Is it possible for oil additives to increase oil pressure?

[Guest Kitskaboodle]

I have used oil additives here and there in various cars over the years such as Slick 50 , Marvel Mystery Oil, Dura- Lube, various synthetics like Amsoil, Mobil 1, etc... In every instance', I don't recall ever seeing any increase in oil pressure. Now here is the weird part.....I just did an oil change on my 90 but this time instead of adding the usual 5 quarts of 10-40 and Bosch filter, I added a 16 oz bottle of this additive I got at a garage sale about a year ago. (4 bottles for $5 ) Anyways, after the oil change I noticed the oil pressure gauge would go two bars higher than it usually does. It typically reads right in the middle. (12:00 position ) Actually, this brings up another question : how many psi is each bar? So if it went up two bars , how much more oil pressure is my engine getting ? Lastly, I can take a pic of the box tommorow if anyone wants. It is from Rain-X

Kit

Edited February 28, 2014 by Kitskaboodle
Grammer (see edit history)

[Barney Eaton]

I guess the answer is both YES and NO

Most additives are there to add more cleaning additives to the oil. There is a chance that these additives could "clean" the port in the sending unit (if it had been clogged) and cause it to read higher..... but in your case your reading was normal.

Other additives are used to keep older cars from burning or leaking oil and they would add viscosity to the oil which could raise the pressure. STP is one of these.... it pours like honey.

In your case, the oil pressure has been reading in the correct range (12 o'clock on the 90-91 gage) and it is unlikely that an additive would raise the oil pressure 2 bars above normal. If this continues, I would pull the sending unit and install a pressure gage to verify that the pressure is high. (2) inspect the port on the sending unit.

Let us know what you find

Edited February 28, 2014 by Barney Eaton (see edit history)

[padgett]

The 3800 uses a georotor oil pump. Combined with the oil pressure relief valve my experience is that they vary very little when warmed up (typ 41-43 psi at idle and 48-52 psi at 2000 rpm (GM spec for the "C" engine is 40 psi at 1875 rpm). That said the oil pressure senders are notorious for failing (was even a TSB) even when new.

As mentioned there are basically cleaners that are thinner than normal oil (e.g. Marvel Mystery Oil) and "Viscosity Improvers" such as STP that are much thicker. In a good engine you will see little change in oil pressure except when cold, a worn engine may show some improvement.

I run 10W-30 Dino oil and change at 3,000 miles. Generally I see a slight drop in pressure before the change that is restored with the new oil. I attribute that to breakdown in the long-chain additives from running (part of the reason I run engines cooler than stock). I saw more of a change in engines (Pontiac 400, SBC) with gear type oil pumps particularly at idle.

Keep in mind that the oil pressure sender is very near the oil pump. From there the oil goes to the cam, then to the mains, and through the crank to the rod bearings. There is a lag between the gauge registering and the time oil gets to the rods. Thick oil takes longer to get there which is why I let a cold engine even in my warm climate idle for a while before putting in gear. I also fill oil filters before installing.

So my choice is not to use additives in any engine's oil system unless there is a special need (used to run a can of STP in a road-race engine because someone I trusted said if oil pressure was lost, it could save the engine for about 5 seconds and would not hurt otherwise.

[Guest Kitskaboodle]

Anyone have a pic of the oil sender and where it is on the 3800? I want to check mine out although the gauge typically registers half way (12:00) most of the time .

Edited February 28, 2014 by Kitskaboodle
Grammar (see edit history)

[drtidmore]

Anyone have a pic of the oil sender and where it is on the 3800? I want to check mine out although the gauge typically registers half way (12:00) most of the time .

Here is a drawing with several of the most common failure items located.

[padgett]

Except that picture shows it mounted horizontal. On a Reatta (C or L engine) it is vertical on top of the oil filter housing.

[Ronnie]

Anyone have a pic of the oil sender and where it is on the 3800? I want to check mine out although the gauge typically registers half way (12:00) most of the time .

This might be helpful.

[jbeary]

Hi Padgett,

I know that I probably have an issue with my sensor, because my oil pressure fluctuates between 40 and off the scale high. I also know that I have a problem with the exhaust valve in cylinder 5. I don't know if the valve is burned or if there's a problem with the lifter. I plan to get a kit from Harbor Freight to do a leak down test so I haven't done that yet. What I have done is to take the valve cover off and while #5 was TDC I pulled the springs and neither intake or exhaust were stuck. However, after putting the springs back on and running the car until hot, the misfire on #5 disappeared and my pressure remained normal. When it cooled down it was back to the way it was before. I don't know what constitutes a sticky valve, but I still don't think the exhaust valve is closing all the way because I can hear it popping through the tail pipe. I had a z-28 with a worn cam lobe and that exhaust valve was stuck closed and you could hear it popping from the carb so this seems like its the reverse and this valve isn't closing all the way. Changed injectors, plugs, wires and ICM/Coil to no avail. Would a situation where there were gas and spark happening while a exhaust valve was stuck open cause the oil pressure to fluctuate wildly? I'm thinking pressure from the ignition cycle pushed through the crankcase could also cause a temporary increase in pressure. Is this possible? Car also shudders when locking into 4th gear and I think that means I'm lacking torque.

[harry yarnell]

Mr. Beary; I think you have two issues. The oil pressure sender fails as you describe. It should be at 12 o'clock (maybe slightly higher when cold).

Did you run the engine without the valve cover to see the operation of the valves?

[jbeary]

Hi Harry,

Yes... It looks, at least to my untrained eye, that the exhaust valve is a little lower than the intake valve. I kind of thought that the spring could be weak so I swapped the intake and the exhaust which seemed to help at first but when the car cooled it went back to missing. This is a dead miss too. The plug looks completely brand new on this cylinder but I smell the gas and know I'm getting good spark and fuel. The engine does not consume oil but with an original radiator and obvious evidence of prior cooling issues I have to think the seat or valve itself is bad.

I have another sender I could try and will start a new thread on what I feel are head issues, but still would like to know if the oil pressure itself could be affected by a momentary increase in crankcase pressure. I mean I know that this is what the PCV valve is supposed to do, right? I did change the PCV valve if that matters. What if the PCV is clogged? Would that change the oil pressure?

[Ronnie]

Have you checked compression on each cylinder?