Dino 10W40 ----> AMS 5W40 oil pressure drop

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May 23, 2004
I switched from Dino Shell 10W40 to AMSOIL 5W40 and my oil pressure dropped! [Confused] After I changed oil and filter I took the car for a drive. When cold Oil pressure was around 5 bar. Drove for 20 min to bring the oil temp to 100.C At 100c the pressure was about 2.5 bar @ 3000 rpm However; At idle the pressure drops to 0.5 bar and my dash oil light comes on. This did not happen with Dino 10W40!! What could be causing it? Is AMS 5W40 has lower viscosity than dino 10W40?
I would check the vis @ 100 of both oils to see if the new oil has a lower viscosity. Normally I wouldnt worry about a pressure drop if the viscosity is lower, but I would worry about your oil light coming on! check to make sure you didnt under/over fill. If it turns out to be viscosity, you may want to try a thicker oil. RL 5W-40 is pretty thick at 100 degs, i think its like a 15.1 or so.
According to amsoil website Kinematic Viscosity @ 100°C, cSt (ASTM D-445) 14.5 I cant find the viscosity for the Dino oil. I did not overfill or underfill. I have been changing the oil since day one and the light never came on. This happened right after switching to synthetic!!
Maybe the Amsoil has less resistance to flow, so there it takes less oil pressure? I don't know why it would go that low though. Could be a mechanical problem or a sensor?.
14.5 is pretty common for a 40wt oil so its not like this oil is very thin. How much pressure drop did you have at idle from the dino 10w-40? I generally experienced lower pressures with m1, but m1 is on the thin side of their posted wt so no surprise there, the 5W-40 you have appears to be pretty thick so you should not have critically low oil pressure with it where your dash light comes on.... I'm using M1 T&SUV 5W-40 which is around 14.7 @ 100 and i get very high oil pressure with it compared to other oil i've tried, including a half-half mix of m1 10w-30 and 15w-50....
I used exact same filter brand (Mann). After changing the oil I drove normally like I always do. I have been using AMS 10W40 and 20W50 in my other VW for a long time and it never caused any decrease in oil pressure! This was my first time buying the 5W40. I have to note that oil pressure is ok while driving it only goes too low at idle!
cweed, I did not have a gauge in my car when I was using the Dino oil. I put on the gauge today since my oil light start lighting up after I changed the oil!
Well, guess you witnessed that the 5-40 is definatetly thinner than the 10-40. Firstly, probably because it's a 5W rather than a 10W (as in 10W-40) or 15W (as in a 15W-40). Secondly, it's a synthetic. The particles are more uniform and the oil flows better than the comparable dino oil. If it's an issue with the oil light (and it would pi$$ me off too), just switch to the AMS 10-40....
Kickster, Until you have a solid oil pressure number from a secondary mechanical guage you realy do not know what is going on! It could just be a bad oil pressure sensor? ALso ehat was the hot oil presure at idle before?
guys the car ran fine just before the oil change. I changed the oil, started the car and drove it. 20 min later the oil light came on. this car has a dummy light no gauge. today I attached a gauge to the car and it showed 0.5 Bar oil pressure at idle. Nothing changed other than switching to synthetic oil.
That's like 7 lbs of pressure. The 5W-40 is not too thin. The car has plenty of oil. Mann filters usually flow well and we can also assume it's not defective. Since you won't state, can we assume the car has low miles and tight clearances plus no clean up going on? My bet's on this.....i.e. your car is flowing oil really well....with some more tolerances that slowed the dino more.... [ June 14, 2004, 10:07 PM: Message edited by: Pablo ]
It is a 1990 vw Golf. The engine is in great shape no oil burning or consumption. It has 180,000 KM on it. but all these info is meaningless, the car ran fine right to the moment I changed the oil. This engine has never seen synthetic oil, can synthetic oil does something to the oil pump?
It would be much easier for you to diagnose if its a problem if you measured your oil pressure with the old oil in so that you could see the difference and whether it is big or negligable.
This engine has never seen synthetic oil, can synthetic oil does something to the oil pump?
Synthetic oil does nothing to the oil pump other than perhaps begin to clean it.....BUT if the car had never seen synthetic before and you were running dino 10W-40 and you went to to a synthetic 5W-40....I'll just bet the clearances are pretty wide on the beast and the oil is flowing through the galleys a LOT better...with lower pressure as shown on a gage. Heck, the difference isn't probably that much....but just enough to make the idiot light come on. What was the pressure at 2K, 3K, etc RPM? - this is more important.
I know this sounds strange, but it seems there was a caller on CarTalk that mentioned a flickering oil light on a VW and it was resolved by switching oil grades. Seems some of them may be ultra sensitive to using the proper grade. Dunno if your car is this way, but check it out. google is your friend. TB
Pablo: I was thinking the same thing, which is why it would help to know what the pressure was on the dino he used.
I agree with everything Pablo said. I would suggest using Amsoil 10W-40 in this vehicle in the Fall, Winter and Spring and use Amsoil Series 2000 20W-50 in the Summer. Also you could use a 5W-50 such as Castrol Syntec all year. Normally I would not suggest using a 10W-40 motor oil in Canada in the winter but a SYNTHETIC 10W-40 should be OK for an older vehicle that has an engine with a significant amount of wear. Also a Synthetic 10W-XX motor oil can work as well as a 5W-XX conventional motor oil in cold weather performance. 180,000 kilometers is about 112,000 miles so it is likely that the engine has a significant amount of wear even though it seems to be runnig well (aside from the oil pressure light). [ June 15, 2004, 05:32 AM: Message edited by: Sin City ]
What was the pressure at 2K, 3K, etc RPM? - this is more important. [/QB]
Pressure is @ 1.8 Bar (1900 rpm) 2.0 bar (2200 rpm) 2.5-3.0 Bar (3000 rpm) 3.0+ above 4000 rpm. The pressure is high while driving. It only goes low at idle! It is a waste to drain the brand new AMSOIL after using it for 2 days. I am thinking of removing 500ml and replacing it with 20W50. It may increase the viscosity just enough to stop the dummy light.
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