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oil light on but oil is full
https://www.slantsix.org/forum/viewtopic.php?t=15027		 Page 1 of 2
Author:  75dartcustom [ Sun Nov 13, 2005 8:38 pm ]
Post subject:  oil light on but oil is full
i put in a new fuel pump today, went in no problem (except for the fact that there is no hand room on that side of the engine under the alternator wedged up against the dist cap)
but when i turned on the car the oil light came on. so i checked the oil. its full. when i drive, the oil light turns off above about 20mph (im guessing as i have no speedometer) and then flickers back on as i slow back down to 20 and stays lit while the car is standing still.
as long as my oil is full i have no problems, correct?
what could cause this?
Author:  SlantSixDan [ Sun Nov 13, 2005 9:43 pm ]
Post subject: 
.
Author:  SlantSixDan [ Sun Nov 13, 2005 9:44 pm ]
Post subject: 
Whoah, STOP DRIVING RIGHT AWAY!

You may well have big problems. The oil light does not indicate how much oil you have in the engine! It comes on to indicate you've got insufficient oil pressure.

Your problem could be a faulty oil pressure sending unit (the device that senses oil pressure and turns on the light below a particular pressure level). Or maybe your leaking fuel pump leaked a bunch of gasoline into the crankcase, diluting the oil and making it too thin to lubricate effectively. Those two problems are easy to fix.

Or, you could actually have low oil pressure, which is extremely harmful to the engine's moving parts, which require constant lubrication under pressure.

This is a really, really basic, fundamental issue. That doesn't mean you're stupid or anything like it, but it means if you want the car to carry on running, and if you want to carry on working on it safely and effectively, you need do some major self-education. Pick up three books before you pick up another wrench, see Here. Obviously, substitute your correct model year (1975) for the model year mentioned in that post. Buy all three titles (the shop manual is a 2-volume set). Do not substitute. Chilton books, Haynes books—garbage. You need a factory manual.
Author:  75dartcustom [ Mon Nov 14, 2005 4:49 am ]
Post subject: 
the old fuel pump that i removed had a spring on the tongue that sticks into the block. there was a barb on that tongue that provided a place for the spring to sit upon.
the new pump did not come with a spring, nor did it have that barb on the tongue. thus, the spring wouldn't have anything to hold it in place. thus i did not put the old spring on the new pump.
could that be causing this problem?
Author:  75dartcustom [ Mon Nov 14, 2005 5:14 am ]
Post subject: 
ok, read FSM. first thing i will do is change oil in case my viscosity is diluted by fuel or there is some blockage in my oil filter.

second thing it recommends to check is the oil pressure sending unit. however, it does not give instructions for replacing this. where is it located in the engine and what is the procedure for replacing it?

after those options have been eliminated the next thing is the oil pump. for that you have to raise the engine. lets hope its not the oil pump.
Author:  VDART [ Mon Nov 14, 2005 5:35 am ]
Post subject: 
oil pressure sending unit is less than $10-- should be on the oil pump side either on the housing (next to filter) or in a threaded hole in the block.. black plastic looking item also has an electrical lead attached----

if nothing else buy a mechanical oil pressue gauge & see what pressure you are getting..... cheap insurance--
Author:  SlantSixDan [ Mon Nov 14, 2005 7:08 am ]
Post subject: 
Quote:
the old fuel pump that i removed had a spring on the tongue that sticks into the block. there was a barb on that tongue that provided a place for the spring to sit upon.
the new pump did not come with a spring, nor did it have that barb on the tongue. thus, the spring wouldn't have anything to hold it in place. thus i did not put the old spring on the new pump.
could that be causing this problem?
No.
Author:  '74 Sport [ Mon Nov 14, 2005 11:15 am ]
Post subject: 
OK, I guess I'm confused. Are we talking about fuel or oil? :?

Changing the fuel pump should not have affected the oil pressure. As Dan suggested, you want to go through this methodically, and by process of elimination you will determine the problem fairly quickly, and hopefully, without a lot of expense.

First, find the oil pressure sending unit. Like VDART said, on my son's '74 Dart Sport, it is threaded into the oil pump housing. Seems like it took an odd size wrench. Anyway, it will have a single wire attached with something like a blade terminal slipped sideways over a "button" on the end of the sending unit. You might first check that wire for a good connection and then trace it back to look for any bare sections that might be shorting out.

If the wire seems OK, you might next invest in the $10 new unit. It's a pain to get to, but it can be done. If you want to buy a $15 mechanical gauge, now's the time to buy some standard brass plumbing fittings and put a "tee" in the oil pump housing, so you can run the idiot light from the sending unit, as well as have the gauge.

If the problem wasn't found yet, you may be looking at installing a new oil pump, or worse. Just take it one step at a time.

Good luck,
Jerry
Author:  SlantSixDan [ Mon Nov 14, 2005 11:56 am ]
Post subject: 
Open the hood, stand next to the right fender looking into the engine bay. Stare directly down at the top of the oil filter. Shift your gaze rearward towards the firewall. Just below the base of the oil filter, pointing to the firewall and with one thin wire attached to it, is the pressure sender. It does need a pressure sender-switch socket to remove and install correctly; auto parts stores have these.

But first change your oil. Leaky fuel pumps can and do dilute the oil into uselessness.
Author:  Dennis Weaver [ Mon Nov 14, 2005 4:52 pm ]
Post subject: 
Quote:
.
Dan was speechless for a second! :lol:

D/W
Author:  emsvitil [ Mon Nov 14, 2005 4:55 pm ]
Post subject: 
Quote:
Quote:
.
Dan was speechless for a second! :lol:

D/W

That's really hard to believe...............

:shock:
Author:  Dennis Weaver [ Mon Nov 14, 2005 4:57 pm ]
Post subject: 
...there is alwez the possibility that you simply knocked the wire loose off of the sending unit while you were fumbling around putting the fuel pump on. if it swings into something metal, it will ground and put the light "on". :idea:

D/W
Author:  75dartcustom [ Tue Nov 15, 2005 9:41 pm ]
Post subject: 
i really appreciate all the feedback. thank you.

i can't work on, or get to, the car until friday. however, thinking over this i think the evidence points to a faulty oil pump. let me know if you agree with this diagnosis.

the oil light came on from 0-20mph. but it shut off once i accelerated past 20 mph. consistently. this tells me that the gauge works, because it turns on and off consistently, and that i develop sufficient oil pressure as i accelerate. from this i am guessing that the pump is not operating at peak efficiency and needs higher engine speed to provide proper pressure. does this diagnosis jive with you all?

regardless i will still start with dummy checks, oil change and testing the pressure via a mechanical gauge. but all input is appreciated.
Author:  Rick Covalt [ Wed Nov 16, 2005 4:03 am ]
Post subject:  Pick up tube Crack
Another area I have seen to check is a partial crack around the oil pick up tube where it screws into the block. This allows air to be sucked in at low RPM and once it revs up a bit it has enough suction to pull oil up the tube. Don't ask how I know this !

Good luck,
Rick
Author:  65 dartman [ Wed Nov 16, 2005 5:14 am ]
Post subject: 
When you change the oil, don't forget the filter (NAPA Gold is reputed to be the best). A clogged oil filter could cause the oil light to do strange things. I had a similar issue in a 77 Aspen as well in my 95 Jeep. New filter solved the problem.
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