Hey guys !

I had a quick survey for you - what does your oil pressure range from in an L98 with higher miles?

So my 87 has almost 209,000 original miles. Before I sold it at 186,000 it held about 25-30 at idle (600 rpm) and in the 50's while cruising. Now that I have it back, once it gets hot in traffic (oil temp 215-ish) at idle it's dipping into the mid teens, 14 being the lowest I've seen it hit. It makes me nervous. Cruising it holds low to mid 40's, sometimes creeping up into the low 50's as it fluctuates...but it does now have a steep 3.75 rear so it's turning about 2200 at 65. This is also the original oil pressure sender.

I know it's got a bajillion miles on it but I am just making sure this is still a safe range. I understand it's showing age, and it certainly should be, but just curious what other folks experience. I am probably too **** but it is my baby after all. :o

Thanks!!

 

Mine is 45 at a cruise around 1700-2000 RPM warmed up. 110000 miles and it has never read any different then that. I can't remember the exact readings cold, they are higher though. I just had a track event and it was 45 at high RPM as well. Mine does not fluctuate at cruise.

 

Spec is 45-60psi anytime your foot is on the gas. You must have 10psi for every 1000 rpm. At idle, it can get down to half of that. 20s-30s is normal.

Mine runs about 65 when cold, averages about 55-60 on hwy cruise. 40s cold idle, 20s hot idle, and sometimes lower if its very hot down here and the engine is hot.

Nothing to be overly alarmed about, it just shows you that the engine is gettin old.

 

Interesting, so yours does not fluctuate? Is it supposed to or not? I watch mine constantly (obssess much?).... Could that signal a problem? I think mine always has to some degree (I bought it at 74k miles), but it can go from 38 to 50 over the course of a minute, but usually hovers between 40 and 45, changing almost constantly. Is there something wrong with the sender? The motor makes no noises and seems solid as a rock.

Sorry, I am just really crazy about this silly car.

Edited to say: Vader, yes, I think it should definitely be showing age and I guess that's just what it is. I suppose that's actually honestly pretty good for the miles and 20 years. My goal is now to see how long it will go.

 

It is possible for the sender to be bad, yes. As could be the connector on the sending unit.

 

It is generally accepted that 10psi per 1000 rpm is normal.
If you are concerned about the internal health of the motor, cut open and inspect the oil filter. Look closely for copper bearing material.

You can also send out an oil specimen and have it analyzed. The cost is minimal, but it really helps to do a comparison from earlier in the life of the engine.

 

Thanks for the responses; my hubby says "It's fine, shut up" But I treat it like a child so I just have to be insane about its welfare.

So it shouldn't fluctuate? Should it be pretty constant?

At 200,000 miles I would expect it to show at least some signs of age. It seems rock solid and so that is truly the only indication. The guy who had it when I sold it did a compression test and said it was remarkably high and did not signal any need for rebuild. That wasn't but about 15,000 miles ago really. We'll see how far it'll go, or at least until I have the funds and time to rebuild like I want.

 

No, it should fluctuate as the RPM's vary.

Being lower at idle compared to cruising down the interstate is normal.

 

I do understand that acutally, but should the pressure fluctuate as you maintain a constant speed? Mine does. Is the sender fibbing?

Is putting a heavier oil in to try and amp up the pressure something you should do, or just accept it's getting old and rebuild once it gets dangerously low? Right now it sounds like it's just fine, just showing age.

 

[QUOTE=VetteBabe1;1562328593]Thanks for the responses; my hubby says "It's fine, shut up" But I treat it like a child so I just have to be insane about its welfare.
[/QUOTE
It is not bad for an oldie. If you put in 20-50 it will probably go up some. If you are really worried, its not that hard to drop the pan and replace the bearings. it can be done in an afternoon.

 

Thanks Spanky !

It probably really is fine now considering what others have said. Honestly it's probably pretty darn good considering it's been raced a little, sprayed, etc. I was always particular about it so I guess it shows.

If it comes apart, it's getting a major overhaul.

 

what weight oil do you run?i would think there would be some looser clearances at 200k.
i would consider some 15w40(diesel oil).it would give you more low rpm pressure without stressing the oil pump to death(exaggeration)with 20w50.

 

I would replace the sender and start running some STP in the oil. Be nice to her and get another 100,000 miles out of it.

 

The fluctuations in readings while cruising might be due to a bad sending unit. On my daily driver (Jeep Cherokee) I had the same issue and the culprit was the sending unit. Pressure varies with RPM but when you are cruising down the freeway at a more or less constant speed (RPM) the pressure should remain about the same. Of course on the Jeep the unit was super easy to get to. On the C4 it looks like you may need to remove the distributor cap (just the cap) or perhaps the wiper motor to get access to it for replacement (at least on a 1988 model year it looks like that would be the case; someone correct me if I'm wrong; I have not had to do this on my C4).

In my opinion it is worth it to have a good sending unit so that the oil pressure gauge reads correctly; like temperature, oil pressure is one of those things to keep an eye on. Better to be safe.

Cheers and keep her going ... 300K miles is the next "mile"-stone, right ..

 

Yep! 300k would be great, but I'm afraid now that I live much closer to work that it would take so long to get there!

 

On my stock 89 with 85k miles, I went from 5w30 synthetic only to 10w30 synthetic & a can of Lucas synthetic oil treatment and it upped my hot idle pressure about 5 lbs.

It is 45-50 when first starting up to as low as 16 on a hot summer day fully warmed up stuck in traffic. Mine also fluctuates a bit when driving at a constant speed.

 

Your oil pressure sounds a little on the low side but not bad for it's miles. As long as it runs OK I wouldn't worry about it. I wouldn't start running heavier weight oil in an older engine. Stick with the Mobil 1 synthetic that the car was designed for and you will probably get to 300,000.

 

VetteBabe1,

What oil is in it (synthetic/dino? 5w30/10/30? Brand?)?

How many miles on this oil change?

What oil filter?

Is the oil & filter being used now same as when previously owned?

If dino, there have been some problems with some oils (e.g. Castrol GTX) which might explain the difference.

Given your location (NC), if using 5w could use 10w (probably year round) with no negative impact and a slight increase in pressure to account for engine age (see your owner's manual, it should say this is ok).

Oil filters can affect oil pressure. Better filters (e.g. Mobil-1) will actually lower the pressure, while crappy filters (e.g. Fram Orange) will increase the pressure.

Since the oil pressure IS NOT steady based on a steady RPM, given the minimal cost of a sendor, I'd replace it.

FYI, senders do fail/leak, so if it is flucuating, it could be a sign that the sender's internal seal between oil and electrical contacts has started to fail, so it might start to leak (case in point, I changed oil/filter on an 85 Lincoln towncar just 5 weeks ago -- no leak -- 2 weeks later, I had to replace the oil pressure sender, it was leaking quite badly).

Not to be an alarmist, but worse case scenario is if the sender totally fails, it could allow all the oil to pump out of the engine and destroy the engine in just a few short minutes.

 

I have 185K and my OP is about 25-35 when oil temp is above 200 at idle and about 55-65 when on the gas.

Add: That is with 10-40 syn blend.

 

I am running 5w30 Mobil 1 synthetic and always have, and a Mobil filter, and oil is about 2000 miles old.

As some of you know I sold the car with 186k miles, and it had better pressure then. I got it back at 205k and the pressure was noticeably lower...I am wondering if the guy hot dogged it a lot (as I didn't) or didn't take care of it as well....or if it's just plain getting old. I shouldn't complain - if it died tomorrow it's had a good life for sure. I think it's fine but just showing the age.