbon/tar on older engines if the oil had not been changed regularly. As the blockage progresses the volume of oil from the pump decreases and it takes longer to build oil pressure. Once the blockage is there, it must be manually removed. Additives and or flushes will not clear the blockage.

 

I honestly don't remember if I changed the oil pump. I think I did but not sure. Going to try to look up some receipts or old pics I took and see if I can find out.

I don't have a motorcraft filter, and I'll be replacing that first.

Question, if the oil pump clearance was off...wouldn't pressure be lower all the time, even when running? Or maybe even fluctuate some? Asking, because as soon as the oil picks up....the pressure is exactly where it has always been and holds perfectly steady.

 

The oil pressure sending unit does not actually give a pressure reading. It is a pressure switch that comes on about 5PSI. So it is on/off only like an idiot light. What you see on your gauge is either on at mid point or off at low point.
You may want to install a real pressure gauge so you have some real data to help go forward with

 

I wasn't sure with this particular truck so that's why I asked haha. Thanks for clearing that up, now I know too.

 

The reason it would be low is excessive clearance in the bore where the two gears ride. When this happens, it takes away from the pressure that it is suppose to build, by having less material to work with. To your question of the oil pressure showing on the gauge, it only takes 4-6 # of pressure to show the gauge working. Even if it is off, the gauge will still show normal, usually. Factory gauges are nothing more than a feel good for the driver. It doesn't reflect true pressure, just what the sender is set to send. A mechanical gauge is the only true way to have a true reading.

Think of a engine cylinder, and the piston is worn. The oil goes by the rings too easily and is burnt in the cylinder. The oil pump is similar as when oil goes by, it isn't building the pressure or volume needed, it cavitates and causes little or no pressure. The sides of the pump are larger than original by wear, causing the oil to go by the gears, and not build enough pressure. When it is hot, the oil is thinner, causing low oil pressure with an old pump.

 

I cannot find the date when Ford began with the fake oil pressure gauges. I can find articles going back to 1990 discussing conversions to make functional gauges.
Reason they made the switch was too many people complaining about oil pressures varying (what others reported).

 

That's pretty interesting. Almost no reason to have it haha. I would prefer a gauge that shows realistic specific oil pressure.