Oil Pressure

Rouxzy · 08-07-2002, 05:37 PM

When I start my car the oil pressure is right where it is suppose to be, 20# per 1K rpm. When the engine reaches warmer temps I seem to lose pressure (according to the guage). I mean it drops right down to just below 20. I replaced the oil sender with still the same results. Any suggestions?

Jim Sims · 08-07-2002, 06:23 PM

What viscosity of oil are you running? Hopefully 20W50 in the summer if you're using Dino (natural) oil.

Jim

bob hodges · 08-07-2002, 06:33 PM

You are not going to have the same press at idle as you are at RPMs. There are a lot of history if you search, but the oil press should be in line with the RPMs so if your at 3000RPMs your oil will be reading 30 etc.

Superman · 08-07-2002, 06:35 PM

The rule of thumb we're used to is 1 bar per 1K rpm, when warm. 1 bar is roughly 15 psi. So if your is just under 20 psi per 1K rpm, you're certainly in good shape.

BTW, my engine made good oil pressure (a little over 1 bar per 1K rpm) before the rebuild and, in spite of getting all new bearings, oil pressure after the rebuild is not just about the same as before. I was hoping for more OP, but I think the lesson here is that the old bearings were not loose.

Adam · Adam's Garage

I think what Rouxzy means is that when the car reaches correct operating temperature, the oil pressure gauge stays at a constant, just under 2 bar, regardless of load or engine RPM.

My 2.7 does the same thing. While warming up, the pressure gauge works perfectly well (2bar per 1k rpm) and then at temp, it sits very low. My mechanic has tested the oil pressure with his own mechanical gauge and assures me that I have adequate pressure, and we have replaced the pressure sender (next to the fan) without joy.

Any ideas?

Jim Sims · 08-07-2002, 07:14 PM

Install the reduced orfice fittings (901.105.361.01) on both cam tower oil lines. See recent issues of "Panorama" and "excellence". Jim

Rouxzy · 08-08-2002, 05:25 PM

Thanks Adam, I did the same with a mechanical oil guage and got the same results as you. I just wanted to make sure that I was reading it correctly.
Thanks Jim for the info. I think I remember reading something about that in one of my issues of Excellance. If I remember right it is because of the new syn oils that run so thin. I'm presently running Mobil 1 15-50. I was just curious that if I ran dino oil 20-50 that I might see a differance in readings. That is if I don't change the orifice fittings. What do you think?

Jim Sims · 08-09-2002, 07:19 AM

In my 2.7l '76S, 35,000 miles since bottom end rebuild, stock oil pump, external oil cooler with front trombone and Castrol GTX 20W50 installed. 90 psi at 3K rpm cold. When up to crusing oil temp (190 degrees F) 30 psi at 3Krpm, 45 to 50 psi at 4Krpm and 50 to 55 psi at 5Krpm. Not linear, but enough pressure. I do not yet have the flow restricting orfices installed in the cam tower lines. You might try dino oil and see what happens. Cheers, Jim

MotoSook · 08-09-2002, 09:36 AM

I have a 3.0 SC motor that was inspected for worn parts by a well respected Rennlister, split case and all, then put back together with new parts to replace the worn ones. I have the same behavior at cold (50-60 PSIG), when at operating temp, less than 10 PSIG per 1000 RPM, more like 5 PSIG per 1000 RPM, and rarely over 35 PSIG on the sender and stock gauge combo (not on a bourdon tube gauge). I'm running Castrol 20/50. This is the first I have heard of a restrictor on the cam tower line restrictor, guess I'll have to make time to read the mags that come to the house.

I was think that the spring on my oil pressure relief (front of motor) was weak and that I need a new one. If the relief acts as a backpressure device to maintain a high OP in the motor, could an old spring create the low pressure on a warm motor? Guys?

The warmer the oil, the easier it is to compress the tired spring, hence the lower OP. Is this logical reasoning for our cars?

Souk H

tholyoak · 08-09-2002, 11:56 AM

I'll echo Jim's comment, get the reduced orfice fittings (901.105.361.01) they were $10 for the pair I believe and the oil pressure went up 0.5- 1 bar dependant on RPM hot. Now I have oil pressure hot of approx 1.5 bar at 1k, and close to 4 bar at 3k and almost 5 bar at 4k. This is with 20 W 50 and oil temp approx 195

See pano or http://www.pcasd.org/tech/tech_mar.shtml
for details

Todd

MotoSook · 08-13-2002, 10:49 AM

I e-mailed Steve Grosekemper about this, but anyone running with the 2.5MM orifice every remove the valve covers to see if they may be starving the area when used with 20/50 dino oil, or any other grade dino oil for that matter.

Thanks,

Souk