72Blazerod

I have 1972 Cutlass with a 350 Rocket that I purchased about a year ago and it has recently developed a problem with the oil pressure idiot light. It seemed to come on gradually. For the past month whenever I would start the car the oil pressure light would come on, but after I stabbed the gas pedal a few times it would go off and all would be fine. I checked the oil level and it was just about at full (over 3/4 full). Today I took it out for a drive, the idiot light came on when I started it, but went off after a minute of two after I revved the engine a bit. But when I was a couple of miles from home the oil idiot light came on and stayed on. When I would slow down to almost a stop, or actually did stop, the light stayed on but when I accelerated away from the stop the light went out for a while only to come back on when I got to cruising speed.

I took at look at the oil pressure sensor (found where it was from a picture on this site - thanks) and it looks pretty new. I am wondering where I should start to try to find a solution to this problem? Is there any way to figure out if there is a problem with the sensor, or could the problem be something in the engine itself? If so, what could it be in the engine? Any suggestions are appreciated.

Thanks

Allan R

Well if the dipstick shows oil is ok, then it's the electrical component. That wire that goes from the sender is pretty much a straight run to the light on the dash. I'd be inclined to pull the sender and replace it regardless of how new it looks. Chances are you're seeing the start of the sender failure. New senders are easy to get and cheap. AC Delco at O'Reilly's is less than 11.00. Rock Auto has them for around 8.00 but by the time you add in shipping, cheaper to buy locally.

BeenThere

Sounds like the previous owner had the same problem and installed a new sender. When the problem didn't go away, he probably filled the crankcase with straight 40 or 50 weight oil. Sounds like your engine is just getting worn out. They don't last forever.

Sampson

I would hook a manual gauge to the port where the sender is located to check the oil pressure. What weight oil are you running? Any visible signs of sludge in the engine?

oldcutlass

X2 on the mechanical gauge.

MDchanic

x3. Check with a manual gauge and get actual pressures and tell us what weight oil you have in there.

If your pressure is truly low, and you are not running something like 5W20, then it sounds like you have a rebuild in your future.

- Eric

72Blazerod

Hi Guys,

I am running 10w30 in there right now. When I changed the oil in May it seemed fine, not sludgey. The oil is very clean right now but it only has a couple hundred miles on it. Where do I get a manual gauge to test this with?

Thanks

RandyS

Every Auto Parts store carries Oil Pressure Gauges.

D. Yaros

"Experience is something you don't get until just after you need it."

Or to phrase it another way:

- Experience is what you get from not having it when you need it.

Redog

I say too get teh mech gauge and hook it up and see what the oil pressure is before you go any futher

garys 68&72

Yeah, those sensors come on below about 5psi and don't fail too often. Buy a gauge, hook it up. If it's correct you have a complete rebuild in the near future.
Btw, driving the car with low oil pressure can turn a rebuildable motor into a pile of scrap really quick.

Sampson

How many miles on a the engine? If your oil pressure is truly low it could be the strainer is stopped up on the oil pick up. These cars had plastic teeth on the timing chain. They typically came apart and got chewed up and stayed in the oil pan. In worst case scenarios they ended up in the oil strainer and could restrict oil flow. Take your time in diagnosing this. Hopefully it is just your sending unit.

Koda

Remember, the dipstick does NOT show the "engine has oil." It shows "there is oil for the oil pump to pick up in the pan." Whether or not the oil pump works, or is obstructed, or anything else, is a whole other story.

J-(Chicago)

Also note that cold oil pressure doesn't mean much when you start reading the gauge. It might show 40 or 50 psi idling in park, but that number becomes irrelevant once the oil is up to temperature and it is in gear with a load on the engine.

72Blazerod

Ok, I have the mechanical gauge and I am going to hook it up. What sorts of oil pressure readings should I be looking for? At Start up? After warm up? How long should I run the engine? (I don't want to run it long if the oil pressure is actually low). Thanks for your input.

redoldsman

Even on an old engine you should have at lease 30 psi at operating speed. At idle it may drop down to 15-20 psi. Sampson had the same thought I had in that the screen may be full of plastic from an old timing gear. If you are really are having an oil pressure problem and that was the case, replacing the pump and screen could fix it. Do you know how many miles are on the engine?

FMB42

That engine, in good shape, should have 35-45 psi oil pressure (according to my Motors service manual). And, like redoldsman, etc say, it should have no less than 30 psi at operating speeds while fully warmed up. I'd drop that oil out into a very clean pan and take a close look at it. You can pour a bit into a glass jar and then look through it at a light for a better view. While you're at it I'd recommend that you change over to a good 10w-40 or even 20w-50 while you're diagnosing this issue. Be sure to keep an ear out for any knocking and the like (leave the windows cracked and the radio off while you're test driving it). If the prob persists than you'll, of course, need to drop the pan.

oldcutlass

It could be as low as 7.5 lbs at idle warm, maybe 25-30 cruising if it has hi mileage.

z11375ss

How many miles are on the engine? This was asked but never answered. This is a good indicator of what is going on.

72Blazerod

The engine has 133,000 miles on it. At least that's what I'm seeing from the odometer.

lemoldsnut

The most expensive gauges I ever bought was this past summer. My 67 had an idiot light. I put gauges on it to be safe. Found out that at an idle warm I had very little oil pressure. Like 4-5 psi. I was hoping it was an oil restrictor that moved or was causing an issue. We pulled the motor to inspect. The bearings were badly worn and we had to build a new motor. But, I am thankful I did not spin a bearing or worse.

Mechanical gauges are a must.

Yes I had to pay to build an engine. But, it did not leave me stranded somewhere and we now have some security in knowing what we have. That engine only had 30k on it.. I am no longer ever going to use oil restrictors on a street engine.

Larry

72Blazerod

Okay, these are the numbers after the test drive. While driving it around town it averaged around 32 psi. When I stopped for a stop sign it would drop down to about 18-20 psi. When I would open up all four barrels, the oil pressure would go up to around 40 psi. The lowest the oil pressure went was after 30 mins. of driving, when I was coasting it into my garage - it went down to about 12-15 psi. There were never any strange noises and all went well. So I am thinking that it was probably the sensor that was the problem.

OR

I am wondering if it may be a wiring problem. My "Generator" light comes on and stays on until I rev the engine (in Park) a couple times, then it goes off and stays off. I just put a brand new alternator in it last summer so I know its charging. It is funny that both idiot light are sending me false readings. Any suggestions?

Thanks for your help!!

oldcutlass

I deleted your other post since we are already discussing it here. 2 separate lights looking for separate signals. The alternator is a completely separate issue. You have a bad oil sender, you might consider using the mechanical gauge permanently. Your oil pressure readings are normal for your engine.

Why did you change your alternator a year ago. Is it a stock unit or a 1 wire?

lemoldsnut

I agree your readings for oil pressure are fine. As for the alternator some have to be spun up to 1500 rpm's to excite them to start charging.

redoldsman

lemoldsnut, I have to politely disagree with your comment about the alternator. I can remember when alternators came into common use around 62 or 63, they were supposed to charge at idle unlike the old generators where the idiot light would come on at idle when you were at a stoplight. I have a one wire alternator on my 54 and a voltage gauge under the dash. It will show almost 14 volts at idle.

64Rocket

I've seen when you buy an alt you need to get the matching external regulator.


Gene

redoldsman

How do you match an alternator to a regulator? I have never heard that but then there is lots of stuff I have never heard of.

64Rocket

If you buy a alt they list a corresponding regulator.

Gene

oldcutlass

This is a problem that 1 wire alternators generally have, no excitation until it goes over a certain rpm upon starting the car.

garys 68&72

You must have been good this year, Santa gave you a pretty good present, a good engine. Those pressures are fine.
As for the alternator, you'll need a voltmeter and a description of the alternator to figure that out (1 vs 3 wire, internal vs external regulator).

rocketraider

What is your idle speed? Too low can cause both borderline oil pressure and alternator not charging.

Rule of thumb: 10 psi for every 1000 rpm of engine speed.

halfmoontrail

It's just me and I guess my risk, but my '68 has a '75 350 in it, at idle warm it is often down around 5 psi on the mechanical gauge. I've put thousands of miles on her with this condition.
Steve

EightballZ

would you guys say that a break-in additive has an effect on the oil pressure readings?

oldcutlass

It may have a small effect but not much, it depends on the viscosity of the break in additive. It may raise or lower oil pressure a small amount accordingly.

rustyroger

I think you have no oil pressure issues, but a bad sender. I agree with installing a mechanical gauge, but I recommend keeping the idiot light. you should spot a light as soon as it comes on, you may not notice the gauge has gone to zero until it's too late.
I don't think it a good idea to use a higher viscosity oil than the manufacturers recommendation, Oil needs to get round the engine asap after startup, all else being equal thin oil does this quicker than thicker ones.

Roger.

Octania

I was taught that DC generators vary voltage with RPM, thus the low output at idle speed and the use of a regulator to limit voltage above the minimum useful speed.

As opposed to Alternators, which vary AMPERAGE with RPM, whereas they produce all the voltage they can right from idle.

redoldsman

I agree with rustyroger in ths it is a good idea to keep this light with the gauge, All it takes is a tee at the sender unit. If the light comes on, you will glance at the gauge quickly. With the gauge under the dash, you are not constantly watching it.