Low Oil Pressure - but only when warmed up?

[blindbug]

Does anyone have an idea on why engine oil pressure might drop considerably when the engine is warmed up? I am getting between 30-40 PSI at ignition and idle. However, when I drive down the road, it drops to 20-30 and once it gets warmed up (180-200F) I stop at lights and regularly get 9-10 PSI. Once I hit the gas to accelerate, the pressure jumps back up to the 20's.

The engine doesn't seem fatigued by the low pressure (it is from 1975, so it's a little worn out, but still running well). I do burn some oil, but not much, and there are some very slow leaks coming from god-knows-where. I can't tell that I have any exhaust leaks, or leaks at the header. Distributor is new (last 1500-2000 miles, so it should be engaging the oil pump without issue.

Is getting a low PSI like this in normal driving a common occurrence? Is it a sign of a larger problem that I might not need to address until its an actual problem? Anything I should check for or replace (maybe a different weighted oil?)?

A few details:

1. I have a new filter (K&N HP-3002) installed just over 1000 miles / 7 months ago.
2. I have had an oil change (Shell Rotella T5 10W-30) just over 1000 miles / 7 months ago.
3. I added an Oil Stop Leak (Lucas) when the oil was changed.
4. I have a brand new Dakota Digital solid state oil pressure sending unit hooked up to a brand new Dakota Digital Oil Pressure gauge.
5. I manually checked, and my oil Dip Stick reads right on full on oil.

Small Block 350 V8 from a 1975 C20, installed in a 1986 C10 Custom with a TH350 trans.

[Pontiac1976]

This link may help @ the bottom of post. When oil start to break down -needs oil change.
miles on motor have all the oil changes been done at right time, pump might be starting to wear out.
Dirt in the sending unit floating up down.
The gauge some times.

>>>http://bowtieguy.proboards.com/threa...re-psi-mistake<<<

[Pontiac1976]

Oh for the Quote:I do burn some oil, but not much, and there are some very slow leaks coming from god-knows-where. to bad you did not check heads the most likely change the valve hats O-ring seals mostly there a little wear out heat age It easier to do with head of but can be done head on just do not drop a vale. If still burning oil the heads bronze valve guides done at a shop, or the rings wear a bit.

[Tiger Joe]

yes it is normal for oil pressure to drop as the engine warms up- oil gets thinner as it is heated up. dropping that low can be one of the signs of bad bearings.

first think I would do is try to some heavier weight oil- maybe a 20-50 or even a straight weight. not a fix, but could be a band aid.

[70GMCer]

Normal....around 10 PSI for every 1000 RPM

[blindbug]

Originally Posted by 70GMCer

Normal....around 10 PSI for every 1000 RPM

My engine idles super low. I think my idle is too low, honestly. Earlier today I was getting idle at 600 RPMs at a light. Engine still runs, and is just starting to shutter if it drops below 600. Maybe I need to adjust my carb to idle at a higher RPM. Have been overhauling quite a bit of stuff, so it might be due for adjustment since fixing and replacing a few bad items.


I might move up to a heavier weight oil at the next change (good suggestion Joe).

I wouldn't be surprised at all if this thing has a bad bearing, a failing oil pump, bad seals and o-rings, or all of the above. I just need this engine to get me going for a while until I can grow an additional arm and leg to swap to an LS or GM Crate.

[Pontiac1976]

Well spark plugs check take pic's plugs label the. In another 1-6 month re check them take pic's see how the plugs come par in that one or even 6 month.
takes 10 to 15 min per-long leaking valves driving will burn holes in the pistons. lol
I had this have along time a go to me on a 305 V8 motor that was supposed have top end redone still ran good even no the 6CYL after was blowing smoke like crazy.

I guessing you have not pop the heads on this motor 1975 is now 2018 the rubbers in heat cold that many years must be very soft still.

[69heavychevy]

I had the exact same issue with my truck. When I pulled my engine apart the main bearings were pretty worn.

[andyh1956]

When you drop the pan to look at your bearings check to see if they are std size. If so you can buy .001" under bearings & take up a lot of crank wear. If the gears in the oil pump & the housing look good install a new Z28 regulator spring.

[Tom]

Your still within factory specs for oil pressure. Keep running it. I'd avoid the stop leak next time though. It just swells gaskets and doesn't help lubricate the engine any. Also avoid 10-40, its an unstable weight. I'd mix 10-30 and 15-40 myself.