Oil Pressure Highway

[jdeignan]

Gents,

I’ve seen a few results using search but wanted your opinions anyways.
74’ 302 suddenly having low (10psi ish) oil pressure on highway speeds.
If I take the exit ramp oil pressure goes back to 70-80psi where it normally sits.

Replaced the oil sender in 2015 (electrical)
Replaced wiring with it
Replaced oil pump and pan a few months ago (WH4x4)
Pump is not a high flow pump.
Filter is Motocraft
Running 10w30 in San Diego.
Oil level is normal.

That should cover most questions. If it is a gauge issue, can anyone explain why it would present faulty readings only at high speeds?
Any recs for a mechanical gauge?

Truck sounds normal at high speeds- nothing significant to report otherwise.

 

[broncochevy]

A bad gound can make the gauge act funny. Did you use any pipe dope on the sender when you installed it? Reason I ask is I did in a temp sender 10 years ago, and it sealed but did not work the gauge properly. Removed it and left it clean; no dope at all. Seemed to work well. Then last year developed a coolant leak. All with almost no driving on the vehicle. Used Teflon tape and no leaks with good grounding at the sender and gauge seems ok too.

 

[Broncobowsher]

I would install a temporary oil pressure gauge. Even if you just zip tie it the hood.

You need to find out if it is a real oil pressure problem or an electrical/gauge issue.

A real oil pressure issue; I can see 2 likely scenarios. There is enough junk in the bottom of the oil pan (bits of broken nylon timing gear teeth) that the pickup is clogging and starving the pump for oil. Another is the oil drain back holes in the heads are carboned up and the heads are not draining back into the block after a long highway run.

The temp gauges doesn't have to be a high end one. Just add a T-fitting so you can watch both gauges. If both gauges drop off together, you have a mechanical problem. If the electric gauge drops and the mechanical doesn't, off to electrical issues. If the mechanical drops and the electric stays up, you are probably looking at the faster response time of the mechanical gauge as the electrical gauge has a slow response time.

 

[jdeignan]

I would install a temporary oil pressure gauge. Even if you just zip tie it the hood.

You need to find out if it is a real oil pressure problem or an electrical/gauge issue.

A real oil pressure issue; I can see 2 likely scenarios. There is enough junk in the bottom of the oil pan (bits of broken nylon timing gear teeth) that the pickup is clogging and starving the pump for oil. Another is the oil drain back holes in the heads are carboned up and the heads are not draining back into the block after a long highway run.

The temp gauges doesn't have to be a high end one. Just add a T-fitting so you can watch both gauges. If both gauges drop off together, you have a mechanical problem. If the electric gauge drops and the mechanical doesn't, off to electrical issues. If the mechanical drops and the electric stays up, you are probably looking at the faster response time of the mechanical gauge as the electrical gauge has a slow response time.

-New oil pan, so I dont think theres any gunk in there. This problem occurred before AND immediately after replacing pan and pump.

-How can I inspect oil drain holes? That could be it.

 

[Apogee]

How can I inspect oil drain holes? That could be it.

Pull the valve covers, take a looksee.

 

[Timmy390]

Pull the valve covers, take a looksee.

I took an old VC and cut the top off. Can run the engine with no mess while taking a look.

70-80 at hot idle seems high to me. My W is 50 at hot idle and 65ish at speed using a mechanical gauge.

Tim

 

[jdeignan]

alrightt quick update- think its good news:

Installed autometer mech gauge.
Truck holds 40psi in park, warm idle. 750rpm ish
Truck holds 30psi in drive, brake on, idle. Assuming 550-600rpm
Any acceleration to cruise ramps up oil pressure to 52 steady.
52 PSI held on highway cruising at 80.

So, assuming those are good numbers- Will a bad sending unit cause bad readings? If its a variable ground gauge, why does an increase in RPM cause my needle to drop?
Ideally I fix this issue because I like the stock gauge look

Currently, my electrical sender/gauge comes right up to 70psi, and will does not fluctuate at all until I hit about 65mph. No change while in Park, drive, idle etc

 

[Broncobowsher]

This is where I would put a T-fitting so both gauges are working at the same time.

There might be a flaky ground. I would run a temp heavy gauge (14?) from the engine to the cluster. That's not the fix, that's just to make sure the grounds are all good.

If you are suspecting the sender, an Ohm meter attached between the sender and ground (must be disconnected from the gauge) and watch the readings compared to the mechanical gauge.

Does the volt and water temp gauges drop when the oil pressure does? Could be an IVR issue.

 

[jdeignan]

This is where I would put a T-fitting so both gauges are working at the same time.

There might be a flaky ground. I would run a temp heavy gauge (14?) from the engine to the cluster. That's not the fix, that's just to make sure the grounds are all good.

If you are suspecting the sender, an Ohm meter attached between the sender and ground (must be disconnected from the gauge) and watch the readings compared to the mechanical gauge.

Does the volt and water temp gauges drop when the oil pressure does? Could be an IVR issue.

I was thinking IVR too. Didnt do a T fitting but can guarantee that the gauge is what is innacurate.
Replaced the sender today- havent taken it on the highway yet but the idle reading is identical to the other one.
How can I really be sure the water temp is dropping? It should drop on highway with increased airflow, shouldnt it?

 

[jdeignan]

This is where I would put a T-fitting so both gauges are working at the same time.

Didnt mean to ignore advice. But I dont have a tee fitting. Ran the elec. gauge, pressure dropped. ran mechanical gauge, pressure good. ran the mechanical gauge, pressure dropped.
Not sure a tee fitting is necessary unless I am missing something.

How can I check out the IVR? (replaced in 2015) Suppose it could be getting too much power at RPMs, and that throws off the readings?

 

[73azbronco]

your wire is flapping in the wind causing low reading my bet. What is your system voltage at speed?

 

[jdeignan]

your wire is flapping in the wind causing low reading my bet. What is your system voltage at speed?

Voltage from battery, or IVR?

 

[jdeignan]

Update for anyone with similar issues:
Tightened the bolt that holds down the wore to the sender and added teflon tape- as stated above I think the vibrations at high speed were rattling the connection. Phew.

Current elec. gauge sticks to 65-70psi which is incorrect (30ish idle, 50 cruising) Maybe it is the needle giving bad readings. Will look to replace that next. Thanks for your help guys

 

[Broncobowsher]

Teflon tape can sometimes be the issue. It is an insulator. If the threads don't cut through the tape the sender might go insulated. Teflon paste allows for thread sealing and electrical continuity. If it is working fine now, leave it. But for reference when screwing self grounding sensors (oil pressure and water temp) the paste is a better choice.

 

[jdeignan]

Good to know! Thanks man