Oil pressure light on startup

#1

I just got done replacing the oil pan gasket (the old one was only about half there and leaked pretty good) on my 325i (the first of many steps to get it ready) and now I’m having a minor concern on startup.

When I start the car cold, the oil pressure light on the dash lights for about a second or two, then goes out. It stays on longer than I remember before I changed the gasket (and removed/reinstalled the oil pump), but that is just what I remember. I never really timed it before. Once it goes out it never comes back on while the car is running, or idling. However, once I shut the car off and start it again, it comes back on for a split second (shorter if the car was only off for a bit).

Is this a common behavior, or one I need to worry about? I don’t have a oil pressure gauge hooked up yet, so I don’t know the exact PSI. Also, I’m thinking it may even just be the weight of the oil, I have 10W-30 dino oil in it now.

Thoughts?

#2

Mine does the same thing. No problems though.

#3

just curious why you went with a lighter weight oil? Seems counterintuitive that the light would be on longer for a lower viscosity oil (of course this is assuming that there was 15 or 20w50 in there before)

Question to the regular racers - what weight of oil do you run?

Does synthetic allow you to run a less viscous oil?

cheers,
bruce

#4

The short answer is that the 10W-30 is what I had in the garage (I use it on my 318i) and I needed oil. Long term, I’m not sure what weight I’ll be running just yet.

The long answer is that this was the first oil change since I bought the car. The previous owner had it changed at Jiffy Lube and I honestly forget what weight was in it at that time. I hate those quick change oil places…ask my why I had to retap my oil pan with an M14x1.25 bolt.

#5

20W-15

#6

Check the sensor. When they go out alot of times they’ll allow oil to squirt right through the sensor. I bet that’s your problem and they are only about 10-15 dollars.

As long as you maintain good pressure you can run a thinner oil in a race motor. Alot of race engines using standard pumps can’t hold pressure at low RPM’s because the oil is so thin.

I run 20w 50, it leaks out slower. :woohoo:

#7

robweenerpi wrote:

[quote]

I run 20w 50, it leaks out slower. :woohoo:[/quote] LOL…Me too.

#8

leggwork wrote:

[quote]Question to the regular racers - what weight of oil do you run?

Does synthetic allow you to run a less viscous oil?

cheers,
bruce[/quote]

I would be interested to hear what the rest of the racers use on the track. My guess is that the odds on favorite is Mobil-1 15W50.

Regarding the question about synthetic and thinner viscosity, the answer is yes, theoretically. These engines were designed for a range of oil viscoisties as low as 5W20. In practice however, almost everybody used 20W50 under the "thicker is better" theory so the most data that exists is with thicker oil.

There are a couple of other things synthetic oil, regardless of the viscosity, provides in a race driven street engine. 1) much better stability at high temps and 2) a little margin for error should the level get low, pressure drop, or any other problem that might restict flow. I’ll add some comments on each point below.

On the issue of thermal stability, it is absolute fact that synthetics are more stable at high tempeatures for extended periods of time. While it is rare to see oil temps above 250F on a gauge, the gauge temp is the temperature in the sump after it has been through the oil cooler. No one really knows how hot the oil is in the piston ring are or the valve seal/stem area. Under race condiions dino oil is probably coking in those area and leaving deposits behind and/or suspended in the oil. Synthetic gives one a little more peace of mind in this area. Particularly for those who do not have oil temp gauges.

Secondly, back in the day when these cars were new and driven in Firehawk and SCCA showroom stock there were several engine failures due to oil starvation with dino oils. This was more prevalent in 944s and E30 M3s than 325s but of course more of those models were raced as well. The problem with 5 quart wet sump systems is that under high RPM the oil pump is pumping as much volume as it can get. In some high speed sweepers the oil is littlerly pulled away form the pick up causing momentary starvation. I blew a couple 944 motors this way so I speak from experience. Most of the showroom stockers back then either insatalled baffeled oil pans or added Accusump products to keep pressure in the system at all times. For those that didn’t have such resources, synthetic oil saved a lot of engines by providing a little extra protection during the momentary starvation moments.

Can you run a 10W30 synthetic in your race engine? Proabably. I hear that 5W20 and even 0W20 is popular in some SCCA circles for the guys that are trying to squeak an extra couple HP. I don’t have the Kahunas to try that light of an oil for a track engine but I have used 0W30 in the past in a track driven E30 with excellent results. Besides, the guys using the super light stuff are probably the guys that rebuild their engine once a month and that is not for this series.

If anyone is interetsed I can get Amsoil synthetics for you at Mobil-1 prices. I might even be able to provide free delivery to SE and Floida region racers which makes it cheaper than Mobil-1.

Don
www.lubedealer.com/dstevens

#9

leggwork wrote:

[quote]Question to the regular racers - what weight of oil do you run?

Does synthetic allow you to run a less viscous oil?

cheers,
bruce[/quote]

I would be interested to hear what the rest of the racers use on the track. My guess is that the odds on favorite is Mobil-1 15W50.

Regarding the question about synthetic and thinner viscosity, the answer is yes, theoretically. These engines were designed for a range of oil viscoisties as low as 5W20. In practice however, almost everybody used 20W50 under the "thicker is better" theory so the most data that exists is with thicker oil.

There are a couple of other things synthetic oil, regardless of the viscosity, provides in a race driven street engine. 1) much better stability at high temps and 2) a little margin for error should the level get low, pressure drop, or any other problem that might restict flow. I’ll add some comments on each point below.

On the issue of thermal stability, it is absolute fact that synthetics are more stable at high tempeatures for extended periods of time. While it is rare to see oil temps above 250F on a gauge, the gauge temp is the temperature in the sump after it has been through the oil cooler. No one really knows how hot the oil is in the piston ring are or the valve seal/stem area. Under race condiions dino oil is probably coking in those area and leaving deposits behind and/or suspended in the oil. Synthetic gives one a little more peace of mind in this area. Particularly for those who do not have oil temp gauges.

Secondly, back in the day when these cars were new and driven in Firehawk and SCCA showroom stock there were several engine failures due to oil starvation with dino oils. This was more prevalent in 944s and E30 M3s than 325s but of course more of those models were raced as well. The problem with 5 quart wet sump systems is that under high RPM the oil pump is pumping as much volume as it can get. In some high speed sweepers the oil is littlerly pulled away form the pick up causing momentary starvation. I blew a couple 944 motors this way so I speak from experience. Most of the showroom stockers back then either insatalled baffeled oil pans or added Accusump products to keep pressure in the system at all times. For those that didn’t have such resources, synthetic oil saved a lot of engines by providing a little extra protection during the momentary starvation moments.

Can you run a 10W30 synthetic in your race engine? Proabably. I hear that 5W20 and even 0W20 is popular in some SCCA circles for the guys that are trying to squeak an extra couple HP. I don’t have the Kahunas to try that light of an oil for a track engine but I have used 0W30 in the past in a track driven E30 with excellent results. Besides, the guys using the super light stuff are probably the guys that rebuild their engine once a month and that is not for this series.

If anyone is interetsed I can get Amsoil synthetics for you at Mobil-1 prices. I might even be able to provide free delivery to SE and Floida region racers which makes it cheaper than Mobil-1.

Don
www.lubedealer.com/dstevens