Sirtubblord

Hello all, I've posted this question a couple of times today with no response so I assume I'm dong it incorrectly as I am new to forums in general. I'm just hoping to find someone who might have had similar issues and how it turned out. I apologize to everyone if I am posting redundantly.
I am new to this forum as I just bought my first 150. It's a 89 4X4 and is in great shape. It has about 120,000 miles on it and it seems to run great. The guy I bought it from said that he bought it from a lady whose husband died and it sat for a bunch of years, hence the low mileage. It does have a little bit of a start up idle issue but once it runs for 30 seconds of so it runs great. Here's my big problem. After I got it home and cleaned it up I changed my oil. Then took it for a 30 minute or so run. It ran fine until I got off the hwy and came to a stop at a light. The oil pressure gauge fell to zero. If I take it out of drive it shoots right back up. When it reads zero it still seems to run fine and doesn't make any noises at all. I thought maybe it had sludge from sitting so I ran two complete oil flushes through it last night using Napa flush and then put fresh oil and filter, and also changed out the oil pressure sending unit. Then took it for the same 30 minute run. Same thing happened. I got it home and checked the oil and it was still so clean that I could barely see it on the dipstick. My next step tonight will be to install an after market oil pressure gauge to see what the exact reading is, but...
Does anyone have any insight on this? I'm frustrated because it only happens in gear after it's been running for a while. And... When I got it home I turned it off, started it back up and put it in gear and it read fine for a few minutes, then the gauge started doing the same thing. I should also mention that the gauges seem a little screwy to me. For instance, when you shut it off the temp and the oil needles stay where they were when it was running. When I start it they all drop back down and then seem to work. PLEASE HELP!
Thanks!

Just call me Sean

iTrader: (1)

Oil pressure sensor is probably clogged.

Sirtubblord

Is that the Oil Pressure Sending Unit? because I put a new one in last night before I tested it. I'm surprised that more people haven't had this issue... I'm hoping that it's just something wrong with the way the gauges are reading and not something bad like a bad oil pump or bad main bearings... I read through some old post and it looks like there is a way to lift the engine enough to drop the pan enough to change the oil pump, but I don't know...

Crownman

Rent an actual oil pressure gauge and check it. But before putting the gauge on it pull the new sender out, then put a bottle up against the block and have someone crank the engine for a few seconds. This should clear any possible blockage in the sending unit hole. If you can get a gauge that has a long lead on it you can leave the hood open just a little and put the gauge up resting on the windshield wiper. Then go drive around a little and watch what the gauge does.

As far as causes for this issue go, It could be a blockage at the sensor. Make 100% sure there's no knocking when it's running. Badly worn bearings can cause the issue. However, just about every time I've fixed an engine with this issue it's been an oil pump that's getting weak.

Sirtubblord

Thanks Crownman, last night I hooked up a new gauge with a new sending unit and it runs at 50 at start up, then 25 when it warms up, then drops to almost 0 when in gear. I'm thinking it a weak oil pump and not bearings because it doesn't knock or anything. My next step I guess is to try and get to the oil pump without pulling the motor. Sounds like a bitch but doable...

riseandrun

Please let us know how the oil pump replacement went. I have a 89 4x4 too. My oil pressure fluctuates as well, just never to 0.

wde3477

What kind of oil, specifically weight, are you running? Suggest a 10Wxx minimum - I prefer 10W40, many use 10W30.


My informal observation is that the older Ford motors tend to drop oil pressure at low engine speeds - e.g. idling in gear. If it's not making *funny* noises, not too concerned here.


Suggest a good quality filter is used - to ensure best flows while pressure is low.


Don't put too much credence in the dash gauges - a good thump on the dash will make the needles on mine jump, usually for the better.


I'm hoping the thing with the gauges (specifically coolant temp and oil pressures) staying put on shutdown, then zeroing out on restart is normal - mine's been doing that for 20+ years. :-)

qdeezie

Rod and Main Bearings are probably worn (or worn out), causing low pressure. Quite common in these older engines. My truck did exactly as you described prior to me installing a new engine. Good luck on whatever you decide to do.

unit505

I've got the 300 with a mechanical oil pressure gauge and the factory sending unit on a tee. My oil pressure runs 55-65 at startup and drops to 25-30 after it warms up at idle. Around 50psi at 1800 rpm. Never to zero. I switched to 10w30 synthetic at 80k miles with no issues and the oil pressure did not change. The factory gauge reads just above zero all the time, but I did not want a "Dead" gauge in the cluster, so the factory gauge is still connected. No matter what oil filter that I use, after a few months the anti drain back valve in the filter fails and I get dry starts after the truck has been parked overnight. I only change the oil every 8K miles and it only gets driven twice a week on average. Once when I go to work on Tuesday mornings and once when I come home on Friday nights. If maintenance has lacked on your motor and there is a chance of sludge or if your burning oil now, synthetic oil isn't good. Swapping to synthetic oil can clean up that sludge and cause leaks around your seals. If your sure that sludges is not an issue and you don't have an oil burner, you can swap to synthetic oil without issue and get allot better top end lubrication. My 300 seems to rev out much quicker with the synthetic vs. the dino oil and at 196K miles, she runs very smooth.

If i were getting zero oil pressure readings, I would remove the sending unit and blow out the oil galley for the sending unit. However, the fact that your getting normal readings at rpms above idle, thats likely the pump, or rod and mains as dqueezie described.

Chris_1

iTrader: (1)

That's an electrical sending unit which is only as good as the wiring to it.
A proper gauge is the only way to know for sure what your pressure is doing.
I do know that I had a garage change a rocker cover gasket once and they dropped so much crap down the holes it was actually plugging the screen on the pickup after 5 miles. Shut it off start it up, back to normal for a few miles.
What did happen then though was my gauge dropped to zero and my lifters started rattling like crazy before I could get it shut off.
I would think that if your pressure really is dropping that low, your lifters would be making quite a racket as well.