Oil Pressure Problems


Written by Karl F. Bloss.


Problem: Oil pressure light comes on under 2000 RPM

I recently experienced a problem with my Vanagon that seems fairly common. When the engine is hot and I stop at a light, the oil light begins to fade on. It doesn't go off again until the engine revs above 2000 RPM. (An explanation for this behavior is given below.)

Mine seems to peculiar in that it comes on solid, not flashing. Nobody seems to be able to explain this.

There are 2 categories of causes:

  1. Incorrect oil sensing system - Your low pressure switch may be bad. According to Ron Salmon of the Bus Depot, there are 2 specs of sending units from VW and one has a lower tolerance than the other. Your oil pressure may be hunky-dory, but the sender doesn't think so. It could also be a bad connection somewhere.

    Also, check the connections on the oil pressure warning systems. Sometimes connections to the idiot light and from the sending unit can get weak and cause a false alarm.
     

  2. Real oil pressure problem - don't panic yet, it may be simple. Some people have reported that Fram and other non-VW oil filters cause higher pressure drops because of restrictive flow. Try a VW "Autobahn" oil filter. Also, I was running SAE 30 oil; try 20W50. Another common problem is the oil pressure relief valve may be sticky.

One way to see what's really going on is to install an oil pressure gauge. This is not straight-forward add-on since the existing oil sending units are binary, i.e. either the pressure is "OK" or it's "not OK", thus you can't just add an electrical lead to a real oil pressure gauge. VDO makes a sending unit and an oil pressure gauge. They also make a sending unit with 2 outputs: the binary output for the idiot light and the analog output for the pressure gauge. Either way, it's not just plug and chug because the sending units don't fit in the existing sending unit spot. If you go with the dual sending unit, you can get an extension hose.

There are some instructions and VDO part numbers on how to do this on the Bus Boys sitethis link leaves vanagon.com. Note that some people have had a bad experience with Bus Boys and have ordered from The Bus Depotthis link leaves vanagon.com instead. I got my gauge and sender there simply because he's right down the road from me. The hose I got from Jim Thompson, formerly of Bus Boys. Can't remember the e-mail, but he hangs around on the Vanagon mailing list.

Another option is to get the single sending unit and then make a 'T' fitting. I've seen some instructions on this in the Vanagon archivesthis link leaves vanagon.com. The stock low-RPM oil pressure sender, which is between the pushrod tubes for cylinders 3 and 4, requires a 24mm deep socket.

September 14, 1997 - Update on my analog pressure gauge installation:

I installed the dual sender on our '87 GL, but didn't get to the gauge yet. On the '87, you have to remove the driver side engine tin, which involves removing 4 bolts; 2 that go into the engine block and 1 each on the front and rear exhaust header. I snapped off one of the engine mounted bolts, so I'll have to drill it out or have someone do that. Remove the sender wire and the old sender comes out easily with the 24mm deep socket. BTW, not much oil comes out of there, so you can do this with oil in the case. I didn't know this until I had to fix a leak (more later) and did an oil change while I was at it.

The VDO extender tube then goes into the sender hole. I initially just screwed it in and tightened it the best I could with some pliers. It later turned out that this was not good enough and I use a bit of teflon tape to seal it up. I left some parts of the thread exposed, just in case it had to ground. I then ran the tube over the forward pushrod tubes. I also cut a piece out of the engine tin and lined the edge with electrical tape so the tube wouldn't chafe as much.

The dual sender goes on the other end of the tube. Now you have to find a place to mount it. I took several iterations to find a good spot where the sender wouldn't be too close to exhaust pipes and not bend the tube too much so that it doesn't get a kink in it. I finally drilled a hole in the engine tin just underneath the forward bolt that holds the tin in place. There the sender metal strap can ground an it's out of the way, yet accessible. We'll see how it holds up near the exhaust.

I haven't run the wires yet, but I did test the gauge and it shows 50-60 psi when cold with 10W30 (I figured I'd be changing oil a few times and this is what I had lots of cases of from my Eagle Talon. I'll put 20W50 back in it when I'm done).

I did also replace the pressure relief spring. You definitely need to drain the oil to do this since it's effectively a second drain hole.

I also did the 5-minute engine flush thing. I'm a little nervous now since I've had what sounds like lifter noise with the 10W30. Admittedly, I didn't let her warm up yet and didn't even get out of our street with the van. I just hope I didn't loosen so much crud that it's clogged up a passage somewhere.

More to come on the gauge installation when I do that. I have figured out that I will run the wire from the sender under the van with some of the other cabling and over the gas tank. From there, it'll go up with the speedometer cable behind the left headlight and through the speedometer cable grommet into the instrument area. Where to mount remains another challenge.

September 21, 1997 - Final word on analog pressure gauge installation:

Having installed the dual sender (idiot light/analog outputs) last weekend, I set about installing the rest of the system. First of all, I rigged the idiot light sender wire to the new sender with alligator clips and went for a drive. The valve tapping I talked about before went away after the van was fully warmed up and hasn't returned. Also, the idiot light would come on about the same time as with the old sender (after fully warmed up and stopped at a traffic light).

I ran 16-gauge wire from the sender along the bottom of the van in the same cluster of tubes where a bunch of other wires go. I dropped the spare tire and used a straightened coathanger to fish the wire over the gas tank, up next to the speedometer cable, behind the left headlight and through one of the rubber tube/grommet things behind the instrument cluster. Again, the coathanger came in handy.

I had picked up some electrical blade and clamp connectors, which were the same size as those on the back of the gauge. As it turns out, they fit well on the screw terminals of the sender and with some soldering, shrink wrap, and electrical tape, I did a reasonably neat job of it. Using clamp-type splicers, I stole power for the gauge from the headlight feed circuit. I wanted a switched circuit so the gauge doesn't bleed power when the van is off.

I took the van for a test spin to watch the pressure cold and hot. Keep in mind I still have 10W30 in the case, which I'll switch to 20W50 when I get a chance. Cold startup I get about 60 psi. Driving 50-55 the pressure goes anywhere between 30-60 depending on how warmed up she is. Fully hot and stopped at a light, I have 8-10 psi. 20W50 should improve that a bit. I noticed that the idiot light comes on around 12 psi. This might be peculiar to my idiot light system since I still think there's some thing wrong with it (e.g. doesn't light up when the ignition is on, but motor not started yet...should come one since oil pressure is 0). At least now I have a better idea of what's going on.

The gauge is sitting on the dash next to the instrument cluster, so I now have to figure out a good place to mount it. I kinda like it to the left of the cluster where it is now in terms of line of sight. Also, I have to steal power for the light yet. I may snag that from the fog light circuit that the PO put in.

Thanks to Sean Bartnik who provided some of the insights since he was 2 steps ahead of me, Ron Salmon of the Bus Depot for providing the sender and gauge, Jim Thompson of Sherwood Automotive and the Old Volks Home for providing the extension hose, and all of the other list members who provided moral support and an "ear."

If anyone else is comtemplating this addition to their waterboxer, I'll try to help in any way I can.

November 3, 1999 - Addendum from Bill Davidson:

I just finished installing the VDO Dual Oil Pressure Sender on my 1990 Westy Syncro. It was a real pain in the butt to get a nice installation in such a tight place, and I thought I would share some of what I came up with.

The stock .3 Bar sender is located behind the engine tin that covers the push rod tubes on the driver's side (You have to gut under the van). It simply screws into the engine block. However, it is in a very tight spot and the after market .5 Bar VDO Oil Senders will not fit into that spot. After reading the excellent article by Karl Bloss [above] and after consulting the Vanagon mailing list archives and after reading the instructions at the Bus Boys site at http://www.bus-boys.com/bbvdo.htm I realized there were two options to connect the VDO sender to the engine block and I didn't like either one of them.

The option described by Karl and the Bus Boys is to purchase the $25+ rubber hose and run it to the outside of the engine tin and mount the sender there. Unfortunately, the hose is 12 inches and it turns out that is a very awkward length because no matter what way you route the hose the sender seems to end up near the exhaust pipes. I really don't like all the bends in the hose or the fact that it is so near the heat of the exhaust pipes... bends and heat are not good for rubber over time. (I wouldn't mind the excessive price for a piece of rubber that looks a lot like the $4.00 hose that goes on the end of a greese gun if it made a nice installation, but it doesn't.)

The option described by several in the List Archives is to use 1/8 inch brass pipe... thread about a two inch piece into the engine block and add fittings to route the pipe to the outside of the engine tin. I really don't like this method because of the torque (and vibration) that will be transmitted by the pipe to its attachment at the engine block. It would be really bad to blow out the threaded opening in the engine block!!

So here's what I came up with:

Mark the engine tin just above the arch between the two lower bolts in the middle of the fore/aft curve, straight out and down from the stock sender hole. I drilled and enlarged it with a round file such that a 5/8 I.D. rubber grommet will fit snuggly, leaving only about 3/8 or 1/2 of a inch of metal between the grommet and the edge of the engine tin.

The idea is that a short hose will thread into the stock sender hole, come straight out and angle down at about a 45° angle, go through the grommet, attach an elbow pointed toward the oil filter, and attach the VDO sender to the elbow, and attach the VDO sender to the engine tin with a 'P' shaped metal hose strap and a sheet metal screw (Regardless of what anyone says go ahead and use Teflon tape on the threads of the fittings... rubber hose will not ground the sender! If the strap has padding or insulation strip it off, the metal strap makes the ground connection for the Sender if you are using rubber hose). This puts the VDO sender just forward of the oil filter, nestled in the curve of the engine tin that runs fore and aft.

I went down to 'Hose & Fittings, etc.' in Reno (I'm sure most large towns have such a place... or contact a place that services construction equipment). I found out I could get a small rubber hose made for about $5.00 or a braided stainless steel with Teflon lining hose for about $9.00. I chose the stainless steel hose because it will withstand heat up to 2,000 degrees and should not deteriorate under engine heat conditions... (also it turns out that the nut on the rubber hose was smaller than the diameter of the hose so it would be difficult to reach into the small stock sender spot with a wrench at extreme angle and get a bit on the nut.... the stainless steel hose is smaller diameter than the nut and makes it much easier to get a wrench on it). After a couple of mistakes I found that the perfect length for the hose is 3 5/8 inches.... for the stainless steel hose, if they cut it to 3 1/2 inches (end of fitting to end of fitting) it will grow to 3 5/8 inches when they crimp the collars of the fittings to the ss hose.

Metric fittings are difficult to find, but it turns out that 1/8 inch pipe threads work great on both the sender and the stock sender hole even though those threads are 11 mm. I got my hose made up with a 1/8 inch male pipe thread fitting on one end and a 1/4 inch tapered female fitting (like tapered gas fittings) on the other end. I got an elbow with 1/4 inch tapered male on one end and 1/8 inch female pipe thread on the other end. The tapered fitting works great in that you can install the engine tin with the hose through the rubber grommet and add the sender with the elbow attached last such that you can choose the angle you want it to end up at... with pipe threads once it is tight that is the angle your sender will be mounted at! I also got my 'P' shaped hose strap at the same shop. (If you want to use the VDO single sender instead of the dual sender you can use a T in place of the elbow above such that the VDO sender is at one end of the T and the original stock .3 Bar sender is at the other end of the T)

Now if you don't like the idea of using 1/8 metal pipe threads on your 11 mm stock sender hole threads and your newly purchased VDO sender threads consider this:

I order the Pressure Adapter Hose Kit put out by VDO. It came in a VDO package, but the hose was labeled with an American hose manufacturer and both fittings had American size nuts and threads (same as I recommended above). In addition, the American to metric adapter fitting that comes with the VDO kit does not fit the 11 mm sender threads any better than the 1/8 pipe thread elbow described above and the nut is sized for an American wrench! Seems that VDO is making a bunch on a hose and fittings and strap you can buy for about $8.00.

I like my installation better that the others mentioned above. It is cheaper, stronger, there are less bends than the $25+ rubber hose kit. Also my hose doesn't touch any hot surfaces and the sender is near the oil filter away from the hot exhaust pipes. And I like it better than using rigid pipe which with enough torque could damage the threads in the stock sender hole.

After calling around to several of the vendors that have been mentioned on the list I finally bought the sender and gauge from Bus Boys (1-800-792-2697) who had good prices and better advice and service than the others... (Yes, that's right Bus Boys! Despite all the negative vibes on the list they were a pleasure to deal with. I talked to Walter and he is giving list members 10% off.) I guess they have a new/better owner.

Good Luck with your VDO Oil Pressure Sender!

Once you have determined that you really do have an oil pressure problem with OEM filter and 20W50 oil, you may still be lucky and it's just a sticky pressure relief valve ball or compressed spring. Remove pressure relief valve and clean it. I've also heard of people stretching the spring out to make oil pressure problems disappear. The part from your VW dealer is only $1.95, so it's probably worth getting a new one. The part number on my invoice says 021115421B.

One other possibility is what happened to Brad Snyder. He apparently just needed to flush the system out. Read the accountthis link leaves vanagon.com from the Vanagon archivesthis link leaves vanagon.com and some pictures of the eventthis link leaves vanagon.com from Brad's homepage.

Otherwise, you're looking at either a worn oil pump or a worn crankshaft bearings. You can get new oil pumps or even 150% output pumps (at least for the Vanagon). If it's a crankshaft bearing, it means completely tearing the engine apart. OK, now it's time to panic.

I did the 20W50 oil change and OEM filter and it still happens, although not as quickly. My next step will be to put in a real oil pressure gauge. I ordered the parts from Ron at the Bus Depot and am soaking the bolts on the engine tin with Liquid Wrench.

Why does the light go out at 2000 RPM?

Jim Davis writes the following explanation:

    While there is a "high" pressure switch and a "low" pressure switch, they both cause warnings when the oil pressure drops too LOW. Since "too low" is a bit of a subjective thing in an engine, VW decided to implement two standards. The higher the engine RPM, the higher the oil pressure should be. If you have just one oil pressure switch with a setpoint low enough (say 4.4PSI, 0.3 bar) to not engage at idle, that leaves way too much slack for when the engine is at high RPMs when the engine should have at least 13.2 PSI (0.9 bar) . The "low" pressure switch is used to alert the driver if the oils pressure dips too LOW while the engine is running at less than 2000 RPM and the "high" pressure switch is used to alert the driver if the oils pressure dips too LOW while the engine is running at more than 2000 RPM.

    More specifically it works like this:
    The dynamic oil pressure monitoring system gets inputs from two pressure switches. One switch is closed with no oil pressure and opens when oil pressure rises to about 0.3 bar, called the .3 bar switch. The .3 bar switch is located between the left (driver's side) two cylinders. The other switch is open with no oil pressure and closes when oil pressure rises to about 0.9 bar, thus called the .9 bar switch. The .9 bar switch is located below the water pump & crank pulley, near the oil pump.

    The monitoring system seems to only "look at" the .3 bar switch below 2000 RPM and ignore the .9 bar switch. Above 2000 RPM the active switch is the .9 bar switch while the .3 bar switch is ignored. Below I've described a properly operating monitoring system. Note that I say "monitoring system" because some of the conditions describe an abnormally low oil pressure condition.

    A. Ignition ON, engine NOT running -- or -- engine running at LESS than 2000RPM

      .9 bar switch is ignored

      1. Low oil pressure exists (below .3 bar), keeping .3 bar switch closed

        Oil light: Flashes
        Buzzer: Silent

      2. Normal oil pressure exists (above .3 bar), opening .3 bar switch

        Oil light: Off
        Buzzer: Silent

    B. Engine running at MORE than 2000RPM

      .3 bar switch is ignored

      1. Low oil pressure exists (below .9 bar), keeping .9 bar switch open

        Oil light: Flashes
        Buzzer: Sounds

      2. Normal oil pressure exists (above .9 bar), closing .9 bar switch

        Oil light: Off
        Buzzer: Silent

    There does not appear to be a condition in a normally operating monitoring system when the light should be on steady.

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