vanagon.com - Oil Pressure Problems — historical view 1999-02-09

Oil Pressure Problems

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:

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.

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 site. Note that some people have had a bad experience with Bus Boys and have ordered from The Bus Depot 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 archives. 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.

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 account from the Vanagon archives and some pictures of the event 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.