[Von (Von)]

For the first 500 miles I ran 15W-50 oil for the break in. then I went to 10-30 for the cooler months over here. Right after I changed oil I noticed a sharp decrease in my oil pressure. It is on the last hash mark just above the "L". Before I changed oil it was reading well over 3/4 of the way on the gauge. I am concerned. any suggestions?

[Daver (Daver)]

Your oil is too thin. These old engines like something around the 30W-40W mark. That is what they were designed to use.

[Von (Von)]

Dave, what weight and type of oil do you use?

[Dave R (Roppa440)]

Before I had it re-built I used a normal multigrade around the 10w-30w mark. But on very hot days the pressure could suddenly drop like a stone. After switching off and leaving it to cool for a little while I could start it and carry on OK and pressure would be fine as long as I took it easy and avoided going up mountains or something.

I ended up getting a single grade 30w which worked really well. Then I started using a 20w-40w or 20w-50w in hot weather.

With the re-build and tighter bearing tolerances I now use a 15w-30w. Or is it 10w-30w? I can't remember but I will recognise the bottle when I see it again!!

Basicly the tighter your engine the thinner the oil you use.

Modern engines are built to a much tighter spec which is why most oils these days are so thin. But our old engines were built a bit sloppy so they need a heavier oil.

Here is the recomended oil weights from the 1970 manual;

Above freezing use a 20w-40w or 10w-40w. Or use a single grade SAE 30w.

Where temp occasionally dips as low as -10F (brass monkeys looking worried) use a 10w-30w or 10w-40w.

Between +32F (freezing) and -10F (bloody freezing) use a SAE 10W or 5w-30w or 5w-20w

Your oil should be ok if it has just been re-built but was it built to a tight spec or the standard spec?

As the pressure dropped with just that change and was alright before it is telling you it prefered the heavier oil. So just give it what it wants and it will be fine.

[Henry (Henry)]

By Ron Morgan (Cartman) on Monday, June 17, 2002 - 07:46 pm:


ive had the same probs with my 383.
the pressure was im sure around 30-40
but put in a 15w 30w i think,and the pressure has dropped to 10,at 2000rpm-15-20 at 4000,has any one any suggestions as to what to use,and is it best to drain the oil and start again..what is the correct pressures it should roughly be at..
and what is a safe pressure to run at and when to stop using!!
cheers,rgds ron

By Hans (72challenger) on Tuesday, June 18, 2002 - 07:26 pm:


My 340 runs 25psi@900rpm (idle) and about 50-55@3000rpm. I have always heard and listen to the next quote: "for every 1000rpm you need a pressure of 10(00rpm) + 10psi". So 20 for 1000, 30 for 2000, 40 for 3000 and so on. And till now I never noticed anything 'bout my engine. (at least nothing that had to do with oil/pressure)

[Ron Morgan (Cartman)]

just changed my oil and filter,putting in kendal 20-40w,gt1.
oil pressure gone strait up to 25 on tickover,and goes up when higher rpm.
problem solved.
the filter used is PUROLATOR PREMIUM PLUS 30001.