Feelin' the Pressure of Low Oil Pressure!

What brand and grade/weight of oil are you using?

A number of us guys are running an oil which gets low-ish on the oil pressure on hotter days.

 

Is this a new problem or has the car always run pressures this low?
What oil are you using?
How many miles on the car?
Has anything recently been done that would impact oil pressure?

308's have a pressure adjustment at the oil pump, but I would not monkey with it unless there is no internal engine factors appearent. If all is well inside the lump, you can screw in the pump adjustment to increase pressure or in some cases shim the pressure relief spring.

DO NOT do this to cover up something sinister like worn main or rod bearings. You will certainly pay dearly if you do.

Good luck and welcome aboard,

John

 

Hi...........

Zero oil pressure is very bad news !!!

Could be a bad pressure relief valve or simply a bad gauge. Have the pressure checked by a mechanic ASAP.

Good luck !!

Frank......23005
www.masiarz.net/bb_resource

 

20W50 should rule out light oil. Frank above is correct in stating it could very well be the guage or sending unit. They are know to be, uhh, well, crap..

Check the pressure with a mechanical guage and compare to what your guage is reading. At least then you could rule out the guage or sender.

John

 

Could be the oil pressure sending unit. Need to get a oil pressure gage on the block to check to see if it is the engine or sensor.

 

Since you just got the car I guess you are not absolutely sure what it has for oil or when it was last changed. I'd start there first.

And it should actually be overfull when cold. The filter drains down. You want to warm the car up, shut it off and check it within a few minutes. It holds 9 quarts.

 

Good point, read the manual on how to check the oil. For a 78, you need to warm it up good, shut down, and wait a couple minutes....I believe the manual states to check after 15 minutes for the most accurate reading. Do not read when cold...it will (should) read over max.

 

Well, the cold pressure is good & you wouldn't want it much higher - but that may be a product of the oil you are using which would be quite thick when cold I think.

The warm pressure is maybe a bit low & I'd be more concerned about the 42 rather than the zero. Lots of 'em register pretty close to zero at warm idle.

As has been suggested, maybe start by replacing the sender and checking all the connections to the guage.

I

 

I have a '78 and mine reads very low when hot as well.

 

As has been said, the senders are guilty of poor signals as they "wear". Mechanical gauge or replace or both.
Philip

 

I have had simular prob. remember a rule of thumb I learned here. 10 lbs for every 1k revs. I was on the borderline until I ran Valvoline Racing 60 weight. I don't think anyone else here will approve but my pressure is fine now. Watch your temp, oil temp that is. when mine gets around 210 is when I have problems. Usually going from intown to freeway even on a hot day will lower my oil temp 40 degrees and increase oil pressure by 10 lbs.

Another note is that the gauge is 20+ years old what can we expect!

I spent 53 bucks on an oil sender with no noticable difference after. However it is a very small investment to eliminate possibilities. I find that if I wait over ten minutes to check oil on a hot day it has already emptied the extra oil from cooler and filter and reads over full. I just change regularly and use 8.5 quarts then add the other pint in a couple hundred miles.

 

a) Change the oil and filter if you don't know when it was last done, and see if that fixes the problem.

b) By a mechanical gauge out of AutoZone or whatever for $15 and stick it on. The hardest part of this bit is finding a crossover that will take the male part of the mechanical gauge and allow you to screw that into the female bit on the engine.

I did this on my 355 and found the gauge in the car to be low by ~ 25 psi. My problem was a bad earth .. easily cured.

Regards,


Pete

 

My Lotus is similar. 80 lbs when revved cold (I use 20W50 as well) and when warm at revs goes to about 45, but maybe 15 at idle. Maybe less! This is normal. If your gauge drops to zero at idle, I'd not panic and suspect the gauge, but get it checked with an external pressure gauge. It will not cost much to do this and you'll either save your engine, or sleep a lot better at night.

Ken

 

As usual the advice here is right on. I can tell you that it actually sounds pretty normal. My car does the same thing, high when cold and will drop very low when idling warm. You said the light doesn't come on though when it drops low, correct? The light does come on when the ignition is on but the cars not running correct?

I also agree that it sounds like you are a little low on volume. It should read above full when stone cold. The best advice is to change it, be sure the correct amount is added and then (this is only my opinion, not per the manual!!) note where the level is when cold and full. It is easier (again only my opinion!!) to check the oil this way. My start up ritual is to check the oil before starting, add any if neccessary, THEN start the car.

The only way to do it properly per the manual is to check it after you park it.

 

I totally understand how anxious low oil pressure can make you feel, and I'm not suggesting that the figures you report are not worth investigating and possibly may need some rectifying, but its worth noting that oil pressure is not what lubricates and cools the engine, its oil flow. and as the oil warms up and becomes thinner you require less pressure to get adequate flow. Its worth bearing this in mind and noting at what oil temperatures the various pressures are associated with. you may have a problem with cooling, does your car have the adjustable flap for the oil cooler?

AEHaas is acknoledged as the expert on oil on this forum and has a very good in depth explanation on this website : http://63.240.161.99/motoroil/ its definately worth reading and can help destroy some of the myths that suround oil.

Cheers for now
Scotty

 

Great post Mr. Iceman! Thanks for the link.

I had a similar concern about my '88 328 and reading this post and previous ones about this subject really helped me understand what is normal for pressure readings.

I've only had my car for a few weeks (just about to change my oil for the first time) and I recently took notice how my oil pressure drops to slightly below 42 lbs during idling. Once I rev it up and get it in gear it goes back to 85 lbs, but I had the same questions as Dano about it being too low.

The prevous owner used 50 weight oil but I'm going to use Mobil 1 10W-40 and see how that works out.