‘87 300SDL…No Oil Pressure

[wjob]

Started fine but had no oil pressure and low oil warning light came on. Shut off immediately and checked oil level with stick which showed it was a quart low. Knew it was only about half a quart low so waited several hours and checked again, which confirmed it was only half quart low. Started again but still no oil pressure plus warning light was on, so turned off right away.

Fact that oil, at least half quart, was pushed up in engine would indicate some pressure wouldn’t it? Can I run an electrical check of sender by disconnecting wire and touching it to ground? If I drop oil pan can I see if there is actual problem with pump and can oil pump be replaced without pulling engine?

Will appreciate thoughts on simplest way to diagnose my problem

Thanks Bill

[oldiesel]

If your 603 actually had NO oil presssure it would have very noisy lifters,you would probably notice. To be safe get an inexpensive oil pressure gauge and the fittings to connect it,remove the sender and connect the gauge.Not essential to buy an expensive gauge as the difference of a couple of psi one way or the other will not matter. Don

[wjob]

Thanks oldies. Do I need to drain the filter before I remove the sender? Also on my 603.961 engine is it best to work from on top or under engine?

[kerry]

You could also take off the oil fill cap while the engine is running and see if oil is being thrown around in there. Wouldn't run it for long.
Even removing the sender switch and running the engine would tell you if there is pressure.

[Palangi]

I am certainly no 603 expert, but I think it has an oil level sensor, not an oil pressure sensor.

[79Mercy]

^^They have oil pressure senders, thats what make the gauge work?

How long did you wait for the oil gauge to go up. Sometimes when cold it can take about 3 sec. to raise.

[Palangi]

Originally Posted by 79Mercy

^^They have oil pressure senders, thats what make the gauge work?

Yep, but the warning light is oil level, not pressure, I believe.

[Hatterasguy]

Originally Posted by Palangi

I am certainly no 603 expert, but I think it has an oil level sensor, not an oil pressure sensor.

They have both.

The guage is run off a VDO sending unit at the back of the filter housing. To remove that just crack the filter housing and let the oil drain into the pan.

The level sensor is for the idiot light in the dash. Its just a time delayed float, that goes off if it gets below the low mark on the dipstick.

If you really have no pressure the lifters would be going nuts. Is the guage just completly DOA? Could be the sending unit, or ground. Just being down a quart or so won't cause you to lose oil pressure. However it will cause a bit more lifter noise as Brian found out. You still had 5.5-6 quarts in the pan, so the pumps pickup was covered.

[Brian Carlton]

Originally Posted by Hatterasguy

Just being down a quart or so won't cause you to lose oil pressure. However it will cause a bit more lifter noise as Brian found out. You still had 5.5-6 quarts in the pan, so the pumps pickup was covered.

Yep, I never figured that out. When 2.5 quarts low, the oil pressure is not sufficient to keep the top end lubricated, although the gauge never shows any sign of it.

[wjob]

Thanks Hatterasguy. It’s my understanding too that “they have both”. Assume VDO stands for “Variable Displacement Oil”? Not sure about meaning of DOA, assume “Dead On ___”? Yes, my dash gauge is completely dead…no reading even after 5/10 seconds of idling.

Can anyone answer my original questions?

1. Fact that oil, at least half quart, was pushed up in engine would indicate some pressure wouldn’t it?
2. Can I run an electrical check of sender by disconnecting wire and touching it to ground?
3. If I drop oil pan can I see if there is actual problem with pump and can oil pump be replaced without pulling engine?

Also, should add that oil and filter have about 4500 miles of primarily highway driving and was getting ready to do oil change.

Thanks
Bill

[tangofox007]

Originally Posted by wjob

Assume VDO stands for “Variable Displacement Oil”?

Don't do that!!!

VDO is a manufacturer (brand name) of automotive instrumentation, etc.

Originally Posted by wjob

Yes, my dash gauge is completely dead…no reading even after 5/10 seconds of idling.

"Dead" and "indicating zero" are two different concepts.

[Jeremy5848]

You should be able to test the oil pressure gauge by disconnecting the wire at the sender and connecting an ohmmeter between the wire and ground. Optionally, pull the instrument cluster and connect directly to the gauge. (The first method is better 'cause it checks the wiring too -- connectors can come undone, wires can break.)

The ohmmeter should show continuity and it will also pin the gauge high or low depending on which way you connect it (+ or - to the wire, other lead to ground). Don't leave the ohmmeter connected for a long time as the battery in it could draw too much current through the gauge and damage it. A few seconds won't hurt.

If the gauge works on the ohmmeter's battery, the gauge is OK. The sender is probably at fault, not an unusual problem, although typically they get flaky before failing. I had to have the sender on my '87 replaced twice before I got a good one. The sender is simply a potentiometer (variable resistor) in the meter circuit that changes resistance with oil pressure. Over time it gets sticky and becomes unreliable.

Jeremy

[wjob]

My plan to do an electrical check is as follows, unless someone explains why it won’t work:

When I disconnect the wire at the sending unit, the gauge should indicate “0”. Then when I ground the wire, the gauge should move to max oil pressure and if it does, that tells me the sender unit is bad. On the other hand, if the gauge indicates higher than “0“ when the wire to the sender unit is disconnected, either the gauge is defective or there is a short to ground somewhere in the wiring.

Also, would still like to learn whether on this 603.961 engine I’d have to pull engine to replace oil pump or could I remove and replace from underneath car?

Thanks
Bill

[wjob]

"My plan to do an electrical check is as follows, unless someone explains why it won’t work:

When I disconnect the wire at the sending unit, the gauge should indicate “0”. Then when I ground the wire, the gauge should move to max oil pressure and if it does, that tells me the sender unit is bad. On the other hand, if the gauge indicates higher than “0“ when the wire to the sender unit is disconnected, either the gauge is defective or there is a short to ground somewhere in the wiring.

Also, would still like to learn whether on this 603.961 engine I’d have to pull engine to replace oil pump or could I remove and replace from underneath car"?

Can someone help me with the above?

thanks



[/quote]

[nhodges]

Before you do anything else you should replace the sending unit on the oil filter housing. 95% sure that that is the problem. A cheap fix. ("Don't look for zebras)