What is the correct oil pressure range for a 1981 633?

[Cougar Dave]

I recently bought an '81 633 CSi with a beautiful body but a totally shot clutch. I normally wouldn't buy anything without driving it but the body was so good I couldn't resist (reminds me of a weekend in Vegas but that's another story). The car did crank and idle fine with no noise or smoke so I took the chance.

I finally got the new clutch installed, and it drives great, except for the oil light coming on at idle. It's fine under acceleration and at speed. I installed a manual oil pressure gauge to be sure the sending unit wasn't the issue. I'm seeing about 40 psi at idle when first cranked (engine cold), 60 psi under acceleration, but down to about 18 psi at idle when the engine is warmed up. I have also noticed a small oil leak that appears to be coming from the rear of the engine, possibly the head gasket. I can see for sure it isn't the valve cover gasket.

So what is the "normal" oil pressure range, and would a head gasket leak cause the pressure to be low? Thanks.

[EuroGeorge]

Oil pressure at idle should be .5-2.0 bar (7-30psi) At speed, 4.0-5.0bar (60-75psi)

[Cougar Dave]

Thanks, that makes me feel a little better. Overall the car is in good enough shape to justify a new oil pump but sounds like I don't need to rush out and do one this weekend.

[alpinacsi]

Replace the oil press sender. It is at the top rear of the head and is often a source of leaks that makes people think the head gasket is leaking. Pressure from this point will be low and the sender for an actual gauge is better placed at the filter housing. Replacing the sender will most likely correct the issue with the light at idle. Don't buy a cheap parts store sender as you will be doing this again in short order if you do.

[Cougar Dave]

I couldn't see any indication of leaking around the sender mounting point but will look again. I like the idea of mounting the sender closer to the filter.

[alpinacsi]

Sender does not normally leak at the threads. They typically leak at the crimp on top where the plastic with the terminal is crimped to the base. Then the leak will trail down the leads and can deposit in various spots. May or may not be the source of the leak but it is a good place to start. Another place to check is the plate at the rear of the head. Also: one of the bolts on that plate has a sealing washer that can leak and goes in a specific location.

[DanMarshall]

I recently bought an '81 633 CSi with a beautiful body but a totally shot clutch. I normally wouldn't buy anything without driving it but the body was so good I couldn't resist (reminds me of a weekend in Vegas but that's another story). The car did crank and idle fine with no noise or smoke so I took the chance.

I finally got the new clutch installed, and it drives great, except for the oil light coming on at idle. It's fine under acceleration and at speed. I installed a manual oil pressure gauge to be sure the sending unit wasn't the issue. I'm seeing about 40 psi at idle when first cranked (engine cold), 60 psi under acceleration, but down to about 18 psi at idle when the engine is warmed up. I have also noticed a small oil leak that appears to be coming from the rear of the engine, possibly the head gasket. I can see for sure it isn't the valve cover gasket.

So what is the "normal" oil pressure range, and would a head gasket leak cause the pressure to be low? Thanks.
What oil are you using? A lot of people are using very light synthetics now and that could be contributing to this issue if you're running 0-40w or 10-40w. On an older engine such as yours I would run 20-50w or straight 50w if you are still concerned. I use Valvoline 20-50w VR1 Racing oil in mine, but lots of people use Castrol with good results as well.

Dan M.

[Cougar Dave]

I am not sure what is in there but an oil/filter change is next on the list. I'll definitely go with a heavier weight oil because of all the issues I'm having.