: Oil pressure specs for 4.1 at idle

07-19-12, 12:20 PM
Hi everyone, Does anyone know the oil pressure specs at idle and in drive at stop for my 4.1L 86 CDV.
The reason for the inquiry is when the car is in closed loop mode and I stop at a light my oil light flickers or comes on.
when I acclerate of course the pressure goes up and the light goes out never comes on while I am driving. I recently replaced the oil switch but maybe the wrong specs? maybe its theshold is calibrated at a higher psi? any thoughts
car is in the shop and I having the mechanic put a gauge on it and give me the numbers see if they are in spec.

thanks in advance for any replies

PS the light does not come on when car is open loop mode

07-20-12, 08:26 AM
Somebody should have the specs but if it has 20-30 lbs at idle I wouldn't worry about it.

07-20-12, 04:35 PM
I have to check my service manual which i have loaned out until the weekend but if i remember correctly the idle hot minimum pressure is around 7 PSI. Scary for those used to 40 psi on some other engines. The oil pressure switch spec on most replacement switches is to touchy. I would suggest that you use only the exact replacement part from the dealer. Do not trust the aftermarket or universal switches you get at the auto parts stores. Get the genuine GM Part even if you have to pay triple what you would at the auto parts store. It will save you lots of aggravation.

07-21-12, 12:25 PM
Normal operating temperature at idle 11 psi, 2,000 rpm 53 psi. I would be :shocked: if you got 53 at 2,000 rpm cruising down the road.

07-21-12, 02:15 PM
Did you get that spec from the 93 service manual? I have not yet checked my 85 manual. One of the great improvements of the 4.9 is the use of a much better Oil Pump. The 4.9 should run better pressures down the line than the 4.1 / 4.5. The 4.1 definitely runs lower pressure at idle than the 4.1 with all else the same. The oil pressures of a lot of GM V8 engines have always troubled me a bit. However they run a long time and the engineers know their stuff. My first few cars where MGA's and MGB's that will run 40PSI at idle and up to 70PSI running down the road. However my first "car" was a 1951 M38 Willys Jeep. The Oil pressure did not even register at idle and never went above 20PSI when hot at any speed. This engine is still running today in a friends jeep.

07-22-12, 02:20 AM
Yep, sure did 92-93 FSM. That should be the same for 91's. I don't doubt they are lower for the older 4.X engines. I noticed a lot of engines in the late 70's drop the oil pressure, even the big diesels dropped down to 20 psi idle and 40 psi mid to upper rpm range. Speaking of which, can you put a 4.9 pump on the other 4.X engines?

07-22-12, 08:49 PM
You sure can - they bolt right up, but the pickup tube/oil pan baffling changed throughout the years, so sometimes you need to change the oil pan to switch the pump.

07-23-12, 05:24 AM
Good upgrade too. More efficient pump builds more pressure with better flow using less drive power.

07-23-12, 12:21 PM
Thanks for all the replies. New info has come up.here is some backround I just had the oil pump replaced 6 months ago with a melling M132 no issue with oil pump and dist gear. I discovered a vacuum leak that has helped the issue while in park. However i am still getting the light in closed loop mode when stopped at a light in drive. but NOT when cold (open loop). I will buy the gm part as my next step. My mechanic says I have no oil pressure issues witch is a great relief to me not to have to worry about clogged oil galleys in the old block. seems like the oil switch to me.

Thanks for all your help

07-24-12, 10:20 AM
Why didn't you have this mechanic replace the switch when he had it out to check the pressure with his gauge? The fact that the engine is in closed or open loop has nothing to do with the oil light, it has to do with oil temperature. Hotter the engine, thinner the oil, hence, lower pressure at idle in gear. Higher engine RPM in open loop vs. lower RPM in closed loop means more pressure in open loop. Yes, I also recommend a GM sender (switch).

07-26-12, 08:03 AM
Hi everyone, I have a deal I made with my mechanic I buy the parts and he sometimes does the work like, A/c repair or anything that needs to be on a lift. If I can do the work myself I do it. I just bought the new switch. i called a GM part supplier the part number they have is an AC/delco D1845a this has a 3/8 male thread so it will not fit my 4.1 which has a 1/4 male thread. I opted for a Standard motor products PS140 with the following specs psi-#2 opens @ 2-6 psi # 1 & 3 closes @ 1-5.9 psi.They calim it is an OE replacement. I will install the switch and check the oil pressure myself. Based on how the car is running the light comming on seems to be all about the idle rpm. I will discuss options with my mechanic and check for more vacuum leaks. see if we can figure out why this is happening and to improve the idle if possible. thanks again for all your help and support.

07-26-12, 08:47 AM
Have you put a gauge to it yet? What is the idle RPM? Just curious.

07-26-12, 10:13 AM
You have never posted the idle oil pressure reading he got. Almost all oil pressure senders turn on the light below 5 lb.

07-26-12, 04:14 PM
Guys when the new switch arrives I will put a gauge on the oil pressure and get some numbers before i install the new switch

07-26-12, 06:13 PM
I just re read your post about the mechanic saying you have no oil pressure problem. That must be his opinion not fact. When i managed a shop and a customer had an oil light coming on, the 1st thing i had the guys do was check it with a manual gauge. An opinion can make you responsible for the customers engine. I presume you did not have to pay for that advice?

07-27-12, 12:01 PM
Yes I did not pay for that advice however he is an excellent mechanic and a value his opinion, and he knows i do some of the work on this car myself as long as it makes sense. I will check the oil pressure with a gauage when i get the new switch. it feels like the idle speed maybe causing this. I am a DYI guy but i'm not a master ASE mechanic. I will let you know the numbers next week. thanks for all your replies you all have been helpful.

08-04-12, 01:48 PM
Hi everyone . I was able to get out this am and check oil pressure. here is what I got. Cold start oil prssure 45 ibs, warmed up in neutral 16 lbs and the same in park at idle. so now I know its the switch. Problem getting the correct one. the one I just purchased has a 3/8 thread not 1/4. any suggestions where to get the right part.

thanks again eveyone for your help!

08-04-12, 06:26 PM
I am sure you posted earlier, where did you get the last one?

08-04-12, 07:16 PM
Rock auto but i found one from a gm dealer hopefully nos i will let you know

08-05-12, 07:31 PM
You need to get the engine HOT by going out and driving it hard to get an accurate hot oil pressure reading. Letting it warm up in idle is not sufficient. The oil will not heat up as much as if it is driven. Good luck and go with the oem switch whenever possible.