Dadgummit -- my oil pressure light came on

PS: engine has been running rather well now for several months, since Carlisle in fact.  Ergo: it is overdue for  figuring a new way to disappoint me.

Is it on at all rpms, or just at idle?

I always have problems trusting idiot lights.  I'd prefer a real gauge, as you say.

You're lucky that I stayed in  Holiday Inn Express recently....

So the question is, as It often is: is the oil pressure actually too low, or is the sender bad?  In the latter case, how does one check?  

Most of the time, especially if the condition has come on suddenly, it is a faulty sender - pretty common, that.

Further: does the sender unit just run the idiot light, or does it produce a signal proportional to the actual pressure?

It is usually binary.....When it gets below a specified pressure (10psi?  dunno) it closes a pair of contacts and lights your dash light.  If the contacts are slightly dirty it could become a progressively brighter light as the pressure drops.

Moreover, is there an easy way to measure the pressure accurately and independently?  

Sure - install a hydraulic oil pressure gauge in place of or parallel with the sender.  Just remember that you'll need a gauge sender with a 10 foot long sender tube (I'm guessing on that length, but my battery cable from the starter to the battery in the front well is 11 feet).

I could, and probably will, order a new sending unit and do an R&R and see if any diff.

Do it.  

Is there a "right" unit to buy, or are they all the same?  

Probably not, and I can't help with this, other than mine is a stock VW sender and seems to work OK.

And what if I wanted to have an actual oil pressure gage, with actual psi levels and a needle that moved?  Could such a thing just be put right there on the engine, for diagnosis?  

Sure - if you wanted one mounted on the same port where the current oil sender is, the length of sender tubing would be inches, not feet, but it's more convenient to see it in the cockpit, no?  I would contact Carey to see what they use and buy that.  My system has a pressure relief valve limiting it to 125psi, so that would be my range (0 - 125) but I don't know what you've got.  Usually a 0 - 80 or so should suffice and you should be seeing 30-50 psi at around 3Krpm.

Lots of questions: who's got the answers?

Beats me.......

....Do Not Drive The Car.....                                                                                                           The Oil Light aka Idiot light comes on when the switch is allowed to ground itself either by the motor not running ( key on)  loss of pressure or, a bad switch.  When the motor is running and has oil pressure it breaks the "ground" contact in the oil pressure switch and the light goes out. I'm going to say it's the switch but to be safe replace it before starting the motor. Since it's an idiot light any VW Beetle oil pressure switch should work as a replacement. 

OK, am getting there w this.  Looked at air-cooled VW website, and they have lots of parts and info too.  They repeat the 30-50 psi range for Type 1s, but also go to some lengths to discuss when the idiot light is supposed to come on, with some units coming on too high (8 psi, they say) vs better if came on at 2.5 to 3 psi).  Further, I have a T fitting on my engine, w/ idiot light on one branch and oil temp ( I suppose) in the other.  Again, on Air-cooled website, I see a few different kinds of oil temperature gauges, and some are supposed to go elsewhere, namely on the low pressure side of the oil system, not at the pressure tap.  [PS: I have a full flow oil filter system] Thee are snsors that go in the holes for pressure relief valves.  Even one that goes in the oil drain plug hole, which I would be real afraid of. So a full system here would be three sensors: low (i.e., "correct") pressure idiot light, an actual sending unit rated to 80 psi with gauge (either electrical or pneumatic line -- I'd like electrical if had a choice) and oil temperature that works properly with my dash needle..  Would consider applying oil temperature sensor in a different place, provided I could do that without drilling and tapping.  

So, here is some really mundane shyt, and I have not a good idea how to sort it all out.  Alan: what do you do for oil temp??  Where put the sender?

Further: as Alan says, idiot light is binary: either grounded or not. My light is not real bright, and seems to dim a bit when RPMs go to idle.  Kinda opposite of what you might think if oil pressure really was off.  And FWIW: my Haynes VW book lists bad bearings and actual low pressure oil as the 4th in a list of four possible reasons for the light to be on and the engine running, with an electrical short in wire and bad sender as higher up the list.

And yes, there is plenty of clean oil in the case.

To test the light and wiring, with the key on, disconnect the wire at the oil pressure sender, make sure it doesn't touch anything. The light should go off.

Now, take the wire and ground it to the engine block. The light should go on. Put the wire back on the sender.

If you have doubts about the sender itself, just replace it. Keep in mind that a stock VW sender comes on at 2.5 PSI. The typical aftermarket replacements (VDO for example) come on at 7-10 PSI, which is too high for a VW engine's warm idle oil pressure and can give a false sense of low oil pressure when there really isn't and would certainly get annoying as it's flashing on and off during normal driving.

Most likely reason your light is dimming at idle is that the alternator/gen simply isn't putting out as much voltage at idle.

Roger that, low turns at idle gives lower voltage, somewhat.  Will try the test and see about the light.  Also order another idiot light sensor like the one I have.  Still keen on a good way to measure the pressure directly.

Suspect an electric gauge is not as accurate as mechanical one - but what a pain running tube to under dash.  Go for a new sending gauge that has idiot light take off along with one for an electric gauge.  Can temporarily hook up gauge for peace of mind or mount gauge in/under dash.  I'd move the oil temp sender somewhere else. 

OK, I'm good for that, as have seen the dual-function-in-one-unit senders -- but where to put oil temp sender?  Will have to study that a bit more closely.  Seems that the plumbing for the oil filter presents an excellent opportunity to tap in a sending unit -- it's plenty accessible.  Has anybody here tried that approach??

Just a review....MANOMETERS measure "DEAD NUTS"  the pressure and vacuum!   Use one and you'll be right on with the info you get/want.

PS...... My Mt Baldy ride today was SPECTACULAR 1 (and i was the only one too) For you potential MT Wilson cruisers  It will be a lot of fun....bruce

I've got a VDO oil pressure gauge for you if you want, Kelly. Came out of Bridget & was hooked to a T'd sender. Read a little low (as they do when T'd). Worked well on the old 1300. 

Just the gauge now—this one, so it sure won't match anything on your dash—the sender went with the engine to a new home in a '66 Bug, where it continues to pull about 30 lbs pressure at 3000 RPM. Mostly.

Let me know if you want it.

I like Aircooled's comment on the oil pressure gauge write-up:

"Due to the design of the VW Bug and Type 4 engine, oil pressures in excess of 45psi cause the oil to BYPASS THE STOCK OIL COOLER.  VW Assumed that "Thick oil is cold oil", and set it up this way on purpose.  So when you put in a monster oil pump, and also use something ridiculous like 20-50 oil, and have 50-60psi oil pressure at cruise, while that SEEMS like a good idea, it's completely unnecessary, and will cause your oil cooler to be "turned off".

I'm glad I'm not the only one who thinks that.

Harbor Freight has an oil pressure gauge with a hose and various adapters that you can screw into the opening behind the distributor to check actual pressure.

Ed, you are on.  Can send??  How much?  PM to

ElFrazoo at verizon dot net

Still looking for best advice for placement of the oil TEMPERATURE sensor.  Hanging off the T- connector in the hole near where the distributor mounts does not, upon careful ponderation, seem like the exact best place.  Details: 2332 engine, electric fuel pump, full flow oil filter, regular VW T1 doghouse and oil cooler.

Also from air-cooled regards the stock idiot light sender:

Oil Pressure Sending Unit (Idiot Light Switch), Stock, All Aircooled Models, 021-919-081B grounds the idiot light circuit which turns the light on your dash, when oil pressure drops below 2.5psi. These do go bad, either by leaking or not opening or closing properly.

for completeness:

http://vwparts.aircooled.net/O...B-p/021-919-081b.htm

Fraz,

Temp sender in oil relief plug, left rear of engine as you look at it.

Dual pressure sender from VDO is a dual pole article that gives signal to the idiot light and a pressure gauge.  I recently installed one from CIP1 that had a black face under the dash on a small face I made from acrylic plastic that I painted black to match the carpet so it was not too obvious.  Like having both readings at least as a baseline.

The warning light connection on the dual sender comes on at a higher pressure than does the one on the stand alone sender.

So, with the dual pole sender your warning light is more likely to come on at idle.

Copy that; think I'll go with the low pressure (stock) idiot light sender..

Frank C: Can you post a picture of that? It's all about having the proper threads to match -- I note these units come in several different threads, metric and English too.

Need to start another thread. I am a dope.  The light that is coming on is the alternator light -- DOH!!  it would appear that the oil light and sender is just fine. I did go to local auto shop and bought a new one, but it was not tried.  I did measure the ohms on each: the one in the car and the new one.  Curious results: one in car w/ engine off reads about 3 ohms, while the new one appears to be open.  I figured the idiot light sender should be normally closed and open (turns off the light) when pressure goes beyond its set point. The new one is opposite?? Is faulty right out of the box?  Can't say.

Anyway . . . i will now post up a thread about the alternator light, which is the one misbehaving, as it turns out.

I bet you have a bad ground. Check them all before you start buying parts!

OK.  Will need to figure out where they all are.  Seems I've seen a nice fat braided copper cable under the car, hooked to the trans, I think.  Where else??

Follow the battery ground to chassis. 

I had the same problem. The idiot that put my car together tapped onto the top of the tunnel under the gas tank. What a pain in the ass as I could not get my arm far enough down the front of the tunnel to put a wrench on the nut...

The idiot light works like this: One leg of the dash idiot bulb is wired to 12v hot. The other leg goes to the " 61" terminal on the alt. When the alt armature is not spinning it is grounded hence completes the circuit and the light bulb lights . When the alt turns above a certain rpm, the ground is broken within the alt and the light goes out. The alt needs a small light to excite the field in the alt and get it to begin charging...

Along with cleaning up the ground connections (always a good idea every Spring), you should get the rear of the car up in the air and clean up the positive connections, too.  The battery positive cable goes to a 5/16" (8mm) stud on the solenoid on the side of the starter, along with the 8-10 gauge charging wire from that big connection on top of the alternator.  They both connect to the same stud on the starter, so remove them both (16mm nut) and clean them up with a knife or sand paper and replace.  Remember to clean any washers used, too. (Cleanliness is kin to SpitzundSparken).

While you're under there, look forward a bit and you'll see the ground strap going from one of the bolts holding the transaxle nose mount in, to one of the studs on the transaxle case.  "Second verse, same as the first"......  Remove it, clean it up (don't forget to clean the mating surfaces on the mount and transaxle stud and any washers) and replace.  

I don't know where your battery ground attaches to the chassis, but that should be easy to find and cleaned, too.  Unless you're Pineapple Bill, that is.  I like to liberally blast the ground connection to the chassis, after it's cleaned and re-assembled, with decent paint or, even better, undercoat to prevent it from corroding later on.

And don't forget the obvious - remove and clean both battery stud clamps (they make special wire brushes for that purpose).  

The LAST thing I can think of is to trace the 12V wire back from your dash "ALT" light to where-ever it gets it's 12V feed and clean that connection, too.  This is not the wire going to the alternator D+ connection, but the one going from the light to +12V under the dash.  I honestly don't think that's the problem, but we might as well cover all bases, because there is a small voltage mis-match between the alternator output and the 12V (battery) feed to the dash light.  It can light faintly when the alternator output that the bulb perceives is equal or lower than the perceived battery voltage.  If the alternator is showing anything over 13V when charging (at the battery connections), then the problem is not with the alternator.  Mine is running 13.52 when charging and doesn't seem to go below 13.2 at idle.

Good luck, Kelly.

Gordon: go see other Dadgummit thread about alternator light.