HELP, no oil pressure...!

[jsveb]

My 930/02 engine has got no or VERY LOW oil pressure. This is after I have had the top end rebuild.

Background:

Well, I have owned the car for about ten years. Back in 2007 I decided to start out on completely rebuilding the car.
This is the thread on that:
My Carrera 3.0 LWT project

In the last parts of that thread, you'll see, I stumpled on broken head studs...
Let me say, the engine ran absolutely perfect in every aspect before me starting taking the car apart. Good oil pressure ( about 1b/1k rpm)

After discovering the head stud problem, I send the engine to Bruce flat6pac. He was very kind to help me out and performed the rebuilt with a quick turnaround.

When I got it back and fired it up, I ran into electrical problems. This is the thread:
Electrical problems, no charge and strange indications

I ended up buying a new alternator from pelican.
Unfortunately it did not solve the strange oil pressure indications.

They would start out high, as normal on a cold engine, but then drop to between one and two bars (EDIT: within seconds), and bounce around in a wonky fashion. I thought I either had a sender or a gauge malfunction.
I tried to change the sender. It didn't change anything. So now it was down to the gauge. Why would a freshly rebuilt engine, not have oil pressure...

This weekend, I put on a wet gauge. By drilling and tapping into the block where the pressure sender is located. Unfortunately that gauge agrees with the dash gauge.

The oil pressure stays about one bar, only ones have it kind of jumped up like the gauge dash did in the beginning.

This has scared the crap out of me. I have e about 30 miles on it, just a swag. I won't drive it anymore in to this has been diagnosed and sorted.


I have been thinking abuot how to trouble shoot this, but having never seen the inside of a case, I am limited to guess work from readin diagrams.
I have found some diagram from Grady and others.
Question: would it be plain stupid to try and blow compressed air into where the oil comes out of the block to the pressure and temp sensor, not seeing this as a fix, but just to see if something is blocking the journals and maybe I would see a temp change in oil pressure?

I guess there are two scenarios:
1. The engine oil pump really does not supply pressure because of an internal clog. In isi a case what do I do?

2. There is something external that prevent the oil put from supplying pressure. What could this be?

The car has got the original oil lines. They have been flushed in mineral spirit.
It has got a brand new Setrab 172 front mounted cooler.


I will stop here for now realizing this is already plenty cluttered as it is.

[johndaroza]

Dose it heat up and keep claiming gets vary hot and you shut it down? Sounds like an o ring to me but??? Not to sure about it?

My first guess. more info please so dose it get hot if you do not have good pressure it will get vary hot! 220 over 210 ease.

[jsveb]

The temp never got much above 80 C (~180F) even though the final part of the drive up to the house is a half mile hairpin type hill climb.
I was attributing this to the Setrab.

So no, it did not get very hot, at all.

I just tried to fire it up again. The pressure rose to approx. 2 bar then dropped down to below one bar. This with rpm at about 1k. All this happens in about 15-20 seconds.

If I then rev the engine to about 3k the oil pressure does go up with the rpms.

[TimT]

1 bar oil pressure at idle is fine. What is the pressure at 3000 rpm? 4000 rpm? 2000 rpm?

My memory is not what is used to be, but I recall 1 bar/1000 rpm oil pressure

So at 3000 rpm you should see 3 bar or about 45 psi

It not uncommon to see 0 presseure indicated on the gauge at idle when the engine is hot....the gauges don't always read accurately on the low end..

what is the difference between the mechanical gauge and electrical gauge through the rpm range?

[E Sully]

Possible the o ring did not seat when case halves joined. Some reading for you.
Low pressure at idle after rebuild
Ultimate Oil Pressure Relief Valve Thread

[jsveb]

Thanks guys:


The case was not split, since it was just a top end.

The dash- and the wet gauge pretty much agrees.

The pressures I mentioned were on a stone cold engine. 65F ambient, using VR-1 20/50.
I would expect it to be more like 3-4 bar initially and then drop to 1bar/1k rpm.

The pressure does not go up as rpm goes up. It just stays down

[HawgRyder]

It sounds like the pressure relief valve on the bottom of the case is stuck in the open or partially open position.
Maybe during the time and rebuild it got a piece of crud stuck in the tube that the pressure valve rides in...and as a result ...the cold pressure coming from the pump is OK...but when it warms up the oil is thinner and will not maintain PSI.
Fix....remove the relief valve (might get a few drips but no big gush of oil)...clean...reinstall...test.
Cheap fix...other than needing a new sealing washer (maybe)...quick and dirty to try.
Bob

[jsveb]

I would like to try that, but want to point out; the pressure drop happens in seconds -Way before the oil warms up.

[jsveb]

The oil pressure relief valve seems to be pretty tight

Any good way of removing this without messing the whole thing up with vise grips etc.?

[Flat6pac]

There is a post at the top having to do with a blade for removing the covers inserted in a socket.
Bruce

[E Sully]

Easy to build engine tool.......

[jsveb]

Thank you

FYI, a 24mm metric socket does exactly not fit... and, a 25mm is not part of basic set.

Of to buy a 15/16"...

[jsveb]

Did some more testing today...

Can any of you guys comment on, why the pressure to rises to about 2 bar and then in about five seconds start to drop?

I won't start it again until I have checked the pressure relief valve.

What should I be looking for when checking the valve?

[HawgRyder]

The "slug" of the valve should slide up and down easily.
That is to say....if you push it all the way up with your finger...and then are able to insert your finger or a tool (peice of wood like popsickle stick?) into the cavity that the spring fits in to...and then pull it down and out with the same ease as inserting....it should be OK.
When you have it out...shine a light up inside...or stick a soft tool up into the cavity to get an idea of how deep the cavity is.
This is so you know if the slug is travelling all the way up.
Also...inspect the slug for scratches, etc.
Bob

[fred cook]

Originally Posted by jsveb

Did some more testing today...

Can any of you guys comment on, why the pressure to rises to about 2 bar and then in about five seconds start to drop?

I won't start it again until I have checked the pressure relief valve.

What should I be looking for when checking the valve?

Probably what is happening, is that most of the oil that had drained into the sump is being pumped up into the engine and the oil tank. Losing that head of pressure could be what is making the difference since the oil pump is having to scavenge oil rather than just pumping it from a bulk source.

[HawgRyder]

Fred...the scavenge side of the pump is not monitored...it just sends oil back to the tank.
Even if the sump were full of oil...I don't think it would affect the oil pressure monitored by the guage.
If the pressure problem were the other way around (starts low...goes high) I would say the tank starts out low or empty...accounting for the time lag in pressure change.
But starting high and going low sounds like a relief valve opening too soon...or one being stuck open or partially open.
If the thermostat were at fault...would the rush of oil to the front account for the change? (not likely).
The relief valve (high pressure one) sounds more like the culprit...opening too soon or stuck.
Jesper...the way I normally grab those relief pistons is with a tool that looks like one of the long reach grabbers (expanding wire arms on one end...push button to activate on the other) except mine is one with the end arms that expand outwards with the "teeth" pointing out when the button is pushed.
The idea being...grab the relief piston from the inside surface...so that the bore is not damaged.
John Walker and the guys probably have a special tool for the job...LOL....but I'm cheap!
Bob

[bpu699]

I asked a similar odd oil question a couple of years ago,and never got a reply that made sense... Somewhat similar to what you are having...

Does you oil pressure plateau at the high end? Meaning, does it max out at 4 or so bar regardless of RPM?

My car has a very good idle pressure 2-3 bar, settles to 2 bar when warm. But then maxes out the oil pressure at a bit over 4 bar... Checked the pressure springs, etc. All looks fine.

Not sure how one gets high pressure at low idle, and yet doesn't max out >5-6bar when running...

Sometimes these cars do odd things...

[jsveb]

The oil pressure never gets above about 2 bar. And that is on a cold engine only for the first few seconds after start up. Then it drops

[Lapkritis]

How is the oil level in the tank? Sorry for basic question but figure that is simple enough to look at. If the system was low then this would explain the unexpected drop in pressure.

[jsveb]

Basic questions are fine.
The engine only has about 30 miles on it. It was topped up with oil, but haven't checked for a while.
I am busy until the weekend, but will get back to it then

Edit: as far as i remember, I added a whole case, 12 quarts, when I filled it up initially. Probably even more since I had a couple of bottles apart from the case.

What is the bare minimum to run? Can I be that stupid...hmmm