230SL Low Oil Pressure?

[mistertj]

Had someone remark to me the other day the the oil pressure in my 1964 230SL was way too low. It normally reads between 30 - 35psi. They indicated that the oil pressure gauge needle should be pegged at 45 most of the time when above idle. The recommendation was to consider replacing my oil pump with a higher capacity one out of a 280SL.
My question is...what is "normal" oil pressure for a 1964 230SL? The oil pump has never been touched but the engine was rebuilt (ring, valves, bearings, etc) about 20 years ago but the car does not get driven all that much.
Any insight/comments would be appreciated.

[WRe]

Hi,
did you read this: https://www.sl113.org/wiki/Engine/Lubrication#OilPressure ?
Are you sure that your pressure gauge is showing the right values? Normally they do but it could be untight. I would check this first.
Next would be the pressure relief valve.
...WRe

[mistertj]

I did read that...but thank you. I was hoping also that someone with a 230SL might chime in as well.
many thanks.

[Mike Hughes]

Mine reads in the upper 1/4 of the scale at idle warm, and goes to peg upon acceleration.

[Benz Dr.]

You can safely run 15 - 20 lbs at idle but it should be pegged at 45 PSI above 1,500 RPM.

 Low oil pressure is generally a problem with worn crank or rod bearings. Oil pumps create volume and oil pressure is produced from tight bearings or any place that oil can squeeze out of a hole or gap between moving parts. Oil pumps can last up to 150,000 miles or far less in a poorly maintained engine and if you had something let go in your engine where it produced shards of metal it will be a lot less than you'd like. I always replace the oil pump on a full engine rebuild and most places won't give you any sort of a warranty without a new oil pump. 

[mistertj]

That is what's strange with mine. Start the engine and it pops right up to just past 30. Rev the engine and it just calmly stays there. I'm thinking there is some other problem.

[Tyler S]

The fact that it does not change from 30 if you rev the engine from idle indicates you may have an issue with the gauge. Does it Vary from 30 hot vs cold? If not then double check the gauge by using an external gauge to get a correct reading.
There are small gears, levers, and a bourdon tube within the gauge that can get gummy or freeze up. Mine used to hang up after the car was shut off. I would have to "bump" the dash in order for it to return to zero. I removed the gauge from the cluster and cleaned and lubed its innards. Good ever since.

[mistertj]

Thank you for the comments. I need to now determine what the threads are so I can get the proper pressure gauge. Guess I'll get a replacement hose at the same time. After 50+ years the one that's on there will likely crack when I loosen it.
Started the car this morning and the oil pressure went immediately to a little over 30psi steady. Rev'd the rpms to over 3000 and then let rpms go to idle (roughly 800), oil pressure needle stayed in exact same spot.

[mistertj]

Mystery solved...I think. Could not find an 8mm to 1/8 or 1/4" npt threaded adapter anywhere that would support a pressure gauge, so I put my compressed air blow gun with rubber tip and a short hose on to the oil pressure meter line. At 15 psi, it read 15 psi. At 30 psi, it read 30 psi. At 40 psi, it read 30 psi. At 60 psi, it read 30 psi. Guess I'll be taking the instrument cluster out to see if I can get the pressure gauge working properly.
Many thanks for all the inputs.

[mistertj]

Took out the instrument cluster and again used the compressed air to activate the oil pressure gauge. Would only go to 30psi. Removed the oil pressure gauge from the cluster and as if by magic...the pressure reading would go to 45psi. Turns out that the circular flat tube was coming in contact with the case and restricting movement. So, I loosened all the screws (3) and pushed in the direction away from the case side, then retightened. It fixed the problem.

[Tyler S]

Thats great! A DIY partless fix is always a good day!