Oil light flashes only when AC is turned on

[BigTDawg]

I need some advice pertaining to the oil pressure sending unit.
I own a 1996 Disco and the oil light comes on only when Ideling and the AC is
turned on. If I turn off the AC the oil light goes out. Also, this problem only occurs when the engine is ideling in gear (auto trans.) or in park. Seems like the oil sending unit may be bad or a bad connection. What do you think ?

Where are the plug connectiors located for the sending unit ? Also, could my serpintine belt be loose ?

Also, where is the Oil Logic unit or computer located ? I'd like to clean the connections and check the wires for breaks and us a multimeter to test. If the problem does not go away then I'll unplug the unit till I replace the oil logic unit. Hopefully a good cleaning will resolve my issue. The flashing light bugs the devil out of me.
Thank you.

 

[robertf]

oil logic unit? its a switch on the side of the timing cover. And its not failsafe, if the switch is unplugged the light stays off.

Something is causing that circuit to close. It might not be low oil pressure, but it would be wise to check with a real gauge.

Its an odd thread so don't plan on an off the shelf pressure gauge to fit.

I tap into the oil cooling lines to check pressure. Mine is 25psi idle, 50 max. I don't know what the specs are but anything over 15 at idle is probably fine.

 

[Phototone]

When you switch the A/C on the A/C compressor comes on and the Idle can drop a few rpm in speed due to the drag from the compressor on the engine. If your idle is low enough to be just on the verge of triggering the oil pressure idiot light, the few rpm drop from activating the A/C is probably the cause. You "could" just set your base idle up a teensy bit.

 

[jeffro0502]

If your truck has lots of miles on it the tolerances in the engine will be greater and if you run a thin oil you will be more likely to have that light flicker a bit at idle under the load of the a/c. If switch is indeed good...try running a thicker oil 20/50. I had a RR LWB with 280k on the clock did this very thing....10/30 got the flicker at idle with the a/c switched to 20/50 castrol and never had it again.

 

[BigTDawg]

Where is the timing cover located on the drivers side or passenger ?
I could not see where the cover is, so I'm wondering if its on the backside near the firewall ? I'll clean the connections and test the wires with a multimeter. I've heard that some companies place the timing chain/gears on the backside of the of the engine. I did find
what appears to be the thermostat connector in the dead center
of the manifold near the water pump.

If all else fails I'll unplug the unit till I buy an oil pressure guage.
Also is the timing cover under the alternator or near which accessory?
I tried to find a picture with diagrams indicating the location. This motor is a little different than my 300Zx TT.

My Disco has 87,600 miles on it. I bought if from my uncle/1st owner so it is in good shape. The Disco has 10w30 synthetic oil, not my choice I bought it that way, I'll switch to 20w/50 at the 90k service.

 

[robertf]

cleaning connections isnt going to help. The flickering light is proof that the circuit works.

It sounds like you need to take this to a shop. Low oil pressure isn't something you fix when you feel like it.

 

[BigTDawg]

robertf, there is no switch on the otherside of the timing cover so you may have the 96 Disco/3.9 V-8 confused with another. I learned the connection is next to the oil filter. Will confrim Monday afternoon.

I believe the pressure is fine, but since I own another car the Disco will sit till I remedy the issue. No motor knock nor ticking sound. The oil pick up tube could be cloggedwith sludge. I do need a pressure guage
which is now on the short list of to-do-items!

I've seen corroded connections on my 300Zx TT, fuel injector connectors and coil packs need attention from time to time. Dielectric
grease remedies most bad connections after light sanding to remove
buildup. With all the issues that Rovers have it would not surpise me to see connector issues too.

 

[BigTDawg]

robertf,

My apologies, I missed the oil sending unit due to a chunk of dirt and oil
and the lack of of that handy tool called a flashlight. Buy a new vehicle and I'ma noob all over again. I wasn't trying to be a wiseguy but my thinking cap was not on firmly.

I tightended the serpine belt, no flashing so far. Going to tap the oil cooler lines and add a real pressure guage and temp guage. Maybe a
vDO duo. I've gotta know if I hever steady pressure or more serious
issues. Thanks for the help everyone!!