Oil pressure acting strange post rebuild??

[mcintosh816]

Ok so I just finished a motor swap with a rebuilt 7 bolt with the balance shafts eliminated. Prior to the swap, on my VDO 0-100psi short sweep gauge, the oil pressure would show about 20 at idle when warm then increase with RPM. Well now my oil pressure at idle is sky high when warm and then drops when RPM's increase. Any suggestions on what may be the cause here? I'm stumped..... the only thing I can think of is maybe a faulty sending unit as I did replace it with a new one when I swapped the motor but what are the odds of that?

 

[TuRBoTaLooN]

Dude, you already have a post about this (http://www.dsmtuners.com/forums/newbie-forum/361549-oil-pressure-after-rebuild-balance-shaft-elimination.html). They don't like making multiple posts about the same thing dude.

 

[mcintosh816]

Dude, you already have a post about this (http://www.dsmtuners.com/forums/newbie-forum/361549-oil-pressure-after-rebuild-balance-shaft-elimination.html). They don't like making multiple posts about the same thing dude.

Ok I'm a moron. I forgot I already posted that and had been thinking I still needed to ask on here. Entirely my f-up! Thanks for pointing that out haha.

Well wait, my question here is different. I hadn't asked about why my pressure would drop as rpms increase. I understand the balance shaft elimination causes higher oil pressures, but this shouldn't lead to oil pressure dropping under load correct?

 

[TuRBoTaLooN]

No worries dude, but I still think you should post this question in your other thread as they are related.

As for your problem, is it possible you wired it incorrectly or have a bad ground somewhere that is causing faulty readings on your gauge? Is your sending unit mounted directly on your oil filter housing? I had a similar issue. My sending unit is mounted directly on the oil filter housing and the wires on it would slowly come loose due to the vibration of the motor and cause the oil pressure gauge to give me all sorts of faulty readings. STM sells a kit where you can mount the sending unit remotely, like on a fender wall or firewall to prevent this.

 

[mcintosh816]

Yea it is mounted directly to the filter housing, so I guess Ill check that first when I run through my first oil change this week. Im pretty poisitive I have the wiring right, but will double check that too.

 

[mcintosh816]

Ok I really dont get it. I checked and double checked my wiring, I installed a new oil pressure sending unit in case the one I had was defective, changed my oil and found nothing odd.... But STILL, as the engine warms up, the oil pressure builds on my VDO 0-100 psi electrical oil pressure gauge. It rises and holds at 80psi and then will drop down and hold at about 40psi while at cruise. Cant figure this one out..... Is this typical considering I have had the balance shafts eliminated but did not have anything in the way of oil pressure relief modification done? Also, what kind of damage can this do to the motor??

Well by fluke, I think I have figured out the issue here. I was about to throw in the towel and order a brand new gauge and sending unit of a different brand.... So I was browsing Egauges.com and sorted through the VDO stuff there. Thats when I noticed that they have two different types of electrical oil pressure gauges.... One that is for the "American Ohm Range" and one that is for the "VDO Ohm Range". I had entirely forgotten about that and I had initially ordered the gauge for the American Ohm Range as I wanted to use the Autometer 0-100psi sending unit already installed on my car prior to the engine swap. Well, when I completed my swap I installed a brand new VDO sending unit not remembering that the ohm range is different. So now I just need to either order a different sending unit or new gauge to match them up and then hopefully finally see what my oil pressure is REALLY doing.

Just a heads up to anyone looking into VDO gauges: PAY CLOSE ATTENTION to the type of gauge and the matching sending unit you buy! Just because theyre both VDO doesnt mean they will actually work together!

.....Man do I feel like an idiot! Ive been pulling my hair out for a month now over this....

 

[TuRBoTaLooN]

Hey man, just a heads up here. Your oil pressure readings sound pretty typical for a built motor with BSE and no oil pressure relief mods. My built 6 bolt with no oil pressure relief mods and BSE would hit 40-60psi while cruising! Port out the relief valve on your OFH. Your gauge is probably fine.

 

[mcintosh816]

Well the thing thats giving me the idea that there is something up with the gauge is the fact that the car sits at about 85psi at idle, and then the pressure DROPS under acceleration to about 40psi. generally idle should be lower while the reading under load would be higher. Pretty much it seems like my gauge is reading backwards.

 

[mcintosh816]

Well just to update for anyone else who might run into this problem, I got the correct gauge/sender combination installed and low and behold, my oil pressure is actually right on the money. Idles steady at about 20psi and doesnt top 80 under load. Note that I have had the balance shafts eliminated and did NOT port my OFH. Thats not to say that the engine builder didnt make provisions in the build to compensate for the balance shaft delete. He didnt specify that info one way or the other when I made the purchase.