Is this normal? I installed a new oil pump recently. The sender on the new pump didn't work (supplied by Subaru, but sender was different [smaller] than original). I put the old sender on the new pump, which worked, but the pressure seemed lower than what I was used to seeing on the dash gauge. I installed an additional mechanical gauge, and these are the readings I'm getting on it (higher than what the factory gauge shows, but these still seem low to me):

 

up to 3500 rpm.....10 psi

3750 rpm..............15 psi

4000 rpm..............22 psi

4250 rpm..............28 psi

4500 rpm..............38 psi

5000 rpm..............51 psi

 

stock '91 EA82, warm engine, conventional 10W30, RPMs kept constant for 15 sec. to ensure stable pressure reading

 

seems to follow a pretty linear relationship from 3500 rpm and up:

pressure = 0.0273 * rpm - 85.5

Edited October 4, 200916 yr by mcrae0104

How "quality" is the mechanical gauge you used?

 

I don't like to see any less than 20 psi at idle when warm. Should easily be up near 40 at 3500 RPM.

 

Something isn't right.

 

GD

$17 worth of quality. I wanted to get a good quality mechanical test gauge, but when that came in at $200 from NAPA, I decided to go the cheaper route.

 

I know that these are not known to produce much pressure at idle (the owner's manual says the gauge may read zero), but I agree that there should be more pressure between idle and 3500ish (I'm no expert--just a gut feeling).

 

Should I look for obstructions somewhere in the system (I have no idea how I'd actually go about doing this)? Perhaps give it some Seafoam in the crankcase to clear things out and then see if the pressure comes up after replacing the oil?

mine shows about half way at any speed driving warm or cold which it should because i still have 30w in there

at idle its just above 0

You don't need anything fancy for a gauge - call up your local industrial supply and get a 0 to 100 psi bottom-mount gauge in your choice of diameter's - some brass hose barb fittings and a couple feet of fuel injection hose. You can easily make something that you can be reasonably sure will read accurately (within 1 or 2 psi) without breaking the bank. Gauge should run about $10 to $15, another $10 for the hose and maybe $10 or $15 for some fittings/metric adaptor's - I've made my own metric adaptor by cutting off the threaded portion of an old sender and drilling/taping for 1/8" NPT....

 

If you really feel like building a nice rig - get some teflon or nylon clear tubing (1/8" will do), and the fittings for it - run it to the cab and mount the gauge there - a nice glycerin filled 2" back mount and a gauge bracket for the dash....

 

There's a ton of ways to do it - the Napa thing you found was a guage marketed to mostly auto-mechanics - who in large measure don't understand how cheap/common that stuff is in the industrial world.

 

GD

Mine runs anywhere between 35psi at idle and 70psi cruising. HIGH Rpm ranges it could almost tickle the 85psi mark. It ran 7ish to 45 with Valvoline 10w-30 in it. I run 20w-50 Castrol GTX in it now FTW!!!!

 

175,783 miles lol.

My oil pressure is somewhere around -40 PSI.. Typical Subaru gauges... break everytime you look at them wrong.

 

Engine usually ran at 70 psi at start up when cold

idle - 25 psi (when hot)

driving - 30-60 psi

 

IIRC from what I was told on this board.. Soob pumps are volume pumps not pressure pumps. The volume of oil being pushed through your engine is way more critical than what PSI. but then again the pressure goes up when you get a lower volume of oil moving (such as cold oil) and the pressure drops as the volume increases.. Somethin like low flow/high pressure high flow/low pressure

My oil pressure is somewhere around -40 PSI.. Typical Subaru gauges... break everytime you look at them wrong.

 

Engine usually ran at 70 psi at start up when cold

idle - 25 psi (when hot)

driving - 30-60 psi

 

IIRC from what I was told on this board.. Soob pumps are volume pumps not pressure pumps. The volume of oil being pushed through your engine is way more critical than what PSI. but then again the pressure goes up when you get a lower volume of oil moving (such as cold oil) and the pressure drops as the volume increases.. Somethin like low flow/high pressure high flow/low pressure

 

I'm pretty sure you're right, cuz my BRAT gauge will show 0 psi after a few

minutes on the highway (3k cruising)

But I have never had a rattle or a knock or a tap come from my engine.

So it must be flowing lots of volume, but with not much pressure.

 

And your formula is correct, volume increase=pressure decrease with the

same flow rate. aka 2 gallons flowing at 20psi is close to the same flow as 1

gallon flowing at 40 psi, or something like that.

 

Twitch