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Loss of oil pressure, what's wrong, what do I do next?

GsxrMike

GsxrMike

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Ok so I feel sort of like an idiot because I changed my oil before an event and I used mobil one full synthetic (I have only changed the oil in the motor once before and I used conventional) and now my motor is loosing oil pressure. It ran great all day right up until the last hill climb that I attempted and my oil pressure dropped to 0. I rolled the truck down the hill until I couldn't avoid a tree and had to restart. Motor fired up and ran up to 20 psi, I got around the tree and shut it down again. I had plenty of oil so there shouldn't be any issue with the pick up coming out of the oil. My symptoms are: Motor is cold I get 45-50 psi at a fast idle, motor is warm I get 15-25 on flat ground, another thing I notice was at one point I had about 30 psi but when I put the motor into gear it dropped to about 10-15 psi and there wasn't a huge drop in rpm. I had my idle set at like 1000 and the rpms dropped to maybe 850-900. The other clue is if I try to drive up a hill I loose all oil pressure, I don't know if it has anything to do with the angle on the motor or just the fact that I am putting the motor under a lot of load.

What do you guys think? Did I f up my motor with the synthetic? If so is there anything I can do short up a rebuild? What else could it be? Oil pump, cam bearings, dizzy gear? Thanks in advance! :bow:
 
is it a mechanical guage? 1st thing I'd do is verify your pressure readings. with a known good mechnical guage.

strictly changing to synthetic oil should in no way shape or form affect your pressure readings. as long as its the correct viscosity.
 
Gauge works, it am definatly losing oil pressure. I have heard if you run a motor on conventional oil for X amount of time that you shouldn't switch to synthetic. I replaced the oil with 10w30 and a new oil filter.
 
Is it an electrical or mechanical guage, and how have you verified that it works?

Martin
 
That should not matter there are a lot possibility's for loss of oil pressure.
 
It is a mechanical gauge and I verified that it works because when it said 0 (or close to it) my motor felt like it wanted to lock up and started blowing smoke. I have another gauge I can test it with but I am pretty sure I am losing oil pressure.
 
Is this the engine that had been in the K5, or the one you had talked about rebuilding and installing?

Martin
 
I wouldn't worry about the switch to synthetic, but it is hard saying what happened. Did the oil pan get hit?

Martin
 
Changing to synthetic won't hurt the oil pressure. There are really only 4 causes for low oil pressure. First is a pick-up tube that fell off the oil pump, then a failed pressure relief spring in the oil pump, then bearing clearances too loose, and last a clogged oil filter. If the engine ran low on oil for a short amount of time it could have easily ruined the bearings and this is what is giving you the low oil pressure.

Like was already said, VERIFY with a known good mechanical oil pressure gauge first then go from there.
 
4X4HIGH said:
Changing to synthetic won't hurt the oil pressure. There are really only 4 causes for low oil pressure. First is a pick-up tube that fell off the oil pump, then a failed pressure relief spring in the oil pump, then bearing clearances too loose, and last a clogged oil filter. If the engine ran low on oil for a short amount of time it could have easily ruined the bearings and this is what is giving you the low oil pressure.

Like was already said, VERIFY with a known good mechanical oil pressure gauge first then go from there.
Click to expand...

So after verifying that the gauge is good should I change the oil pump and if that doesn't do it, build a bad ass 406?

Edit: Oil filter is brand new, it has maybe 5 hours of run time on it? The motor, from what I can remember, was very clean inside (no sludge or tarnish)
 
GsxrMike said:
So after verifying that the gauge is good should I change the oil pump and if that doesn't do it, build a bad ass 406?

Edit: Oil filter is brand new, it has maybe 5 hours of run time on it? The motor, from what I can remember, was very clean inside (no sludge or tarnish)
Click to expand...

I would first verify the gauge is reading correctly, next i would change the oil filter with a Wix filter, then if the pressure is still low i would drop the pan and start inspecting for a pick-up tube that fell off. If the pick-up tube is still attached i would then start pulling some rod and main caps and look at the condition of the bearings (post pics and i'll look at them). If that all looks good THEN install a new oil pump AND screen and have someone tack weld the screen to the pump so that there is never a chance of it coming off in the future.
 
4X4HIGH said:
I would first verify the gauge is reading correctly, next i would change the oil filter with a Wix filter, then if the pressure is still low i would drop the pan and start inspecting for a pick-up tube that fell off. If the pick-up tube is still attached i would then start pulling some rod and main caps and look at the condition of the bearings (post pics and i'll look at them). If that all looks good THEN install a new oil pump AND screen and have someone tack weld the screen to the pump so that there is never a chance of it coming off in the future.
Click to expand...

Stick with what Scott said, he won't lead you astray. That being said we all need to see the readings from a "known good" gauge.
 
Like they say. If the oil has been changed regularly, and you have not been running a nondetergent oil, then the synthetic didn't bother anything.

My WAG, is pickup tube problems.
 
Hills

First I think that you should verify it with a real gauge, not your internal gauge. I had one blazer that read that it was going to explode, never did. There are several questions that I think are being missed, I also think that many descriptive details of the problem are being left out.

How big of an angle did the hill have?
What was your throttle load?
How hard had you been running it all day?
Do you have an additional oil cooler installed?(I had a PO that installed one on my 91, I liked it)

But try to be really descriptive when talking in the forum, that helps when others cannot be there in person and only have your words to go on and try to help.

In my 91 I put Royal Purple, expensive but ran like a dream, and that motor had 161,000 miles, PO ran MOBIL 1, my blazer killed it and destroyed it fast. Have not had to change the oil yet in my 84, but will run Royal Purple also.
 
I recently swapped the 10w30 conventional in my Blazer I was using after a rebuild for synthetic oil, and my oil gauge acts differently.

Before, with conventional, the psi was all over the place (15-55psi), and it would hover lower at operating temp (15psi at 500rpm idle).

When I changed out to Mobil 1, the truck runs about 50lbs at cold startup, and once it warms up, it sits right about 20psi. Normal psi for my ZZ4 is 40lbs at 2000 rpms, which is spot on.

Granted the volume of oil may be slightly off, but bottom line is I did see a difference in behavior out of my gauge when I went to synthetic.

I also work on big old W126 Mercedes, and a huge word of caution from other Mercedes mechanics was not to go to synthetic unless the motor's been rebuilt, as old motors w new synthetic oil would have a tendency to spring leaks.
 
Well, I lied slightly when I said that the synthetic would not have any effect. One quart would not have much, but a total changeover will usually increase oil pressure across the board. Particularly when hot.

The problem with older engines leaking when switched to synthetic has largely disappeared.

That problem dates back to the earliest days of Mobile One. If you switched to that in a high mileage engine, it would run fine for a week or so.
Then, the gaskets would begin to leak, gradually getting worse and worse.
So the story went out that synthetic oils were "thinner" or what have you and would leak out.
That story got a boost when it was discovered that if you switched back, the leaks would go away.

However the oil makers knew the oil was not thinner, so they started looking for the real cause.
It turned out that the original oils had ingredients that caused the gaskets to swell.
The synthetics did not have those.
When the synthetic was put in, it gradually washed them out and the leaks started.
As soon as the old stuff was put in, the gaskets begin to swell and the leaks stopped.

Nowadays, all the name brand synthetics have gasket swellers, and the problem is pretty much a thing of the past.

On my 1948 Ford tractor, which was rebuilt about 1970 or so, I run pure Amsoil 20W-50 with no leaks.

The original Ford manual stated that the normal minimum oil pressure for this tractor is 1 pound of pressure per 100 RPM.

Normal idle speed for this engine is 500 RPM, which means the factory was perfectly fine with an idle oil pressure of 5 pounds!

That was about the pressure it had when it idled cold.

When I switched to synthetic 20W-50 from name brand regular 20W-50, my lowest pressure is 20 pounds hot.

J.
 
A broken lifter or a broken rocker arm stud, rocker, severly bent pushrod..... can do EXACTLY what your engine is doing. Especially if you did it during the hill climb at high rpm bouncing around and the lifter got pitched out of its hole rolling around in the valley. It will do EXACTLY what you are describing. You have something going on since your idle is off 150 to 200 rpm which it would do if you broke one of the above. It that isnt it, its time for a rebuild....you spun a bearing or something happend to open up clearance substantially real quic to do what you are describing.
 
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