supposed oil pressure problem

[buck88]

il be driving my 86 jetta gl around and for some reason the oil light will come on and buzz, then it will go away then later it will start again, it just randomly comes on, the oil pressure sending unit was changed, and the oil is the thickest there is 15w-40 so i basically have no idea what is wrong, and i dont think its a pressure problem mostly because when im driving i dont notice the car doing anything funny when the light comes on....wtf? anyone have a suggestion?

[buck88]

Someone Must Have Some Explanation!

[buck88]

i changed the sending unit that is sitting above the oil filter, but if there is a second one i dont know where it is

[zagrot]

check for bad connections, if shaking the wire harness replicates the problem then do some wire repairs.

[gdaniel]

Well, it is not so random. i have a 96 golf3 1.8l and a 90 jetta 1.3l and both do the same thing.

Basically the 2 oil sensors are for low and high pressure:
- one for minimum idle oil pressure (around 0.3bar (0.15-0.45bar) )
- one for minimum pressure over 2000RPM (depends on the engine, 1.5bar (1.4 - 1.6bar) for 1.3l and 1.9bar (1.8 - 2.0bar) for 1.8l .....)

If the idle oil pressure is lower than the low-sensor threshold then the oil lamp will blink only.
If the oil pressure at 2000RPMs or more is below the high-sensor threshold you will hear a buzz acompanying the oil lamp blink.
It looks like a well-built warning system for oil pressure problems or failing oil pumps.
Usually reving it over 2700 and disengaging the clutch for a quick return to idle rpm would stop the alarm, but is impractical to drive a long way trying to match the speed and gear not to use the engine's 2000-2700rpm range. (for manual gearboxes )

So i assume that the oil pressure is below high-sensor threshold when the lamp and buzz starts, due to internal wear. I am imagining the oil pressure with RPM graphic getting a little bent downwards around 2000-2600 rpm just enough to sound the alarm when the oil gets hot.

Sad.

I tried with oil 'stabiliser' recommended by someone from Canada on this forum but it didn't work 100%. The alarm starts now only when loading the engine while hot, on a steep road, while before it would start on level ground at a fair speed...

Somebody correct me if i'm wrong.

[88JettaGli]

I have 88 jetta Gli 8v with 285,000 kms and when I ran 10w30 in it the oil light and buzzer would come on. My VW mechanic says the vw engines run hotter than north american engines plus my engine has lots of kms so they need a heavy oil. I put 20w-50 in summer and winter and have not had a problem since.

[Doug Tatham]

I have the same problem with my 91 jetta and I'm still working on it. Unfortunately there are several possibilities. The first thing to do is connect a oil pressure gage instead of the sending unit and start the car. Watch the pressure for about 15 minutes of idling. If it doesn't drop below .15 bar for cyl head connection then you probably need a new sensor or sending unit (located on back of instrument panel). My pressure was really falling. I discovered that the impeller wasn't spinning my water pump and a new pump helped buy didn't fully correct the problem. Possible causes: Bad oil pump, debris clogging screen on oil pump, debris sticking releief valve on oil pump open, excessive wear (clearance) on main bearings, rod bearings or crankshaft, Clogged oil passages.
Solutions: Try engine cleaner (lubrication system) and add lucus oil treatment when you refill. Check for loose oil filter or other oil loss. Drop your oil pan and check out the pump and bearings. Plastigage your bearings (especially the rod bearings). If the pump is pumping properly and can't maintain pressure, it because the pressure is bleeding off somewhere.

[Doug Tatham]

This is an addendum to the last. Check the backlash (gap between gears) on the oil pump. I bought a "new" remanufactured one and discovered after a lot of searching for problems that the pump was bad. Max spacing allowed is 0.08 inches. Two sensors since I haven't seen them listed are:
1. on oil filter connector
2. On side of cylinder head opposite timing belt.

[HeldtheViolets]

hi,

I just bought an '89 Jetta GL from a friend of mine at work.. when I asked her when the last time she got an oil change was, she looked at me - completely deadpan and said, "you have to do that?"....
I changed the oil immediately - and now I've had the oil light on without buzzing once, and oil light plus buzzing once. It was last night, actually, with the light and buzzing action. I mentioned something to my best friend about it and he suggested my oil pressure sensor.. but he's never worked on a volkwagen as he's a nissan guy through and through. I thought I would research it some on this site before I got a sensor.. interesting to know that it did both flash and/or flash and buzz. I also had no idea that there were two pressure sensor things.

I just ordered a Chilton's. This car is going to drive me crazy.

-Elisha