Oil pressure goes to zero when hot

[cucvegas]

I replaced the oil pressure gage and transducer on a 1993 Humvee with 6.5L GEP (transducer and Gauge were bad).

When startting cold, the oil pressure is reading 45. When it gets hot the pressure gets much lower (around zero) and fluctuates. Tempuratrue is around 200 when revving it hard in neutral.

I did not change the oil when I bought it a year ago, and I’ve only gone 350 miles in one year, so the oil may be very old and thin.

Should I first just change the oil, and is there a thicker oil that may register better?

I have a Fram PF5 filter from my cucv and 2 gallons of Supertech 15w40. Any other filter and oil suggestions?

When revving the engine really hard it looks like very minor heat waves coming out of the oil fill, but no smoke and it does not rattle the fill cap when it is placed on it. So maybe very minor blow-by.

The engine main seal has a minor leak when parked with oil drops about the size of a couple quarters, but the Oil level is fine. Very black, though and needs to be changed.

Thank you for all your advice!

 

[Katavic918]

Change the oil. Rotella 15/40 is good. If that doesn't fix it, install a good mechanical test gauge where your OP transducer is and get an accurate reading. Then go from there.

 

[cucvegas]

UPDATE:

Changed oil and filter (15w40).

Now it idles around 5psi and goes to about 30 when revved.

 

[Wire Fox]

...while this isn't my most productive post, this reminds me that I should change my engine oil. It doesn't have very many miles on it, but it sure has been in the engine for a while.

This is also probably the right time for me to swap the dipstick out with the DWF one I have on-hand.

 

[papakb]

The rule of thumb is 10 psi per 1K RPM. If your using Walmart oil in your vehicle your asking for trouble. Your far better off using a quality oil like Rotella or Delo 400 in your truck. Also, don't go cheap on your oil filters. Here's a link to the Hummer knowledge base with listings for filters: http://www.hummerknowledgebase.com/parts/list/005.html

If you have any question about the actual oil pressure pull the doghouse and "T" in a mechanical gauge on the back of the engine block. Pressure dropping to zero is usually caused by bearing wear, low oil, or a bad relief spring in the oil bypass circuit.

 

[98G]

Change the oil. Rotella 15/40 is good. If that doesn't fix it, install a good mechanical test gauge where your OP transducer is and get an accurate reading. Then go from there.

This.

I question the accuracy of the measurements. Does it sound like zero oil pressure?

Add me to the rotella crowd. Along with the anti drainback WIX filter.

 

[Wire Fox]

"Never FRAM" is my motto. Their anti backflow value is literally cardboard... another +1 for Rotella. I use it in the HMMWV and my motorcycle, since it meets the JASO spec needed.

Sent from my Nokia 6.1 using Tapatalk

 

[Bulldogger]

Buy an inexpensive mechanical oil pressure gauge from the auto parts store and plumb it in place of your dash gauge. Fire her up, note the pressure. Warm her up and drive around a bit, note the pressure. Then report back here with the results.
I had this same problem. In my case my military dash gauge was old and inaccurate. I had/have good oil pressure within specs cold and hot. Bought a new dash gauge after proving the true pressure and went on to other maintenance.
BDGR