low oil pressure when hot

[jeff_gates]

66 Bronco but that is where it stops.
84 351W unknow condition or millage

When the engine is cold it's oil pressure around 40lbs, but when hot it drops to near zero.

I just did a compression check

1. 130
2. 130
3. 130
4. 135
5. 140
6. 139
7. 140
8. 140

What all do you suggest?

Thanks,
Jeff

 

[Broncobowsher]

Rings good
Bearings worn.

Pressure is the restriction to flow. The quick fix is a step up in oil weight.
Above that a high volume pump.
Next is an engine rebuild. The cam bearings are often the cause and they don't swap without pulling the engine.
Swapping rod and main bearings during the high volume pump install will get you more.

 

[jeff_gates]

I was thinking a HV oil pump and new main bearings, any suggestions on brands?

Thanks.

 

[Broncobowsher]

Most people get the Melling HV83, which is really good.
But my choice is the Melling 10833. It has some nice features like a pump support in the cover and an upgraded oil pump shaft is included.

I would also do (or at least inspect) the rod bearings as well.

 

[spap]

Add some STP keep you going until the rebuild. Haaa. I'll get roasted for that one

 

[SteveL]

Going with a hv pump may have clearance issues with the oil pan. I did a little grinding on the casting to make I fit.

 

[73azbronco]

Try STP I hear good things.

Seriously, zero psi is bad, so is the gauge accurate? If you have zero you should hear lots of banging clanking, cuh-pow noises. Is it zero at idle but goes up with revving? Is your setup stock? I mean harness and sensor? If so old cars tend to lose or increase resistance with heat. Can you try a mechanical gauge?

 

[gorf]

Low on oil?

 

[DirtDonk]

Definitely verify the gauge rating ASAP.
Do the fuel and water temp gauges read low as well?
For a quick test you could ground the pressure sender wire out in the engine compartment and then turn the key on. See if the gauge goes all the way to the top in a few seconds.
That's not a conclusive test by any means, but it gets you at least some more data.

Paul

 

[B RON CO]

Hi, what weight oil do you run? How long have you had low oil pressure? If you use 10W-30 I would try 20W-50 and a Quart of Lucas oil treatment. Also oil pressure should rise @ 10 psi for every 1000 RPMs. Good luck

 

[Rustytruck]

drop the pan and replace the rod and main bearings will buy you time. Pain in the ass but will buy you time. Time to find another motor rebuild it then swap it out when ready. or try a wix oil filter maybe the bypass valve in the filter is fubar. Dont use a Fram filter.

 

[73azbronco]

FL1A all the way.

 

[jeff_gates]

Some Google searches and people state the older engine main bearings wear down, and they suggest Lucas, I'm guessing STP would do the same.

I'm using a cheap machinal oil pressure gauge, Sunpro CP8216, so I'm guessing it's between 0-100% good.

I use K&N oil filters and 10-30W, I will change it to 20-50W.

 

[MS73HD302]

I've had good luck with 10-30 and the Lucas oil stabilizer + FL1A oil filter. Mine would drop to 10 if good and hot with the Lucas it held 20 at idle no matter how long it was driven

 

[DirtDonk]

I'm using a cheap machinal oil pressure gauge, Sunpro CP8216, so I'm guessing it's between 0-100% good.

Exactly!;D
Might want to check the gauge then too while you're at all this figuring out. I've never tried it, but would not blowing compressed air into the sensor tube net the same results? Leave any oil still in the line, then set your air pressure regulator valve (assuming you have, or can access a compressor?) to a couple of given pressures. Starting at 10psi then going to 20psi and so on.
If your two gauge readings coincide, that's another level of confidence you can have in your gauge.
Your original electrical gauge is not functioning? Could it still be connected temporarily as a quick comparison?

I ran 20w/50 oil for years in my 302. Heavier than recommended, but it's what we had at any given time at the house because it worked in all of our vehicles. That engine had 70psi cold and 40psi hot on the stock gauge. Exactly what the factory manual states is to be expected with our engines. At the end of it's life (with me anyway. I sold it still running) it would go as low as 30psi when hot at idle.
The factory gauge is dampened so does not react to rpm quickly like an aftermarket gauge usually does. Watching the pressure change with rpm you can practically use a mechanical gauge as a tachometer!
Not the same thing with the factory gauge, but in some vehicles it was actually pretty accurate.

Paul

 

[blubuckaroo]

I've never had one of these old vintage engines happy with 10W-30 all year round. It's good for the winter though. They actually run best with the SAE 30 they were run on back in the day.
I like to use the 15W-40 oil typically used in diesel engines. Rotella, Delvac, Delo 400 etc.

 

[73azbronco]

I was skeptical of multi vis oil, until I studied it in college. Pretty amazing stuff. It knows when it's hot, and gets thick, and knows when it's cold and gets thin.

 

[half cab]

Pretty amazing stuff. It knows when it's hot, and gets thick, and knows when it's cold and gets thin.

Sooo that's how it works ;D

 

[Timmy390]

I like to use the 15W-40 oil typically used in diesel engines. Rotella, Delvac, Delo 400 etc.

That's what I run......

Tim

 

[toddz69]

I like to use the 15W-40 oil typically used in diesel engines. Rotella, Delvac, Delo 400 etc.

Do you feel it gives you a little more pressure?

Todd Z.