Oil Pressure.

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May 1, 2009
I'm new here...so be patient.

1st dumb question.....I've just had the bottom end of my motor re-built,and the oil put in the car was Castrol 20W50 GTX.I'm not entirely happy with the indicated oil pressure.

I have some 20W50 AMSOIL. Can I use it,and will it increase / decrease oil pressure,or make no difference.

What oil did the engine call for? When you say not happy with pressure, what exactly do you mean?

Doubt you'll see much pressure difference in changing brands unless you go from dino to synthetic in which case the pressure "might" drop slightly with the synthetic.
The oil pressure guage has markings at 0,25,50,75,100 lbs pressure I suppose.

When cold,the needle rests at about 75.After about 30 minutes of running,half at highway speed,the needle rests at 50.

The first stop,after getting off the highway,the needle will go below 25,but rises as soon as you start to accelerate.

If you turn off the motor for about 20 minutes,on re-start the needle will rise to about 75 on acceleration.

The oil called for is 20W50.

Normal ?
Normal for what engine?

I don't know about the numbers, but everything you describe is normal. Hot idle should have the lowest pressure. Cold high-rpm should be the highest. Changing oil won't change much.
It would help to know the vehicle and engine.

25psi at idle is not abnormal. Running another 20W50 will make no noticeable difference in pressure.
75 psi cold, 50 psi hot at road speed, 25 psi hot at idle. These are very good pressure numbers. Sounds very normal and right.
Thanks for all your responses...I'm feeling a little more comfortable now.
Last night,I went to a scheduled appointment with the garage for an oil change,and a slight carb leaning.
On the way home after the service,I took the scenic route,never exceeding 50 mph.It's about a 30 mile drive,and the oil pressure never went below about 60 !!

Go figure
I had a '70 MGB with 125K, non-rebuilt miles on it (one valve job, but no lower end work) and it ran 18psi at hot idle with 20W50 and about 50 psi at cruising speed. Was running like a top when I wrecked it and the engine went into another guy's BGT and it ran at least a coupla years after that until I lost touch with it.
20-50 on a new bottom end, i dont think so. drop it out and put something like 5-30 in. i would make sure to use the oil reccomended by manufacturer. but that is way to thick of oil for a new bottom end. the oil has troubles making it to the bearings quickly
you got to remeber the viscosity specs for oil back then do not transfer to the same weight of oils today.

It hasn't changed except for some minor tweaking of the 20W part. For all practical purposes, it hasn't changed.
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