Oil Pressure Guage on '79 350SL

[simonward78]

Hello,

The oil pressure guage on my 350SL seems fine when the revs are above about 1000rpm, but when at idle it drops to indicate '2' or just below (the scale reads 1 to 3).

Is this something to be worried about, I bought the car a couple of weeks ago and I'm sure it didn't do this in the first 2 weeks.

I consulted the manual but the scale appeared different and this has confused me somewhat!

Thanks in advance.

 

[Mikesmerc]

Hi Simon
my 72 350sl idles at an oil pres of 2Bar when hot. You will find the longer the spin the hotter the oil temp will get thus dropping oil pressure. Perhaps you bought it in the winter months which kept the oil cooler when driving resulting in a higher oil press. You will notice when you start from cold you will have full press but as the oil heats up and gets the lighter it flows through bearings etc more easily resulting in lack of pressure . My opinion is that your engine is still quiet healthy for its age, I used to own a 200d and when hot it had no oil press. what so ever. Didnt last long but didnt care she was very tired indeed.
1Bar=15psi, 2=30 and 3=45.
When engine revs increase so does the oil pump resulting in full oil press.
I would worry if you were doing say 40mph and press was dropping.

Regards
Mike

 

[Mikesmerc]

Hi Simon
my 72 350sl idles at an oil pres of 2Bar when hot. You will find the longer the spin the hotter the oil temp will get thus dropping oil pressure. Perhaps you bought it in the winter months which kept the oil cooler when driving resulting in a higher oil press. You will notice when you start from cold you will have full press but as the oil heats up and gets the lighter it flows through bearings etc more easily resulting in lack of pressure . My opinion is that your engine is still quiet healthy for its age, I used to own a 200d and when hot it had no oil press. what so ever. Didnt last long but didnt care she was very tired indeed.
1Bar=15psi, 2=30 and 3=45.
When engine revs increase so does the oil pump resulting in full oil press.
I would worry if you were doing say 40mph and press was dropping.

Regards
Mike

 

[mlc]

350 SL oil pressure

I also have a 1972 350SL. The owners handbook states that the oil pressure should never drop below 10 LBs (about 2/3 Bar) at tickover. In practise even on the hottest summer day in the UK and after a hard run I have never gone below around 25 LBs. Remember this car was built for the US west coast, not rainy UK!

Once you are at anything more than a fast tickover I would expect the gauge to go to the maximum, (45 LBs / 3 Bar).

Finally choice of oil is relevant here. I think you should be using a traditional (fairly thick) oil, I use GTX. If you are using a modern thin oil then not only is it unsuitable but the pressure will be too low.

Hope this helps.

Mark.
1972 350SL Manual to play with
Mondeo Ghia X for the real world

 

[Mikesmerc]

How many miles have you on clock Simon (Mark) as I suspect more miles less pressure. My one is pushing a quater of a million hence the slightly low pressure. Will start to worry when she idles in drive at 1 bar, but I suspect I will get another 100k out of her by then .
Regards
Mike