Loss Of Oil Pressure, Ways To Troubleshoot?

Big Tom · December 19, 2007

I have a mid 90's GMC Sierra 1500 4x4 with the 5.7L motor, and I've lost oil pressure. Strange thing is it comes and goes sometimes, no I'm not driving the thing when the guage shows no pressure but I'll be driving and it quits so I pull over shut it off look around... everything seems fine, try turning it on again and now I have pressure. Then later it calves out on me again. So it's parked until I can figure this out. Now some people instantly say rip into the motor but being this seems somewhat intermitant I want to eliminate any simple problems before the wrench's really start turning

How can I test the dash guage? How can I test the sending unit?

Any other ideas what could be causing the troubles and I should look into?

redvett · December 19, 2007

If it quits you have no oil pressure and the fuel pump stops. How many miles and have you changed oil & filter since the problem started.

Nytemare · December 19, 2007

sounds to me like you may have a collapsed filter.

Big Tom · December 19, 2007

sounds to me like you may have a collapsed filter.

I've never heard of that condition, trying not to sound stupid but what can cause it? I'm assuming you're talking about a oil filter, just using a junkie filter can do this?

If it quits you have no oil pressure and the fuel pump stops. How many miles and have you changed oil & filter since the problem started.

About 190,000 miles on the truck and the motor doesn't actually stop I just watch my guages closely and when I noticed the pressure dropped I pull over shut it off and try to figure out what's happening, but when I start the truck up again the pressure is back. And no I havn't done an oil change since it started and I can't recall the last time it was done, probably getting close to due I'd imagine

lerbud · December 19, 2007

either its the filter or probably a bad oil pressure sending unit.

redsled2007 · December 19, 2007

First of all before you tear into your motor, make sure you have no oil pressure. Other then the gage or light indicating such, did the "Check Engine" light come on? How about clicking noises from the lifters? Smell anything? If it didn't, more then likely it's a sending unit. But to make sure I'd hook up a direct pressure unit and then start it up and see if it's got pressure. I had the oil pump pick up tube come off once with the same symptums. Good luck

Zembonez · December 19, 2007

Many high mileage GM engines have a lot of wear to the main / rod bearings and can lose almost all pressure at idle. If so, it's time for a rebuild. If the problem happens above idle and the engine isn't rattling like hell, I think you have a bad sending unit or pressure gage. Actual lack of oil pressure doesn't last long before you grenade an engine... perhaps from a clogged pickup screen or failing oil pump.

Good luck.

Nytemare · December 19, 2007

sounds to me like you may have a collapsed filter.

I've never heard of that condition, trying not to sound stupid but what can cause it? I'm assuming you're talking about a oil filter, just using a junkie filter can do this?

Thats exactly what I mean man. It doesn't just happen to cheap oil filters though. Never heard of it happen to a SBC, but the little 4 bangers do it quite often.

I believe it happens on the line, just every now and than one bad one squeaks through, it happens more in the smaller engines just due to the filter being smaller and easier to screw up.

your sending unit is either behind the distributor or on the driver side of the block in the lower right hand corner between the manifold and the oil filter. remove it and hook up a handheld gauge there you can see if your pump is putting out pressure. If you cant do it yourself, It should be like 20 min work at a competent garage, and than you'll know for sure.

Big Tom · December 19, 2007

First of all before you tear into your motor, make sure you have no oil pressure. Other then the gage or light indicating such, did the "Check Engine" light come on? How about clicking noises from the lifters? Smell anything? If it didn't, more then likely it's a sending unit. But to make sure I'd hook up a direct pressure unit and then start it up and see if it's got pressure. I had the oil pump pick up tube come off once with the same symptums. Good luck

No check engine light, no odd noises from the lifters and no weird smells. This happened just recently and as soon as it happened I basically got to where I was going and parked it so I have no idea if perhaps with a little more driving those symptoms would've come up.

I did a search and read d**n near every post with the topic "oil pressure" and it seems pretty much all the same, before doing anything check the levels, and then get a manual pressure guage and determine if there really is no pressure or not. Until then I won't know what's going on be it serious or simple. Hopefully it will end up being simple and I'm back on the road, I wouldn't look forward to a complete rebuild this time of year.

Gripenfelter · December 19, 2007

If it was a collapsed lifter there would be noise all the time and it wouldn't be an intermittent problem.

Does it only do this when the truck is hot? Ever do it on cold start up? Any hesitation off idle? Any surging at idle?

I would change the oil and then attach a MANUAL oil pressure guage to your engine. tape the guage to your windshield and check to see if it ever drops. If it doesn't, its your oil psi sending unit that's bad.

Big Tom · January 3, 2008

Does it only do this when the truck is hot? Ever do it on cold start up? Any hesitation off idle? Any surging at idle?

The problem was all the time cold start or hot, no hesitation or surging at all it idled smoothly but you could just watch the oil pressure gauge moving constantly between 200kPa and 0kPa. Problem seems to be fixed though! So I figured I best reply to my own thread and say what was the problem in case someone in the future uses the search and has these same symptoms.

I went out to the truck and checked the levels, still good, fired it up and still able to watch the needle dancing between 0-200 but I had to get the truck back to the farm which was about 15 miles so as long as I kept the RPM's up by driving in a lower gear the pressure stayed somewhat solid over 100kPa so with the 1-tonne Duramax dually closely following me we started driving home and stopping to check things out every few miles, about half way there I stopped and could hear a slight ticking sound... shut it off and checked the oil well it's hardly on the dipstick now? Odd I knew I checked it... so fine went and got 5L of oil and topped it right up and ticking went away and pressure came up and stayed up this time. So drove home the rest of the way no problems, pressure was good and parked it in the driveway. Next morning went out to take it out to the shop and there was a decent amount of oil under the truck in the fresh snow, fired it up and the gauge started dancing again... well best get it in the shop and see what's leaking. And basically from where it was parked it was almost a solid stream of oil all the way into the shop.

Jacked/blocked the truck up, and the oil looked like it was coming from the filter, but in fact it was coming from the oil filter adaptor that turns the oil filter sideways on these motors, took the 2 bolts out and the O-ring had a break in it and was brittle and the top seal just crumbled when we tried to take it out. So cleaned it up, went to GM the next day and picked up the $8 seal kit, put it back together and hasn't lost pressure since and it's been going for about 700 miles.

So the seal mustof went originally and was causing me to loose oil and the engine couldn't seal properly and build up pressure and that's when I parked it and made this post. If there would've been snow or pavement and not back country roads I might have noticed the leaking oil sooner and pin pointed the problem sooner

But hey, another high mileage GMC back on the road to rack in some more miles before it dies... nothing wrong with that outcome