oil pressure gauge

[nate213]

i just installed an oil pressure gauge in my bronco. its a 66 with a 302 engine. i am wondering what should the psi be when operating properly?

 

[bknbronco]

My factory guage always says over 80

 

[aerohead.jr]

Between 20 and 40psi

 

[Airmapper]

Mine starts at about 40, then gradually drops under 10. I'd say 40 is probably better, I don't think the dropping is good but I don't know how to fix it.

40 is dead center of the stock gauge, so I'd say 40 is probably what it was intended to be. Hopefully someone can confirm and explain in more detail.

 

[Broncobowsher]

10 PSI per 1000 RPM is a good rule for a minimum. There is a relief valve to limit top end pressure.
You can increase pressure by reducing flow (pressure is the restriction to flow) by running thick oil. I would rather have less pressure and better flow of thinner oil, to a point.

 

[nate213]

10 PSI per 1000 RPM is a good rule for a minimum. There is a relief valve to limit top end pressure.
You can increase pressure by reducing flow (pressure is the restriction to flow) by running thick oil. I would rather have less pressure and better flow of thinner oil, to a point.

i run 10/30 oil in it. it tops off at 50 while idling. it should rise when the RPM's do? this is my first old car with gauges i actually have to pay attention to. im kind of new at it.

 

[Broncobowsher]

If you are getting 50 at idle then don't expect much of a rise with engine speed.
Also note that it will drop when the oil warms up and thins out (oil warms up much slower then water).

 

[nate213]

If you are getting 50 at idle then don't expect much of a rise with engine speed.
Also note that it will drop when the oil warms up and thins out (oil warms up much slower then water).

is the oil pressure gauges job to tell you that you have oil in the motor?

 

[bknbronco]

50 sounds good. When it says 5 then shut er down and add more oil!

 

[Broncobowsher]

is the oil pressure gauges job to tell you that you have oil in the motor?

NO! it is NOT a level gauge. I have known a few engines destroyed because the oil level ran low but the pressure gauge (or light) didn't alert the operater. 40PSI of solid oil or 40 PSI of foamed oil will still show up at 40 PSI. But foamed oil doesn't lube like solid oil does.

What does the oil pressure tell you? depends on how you can read it. You can tell if the oil is up to temperture, you can tell if the engine is worn out, you can tell if you are overheating the oil, you can tell if the oil pump drive has failed, you can tell if the oil is too cold to be romping on the engine. It is a gauge to one factor of what is happening.

 

[patterdale]

I had a 97 f150 witha 4.9 inline 6. I filled up with fuel and hit the highway. The next time I slowed down for fuel I thought I was leaving engine parts all over the road. The guage did not drop til I let off the gas pedal. The engine took 5 qts of oil to get back to full on the dip stick. Long story short part of the pan gasket blew out. It was silicone, one of fords better ideas. Had it fixed and ran it up to around 200k miles and sold it. The "idiot" lights that were in vehicles around the time of our broncos didn't come on until the oil pressure was down to around 3-5 psi. 40 is a good pressure but check it with a mechanical guage to make sure your electric guage is accurate.

 

[ghost66]

My turn to ask a question, I noticed my Bronco would generally be at 40 psi around town and on the freeway but when I pulled of the freeway and stopped at a light or stop sign the pressure goes down close to 0. Pull away from the light and it goes up to 40psi again.Replaced the oil pump, cleaned the filter, changed the sending unit, and then thought maybe it's the guage so I changed the guage. Still doing it, the Bronco drives smooth makes no knocking noise has excellent pickup and doesn't smoke or burn oil. What else can I try? Only does this after driving at highway speeds.

 

[patterdale]

My turn to ask a question, I noticed my Bronco would generally be at 40 psi around town and on the freeway but when I pulled of the freeway and stopped at a light or stop sign the pressure goes down close to 0. Pull away from the light and it goes up to 40psi again.Replaced the oil pump, cleaned the filter, changed the sending unit, and then thought maybe it's the guage so I changed the guage. Still doing it, the Bronco drives smooth makes no knocking noise has excellent pickup and doesn't smoke or burn oil. What else can I try? Only does this after driving at highway speeds.

Did you "clean the filter" or change it? Unless you have some special filter there is no "clean" to it. Unless of course you are talking about the pickup screen.

You make no mention of the age of the engine or any mods to it.

The answer depends on a lot of factors but the most important is this. No matter what engine you run use the oil recommended in the manual for that engine. Tolerences in the engines of differing age vary and non recommended oils will not perform properly. I had an old tractor that went through 10w40 like a fish through water. (I could buy it in big jugs cheap) Once I switched back to the recommended SAE single wieght oil It pretty much quit using oil all together. Same goes for automotive engines.

There is a reason engineers recommend a certain oil for an engine. A lot of times we create our own problems by thinking we can "improve" on an idea. Usually it's a 50/50 crap shoot to see if we actually achieve our goal.

If you have the right oil and everything else in place your engine is probably nearing time to rebuild. A new set of rod and main bearings might buy you a good chunk of time but it's a bandaid.

 

[ghost66]

Did you "clean the filter" or change it? Unless you have some special filter there is no "clean" to it. Unless of course you are talking about the pickup screen.

You make no mention of the age of the engine or any mods to it.

The answer depends on a lot of factors but the most important is this. No matter what engine you run use the oil recommended in the manual for that engine. Tolerences in the engines of differing age vary and non recommended oils will not perform properly. I had an old tractor that went through 10w40 like a fish through water. (I could buy it in big jugs cheap) Once I switched back to the recommended SAE single wieght oil It pretty much quit using oil all together. Same goes for automotive engines.

There is a reason engineers recommend a certain oil for an engine. A lot of times we create our own problems by thinking we can "improve" on an idea. Usually it's a 50/50 crap shoot to see if we actually achieve our goal.

If you have the right oil and everything else in place your engine is probably nearing time to rebuild. A new set of rod and main bearings might buy you a good chunk of time but it's a bandaid.

74 Bronco original engine no mods to it has 79k miles on it, cleaned the screen replaced the oil pump and of course changed the oil and the filter. Uses 10w30 oil. Really needs a rebuild with low mileage and runs perfect except for the dropping oil pressure after running at highway speeds. Why would it go back to 40psi as soon as I take off from the stopped position. When it gets started up at any time it sits at 40 psi, if I don't get on the highway it is always at 40 psi the only time it drops is when I come to a stop after being on the highway for say maybe 40 minutes at 65 pr 70

 

[jim3326]

I remember reading an article a while back, it was Bob the Oil Guy or something like that, and it stated that all motor oil goes to 3 wt after it gets to operating temp. The listed wt is the cold flow wt and the higher the number the longer it takes to get to 3 wt. I forget the relation with multi-vis. I thought I saved the website but I can't find it now%)

My 289 would start off at 40 at idle and 70-80 going down the road. After it warmed up to operating temp. it would be 10 at idle and 40-50 going down the road.

If yours is going to 0 at warm idle I would say it's close to worn out. I think 'back in the day' these engines were designed to go about 50-80k miles before needing a rebuild. As I recall the warranties were only 30-50k miles.

Jim W.

 

[patterdale]

Ther's an waaaaaaay outside chance that your drain back openings in the head/block are restricted or plugged and not allowing the oil to get back to the pan as fast as it should. Is there a crap pile of sludge in the valve covers? I'm just remembering some of the scenarios that I have come across over the years. The engine will maintain pressure at highway speed with little to no oil and then drop off the second you let off the gas. Don't ask me how I know this.

 

[Rustytruck]

if you suspect your oil pressure is running low change your brand of filter. I prefer Napa gold or the wix premium filters, pressure readings were much more stable with good filters. Using 10 w oil in an old design motor is not a good Idea. old motors were not designed to run these oils. Mainly the lower thermostats they used caused much larger cylinder bore taper wear. the oil rings running up the taper cant control such light weight oil and your oil consumption will be much greater. cold motors consuming oil foul plugs and leave more deposits in the ring lands making them less effective and fouling with even more oil. 20-30, 20-40 or straigt weight 30 would be better.

 

[ghost66]

Thanks for the tips, the 10w was only in there for about a week and we'll be checking the drain back openings on Monday. My mechanic suggested this also. Old guy in his late 60's filling in for the reg guy today who went on vacation. If this fixes the problem I'll be touting Old Guys Rule for awhile. If not then I guess a rebuild is in the works.

 

[DirtDonk]

i run 10/30 oil in it. it tops off at 50 while idling. it should rise when the RPM's do? this is my first old car with gauges i actually have to pay attention to. im kind of new at it.

Generally speaking, the factory gauges were dampened enough that your oil readings remain very stable during changes in rpm. You might see an overall change if you maintain a certain rpm for awhile, or you might not.
The main changes came with engine temp changes.

With aftermarket gauges however, you're likely to think you've installed a tach instead of a pressure gauge! The pressure can increase and decrease rapidly with rpm changes.

Ford stated the expected pressure range on a fresh engine to be approx. 70 psi cold, and 40-45 warm. That's what my gauge said all through it's working life. Every once in awhile going just above 70, to just below 40 when hot.
Always had 20w/50 in mine, but my new one will be using thinner oil to start with.

As was mentioned, no matter what your average pressures are, as long as you have at least 10 psi at idle and another 10 psi per 1000 rpm, your engine is safe and happy.
That's an old Smokey Yunick rule-of-thumb that they came up with during all the engine testing they performed when building Chevy race engines back in the day.
Still holds today.

The "W" in the oil ratings stands for "Winter" to denote cold performance, and the higher number the viscosity when hot. Basically just gives a consistent comparison point when considering an oil's hot and cold characteristics.

Paul

 

[ghost66]

Looks like a rebuild is where I'm going. Drain back openings are clear, changed to 30 weight and although it doesn't go to 0 it still goes to below 10 when stopped. Wife is complaining and says drive it till it goes, I say throw a rod and it's a new motor and not a rebuild. What do you say? What would you do and how much is this going to cost me?