Oil presure surging

[Howard Jones]

What would cause the oil pressure to pulse between 55 and 40 at constant 3000 RPMS in a SBF. Already replaced oil filter. No help. 8 quarts in motor. Oil level correct, as I have a remote filter mount and oil cooler in the system it needs this much oil to be full. I am also using a 7 quart Canon road race type pan.

It also does this at idle with the same symptoms.

Everything seams OK motor wise. No unusual noises or anything like that. No leaks.

The oil pressure pulses like a heart beat about ever 7 seconds or so from 55psi down to 40psi for about 1-2 seconds. It then climbs right back to 55psi again quickly up for about 5 seconds.

Nothing has been changed in the oil system since first built 5000 miles ago. It has always run at about 55-80 psi at constant cruise speed 3000 RPMS. I just noticed this yesterday for the first time.

Any ideas?

 

[Alex Hirsbrunner]

Hi Howard,

It might be a broken pressure relief spring in the pump, but I think it would have to be a pretty unusual failure to result in the O/P always repeating the cycle at the with the same interval. Does it also cycle at the same rate (7 seconds) when at idle?

By any chance, do you have an accusump or similar accumulator?

The only other thing I can think of is if you happened to bottom out and push the bottom of the oil pan just close enough the pickup that it is getting sucked against the bottom of the pan, slightly deflecting the pickup tube and then releasing it over and over. Most pickup tubes are designed to prevent this however, so this would be a real long shot.

Apparently 944s experience this problem also:

http://groups.google.com/group/alt.autos...a8b126eb4fcdeb8

(you will need to scroll to the top of the posting, as google seems to force you down to the bottom of the discussion with this link)

Regards,

Al

 

[Dave Wharran]

Howard,
Pickup tube cracked or broken very close to oil level allowing the pump to suck/entrain air?
Something trapping oil in head(s)slowing drainback to the pan?
Does driving/cornering change the symptoms at all?
Adding an extra quart make any differerence?

Oil flow through the pump at a constant rpm should be constant, so flow and thus pressure should remain fairly constant as long as the pump isn't starved for oil or have a leak in it's suction line.
I can't think of any oil "users" that would vary their use based on a timed cycle.

Clevelands supposedly trap oil in their heads lowering the available suction level while running.


Since you haven't had this problem the first 5K miles, something has obviously changed, broken, plugged oil return to the pan or ??


Dave

 

[Dan Haynes]

I agree. Replace the oil pump. get a new pump, and pickup. These are the most likely culprits.

Dan

 

[Jac Mac]

Howard, While I agree with the other possibilities, do you have an electric oil pressure gauge, if so does it run off a full 12 volts or of a voltage regulator. This type can give the type of readings you describe if the regulator is faulty. I would double check by using a basic manual type gauge just to verify this first. The possibility of the pan bottom flexing should be able to be checked with the car on a hoist or over a pit and have a helper run up the motor while you touch the pan bottom.
cheers Jack.

 

[Howard Jones]

Re: Oil pressure surging

Oil pressure gauge is a basic mechanical type. Tiny oil line to gauge. Oil pan has no damage externally. Oil capacity is full as before so I don't think adding oil will help. I'm going to have to drop pan and have a look I guess. Surge cycle is the same at both idle and at constant cruse (3000) speed. When I changed the filter the oil looked normal. I poured the contents of the filter through a coffee filter to look for metal or something that doesnt belong there. Found nothing the eye could see.

The sucking pan thing might be a good place to begin.

Has anyone ever broken a oil pick up tube by "curbing" the car hard on track? I did take a fairly hard hit to the bottom of the car last fall on track. Maybe it took this long to finally fail.

By the way, how would you test a oil pump (stock SBF) off the car?

 

[Russ Noble]

Re: Oil pressure surging

With those symptoms I would go for the relief valve. Probably sticking slightly. Also 40psi at 3000 I don't think would hurt anything. I wouldn't worry about it unless it got worse, it could even come right. However nothing like a precautionary teardown if you've got nothing else to do /ubbthreads/images/graemlins/lol.gif

Regards

 

[DMatt]

Re: Oil pressure surging

All very interesting theories...It could be any one of these things. I think I would start by trying a new gauge with new line before ripping into the motor. Maybe you have a small piece of trash in the line or the gauge is failing. Another thing you might be able to try, is there another place you can install the fitting for the tube? Maybe getting the pressure reading from another location will give some clues.

 

[Gregg]

Re: Oil pressure surging

Howard, I would check the connection at the guage first, then DMatt's suggestions prior to going into the engine. What about installing a second guage in the engine compartment to compare readings?

 

[Howard Jones]

Re: Oil pressure surging

Ya, I was thinking it might be the gauge also. I'll get another and check that first I guess.

Do any of you GTD guys know if you can drop the pan without removing the cross brace for the motor mounts? The main reservoir clears it at the rear but I was wondering if the pickup would clear as it is removed. If a standard pan will come off I think mine will.

 

[Russ Noble]

Re: Oil pressure surging

Howard,

Why do you guys always want to shoot the messenger? /ubbthreads/images/graemlins/lol.gif Whilst it COULD be the guage, blaming a mechanical guage IMHO is desperately clutching at straws, but it is a relatively easy one to eliminate. What is the oil pressure at high revs? If the variation was caused by a restriction on the pickup side it would become worse as the revs increased if it was a leak caused by a broken pipe etc it would have more effect at low revs. I still think it's the relief valve, particularly if the problem goes away at high revs. /ubbthreads/images/graemlins/twocents.gif

Regards

 

[Jac Mac]

Re: Oil pressure surging

Howard,
If when you "curbed" the car the gate system in the pan may have been distorted & as a result the "gates" may be jammed shut in which case the oil will not fill the area around the pick-up as quickly, or one of the gates could have broken off its hinge's and now be trapped under the pick-up screen. Had that happen once and it caused much wider reading variations than you are getting. But you say you have a very small gauge line/restriction.
One thing Howard, it is more painful to debate and agonise over things like this than it is to get your hands dirty and pull the pan off and put your mind at rest.

Regards Jack.

 

[Jim Nielsen]

Re: Oil pressure surging

Had this same problem happen. The oil pump pickup was not tightened securly to the pump.

Good luck
Jim

 

[Howard Jones]

Re: Oil pressure surging

I'll pull the pan down and have a look. Only thing to do really. The more I think about it the less I think the gauge is bad. The needle moves freely and seams to follow whatever presure is there.

 

[Howard Jones]

Re: Oil pressure surging

Hey, Check out www.greengauges.com You can get gauges with all kinds of background colors, bezel shape, pointer colors, bezel colors. This would be a good place to start on a set of gauges. Custom made your way.

Oh and I ordered a new pump and gasket set from summit. I have been fairly reluctant to rev it much but did run it up to 5500 just to have a look. In the short time it was there the pressure was above 50 psi. I didn't hold it at 5500 long enough to see it it had the heart beat symptom.

I'll fill out this thread after I have it apart.
Lots of good advice. Thanks guys! Any other ideas?

 

[Mark Worthington]

Re: Oil pressure surging

I predict safety wire in Howard's future. /ubbthreads/images/graemlins/smile.gif

 

[Howard Jones]

Re: Oil pressure surging

Mark, I learned that one when the friggin starter damn near fell off the car last fall at Thrunder Hill. You can bet all that hardware holding on that pickup tube and oil pump is gonna get wired!

You know I knew this when I used to race bikes. Things fall off them and it HURTS!!!! It's funny how you forget such hard learned lessons with time.

 

check out this oiling system modification kit I found on ebay, It might help you out,let me know, Joe /ubbthreads/images/graemlins/driving.gif

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&rd=1,1&item=8052077475&sspagename=STRK%3AMEWA%3AIT

 

[Jac Mac]

Re: Oil pressure surging

Howard, So your starter nearly fell off, maybe your motor is trying to tell you something, I seem to remember you advising some one to mirror balance a flywheel in the past. Did you use this method on your own motor. It will be interesting to see if any other bolts etc are loose when you remove the pan etc. For what its worth a reputable crankshaft manufacturer (US based) told me some time ago to find a shop with a specific brand of balancer and trained operator regardless of distance from my location. Since using this facility I have had ZERO problems with bearing wear and balance issue's, something I wish had been the case while using older type machines in the past. While mirror balance works for production car that never see's high RPM,or a get it going for tomorrow situation, you cannot beat balancing the actual components as one unit for a dedicated high performance application. It only takes a small amount of runout on the locating spigot at the rear of the crank (or a burr/grit etc) along with a similar thing on the flywheel, clutch cover to add up and throw the whole lot out of balance.
Interesting that Mark brought up the safety wire thing, wasnt he talking flat cranks on another post, perhaps he has been there/done that too.
Regards Jack.

 

[Howard Jones]

Re: Oil pressure surging

Jack, I agree that a complete balance of the entire rotating assembly is the best way to go. If I remember correctly the post in question was about not wanting to take apart a new motor and still put on a different flywheel. You will of course at best duplicate the original flywheel's balance in relation to the rest of the motor. Mine was a factory balanced SVO crate motor and came with a 5.0 flywheel. I had the GTD V6 flywheel/clutch balanced to less than 1 gram difference from the original. So It's the same as it came form Ford. For whats that worth.

This is OK if the motor in question is used for what it was intended. SVO crate motors are not race engines nor do I use mine as one. My motor has a 6000 RPM limiter on it so it's a long way from race engine revs. and I find myself making shifts at a little over 5500 nearly all the time.

There are a lot of guys running stock 302's up to 5.5K-6K all the time and they live long lives as street motors. I maybe use my car on track 2-3 times a year and, for now anyway, that's all that's in the budget.

This engine sat for nearly 6 months over the winter without use so that I could have my gearbox worked over so I suspect that it's just what most of these guys are guessing it is. A stuck relieve valve in the oil pump. The starter fell off because it was loose, not lock tighted and not safety wired. It is now as are a lot of things on my car. The oil pump and pickup will be in a couple of weeks. I'm not Roger Penski. I have to learn just like everybody else.

Would I like to rebuild my motor, and do a full balance? Of course I would. I will go through this motor someday for sure. Do I have the money to do it now? What do you think?

By the way, could you tell us what kind of balance machine and which shop you are talking about? Maybe some of us might be able to use the information. That is the point of this forum.