Gold Digger wrote:
Oil pressure is always high on cold start up. It takes a few minutes for the engine to reach operating temp, and from there the oil heats up and starts to "thin" out, for lack of better words.
My R runs about 4kgs at start up and at temp runs about 2kgs at idle. Of course, when you are raising the RPMs during acceleration, the pressure goes back up. You want to make sure you are getting oil to the vital parts of your engine.
Yeah, what Gold Digger said. With the addition that the difference between cold start up pressure at idle and hot at idle can tell you a lot. It's why I mentioned it.
Different engines with different oiling systems, different oil pump designs, etc... can behave a little different from each other, but one thing is pretty common to them all. Depending on oil thickness, it's viscosity, you can get a good guess what your internal clearances are, and thus about how worn out your bearings and oil pressure barrier components are.
Less pressure to the gauge doesn't always mean shot bearings though. If there is a break in the barrier, the path it follows, it may only mean that there is an oil pressure drop just before the gauge somewhere. I'm new to the RB's so I don't know the exact oil flow path from the pump just yet, but as an example I had a 429cj with a wiped rear cam bearing that lost almost all the remaining oil pressure before it hit the gauge. I thought something catastrophic had happened but when I pulled it apart everything was perfect except that bearing. The cam was hardly marked at all, just a few fine lines. Could have just been a bad bearing whose babbitt separated and flowed right on out... Not sure though. I'd hate to admit that it may not have been replaced at all and I over looked the shops instillation of the cam bearings where I sent the block to be vatted and have them installed. A possibility though I suppose. Still think something cycled through it to get that far into the copper though. Anyhow, long story short, the engines oil side wasn't worn out, just one rear cam bearing right before the gauge, so the gauge read scary.
Generally speaking though, and having lots of experience racing with the Toyota 20R, 22R and 22RE variants with their planetary gear oil pump, if they start up fairly high with a regular weight oil say Valvoline 20/w50 and don't drop much or at least not below 30psi then it has a decent lower end. I always ran straight 50w Valvoline in my 22R's and built the engines for 70psi cold idle and 30psi hot after a race. At 7,500 RPM, my rev limiter, it be at about 90+. So like Gold Digger said, it will/should come up with the revs.
I have seen some odd stuff from time to time though on friends cars. Like a blockage (silicone and gunk) to the gauge line acting as a check valve of sorts. Pressure slow to build at the gauge and extra slow to bleed off when you shut the engine off. As slow as it was to build pressure I had originally though it was just worn out, but that would have meant it should have dumped gauge pressure really fast if that were the case due to the lack of back pressure because of extra clearance. We pulled the fitting in the block and I took a small drill bit and extracted a clump of silicone. Dumped an extra quart in and had him fire it up to flush the line out. Hooked it all backup and everything was just as we hoped... back to normal.
You can also see a bit of behavior differences between oils. Standard heavy oil can have a high start up pressure but then drop off at high temps more so than a fairly heavy synthetic would. Example is my 460 truck motor with regular 20/w50 starts at 65psi and hot idle at 35psi, but with full synthetic 20/w50 it starts at 58psi and hot idle at 40psi. A lot less of a swing and a lot more enjoyable to see.
I think of most of my stuff as equipment, my 'upbringing' I suppose, so I'm always a gauge watcher. Always listening for sounds, hiccups, vibrations and anything unexpected. Plus the last 15 or so years working in all types of industry has taught me a lot. Your equipment talks to you and an early warning sign of eminent doom, lots of work and broken parts can be seen in the gauges if you know the behavior of the machine and what it normally does in differing circumstances. Noticeable variances from that means it's asking for some attention because something is happening that probably isn't good...
On another note though, I have seen rock solid engines with what I would normally consider 'fairly low oil pressure'. Chevy small block V8's most often. It's just there design... 30 to 40 cold and 10 hot is common. There's still oil to the gauge and it has pressure! With those motors that's a win!
In short though, What ever I have that get serious use, I want to see 60-ish cold and at the very least 20 hot idle, if not then I'm pulling it apart to fix it. Hope these ramblings may help and give you a few different avenues to see the oil pressure story from.
Modified by Tofubadguy at 10:40 PM 1/23/2010