No oil pressure

[Jim Richards]

I just finished the engine assembly and installation back into my car. I disconnected the fuel pump and ignition so that I could try to build up oil pressure prior to actually starting the engine for the first time. I cranked over the engine for a few 30 sec intervals and did not see pressure build up. I did note a pretty good leak at the right cam oil line (overtightened and deformed the sealing ring - oops!), so I know oil is getting around. I'm just not sure how much or at what pressure.

I pulled out my oil pressure sender (is not a new sender) and tested it on the bench with air pressure (up to ~120psi). Using my ohmmeter, I observed the resistance value increase from ~10 ohms to over 200 ohms. I put the sender back in the car and cranked it over while measuring the resistance. The value went from ~10 ohms to ~15 ohms. I borrowed an old sender (correct p/n) from a friend and the results were the same. I know that I could have two worn out senders, but it's not real likely. But to be safe, I'll order a new sender to try out ASAP.

Any advice for the next steps to resolve this low oil pressure problem? Thanks!

[asphaltgambler]

Try using a hand held mechanical oil pressure gauge installed at that port (mechanics type). Then see what the readings are.

[Tim Walsh]

Hmm.. sounds like you've got some sort of Oil Pressue.. stuck gauge?

If you turn the car to "ON" with the sender unplugged the needle should shoot to the top. If it doesn't I'd assume one of two things, either the sender wire is grounded somewhere, or the guage is bad (bad internals or a stuck needle)

When I ran into this problem I used a mechanical guage to confirm it was in instrumentation problem.

[Jim Richards]

Tim, it shoots to the top when the wire is disconnected from the sender. I also tried a second gauge.

Where's a good place to find a mechanical gauge that'll screw in to the engine case? Thanks guys!

BTW Tim, I tried calling your cell phone but the # isn't in service. You change numbers? Talk to you later...

[Eagledriver]

Just start the car and see what your oil pressure is. I've never tried this "crank til you get oil pressure" technique but I suspect you won't get much pressue at 50 RPM.

-Andy

[Eagledriver]

By the way if you have MFI the next post you have will be why won't my engine start and the answer will be that it takes alot of cranking to prime the MFI. Not trying to disrespectful--I've just seen this before.

-Andy

[Shuie]

Does it peg when you turn the ignition on? Or does it always stay at the same value?

Have you traced the wire back from the sender to make sure its not shorted out or broken somewhere?

[Jay Auskin]

Jim, I cranked my rebuild forever. Then, I decided to start it, and had to quickly shut down because of no oil pressure on the gage. I cracked an oil line a bit, and it spewed out...hmmm, looks like oil to me.

Then, I tapped the gage, and realized it was stuck from sitting too long. If everything indicates oil pressure, then you probably have it. But of course, be sure.

I'm glad to hear you're firing the purple....ahem....aubergine beast up.

[P Clingman]

Try cranking with no spark plugs in it will turn much faster plus there is no load on the bearings its a better way to flush clean oil thru the crank
and bearings before startup also use a machanical oil pressure gauge
for startup. Palmer

[Porsche_monkey]

I couldn't get oil pressure until my engine started, then it jumped up right where it should be..

[Grady Clay]

Jim,

I’ll second the mechanical gauge suggestion. Almost any auto parts store has them. NAPA certainly.

Is there any chance that you had a plastic “cap plug” in an oil line?

Let me know if I can help.

Best,
Grady
gradyclay@hotmail.com
303-756-7308

[Jim Richards]

Thanks guys! I'll try to pick up a mechanical gauge tomorrow since it's a holiday today. I'm not sure how to interface it to the engine. I guess it'll become more apparent (sp?) when I see the gauge.

My gauge in the dash appears to work well. I can unplug the wire from the sender, and the guage pegs at the top...just what you'd expect when the resistance is infinite. When the key is turned on, but the engine isn't yet started, the gauge comes off the bottom peg slightly and the red (low oil pressure) light comes on. All as one would expect. EDIT - no, that's really not an oil pressure light light. Doh!

I'm pretty gun-shy about trying to start the engine without first verifying oil pressure. I've dumped a hell of a lot of money into this rebuild and would hate to frack something up. I'll give this some more thought. I will probably yank out the spark plugs and try that once.

Andy, thanks for the heads-up on the long time to prime the fuel system. It's these kind of experiences that y'all share that make this board such a fantastic place.

Grady, I don't think there are any foreign objects (cap plugs, etc.) in the oil system; however, I can't guarantee that as I had the machine shop (Comp. Eng.) assemble the short block for me, and I and a friend assembled the rest. I'd like to give you a call sometime today to discuss this problem.

Once again, thanks guys for all the help!

[asphaltgambler]

Most hand-held oil pressure gauge kits have adaptors / reducers already with it.

[Jim Richards]

Thanks! I'll get one in the next couple of days and report back. Wish me luck, or better yet, oil pressure!

[asphaltgambler]

If you cracked an upper oil line and oil came out I believe you're ok. But caution here is best by waiting to make sure via mechanical gauge. Good luck.

Hey , by the way who did your machine work?

[cstreit]

Jim,

Mechanical gauge for sure. It will calm your fears about starting it. I'll second removing your spark plugs to help the engine turn over. I can usually build up between 20-40 pounds of pressure just turning the engine over this way. It may take 4-5 successive tries to get there though.

I would seriously recommend not starting the motor untill you're sure...

[Jim Richards]

Walt at Competition Engineering. I'll give him a call tomorrow to get his thoughts. The more advice the merrier, I guess.

Chris, thanks for your inputs on this. I would prefer to take the cautious approach, too.

[Jim Richards]

Originally posted by Jim Richards
I put the sender back in the car and cranked it over while measuring the resistance. The value went from ~10 ohms to ~15 ohms.

I pulled the plugs and measured the oil pressure sender's resistance while my wife cranked over the engine. It was up just over 19 ohms, no doubt due to the engine spinning faster. After connecting its wire back to the gauge, and cranking again, the oil pressure was showing slightly higher than before, maybe nearing 10 psi. Next try will be after I get a mechanical pressure gauge.

[}{arlequin]

subscribed.... ready and waiting for part deux

(wishing you high psi's)

[Jim Richards]

Thanks Dave!

I'll try to update the story tonight or tomorrow night.