Oil Pressure Drops out quickly

[Shertzy]

I have a 95' Bronco 5.0. No problem with the start up. Gauges all look fine. After 1/4 to 1/2 mile the oil pressure will drop and the truck will quit. Let sit for a little and start up everything fine, then the oil drops and truck quits.

 

[bidibronco]

Sounds like you may have bad bearings. Anything from mains to rods to cam bearings. If it's not cold in your area try using a thicker oil like 15w40 or even 20w50. There's plenty of fellows on here that run that. Also, invest in a "wet" guage oil guage and that may tell the truth a little better. If anything, put in a new fuel pressure sensor.

 

[BroncoJoe19]

I have a 95' Bronco 5.0. No problem with the start up. Gauges all look fine. After 1/4 to 1/2 mile the oil pressure will drop and the truck will quit. Let sit for a little and start up everything fine, then the oil drops and truck quits.

Are you sure it is not the other way around?...

Maybe the engine stops, and then the oil pressure drops?

When you first start her up, what kind of pressure do you get, and if you let it idle in the driveway, how long will it run before it stops?

Does your check engine light come on while it is running?

 

[Broncobill78]

Bidi's right, it's probably the main bearings. A gauge is easy to install and would be the first thing I'd do. The *second* would be to change the oil to 20/50 and see how/if that changes the pressure. If you have better oil pressure running a 50wt. oil than you have bearing problems (not the end of the world though, I've had friends run engines like this for 1 or 2 yrs until they could get them rebuilt)

 

[Seabronc]

One other simple possibility is a bad oil filter that is in bypass mode. Wouldn't be a Fram filter would it? I use Baldwin which is primarily used on heavy equipment and has one of the best reputations for reliability.

Good luck,

 

[BroncoJoe19]

Automatic responses please...

What goes together?

Pizza and... Beer

Football and... beer

Low oil pressure and... worn bearings.

I understand how a low oil level, or a worn oil pump could give low pressure, but I don't know how the bearings contribute to the oil pressure. I had two V6 fords with low pressure and was told that it was either the pump or worn bearings, but no one ever explained to me how the bearings come into play. So I don't understand how a engine could have NORMAL oil pressue on start up, and in a short period of time a minute or two (in this case 1/4 mile) the pressure could drop to the point that the engine shuts off. I imagine that when the engine heats up, that the bearings expand, and I guess that doesn't allow them to push oil around as they should. COuld they go from NORMAL to so low that the engine shuts down?

What causes the engine to shut down? Is it that the engine is starting to sieze? or is there some kind of sensor that kills the power if the pressure gets too low?

 

[bidibronco]

Actually, it's because when you first start the engine that's when the oil is at it's thickest hint's why to try 50wt. After the engine is at operating temperature the viscosity gets a little bit lighter. No matter how "good" the oil is it's a fact, after the oil gets warm it gets a little bit thinner. Now what makes the pressure in the engine is the oil pump however, if your bearings are bad then the oil is moving much faster around the "bearing passages" thus leading to lower pressure. It's kind of like an oxy ***** (I think that's what it is, double negative or something?) anyways, it's like putting water threw a 1/2" hose at 50psi and then (with the same exact pressure from the spicket) running it threw a 1" hose, the pressure isn't quite the same on the hose. Man, I hope this makes sinse?

 

[BroncoJoe19]

BidiBronco,

That is the best explanation I ever got, and yeah, it does make sense.

Thanks!

So what about the engine quiting when the pressure gets low, it is starting to seize, or is there a safety sensor that cuts power so that there is no internal damage?

 

[Broncobill78]

Think of a garden hose. When you turn it on and the end is open & unrestricted the water dribbles out, but if you acclude the end with your thumb the water jets out and you can *feel* the pressure on your thumb right ? Same deal with bearings. When they're new and everything is tight you should only have one or two thousandths of an inch clearance (0.001"-0.002"). When the engine starts the crankshaft spins on a that small 0.001" wedge of oil and the pump forcing the oil through those small restricted spaces is what creates your oil pressure. Once the journals & bearings become worn the pump is now pushing the oil through much *larger* spaces so the pressure falls, same as with the garden hose.

The engine will have NORMAL oil pressure when it starts for two reasons, one is that the oil is cold and when it's cold it's more viscous (this is why oils have two numbers 10/40, 20/50, etc. When it's cold the viscosity rating is 10, when it's hot that rating the rating is 40) and the thicker the oil is the higher the oil pressure will be. The second reason is that as the engine heats up everything expands. You may well have a main bearing clearance of 0.002" when you first start it but after 5-10 minutes you're looking at 0.005" or 0.006" and that will cause the pressure to drop as well. Combine the two you get good startup pressure that quickly drops off.

 

[BroncoJoe19]

Thanks guys... I got it. Those explanations make sense.

So what about using STP or Motor Honey?

 

[Broncobill78]

Well, yeah, I guess, maybe, sort of. Those additives *are* designed to increase the viscosity of the oil but to be honest I've never been a big fan of oil additives. The main problem is that you really don't know what viscosity your oil is once you dump in a can or two. Now I suppose there might be some merit to popping in a few cans and seeing if the pressure comes up and if it does using that to make yourself feel better about switching to a 50wt oil but you would in all reality probably need at least 2 or 3 cans to raise a 30wt up to a 50wt if not more and then you're still left with the gummy residue clinging to everything when you drain it to add the 50wt. For pretty much the same $$$ you can get 6qts of wal-mart brand 50wt & a filter to toss in as an experiment to see how much it raises the pressure when hot.

 

[bidibronco]

I would rather have a winning lotto ticket but I'll go with BroncoBill on his thing. A quick 20w50 and a filter for a little cash or all that other headache stuff?

 

[BroncoJoe19]

hehehe... you guys got me sold. Next oil change I'll use 20w50 in my Winstar.

Do you have any thoughts on the synthetic stuff?

I think that I had seen one for high milage cars.

It would be an interesting experiment to hook up a oil pressure guage, and try different oils, but I don't really care that much, and it is currently 24 degrees out there.

 

[bidibronco]

OH! IF it's THAT COLD then go with a little lighter like the 15w40 or you'll do more damage than anything. To thick when it's cold is BAD JUJU MAN! Other than that, I'm all good with synthetic other than the first 1000 or so miles of a rebuild. Synthetic just wont let the rings set right or let the lobes on the cam get a "proper break in" and so on and so forth.

 

[Seabronc]

I've been running 20W50 with a quart of Lukas for several years with winter temps down to 5 degrees to put off the inevitable, (change or rebuild the engine). Below 10 degrees it turns over a little hard so a good battery is in order, but once it starts there is no problem. Like I said, I use a Baldwin filter, probably the best and most reliable filters on the market and used primarily on heavy equipment.

However, a bad filter going into bypass will give the same result as worn mains and could drop the pressure low enough to cause some engines to quit if they have a pressure safety switch. Just a possibility /emoticons/[email protected] 2x" width="20" height="20" /> .

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Just adding a note: Prior to 20W50, Lukas and Baldwin filters my oil pressure did the high/low thing but especially since going to Baldwin filters I have never had my pressure drop below 25 lb. which it did with regularity when stopping at lights.

 

[Jersey]

I would still recomend putting a manual pressure gauge on it to test and be sure. If the seal in the sender is bad, the oil will leak faster through it when it gets warm, dropping the pressure signal to the gauge itself. Not to mention the fact I have replaced several times the oil press./temp portion of those peticular dash setup. Although it is very possible the bearings or pump is bad, better off knowing for sure.

 

[Broncobill78]

I have to agree that a mechanical pressure guage should definately be on the list. There can be all sorts of issues with the stock electric guages. I'm sure it's giving a proper indication from the description of the problems but there's a LOT to be said for knowing just what your exact oil pressure is in numbers, not: "well, it's usually between the "S" and the "U" on "pressure" but now it's down somewhere around the space between "oil" and "pressure", so is that good or bad ?" Knowing what your actual numbers are is very helpfull.

SeaBronc, you ever try the Oberg filters ? I ran them on my 460's and loved them.

 

[Seabronc]

I have to agree that a mechanical pressure guage should definately be on the list. There can be all sorts of issues with the stock electric guages. I'm sure it's giving a proper indication from the description of the problems but there's a LOT to be said for knowing just what your exact oil pressure is in numbers, not: "well, it's usually between the "S" and the "U" on "pressure" but now it's down somewhere around the space between "oil" and "pressure", so is that good or bad ?" Knowing what your actual numbers are is very helpfull.
SeaBronc, you ever try the Oberg filters ? I ran them on my 460's and loved them.

Ditto on the mechanical, I've run one on mine along with the factory gauge. The sender of the factory gauge is another part that I suggest getting from someone else than one of the large, popular, chain auto parts places. I got my last one from the Ford dealer and the factory gauge agrees with the mechanical, ( at lease with the mechanical it is possible to make some real assessment about the pressure reading), too bad someone hasn't come up with one that fits in place of the factory gauge.

Actually Dave I had not heard of Oberg, but I will look into it. There are good brands and bad ones and FRAM :-& is on the bottom of the list as far as I'm concerned.

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[Broncobill78]

too bad someone hasn't come up with one that fits in place of the factory gauge.
Actually Dave I had not heard of Oberg, but I will look into it. There are good brands and bad ones and FRAM :-& is on the bottom of the list as far as I'm concerned.

Fred,

Here's a link for Oberg. They're up at or near the top of the list IMO. I figured that if I was going to spend $6K-$7K on an engine I could at least spend $50 on a filter. I ran a dual screen filter, the first screen was 60 micron & the second was 120. I agree on the Fram, you'd get better filtration from one of those toilet paper filters.

http://www.obergraceproducts.com/

A mechanical guage w/actual numbers that replaces the factory unit *would* be a pretty slick upgrade. Better still maybe an aircraft type dual guage that displayed oil pressure up top & tranny temp underneath.