Oil Light Comes on only at operating temp. idle

1984george · Post by **1984george** » Sun Feb 21, 2010 8:42 am

My Rabbit has been doing this since I got it last summer. I check my oil regularly and have it changed about every 4k. I was told once this may have something to do with oil pressure?

The light only comes on when I'm at stoplights at full operating temperature, or for instance, if I'm on the interstate and decide to put it in neutral for a second, it comes on then. It hasn't seemed to hurt him in any way....it's more annoying than anything, especially during intown driving.

Any way to either get rid of it or fix the problem so the light won't come on?

bscutt · Post by **bscutt** » Sun Feb 21, 2010 9:47 am

You could have low pressure at idle from things like worn main bearings or intermediate shaft bearings. Best bet is to hook up a mechanical oil pressure gauge to the engine to verify that you are getting a good reading when hot and idling. You could just buy a new pressure sensor but you're better off getting an accurate reading. Idiot lights are next to useless and I'll never understand why VW did not put in real gauges for this, not even on my 06 TDI.

1984george · Post by **1984george** » Sun Feb 21, 2010 10:21 am

bscutt wrote:You could have low pressure at idle from things like worn main bearings or intermediate shaft bearings. Best bet is to hook up a mechanical oil pressure gauge to the engine to verify that you are getting a good reading when hot and idling. You could just buy a new pressure sensor but you're better off getting an accurate reading. Idiot lights are next to useless and I'll never understand why VW did not put in real gauges for this, not even on my 06 TDI.

Cool. If I hook up a mechanical gauge to verify my pressure and it is good, then is there a way to get rid of that annoying idiot light? I would imagine there's a fuse for it, but it probably controls important things to like blinkers, lights?

Vincent Waldon · Post by **Vincent Waldon** » Sun Feb 21, 2010 1:21 pm

It's probably the most important light on your car... since if there's an oil pressure problem and you don't know about it because the light is bypassed the engine will very soon grenade.... $$$

In my mind the last thing you want, so might make sense to track down the root cause... even if it's a 10 buck sensor.

If the light is coming on at idle when the engine it hot it's most likely doing its job of warning you that you have very poor oil pressure when the engine is hot and the oil is thin. As previously posted a oil pressure gauge is an excellent diagnostic at this point... if it's an 84 on its original bearings there's a good chance there's engine wear here... luckly both the main and rod bearings can be replaced with the engine in the car by removing the oil pan. If the intermediate shaft bearings are the big reason you have low oil pressure the engine pretty much has to come out.

But, step 1... find out what your oil pressure actually is.

The red light is an oil pressure warning, not an oil level warning, and in general it means "stop the engine right now".

bscutt · Post by **bscutt** » Sun Feb 21, 2010 2:08 pm

Vince is absolutely right, if that light comes on and it is functioning properly you definitely have an oil pressure problem that could lead to engine destruction. My comment about absolutely useless warning lights is my experience with 1) they do not give enough information to know a problem is starting and progressing as you would have with a reliable pressure gauge and 2) I have had problems with sensors going bad or even problems with sensor wires shorting and giving intermittent lights coming on when in fact there was no pressure problem. Either way a good mechanical oil pressure gauge is the way to go to diagnose the problem. BTW thicker oil would raise the pressure but in cold weather, thicker oil can cause hard starting problems and poor lubrication when cold causing more wear problems, so find the root cause and fix it before you get more engine damage.

82vdub · Post by **82vdub** » Sun Feb 21, 2010 2:36 pm

If the idiot light only comes on at idle and immediately goes out with any slight raise in engine RPM, then it's likely that you have low oil pressure. If it goes out at about 2000RPM engine speed, you could have a bad sensor. These have a dual sensor system where one monitors pressure above 2000RPM and one monitors pressure below 2000RPM. If the 2000 RPM seems to be about where your sensor quits yelling at you, the sensor could be bad, a loose wiring connection, or you could have the symptoms as mentioned above. It's been telling you for 6+ months to look at the car, now's the time to look closely at it and find out what's wrong.

1984george · Post by **1984george** » Sun Feb 21, 2010 3:12 pm

Okay, I believe you guys when you say it should be checked. I'll try to find out what the oil pressure is and replace what needs to be replaced. I don't have an RPM gauge to tell when it goes away, but 2000 seems about right, because it goes away just as I apply the gas.

1984george · Post by **1984george** » Sun Feb 21, 2010 3:27 pm

Another thing: If I do check the oil pressure, what should the numbers be?

Vincent Waldon · Post by **Vincent Waldon** » Sun Feb 21, 2010 3:40 pm

Here's some additional info for you Daren... including the details behind the only pressure spec VW gives:

http://vincewaldon.com/index.php?option ... &Itemid=28

Because you have a 1984 you may or may not have the dual-pressure warning system (look to see if you have a second pressure sensor at the oil filter flange to go with the one on the driver side of the head) but the notes on specs and steps you can take to improve your oil pressure all apply.

1984george · Post by **1984george** » Sun Feb 21, 2010 3:47 pm

Vincent Waldon wrote:Here's some additional info for you Daren... including the details behind the only pressure spec VW gives:

http://vincewaldon.com/index.php?option ... &Itemid=28

Because you have a 1984 you may or may not have the dual-pressure warning system (look to see if you have a second pressure sensor at the oil filter flange to go with the one on the driver side of the head) but the notes on specs and steps you can take to improve your oil pressure all apply.

Thanks!

Post by **Fatmobile** » Sun Feb 21, 2010 4:33 pm

This guy grabs used gauges and senders from local salvage yards.
http://forums.vwvortex.com/zerothread?id=4601968
$25 shipped is a pretty good price.

With stock, electrical gauges/senders you don't end up with a pressureized tube of oil in the passenger compartment.

1984george · Post by **1984george** » Sun Feb 21, 2010 6:10 pm

Fatmobile wrote:This guy grabs used gauges and senders from local salvage yards.
http://forums.vwvortex.com/zerothread?id=4601968
$25 shipped is a pretty good price.

With stock, electrical gauges/senders you don't end up with a pressureized tube of oil in the passenger compartment.

That's a good deal thanks for the information.

82vdub · Post by **82vdub** » Sun Feb 21, 2010 11:36 pm

There's a reason why there's a light on the dash, it's there to indicate that something isn't normal. I thought it was nice that VW actually attached a buzzer to it too.

2000RPM is more than just moving the engine off idle. The 2000RPM point is right about (or exactly) when your alternator lights turn off after you first start the car and raise the RPM's. The alternator on these don't charge the system until the car reaches that 2000RPM point.

1984george · Post by **1984george** » Mon Feb 22, 2010 6:43 am

Well I've been checking prices of mechanical fuel pressure gauges and the cheapest one I could find was for $30. I'm not trying to be a penny pincher, I've just spent a lot of money on a lot of things lately.

What if I just replaced the sensor on the block and the sensor on the oil filter flange? Given that the new sensors worked and it stopped making that noise at idle, I'd be okay right? You guys are the experts though so let me know. If I have to I'll buy a gauge then try to return it after I test my pressure.

82vdub · Post by **82vdub** » Mon Feb 22, 2010 10:00 am

What if you spent the money on the oil pressure switches and that didn't solve the problem? IMO, get the mechanical gauge and test your oil pressure system and then keep the gauge for future use on future cars/projects. Don't return it. IMO that's just not right to "borrow" a gauge at the expense of the store/manufacturer. They're in the business of selling product, unless it's on a rental program. If you want to borrow a gauge, then see if you can borrow one from someone, or some auto parts store that will rent this type of equipment.

Test your oil pressure. Spending the money on new switches may mask the problem, only to have it rear it's ugly head in a week, month, or year. You'll be masking the problem and have no data as a basis to know what's going on inside your motor. Find out what the problem is first then address the problem with a solution.