oil pressure drop

2002 S10 4.3 with about 38k on it. Noticed last night that oil pressure gauge was reading lower than normal. Midscale is 275 kpa (39 PSI) and it normally runs about there or higher when hot at highway speed Last night it was down about 1/4 scale at speed which it normally only would go when at idle stopped. Crawled under and noticed small amount of oil on the filter but no dripping. Difficult to check oil level when hot and with flashlight so added about 3/4 quart and restarted. No real change, so left it until morning. Checked oil level and it was now actually a bit above max on dip stick so wasn't really short of oil. Started it up and it read 2 bars above midpoint ( there are 4 bars per quarter of gauge range which is pretty normal. Took short drive to store and back. By the time I was back home the reading had gone low again. Gauge needle moved more with rev change than last night but still seemed to go to 1/4 point above idle. Read somewhere that senders can go and oil will be in plug. Wonder if that might be the source of oil on filter, assuming sender is near filter base. Is this a common problem on these motors? Could I be losing pressure hot or maybe sender is now measuring wrong when hot.
Reply to
Ken Hilson
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Before getting worried put a mechanical oil pressure guage on it and see what the pressure really is and if it's cause for concern.

Ted

Reply to
Ted Mittelstaedt

Thanks, Anyone else with s10 experience? As I don't have a mechanical gauge I might just change the sender. I do have another electric gauge but don't know if the sender will fit.

Reply to
Ken Hilson

you are not likely to get a consistent reading when the oil is hot - if the oil is greatly; above full, or below add.

and it is hard to get a consistent read at hiway speeds - why - if everything is working? dunno.

at temps above 85=B0F oil thins very quickly, and cause the oil pressure to fluctuate. you'd think that there would be a steady oil pressure reading at this time.

with only a warning light for oil malfunction - it eliminates some of the oil issues.

and too, not all oil reacts in the same way as far as pressure is concerned, I find.

"synthetic" is likely to give a more consistent pressure reading.

mho vfe

Reply to
fiveiron

Reply to
sdlomi2
2 wires. The sender paer says it's 1 blade , so why 2 wires and the pipe thread looks larger than 1/4 (which I thought I saw somewhere as the fitting size) Thanks
Reply to
Ken Hilson

No, it will not cause a drop in pressure. The front and rear main seals on American v8 and v6 engines (and all engines that I know of) are not exposed to oil gallery pressure, just splash and spray from the front and rear main bearings. You could remove the seals and run the engine, and it should have normal oil pressure (at least until all the oil sprayed out after a while... ;-)

Reply to
Steve

Reply to
Ken Hilson

oil pressure gauges seems to give erratic readings, not that they are in error, but something causes it - aside from temperature / oil level.

I expect a mid-scale reading at highway speed, and at times in stop and go city traffic (is there any other kind) it dips - real low.

Why the yo-yo readings?

mho vfe

Reply to
fiveiron

Somebody must know where the sensor is located?

Reply to
Ken Hilson

  1. Your sending unit is bad and is intermittently dropping out.
  2. Your oil pump is bad and the pressure is dropping considerably at low RPM.

--scott

Reply to
Scott Dorsey

Oil level has no effect on oil pressure whatsoever, until the oil is SO low that you get air sucked into the oil pickup (a bad thing).

That sentence doesn't make much sense to me. Oil pressure depends somewhat on engine RPM, so it *should* drop when the engine drops to idle. Some engines show much more variation than others.

Some factory "oil pressure" gauges aren't gauges at all. The sending unit is just a switch that closes at (say for example) 5 PSI, and the gauge snaps up to a nice happy mid-scale reading and just sits there. The fluctuating oil pressure that a REAL gauge shows causes idiot customers to complain that something is wrong, even though its perfectly normal.

Reply to
Steve

Have a 2002 S Blazer myself auto 4.3 with 4X4. Also have the factory service manuals right here .

Your OP sender is under the distributor and is a long unit connected into the oil gallery with an elbow. The wiring comes directly back off the unit and it has two wires.

Book says 6 psi minimum at 1000rpm 18 at 2000 and 24 at 4000. with 5W30 oil.

Reply to
Steve W.

Thanks very much., Steve. Those specs are way below what I was getting before but I am still above them now. I have used 5w30 synthetic since the 3rd oil change. I might try 10w30 next change. I don't suppose the manual indicates if the distributor has to be pulled to change the sender as I can just get a glimpse of the sender? update- Didn't get to post above earlier today and went off to talk to dealer service fellow. He printed me out a copy of all the engines specs including the oil pressures you posted. Sender is apparently difficult to get at. He asked me if I have lost any coolant. Unfortunately I have an external leak (again) at the thermostat housing but even with that the coolant hasn't gone down yet. Reason is that he has seen one of those engines that had an internal coolant leak into the oil, thinning the oil and causing a pressure drop. No sign of white slug in the oil fill cap. Hate to drain away $25 worth of synthetic that I put in just a short time ago but maybe I'll change it to 10w30 cheaper dino stuff and see if the pressure returns ( and then goes away again) . One further issue is that when I changed it and when I just was checking things I noticed oil on the cooler lines at the crimps. Since the power steering pump above those hoses was wet I assumed a leaking power steering pump, but a mechanic at the dealer said it could be the oil from the line blowing up to the pump.He advised me to clean really good , start it and look for source of oil or put dye into one of the oils to determine which it is. He didn't think a leak there, unless real bad, would drop engine pressure. Ken

Reply to
38racing

It can be removed with the dizzy installed BUT not easily. You need a special wrench that fits it. The book says you need to pull the dizzy but looking at the location on my engine there is room enough to get it out. You WILL see coolant in the oil if it is there. Even a small amount will show up on the dip stick. Those oil lines are prone to leaking after time. A little oil film is somewhat normal. If you clean the lines and then see oil dripping while it is running then you need new lines or seals for the connections. I would bet the oil your seeing is from a minor seepage from the PS pump. Not uncommon.

Reply to
Steve W.

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