Low oil pressure

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Hello, new here!

I have a '95 Chevy Blazer (4D, 4WD, 4.3L Vortec) that has given me a few good years with a few minor problems (alternator, tires and shocks, clogged up EGR valve, worn out side mirror) and one major (manifold gasket).

Recently however, I have been experiencing very low oil pressure (less than 20 at rest, barely 40 while driving) compared to what I was previously getting (60-80). This is with oil reading OK on the dipstick. There is also a "Check Gauges" light coming on on the dash when at idle.

With the help of a mechanic friend, we replaced the oil sending unit first. This actually dropped the oil pressure to where it is now reading nearly 0 at idle and barely over 20 at high RPM's. While doing this, we also replaced the oil filter (just was time) and noticed how dark the oil was. When we got the car, we put Amsoil in it and I've put appx 15k miles on that oil.

So fast forward a few weeks and we changed the oil and it was EXTREMELY dirty and all kinds of nasty crap came out. We also ran some cleaner through and changed the oil once more.

However, the oil pressure has not changed. The only idea our mechanic came up with is that possibly the filtering screen for the oil pump had gotten clogged up and it just may take some time to clear it out. I've driven it around a few days with no appreciable difference and the oil still looks nice and clean on the dipstick.

Any ideas? I'd rather not blow up my motor or do any (more) damage to my engine if I can help it. :)

posted by  Gaidal

First, put a pressure gage in place of the sneding unit and measure the oil pressure directly. This will differentiate between a gage or other problem in the dash vs the sending unit

if pressure is still low, drop the oil pan and see if the screen in the bottom is full of crap and sludge. If this doesn't help, at best, you are looking @ an oil pump, worst, an engine rebuild due to excessice clearances in the main bearings

posted by  tbaxleyjr

It might be the oil pickup stick located at the bottom of the engine,it may be to low to pick up any oil

posted by  archangle

Thanks for the suggestions so far.

One thing I should add is that I haven't been able to detect any appreciable difference in the car's performance or operation during all of these troubles. Hopefully that at least rules out an engine rebuild....

posted by  Gaidal

i am having a similar problem with my 93 toyota pickup and my problem was being caused by the oil pressure switch located somewhere near the oil filter. is it possible that the oil pressure switch may have been damaged during an oil change?

posted by  vette2004


posted by  Wally

No additives to the oil as far as I can tell.

However, I have been using a synthetic oil (Amsoil) for my duration of ownership of this car (~1 year). I'm sort of at a loss as to why the oil was all junked up. We were using OW-30, which I was also told by another mechanic is probably a little too light for my car (should be using 40). However, the car ran OK with good pressure for a good while.

My father, however, may have decided to throw some fuel additive in without my knowledge.

As far as I know, we didn't pull debris per se from the oil pan, but just junky oil. I think the next step will be to pull the pump off and see if the screen is clogged.

Like I said, though, the car still runs well so hopefully that's a good sign that I'm not doing any damage from lack of pressure?

posted by  Gaidal

Don't ever for a minute think you may not be doing engine damage to an engine when it's not being properly lubricated. It's a universal hell yes your busting the sh*t out of the poor thing.

You didn't happen to put HD oil in and before it was running not HD oil, did you?

Pull the oil pump off to check the screen? Oh boy.... :screwy:

posted by  DodgeRida67

Sorry if that sounds ignorant but it came from this:

Also someone else I know in person made reference to a filter/screen in front of the intake on the oil pump.

Anyway yeah I had a log of oil changes from the guy who owned the car before and he had been using Amsoil for several years.

posted by  Gaidal

Putting HD oil in an engine that has been using non-HD oil for most its life and significant amount of milage will ruin an engine.

posted by  DodgeRida67

Exactly - why he needs to rule out false readings by the gage on his dash then get the oil pan off of the car like both of us told him and find out if his oil pan is full of crud

posted by  tbaxleyjr

Sigh. Well looks like at least a blown bearing.

Thanks for your help, everyone. I'll probably just bite the bullet and get a new motor.

posted by  Gaidal

Since you have a lot of crud, been running the engine with oil pressure betwen 0-20PSI, I'd suggest you do that.

posted by  DodgeRida67

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