oil press gauge drops after 3,500

M

mannysc

Registered User
the stock oil press works great until 3,500 then it drops down to zero and check engine light comes on ive noticed some oil leaking from end of sending unit, at idle or anywhere before 3,500 it reads 3/4 of the gauge.

it dont knock lifters dont clatter and when I let off it goes right back up.
it dont vary around corners or stoping and taking off just with rpms .

ill put a real gauge on it today but any guesses, whats wrong?

so far my buddy says oil press bypass in oil pump I say its a bad ground ,

and ive been told its a bad sending unit "leak "

any guesses? like to see who is the best at this blind folded troubleshooting.
 
gunk in pick up tube

Is it possible the pick up screen is partially clogged? Sounds like the first attack should be the sending unit leak. My buddies 89 will drop pressure every so often, only for a couple seconds, then rises back up. I'm pretty sure it's a loose connection since it happens at varying rpms and speeds. Engine is a fresh rebuild. HHMMMMM, only drops above 3500? Will it drop pressure with different loads on the engine?(neutral or in gear) Good luck, JJ
 
its weird its at 3,300-3,500 unloaded loaded dont matter,
and water temp gauge went out last week so they may be related I just thought the water temp sending unit was bad it may be deeper issue.

engine has 900 miles on it since rebuild, carillo rods, wisco pistons, 95 oil pump,
when i was polishing the oil pump I like bling bling,

I noticed the bypass valve sticking so I worked on it and thought it was resolved it may be sticking opened .

or maybe spring is broken, letting pressure bypass at low level.

Ill have to check it out but today I have to play vw diesel mech,

rebuilding a vw diesel engine worlds stupidest engine design.

so ill find out this weekend but keep the guesses comming interesting to see who was right Im stumped and she stays parked till I know for sure.

hate to mess up all that money it cost. think Ill try a new sensor thenif that dont work bolt on stock oil pump and try it see if it stops acting up. and
 
If the mechanical gauge still shows a pressure drop, then the best idea I have is a pickup that too close to the bottom of the pan and getting sucked down, closing off the opening.

If the mechanical gauge shows OK, then it'd obviously be a bad sender.
 
Re: ...

Probably the first step is put in a real preasure guage to see what it read at 3500+rpm.

There a chasis ground... by the battery on the front frame, that could effects
the level on the guage. If its off ... the guages would read a bit lower. But I don't think that is the problem, cuz is rpm related

There's another oil sensor for oil level on the side of the oil pan for monitoring levels.

What I think it might be doing is all the oil got pumped up too fast at 3500 rpm and leave oil to an unsafe level in the pan... cause by the oil pump, pumping too high of a volume.

Hope that helps...
 
Re: Oil Press drop

Manny:
First thing is to get a mechanical guage. I've got a Stewart Warner 80 lb guage if you want it.
Second overfill the pan by a quart and a half anf see if it makes any difference. Could be you are storing oil in the top end and running your sump low.
George Clarke aka the SonySC@hotmail.com
 
today I added a quart of oil its over filled, and it didnt fall until 5,000rpms

so it is oil staying up top. never did this before i installed the 94-95 oil pump,

gonna change oil and check oil pan for any debris the oil pickup had a crack i welded where brace connects it may have broke and is sucking air when reved

hate to have to pull engine but oil pan is hard to do in car.
 
mannysc said:
today I added a quart of oil its over filled, and it didnt fall until 5,000rpms

so it is oil staying up top. never did this before i installed the 94-95 oil pump,

gonna change oil and check oil pan for any debris the oil pickup had a crack i welded where brace connects it may have broke and is sucking air when reved

hate to have to pull engine but oil pan is hard to do in car.
Click to expand...

note to self: Move custom oil pickup system project # 863.5a to front burner

'bird
 
I found the problem it was the sending unit they have a mechanical
pressure sensing device well it got a crack in it.

it leaked oil past the spring loaded piston and into the second chamber when oil pressure gets high it fills the second chamber equilizing pressure on both sides so oil pressure cant fight spring and thus no oil pressure read.
 

Attachments

  • 216835304eYumvT_ph.jpg
    216835304eYumvT_ph.jpg
    14.8 KB · Views: 102
oil Peasure?

Mine drops under load, But it fluccuates about a quarter inch when cruising, but it stays in the norm zone, it zeroes out accationally when turning into a parking spot, or a/c, fan are on. I just read above about over fill by about 1 1/2 qrts, will this hurt anything, could this diognose my prob? I just wonder if I have a week oil pump. I dont want to pull the motor since i just did a gasket job, with new heads.
 
EATONBIRD said:
Mine drops under load, But it fluccuates about a quarter inch when cruising, but it stays in the norm zone, it zeroes out accationally when turning into a parking spot, or a/c, fan are on. I just read above about over fill by about 1 1/2 qrts, will this hurt anything, could this diognose my prob? I just wonder if I have a week oil pump. I dont want to pull the motor since i just did a gasket job, with new heads.
Click to expand...

Stock gauge is pretty much worthless, lose connection or bad sender will give low oil pressure readings and turn on the check gauge light. If you really want to know what's going on install a tee at the sender and plumb it to a manual gauge.

Overfilling the motor will not increase oil pressure. I have never heard of anyone here having to replace the oil pump, but some have had the oil pressue relief valve hang open, but that would be ultra rare.

I'd start with checking the sending wire connection, then switch senders, then install a manual test gauge.

David

PS: Here's a picture of the sender and wire connection I'm talking about

attachment.php
 
Last edited:
I am in Auburn, Northern IN. I forgot to mention that when the gauge zeros the engine wants to die. and it sputers really bad. I had read this post and others, and I understand that the presure gauge is basicly an idiot light. I tore it down to the short block because I had what I thought was a blown head gasket (come to find out the gaskets were ok, the passenger side head was severely craked) so i thought that was what caused the drop some how. But it continues to drop and cause it to sputter. I can check the sending wiring to see if its in tact. If that is the problem would that cause the sputtering and wanting to die?

All help is welcome and appriceiated!
Thanx
 
Last edited:
sputtering and trying to die sounds like an ignition problem. If it is intermittent you could have a number of issues. I'd start with checking all connections for electrical items under the hood, unseat and reseat. That the oil pressure gage moves around during this makes me wonder if it isn't an issue related to battery power. You should inspect all your grounds, and your battery cables, as well as the connectors on the alt.
 
That sounds like a good place to look. Just to paint the whole picture, Performance wise, she runs great. Plenty of power. I do get a check light about a mile after start up/take off. When I come to a stop she seems to want to take off, like its under load, feels somewhat like its vibrating. I let off the brake and without touching the gas its picking up speed. Not fastly but more then prolly should. If im doing thirty mph i dont even have to touch the gas, it idles there. When I pull into a parking space while cranking the wheel and brakeing quickly the oil preasure gauge zeros, a red light flickers, it sputters, and wants to die, sometimes it does. I dont know if all this is connected, or if one plays on to the other. I have a k&n, my blower is slightly ported, I took the cats off, and no mufflers for now. I do have a manifold to tip exhaust so its not dumping under the car. these are the only things not factory to my knowlege. I have the famous toggle switch fan setup. Figured i better tell all so you know more about the situation.

Thanx
 
Auto car? Have you made sure that the TV cable is attached to the throttle body still and has it's bushing so it's a tight fit?

If idle rpm is above 700, then you likely have a bad vac leak, or your idle air controler is faulty. I'd start with the vac leak. It sounds like you took stuff apart, my guess is that something didn't go back together tight. If off throttle, idle RPM is too high certainly check all your connections. In particular the IC tubes, and the plenum that bolts to the intake manifold. Check all the vac lines as well, make sure they are not damaged.
 
It is auto. Rpms are right around 700 when in drive at a stop. I will check the cable. Is there a vac diagram or routing guide? I am not so concered about oil presure any more. Car uns to good eccept parking fast prob and wanting to take off when at a stop. I am hooking a mech up soon.
 
Last edited:
Should mine have a thorttle return sping on the throttle backet? Since i have owned mine it never had one? Where goes the vaccum for the egr top com from?
 
Last edited:
You must log in or register to reply here.
Back
Top