Well I changed My oil today, and I noticed that the oil presure now is low.

On 90C oil the presure in neutral is 1.9-1.8Bars. In gear the preusre is 1.6-1.7Bars. If the fans turn and in gear the presure is 1.4-1.5Bars.

The oil I put is 5w-30 Mobil1 Claen 5000 and Mobil1 M1-301 Filter and a half a cup of seafoam.

 

I don't think that the oil you are using is Mobil 1.

It is mobil 5000, which is conventional dino oil with some additional detergents. You should be running full synthetic (ie Mobil 1)

 

ah, I know, couse it cheap. How ever I'm going to change again in like 1500Miles, couse I used Seafoam in crankcase. So next oil change is going to be fully syntetic, and tranny oil too.

 

I have a '93 100CS quattro. My oil pressure is at the highest, 5 bar. When I'm stopped at a traffic light sometimes the needle goes down to 2 psi. I use Castrol 10W-30. Should I use synthetic? The car has 160k miles on it. Thanks.

 

yea, full synthetic is always best, i use castrol syntec, it has label on it that says "specially formulated for BMW, Mini, and Volkswagen"

cant get much better than that

 

The viscosity of your oil is going to directly effect your oil pressure.

As long as it does not drop off to 0, then your pump is gone and well so is your car.

I know this is not a Diesel, but diesels are super tempermental about changes to oil viscosity. I used to have a truck that when I changed the oil it would drop to nearly no pressure. After a month or two (viscosity goes up) the pressure would sit right on the "normal" line on the gauge. Using the Seafoam product probably grossly reduced your viscosity since it is meant to break up sludge right (which makes me wonder why you would use such a product?)

Now if you want to talk about the positive and negative effects of low viscosity oils... well make a new poll. Personally, I go with a 10W30 in my Audi because as great as these 0W50 and all synthetics sound, I aint buyin it. PS MSA10, 10W30 got my car to 180K and yours to 160... I think it will be alright.

 

I've got 2,5-3BAR in neutral, when engine is cold it pumps to 5bar,

It should be at least 2bars at 2000rpm, oil temperature 80C. if it isn't, you have a problem

 

at 2000 RPM I get around 3bars with 90C oil.

I use seafoam to just clean a bit. You know from previous owner, you never know what he used. so I just do to make sure that evrything is clean and functioning.

and castrol syntec is not syntetic, however it like dyno oil but very high level.

the regular mobil1 oil with gray cap is true syntetic.

and I did not see almost no sludje, but you never know.

 

so you saying it okey, then I stop woring and just check the presure periodically.

then I will put 5w-40 if exists or 10w-30/40 with full syntetic oil.
and fresh tranny fluid too.

 

2psi is way too low. To accurately measure oil pressure you have to use a calibrated mechanical or electrical gauge. The factory mounted gauge on the dash is not accurate especially after many years of service.