96 Suburban, Low Oil Pressure, Burning a Little

[Jefferino]

Okay so I just got a 1996 Suburban that I didn't know much about the history of, just that it had a blown intake gasket for some time and the previous owners just kept filling with water. I have rebuilt the trans, transfer case, fixed the intake manifold gaskets, water pump, and full major tune-up.

I just took it on a 2800 mile trip (over about 12 days) from DC to the panhandle of Florida stopping in NC and GA on the way. On one of our last days, I left it running and my wife was in the car as I ran into a store to get some supplies/food for our trip home. She ended up coming in with our daughter and when I came back out and started the truck as it was running at idle the oil pressure light came on...I completely freaked!

As I drove it went up and hovered between 25 and 35/40 most of our drive for that day which was roughly 350 miles. When stopped at lights it would drop to between 15/20 unless I put in Neutral and went closer to 20.

I am assuming/saw a couple things,
1) it had 5w30 in it as are the specs and in the hot humid south last week probably could be part of the issue.
2) after driving over 2000 miles it probably was getting a little thin anyways
3) I probably should have 10w30 in it anyways.
4) It could be the sensor since it bounces around quite a bit unless I am on the freeway
5) When under load the pressure seems to drop a little and when I let off the throttle it seems to jump back up sometimes

The question I have is that at 161,000 miles (now after the trip) and it running great, should I put something like a high mileage 10w30 and a bottle of lucas oil treatment in it? I have heard others say 10w40 or even 20w50...I live in DC which can get pretty warm in the summer and I just want this truck to live longer and am HOPING it has nothing to do with the bearings...

Thanks in advance!

 

[addyguy]

If it had a blown IMG 'for some time', chances are the bearings have suffered, sorry to say.

Does it knock/tick/clack?

Try a 10W-30 HM oil and see how it does.

 

[Bgallagher]

+1 one possible bearings.

You could also try replacing the PCV valve and upping to 10w-30 or 40 oil. Might help if it isnt bearing related

 

[CATERHAM]

First welcome to BITOG!

15/20 psi on idle is fine.
Not sure why the OP light came on.

The OP should not vary by load, just rpm (and of course oil temperature). So yes it could be a sensor problem if the OP drops when you step on the gas. The sensor is the first thing I'd check, it doesn't sound like the engine. In the meantime stick with the spec' 5W-30 oil.

I

 

[hemitom]

How much oil did it burn on the trip?
Depending on consumption i would try a high mileage oil in 5w30 or 10 w30 before going to thick.( for no reason.)

 

[SteveSRT8]

No additives are necessary unless you want to clean it.

Just go up a grade each OCI and watch the pressure.

Also note the sending units are notorious for failing, please confirm the pressure with a REAL gauge first. 20 is not too bad at full temp.

 

[Jefferino]

It burned about 1 quart in about 2800 miles. No real ticks knocks or anything that I can hear. It actually runs real smooth which is why I am so confused. The light came on when the pressure was REAL low but like I said it was after sitting idling in 90+ degree heat in a parking lot with the a/c on (for my 2y/o)

The IMG from what I know had been blown but the previous owner NEVER let it overheat, just kept adding water to the radiator. Hoping that the bearings aren't bad yet as I was hoping to keep driving it for a while before dumping more money into it. I love the truck but got it cheap and am trying to not have to pull the motor just yet as we have another baby on the way and trying to save as much $ as possible

 

[Jefferino]

In the past on some of my cars that i used to race I used M1 all the time...with what this engine has been through any thoughts on which HM oil would be good? Just a decent Valvoline, Castrol or Mobil? Not sure if I need to do full synthetic since it has already probably never been used before...

 

[dave1251]

Use the HM 10W-30 no need for the lucas do not buy unless you have a little extra money to spend on nothing. If your oil pressure idiot light does not come on you good to go for a while. If not try 10W-40 or 15W-40. Adjust your viscosity to provide adequate pressure. Put some money back each month to save for a possible engine rebuild because if your Suburban is having problems maintaining oil pressure it could go at anytime. Or you could look back 10 years from now and your SUV still could be running. But I would be saving as much money as possible for possible repairs. Also with a manifold gasket issue that was not fixed for a period of time I would not rule out sludge as the issue for low oil pressure also.

 

[abycat]

Id say first do the easy and obvious. Dont rely on that guage unless it is aftermarket. You can see if it is just the guage by cleaning and checking contacts. You could pick up a new old one at an autowrecker and see if the behavior changes then you know if its the guage or not. MY second choice is what i would do if i owned it and wanted it around for alot longer.

Drop the pan and check if the pickup is loose or not in the right position. If oil pressure changes when you hit the gas you might be rocking the pickup back and forth.

An oil pump is pretty cheap and you already have the pan off so (I) would throw one in, if i wanted to keep it alot longer. And also it is pretty easy to check at least half of the bearings while your in there. That would rule out the other thing that could cause the issue. good luck and welcome!!

 

[JGW]

Originally Posted By: CATERHAM
First welcome to BITOG!

15/20 psi on idle is fine.



+1

 

[Jefferino]

Thanks everyone so far. Just had a couple other questions that I was wondering hoping you could answer that I asked above. Also...is 25-35/40 okay for while driving/accelerating? I just hate that the darn thing bounces all over and that it had that stupid warning light pop on and drop so low when I was just about to head home from my trip.

 

[SteveSRT8]

I run a fleet of GM v8's and have for 40 years.

Your oil pressure is fine. I believe the minimum is 8 and fuel cuts off at 6 on your truck. But you simply cannot trust the factory gauges. Change the sender, it's cheap. Then connect an aftermarket gauge as well to verify if you really have an issue.

 

[morepwr]

35/40 PSI while driving is just fine. Those engine didnt make a lot of oil pressure even when new. 20 at idle is not a problem. If when it really gets hot and drops below 10 at idle to trigger the light, then you probably have a decent amount of wear on the bearings or crankshaft. I would not worry a bunch and just go up to say a 10w-40 oil instead of the 5w-30 and see if that helps.

But like others have said, check it with a real gauge first to see if you are getting accurate reading from the factory sending unit.

 

[rainman49]

Used to have a '95 Suburban that we ended up donating to our church four years ago. It had similar oil pressure with 5w-30. Owner's manual said I could use 15w-40, so that's what I used. The Sub is still running today, ferrying around teenagers in our youth groups.

 

[Brigadier]

Check the sender. It might be physically leaking oil. I had this happen on my 85 Z28 305 V8. Oil pressure suddeenly dropped, no engine noises, and oil usage went up. Had the oil pressure sender changed and all was normal. It was physically leaking oil.

 

[Donald]

Get a mechanical test gauge you can screw in to test, but you may need a tee as I think it will shut down the fuel pump if the electric sender does not do its thing.

I do not think that oil pressure sounds too bad. I was running PP 5W30 in my 93 Suburban 5.7L.

Don't let the tank get empty. The fuel pump likes to croak.

 

[dave1251]

Originally Posted By: Donald
Don't let the tank get empty. The fuel pump likes to croak.


Agreed I bought a used 99 Yukon once. I should of changed the fuel filter as soon as I bought it. Needless to say I had to buy a new filter and pump about 6 weeks later.

 

[ammolab]

Run some of your sump oil off to one of the labs... If your Copper and Lead levels are normal you can be pretty sure that your bearings are in decent shape.

 

[Jefferino]

Originally Posted By: ammolab
Run some of your sump oil off to one of the labs... If your Copper and Lead levels are normal you can be pretty sure that your bearings are in decent shape.


Interesting...can you give me more information on this? I was about to change the oil today after work or tomorrow. I picked up some Valvoline Max Life 10w40 and a Fram ExtraGuard filter.