Low oil Press....maybe???

[DMC3165]

Let me preface this by saying I previously owned a D with a bad engine. It would knock and bang and most noteably wouldn't build oil pressure and the water temp would constantly heat up even with the fans on.In addition it had 3XX,XXX miles on it. Having said that.......

Recently I started noticing that my oil pres seems kind of low. About a month ago I switched over to 15W-40 Delo but the gauge seemed low even before that. I was surprised that even after changing the oil the reading on the gauge had not changed. It would fluctuate a little bit so I assumed the sending unit was going bad. I ordered a new one from DMCH and installed it today. Now it reads even worse!! While running on the highway at normal operating temp at 22-2500 rpm the gauge reads about 55-60 psi. At idle before I changed the sender it would read about 20psi now it reads about 15! I recently put in a new sending unit for the oil light so I know that's working and the light hasn't come on. I also noticed the water temp is normal and when the fans come on the temp goes right back down to about 160. Even with the A/C on the temp always holds at 160.

On that note the motor seems fine. No smoke, has plenty of power (for what it is) and is running quietly with no valve train noise or any other abnormal noise for that matter. I pulled the dipstick the oil is clean and has roughly 800 miles on it right now.

Could it be the gauge in the dash? Could I possibly have an engine problem that is getting ready to rear it's ugly head? Engine only has 50K miles on it. I'd have a hard time believing it's getting ready to go. Outside of that one gauge everything seems perfectly fine. Thoughts??????

:confused:

[DMCMW Dave]

If really in doubt get a screw-in mechanical gauge and measure it.

http://www.amazon.com/Engine-Oil-Pressure-Tester/dp/B002TK7CFK for example.

[Michael]

A correctly calibrated sender unit should read low psi at idle. I often see mine between 10 and 15 at idle and in gear. You should however see approx. 40-50 psi with warm oil at higher rpm. So the question is, what are you showing at road speed?
Edit, just reread the post...I think you are fine as long as your gauge is correct.

[DMC3165]

I'm just curious. What should the oil pres be for our motors at operating temp? (idle and highway 22-2500 rpm) That would be considered up to spec.

[content22207]

3035

Bill Robertson
#5939

[Michael]

Oppps, I was just in my car and looked at my gauge...I thought the oil gauge maxed out at 60psi(going from memory), turns out it maxes out at 80psi, so my estimates of what I was running were low. I'm in the 3/4 neighborhood of 60 psi at road speed/warm oil.

Still I think your readings are correct and ok. With a new/correct pressure sender unit, don't be alarmed to see the pressure fluxuate a lot more with engine speed. I have read more than a few times the original sender unit was mic-calibrated(some soruces say it's completely wrong) and gives much higher readings. On the original cars, it would be perfectly normal to see the gauge pegged with even slight rpm, and sometimes the gauge would just stay pegged as long as the engine was running, so I can see how all of a sudden seeing an accurate reading for the first time would cause alarm.

I personally don't trust the gauges themselves either. I use them to tell me when things are not normal(ie, if my voltage dropped or pressure dropped from what they normally read). For an accurate reading of my actual batt. voltage, or oil pressure, I would not put a lot of stock in them.

[content22207]

... I have read more than a few times the original sender unit was mic-calibrated(some soruces say it's completely wrong) and gives much higher readings. On the original cars, it would be perfectly normal to see the gauge pegged with even slight rpm, and sometimes the gauge would just stay pegged as long as the engine was running....

None of the professional reviewers (Car & Driver, Road & Track, Motor Trend, etc) mentioned that. In fact, instrumentation is one of the few things nearly all reviewers agreed upon as excellent.

If your oil pressure gauge is pegged up, that means the terminal has fallen off the sending unit, or wiring between it and the gauge is broken.

Bill Robertson
#5939

[Bitsyncmaster]

If your holding 160 deg on water temp than you may just have a voltage or ground issue on your instrument cluster.

Your still reading safe oil pressure so not to worry. Now if your oil light comes on and you read low pressure on the gauge then is the time to worry.

Try cleaning your fuses first.

[Jonathan]

Oppps, I was just in my car and looked at my gauge...I thought the oil gauge maxed out at 60psi(going from memory), turns out it maxes out at 80psi, so my estimates of what I was running were low. I'm in the 3/4 neighborhood of 60 psi at road speed/warm oil.

Same here. Mine hovers around the 1st mark at low RPM's and around the 3rd mark at highway speeds. If it's equal spacing on the scale, call it ~20 psi and ~60 psi. Which if looking at Bill's Volvo document (thanks for posting that Bill :)), is right about that 57 psi.

Another ODOC member posted recently about his low oil pressure situation with sort of the same concerns. Seems like a good candidate for someone to draft a good summary up and send out to everyone...

[DMC3165]

Based on bill's chart (thank you also for posting) I think its perfectly fine. Based on the minimum of 14.2 psi at 900 rpm and 57 psi at 3000, my readings are slightly higher then those by 3-5 psi. But I doubt the gauge is that exact.

I wonder why it was reading so much higher before?

[Michael]

None of the professional reviewers (Car & Driver, Road & Track, Motor Trend, etc) mentioned that. In fact, instrumentation is one of the few things nearly all reviewers agreed upon as excellent.

If your oil pressure gauge is pegged up, that means the terminal has fallen off the sending unit, or wiring between it and the gauge is broken.

Bill Robertson
#5939

Here is one of the posts I found on DMC News, I know there are others that say the same thing, only different reasons(wrong sender from Volvo, etc.). Like most things on the web, I take it with a grain of salt.


You cannot trust the reading of a DeLorean oil guage unless you have
replaced the sending unit with a proper calibrated unit or had the
OEM unit "cleaned". The OEM senders never had the correct resistence
because of a coating on the contact arm inside the unit. The OEM
units read too high 99 percent of the time.

Here is another from DML:

Erratic readings of the oil pressure gauge is common due to an
incompatibility problem between the factory installed sending unit and the
gauge.

[DMC3165]

Really not sure if I have a brewing problem or not. I'm calling Grady Tomorrow and will have him check it out just to be sure.

Does anyone know if oil pumps can go bad? Or could it have something to do with the fact that its 95 degrees outside? I'm honestly just not sure about this.

[content22207]

Oil pumps do wear out, but that's usually a high mileage thing (the pump is as rudimentary as can be -- two intermeshing gears)

Are you using multi viscosity oil with a low base weight (the first number). As the polymers that make it behave like thicker oil break apart, the oil becomes more & more of the base weight only. Motorcyclists have particular problems with this (their motor oil also circulates through their transmissions), but any shear force -- such as cam shafts against valve tappets -- will break the polymers apart. Remember that the higher viscosity number is a multiple of the lower viscosity number: 10W40 oil has nearly twice as many polymers as 20W50 oil.

The other thing to remember is oil pressure is created by restrictions at the far end of the flow (cam shafts and main bearings). If a mechanical oil gauge confirms low pressure, it is possible you have spun a main bearing.

Bill Robertson
#5939

[DMC3165]

I'm currently running 15w-40 Delo oil. I honestly don't think I spun a bearing or anything like that, but I won't rule anything out just yet. While I'm not sure if I have a problem or not it concerns me enough to make a phone call and get it looked at by someone who knows more then I do.

[DMC3165]

Just one other thing I'd like to add to this. I started noticing a drop on the gauge around the same time I was experimenting with zddp plus. Could that have an adverse effect on the engine in anyway?

[David T]

The additive could have affected the viscosity. My first thing would be to dump that oil, change the filter and then using a mechanical gauge, check the oil pressure.
David Teitelbaum

[content22207]

Why not just buy or borrow another sending unit first.

Bill Robertson
#5939

[DMC3165]

The additive could have affected the viscosity. My first thing would be to dump that oil, change the filter and then using a mechanical gauge, check the oil pressure.
David Teitelbaum

It was on the previous oil change that I used zddp and it wasn't in there very long. Maybe 2 months and roughly 1000 miles. The current oil is straight 15w-40. I was curious if that stuff could possibly damaged something in the engine.


Why not just buy or borrow another sending unit first.

Bill Robertson
#5939

The sender is new. I ordered a new one and replaced it Saturday and after that the dash gauge just looked worse at times. But not all the time which is why I'm not entirely sure I have a problem or not.

I'm just trying to cover all my bases before I bring it to Gradys.

[David T]

General Rule-Of-Thumb for oil pressure is a minimum of 10 psi at idle in a hot engine and 10 psi for every additional 1,000 RPM. Always try to consult the engine specs for manufacturer's recommendations. Even though the oil and the additive wasn't in there very long the additive may have altered the viscosity adversely. No way to properly check it so the easiest thing to do is to just replace it. You have to do the filter too because if you don't, a lot of the old oil will remain to contaminate the fresh stuff. The reason you have to check with a mechanical pressure gauge is there are too many things that can affect the accuracy of the electric gauge. If there is ANY doubt about the pressure, the mechanical gauge is the only accurate way to check it. These are things you can do before you take it to anyone because these are the things they will do to rule out any problems. Very rare to have an internal problem unless the car was seriously overheated or run low on oil. If you do have internal damage it probably isn't the pump anyway!
David Teitelbaum

[DMC3165]

So my paranoia brought me to Grady's today. Rob checked the motor and said it's perfectly fine and running very well. So what's up with the gauge?

Well I ordered the new sending unit because it would occasionally read low while driving down the highway at highway RPM's (2500). Sometimes it would read about 60 sometimes would read a hair over 40 but never less then 20 at idle. With the NEW DMCH sending unit it would read worse at idle but the same while driving.Which would make me freak :nervous:

As it turned out the needle in the oil pres gauge would occasionally "stick" on it's way up not going past 45 psi. So Rob replaced the gauge and now 60 psi @ 3000 rpm every time. But the low idle still didn't look quite right. It was now below 20 psi with a warm engine at idle. Roughly halfway between 0-20. What i didn't realize is with the A/C on the idle was down closer to 650 RPM's. When I shut the A/C off the idle would pick up to about 800 RPM's and the oil pres gauge would move up accordingly. It would now read just at or below the 20 psi mark which is exactly where it should be (roughly 15 psi at around 900 rpm's). He did also confirm that some of the factory units did read slightly higher then what the oil pressure actually was.

So I guess I now have a hyper accurate oil pres reading (just kidding). But it does read very well and I'm glad I brought it to him.

I thought this could serve as a cautionary tale to anyone else that may be having trouble with oil pres readings. It could just be as simple as a 30 year old gauge that's sticking.

One footnote: while I was there I treated myself to a new "used" binnacle and lens. For me it was a rather bright spot and a nice diversion in what's otherwise been a pretty rough month. just thought I'd mention it.

:smile: