I just performed an oil pressure test using the $30 harbor freight gauge. It worked great!

2004 DII with non original 4.6. Unknown mileage (suspected under 100k).

I really did the test just to know. No reason to suspect low oil pressure.

Notes: cold idle was right after startup once the rpm settled down to 1,000rpm or so. Bone cold motor. Hot idle was with about 170 degrees water temp. That’s as hot as I could get it without driving it. This time of year it runs around 170 degrees all the time with the in-line thermostat and heavy duty fan clutch.

Rotella 15w/40 and a big K&N oil filter. Changed the oil about 150 miles ago.


Cold idle: 56-58 psi
Cold 2k rpm: 58-60 psi

hot idle (172 degrees water temp - that’s where it idles now with cold temps and the in-line stat): 28psi
hot 2k rpm: 56 psi


The 55-58 psi numbers are on point. 28 seems a little high for hot idle?

The truck ran for about 15 minutes with me revving it at 2-3k rpm to heat it up before I measured the “hot” numbers.

 

even though your temps are 170 the oil is not even close to operating temperature
you should drive it for a good 30 min highway drive then test the hot idle

 

@redwhitekat yeah, I would be surprised if the oil was at operating temperature.

Now that I know what to do it’ll be easy!

 

@arains44 I did a grocery and storage unit run then took the long way home @redwhitekat is correct you need 20 to 30 minutes of driving after you hit normal operating temps.

But the cold idle is good

 

Oil heats up much slower than coolant. I have an oil temp gauge and it takes at least 10 minutes of city driving to get the oil to the lower bound of the operating temperature range.

 

Exactly. And this even takes longer in cold climates. 19° F yesterday...oil's like cold gravy down there in the pan. Always let our vehicles idle at least a minute before even dropping them into gear.

 

I might do another test today after a long drive. The gauge is a little bit of pain to connect, we’ll see if I can make it happen again today...

I have no oil temp gauge - I’ll just drive it for a while and let it get it good and hot.

I usually let my truck idle for about a minute before pulling out of the garage, and then I usually wait until the it’s over 100 degrees water temp before I leave the driveway. That’s usually about the time the SAI shuts off.

 

little advise from my experience when you drive it for 30-45 min and are ready to perform the test let the disco sit for 5-10 min let that oil drain into the sump or when you connect your gauge it can get messy

 

I opted against doing another Oil Pressure Test today. While my test yesterday wasn’t conclusive I think it points me away from there being an oil pressure issue which I think would have shown up with that test.

I’ll probably revisit this down the road and do another test when my neck is less sore from laying under the truck.

Trucks running good. Now on to diagnosing the subtle tapping noise at hot idle... :/