Oil Pressure Light keeps coming on

[Ox-Ford Farm]

Hi,
I am working on an old Jetta (1984, TDI GL) that has been sitting for about 10 years. It belongs to an elderly lady who no longer drives. She wants it running again. Over the past several years, I have started it every now and then to let it sit and run. I drove it about 2 miles to a gas station a few years ago, and other that that it has not moved. It has 152,000 miles on it. I put a battery in and got new tires and took it for a drive the other day. I put some Sea Foam in it beforehand. I drove for about 40 miles and then parked it. The alternator was bad, so I replaced it and changed the oil, oil filter, air filter, and fuel filter. After that, I started it and the oil pressure light comes on when I hit higher RPMs.

I thought the sea foam may have dislodged some gunk, so I changed the oil and filter agian (it had a NAPA filter to start with. At the first change I used an STP, second change I used a K&N. Same thing was happening, so I put some Marvel Mystery in it, let it idle until it got hot (around 30-45 min), then changed the oil again.

I have changed both pressure switches (one at the filter and one at the top of the block), put a new oil pump in, and it still does the same thing. It idles fine, but when I rev it up the light comes on. The engine is as clean as it can be on the inside. It can't be a senor wire because the light comes on at the exact same rmp level every time (and I have done this at least 25 times).

Any ideas as to what I should do?
-Seth

 

[MukGyver]

Hi,
I am working on an old Jetta (1984, TDI GL) that has been sitting for about 10 years. It belongs to an elderly lady who no longer drives. She wants it running again. Over the past several years, I have started it every now and then to let it sit and run. I drove it about 2 miles to a gas station a few years ago, and other that that it has not moved. It has 152,000 miles on it. I put a battery in and got new tires and took it for a drive the other day. I put some Sea Foam in it beforehand. I drove for about 40 miles and then parked it. The alternator was bad, so I replaced it and changed the oil, oil filter, air filter, and fuel filter. After that, I started it and the oil pressure light comes on when I hit higher RPMs.

I thought the sea foam may have dislodged some gunk, so I changed the oil and filter agian (it had a NAPA filter to start with. At the first change I used an STP, second change I used a K&N. Same thing was happening, so I put some Marvel Mystery in it, let it idle until it got hot (around 30-45 min), then changed the oil again.

I have changed both pressure switches (one at the filter and one at the top of the block), put a new oil pump in, and it still does the same thing. It idles fine, but when I rev it up the light comes on. The engine is as clean as it can be on the inside. It can't be a senor wire because the light comes on at the exact same rmp level every time (and I have done this at least 25 times).

Any ideas as to what I should do?
-Seth

I would be surprised if the oil pressure is truly low, as it only takes a short time to burn out the turbo. assuming turbo is still okay? It would be helpful if you had a oil pressure gauge installed so you could see what is going on. If those are like the mk4 jettas the oil pressure light does not register at idle. only after the rpms come up above (I think 2000). So the fact that you have no light at idle could mean nothing.

 

[Vince Waldon]

The alternator is an excellent suggestion... you're looking to make sure yours has the "W" terminal... it feeds both the tach and the oil pressure warning system.

Failing that, getting a gauge on the situation is also a great idea... if it's a sensor issue that's one thing but if you actually have low oil pressure you should probably park the car till you get it figured out. Given that you've replaced the pump etc the next suspect would be rod/main bearing wear.

Some additional dual-sensor oil pressure troubleshooting info here:

HOWTO: Diagnose the Dynamic Oil Pressure Warning System - VinceWaldon.com

Do any of these symptoms sound familiar??? “My oil light has started to come on when my car is hot” “The oil buzzer goes on after I’ve driven on the highway for a while… if I rev the engine the buzzer goes off” “My oil light came on but my oil level is fine” “My oil buzzer comes on when the...

vincewaldon.com