Low oil pressure @ idle

[BoMbS]

My first post, so take it easy on me.

A little background first...

I just bought a 1990 Ranger Custom 2WD with the 2.9L V6, and AL4D tranny. Bought it for $1200 at an auction, so I didn't get to test drive it. I've had it now for a week and here's the problem.

When the truck starts it has great oil pressure (stock oil pressure gauge) and when driving oil pressure is normal for the first few miles. After the engine gets warm, and only after the engine gets warm, it will stutter when I stop and idle at red lights and the oil pressure gauge will drop off the map. I'm talking below the little red line that means zero! This terrified me when I first saw it because I know the damage you can do with no oil. The rest of the way home (30 mins or so), it did the same thing every time I would stop. Oil pressure remained normal while driving, but would drop to nothing when I stopped. Also if I shifted into neutral at red lights and rev'd the engine a bit, the oil pressure would not drop as low, but would still drop below normal.

I've done some research, and this most people seem to say this means that my engine is ready to die. (Cam bearing damage?) Any help or thoughts on this are greatly appreciated as I have parked the truck until I figure out what to do... New engine, Rebuild, Sell the thing... I'm really not sure

Sorry for the long post, I hope I covered everything...

 

[MAKG]

If your engine isn't making awful sounds, it's not about to die.

What you describe is entirely consistent with an electrical "brown out" at idle. Have your charging system tested.

This is the risk of using an electrical gauge.

Ford only made it worse by using a SWITCH! It only has two positions -- on and off -- and any other variation is your electrical system not regulating well.

The first hint that this gauge is BS is that it doesn't go up when you rev the engine high. The oil pressure itself does.

 

[Ranger5.0]

Ya, i never trust factory electrical gauges... All they are is a presure switch that was good for runing an idiot light, not an actualy gauge. I would go with what makg said, and also take a look at the gauge its self, and the pressure switch.

 

[BoMbS]

I got a mechanical oil pressure gauge today. Where on my engine is the oil pressure sending unit located? I can't seem to find it in my Haynes manual...

 

[Jspafford]

Driverside of the motor, front bottom. Real close to the power steering pump.

It will be sticking out towards the front tire and have an adapter of sorts on it.

Shouldn't be hard to miss it will have a plug on it.

You get to it from under the hood normally.

 

[BoMbS]

Thanks for the help, I found it right away. So I got the new mechanical gauge installed and unfortunately it only brought bad news.

When I removed the oil pressure sending unit, I noticed that the oil came out GREEN! At first I thought I had unscrewed the wrong sensor and that somehow I had removed a coolant sensor of some sort, but no, sure enough my oil is just full of coolant...

I immediately opened the oil filler cap to find a mess of yellowish-green sludge, telltale sign of coolant/oil mixture. I kick myself for not checking the fluids before I bought it, but too late now...

So I finished installing the mechanical gauge anyway, fire up the truck and get 40-45 psi at cold idle. I drive the truck until it warms up and when I stop at a red light, the pressure drops to 2-5 psi. When I rev it up it gets to about 20 psi max. I don't know if this could be happening because of the coolant in my oil or not, or if the low oil pressure is unrelated. Perhaps the coolant in my oil caused the engine to wear causing low oil pressure, I don't know... please enlighten me.

Coolant in my oil means cracked heads, most likely right? Any input is greatly appreciated. Sounds to me like I bought a lemon, and need a new engine...

Thanks for helping.

 

[skippy]

lmc yruck ranger catalog has upgraded 2.9 heads for under $300,check yours at machine shop first,may just be a gasket issue.fwiw.good luck!

 

[MAKG]

This is a 2.9L. If it's just a gasket, I'll eat it....

The spec is 40-60 PSI at 2000 RPM with the engine fully warmed, and it really doesn't sound like you met it.

I doubt the immediate cause of the low oil pressure is the coolant. But it probably ate cam bearings (as well as other bearings), which would cause low oil pressure.

So yes, this thing needs a rebuild, most likely. If you were going to tear off the heads, I'd suggest looking at the bearings first. Crank and rod bearings are of course easier to get at than cam bearings, so I'd look there first. A chewed up crank and hosed connecting rods gets expensive. But they MIGHT be fine (though I wouldn't bet the house on it).

 

[skippy]

yeah,most likely the engine will need reworked and for sure investigation is in order.if it's just a gasket,you'll eat what mike?the entire engine or just the gasket?

 

[MAKG]

Just the head gasket... I get plenty of iron in my diet, thankyouverymuch.

 

[skippy]

10-4!

 

[skippy]

Thanks for the help, I found it right away. So I got the new mechanical gauge installed and unfortunately it only brought bad news.

When I removed the oil pressure sending unit, I noticed that the oil came out GREEN! At first I thought I had unscrewed the wrong sensor and that somehow I had removed a coolant sensor of some sort, but no, sure enough my oil is just full of coolant...

I immediately opened the oil filler cap to find a mess of yellowish-green sludge, telltale sign of coolant/oil mixture. I kick myself for not checking the fluids before I bought it, but too late now...

So I finished installing the mechanical gauge anyway, fire up the truck and get 40-45 psi at cold idle. I drive the truck until it warms up and when I stop at a red light, the pressure drops to 2-5 psi. When I rev it up it gets to about 20 psi max. I don't know if this could be happening because of the coolant in my oil or not, or if the low oil pressure is unrelated. Perhaps the coolant in my oil caused the engine to wear causing low oil pressure, I don't know... please enlighten me.

Coolant in my oil means cracked heads, most likely right? Any input is greatly appreciated. Sounds to me like I bought a lemon, and need a new engine...

Thanks for helping.

i wouldn't say "lemon",just a good project.how many miles on the clock after 17 years?is the truck in good condition?if it is,just get a long block or rebuild yours.$1200 doesn't sound so bad to me,must have been something you liked about it to buy it in the first place.so have fun with it.

 

[mikhail]

id go with a 4.0, dont even bother wasting your time with a 2.9L its powerless and it has problems, such as the head design being the biggest one. if your going to have your motor out, might as well put in another one, unless youre on a tight budget...

 

[AlvinsRanger90]

4.0 swap straight forward plug n play?

 

[rusty ol ranger]

4.0 swap straight forward plug n play?

This has been a dead thread for 13 years.

4.0s arnt all they are cracked up to be either.