Oil Pressure Specs

Oil Pressure Specs

Postby AveryStella [OP] » December 20th 2020, 12:52am

I have a 1993 Chevy Astro with a Tiger Provan camper build. My 4.3l has the CPI injection (VIN W), and it has about 80,000 miles on it. I bought it at 70,000 miles and I do not know about it's maintenance history. It did have some lifter tick on and off which cleared after running Rislone and switching to 15w-40.
I'm having trouble finding a definitive set of oil pressure specs and found some conflicting information across years between what's written in the Haynes manual and other sources. I'm concerned about low oil pressure.
I hooked up a mechanical gauge and found the following topped off on 15w-40 with a quality oil filter. Unfortunately I don't have a tach with which to measure my RPM.

Cold at Startup
30 psi at idle, no more than 40 psi when revving the engine high with no load in park.

Hot
7 psi at idle in park, 6 psi idle in drive
35 psi while accelerating onto highway onramps
25 psi while driving 55 mph on flat highway in OD
32 psi while driving 65 mph of flat highway in OD

If these values are too low, I know that possible culprits could be
1) Bad o-ring on oil pickup tube
2) Clogged screen on oil pickup
3) Bad oil pump
4) Worn main bearings or other worn engine components
5) Other culprit?

Should I be worried? Thanks in advance!
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Re: Oil Pressure Specs

Postby Mmusicman » December 20th 2020, 1:15am

AveryStella wrote:Should I be worried?

Sorry to say... Maybe...

Mine idles at about 35-40psi (hot) and about 50-60psi cruising speeds (hot)
(naturally, cold pressures are even higher)
My engine has over 240K and my oil pump is stock original.

People will tell you it's ok to have lower oil pressures.
Your's however, seem quite low.

It's also concerning that you would have lifter tick at only 80K.

I know that possible culprits could be
1) Bad o-ring on oil pickup tube
2) Clogged screen on oil pickup
3) Bad oil pump
4) Worn main bearings or other worn engine components
5) Other culprit?

Sorry to say.. I'd be less inclined to believe the trouble is #1, #2, or #3... and unfortunately be more inclined to #4 worn parts (due to some possible neglect).
But there is a chance it could be these too.

Yes.. run some cleaners, but quickly flush too.
Heavier viscosity oils will improve oil pressure on a "loose" engine.
15w-40 should be good.
Be sure to replace oil AND filter after cleaning too (filter may be clogged after cleaning).

Some people have reported higher pressures doing the "oil cooler delete"... mine was unaffected, but was already good.

The fact you have high pressure cold and it drops significantly hot, sort of tells me you may more likely have clearance issues, and not necessarily pump issues, since it is actually capable of producing some pressure. But clearance issues (wear) can affect the gear in the pump, as well as bearings (and other parts).

If you should ever decide to pull the pan and replace the oil pump.. I strongly recommend a "high volume" pump.
I've used them for decades without issue, and always have good flow and pressure.
It won't "fix" a worn engine.. but it will help deal with it.

Of course, there's always a chance the oil sender could be bad too.

Good luck
Last edited by Mmusicman on December 20th 2020, 2:19am, edited 1 time in total.
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Re: Oil Pressure Specs

Postby AveryStella [OP] » December 20th 2020, 2:17am

Thanks, guys. I forgot to mention that prior to my last oil change I did the 5 minute flush with Motor Medic with no appreciable change in oil pressure afterwards. Bummer.
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Re: Oil Pressure Specs

Postby MechBob » December 20th 2020, 2:55am

I could give you history about Gm engines,years and oil pressures,but take too long.Looks to me like you are headed for disaster.I would drive it "gently'.If you had a rebuilt engine,and had wide spread of oil pressure,can happen,and be fine,sometimes they cut the crank too wide where the rods connect,etc.BUT,the biggest key is you have/had lifter noise.In the"old" days(carb and tbi),if the oil lamp stayed out at idle,it was considered fine.Strangely,GM went back to this,in the 2000's, probably because they had been producing so many engines with poor quality.So,some info.Yes,a poor quality oil filter can affect the oil pressure.My oil pressure tester,takes place of the oil filter,taking that issue out.Do you trust the gauge you bought/borrowed?However,because of the lifter noise,i really suspect internal engine wear,and probably all the soft bearings.Could be previous owner ran it a bit long with leaking intake gaskets,and bearing wear happened.A high volume pump(NOT high pressure!) can/might mask it for a while.But you gotta pull the pan,anyway!Pull the pan,pull the rods and mains,and inspect.If they are "bad" but not "horrible"you could replace them,and live with bad camshaft bearings,as no reciprocal motion in a camshaft.Anyway,if you want original numbers from a old GM 94 service manual-
Oil pressure minimum-25-50 psi @1200 rpm
42-60 psi @ 2400-5000 rpm.
BUT,like i have said,that was back when GM was more "customer oriented".I would plan on dropping the oil pan and checking it out further.you still might be able to save it before a rod comes out the side of the block.
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Re: Oil Pressure Specs

Postby chevymaher » December 20th 2020, 3:02am

I had this issue I replaced the oil pressure relief spring with one form a 302 camaro Z-28 and ran 15-40 oil as suggested. It brought idle hot up to just under 20 lbs.

This is the part. I dropped the pan and took the oil pump out. Did not get the oil pan off but i never took anything else loose.

Put it back together and used same oil pan gasket. Idle will still be down but running pressures will go up a bunch.

This spring fits and works in the vans oil pump. I got one in mine right now. 94 engine same thing you got.

https://www.summitracing.com/parts/mel- ... /year/1969

Edit: Your engine already has a high volume oil pump. It is the pressure that needs to be adjusted. It is a loose engine but it can work a long time. I was revving the piss out of mine racing it for years after I did this.
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Re: Oil Pressure Specs

Postby ptysiek » December 20th 2020, 2:25pm

Sorry colleagues. I don't know about these modifications. I see that you are driving on 15w40 oil, and I have 5w30 in the traffic jam and I ride it. Only I have a 97 and a 4.3 engine. Is the 15 w40 too thick?
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Re: Oil Pressure Specs

Postby AveryStella [OP] » December 20th 2020, 5:42pm

Thanks again for the great help everyone.
Some key take-aways for me are to drop the oil pan and inspect rods and bearings, as well as pump and pick-up. Maybe changing the pressure-relief spring in the pump can buy me more time with the engine if that brings oil pressure back up.
Then I'd have to figure out what caused this in the first place. If there is a lot of sludge build up I could attribute it to poor maintenance by prior owners. What else, though? Someone mentioned leaking intake manifold. What symptoms would point to that? I don't seem to lose any coolant. For what it's worth, I don't seem to have any oil leaks and I don't really burn any oil between road trips either.

Thank you!
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Re: Oil Pressure Specs

Postby chevymaher » December 20th 2020, 9:37pm

ptysiek wrote:Sorry colleagues. I don't know about these modifications. I see that you are driving on 15w40 oil, and I have 5w30 in the traffic jam and I ride it. Only I have a 97 and a 4.3 engine. Is the 15 w40 too thick?

No it isn't I run it in everything. It is what the boat calls for. My 4.3 in the van has had it since the engine was new right after break in.
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Re: Oil Pressure Specs

Postby AveryStella [OP] » December 20th 2020, 11:25pm

. . . Also, I just cut open the oil filter I used when I did the engine flush with Motor Medic and there was no sludge or gunk to speak of either.
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Re: Oil Pressure Specs

Postby AstroWill » December 22nd 2020, 1:39am

I would say that you are probably on the verge of a rebuild or replacement. Depending on what you can/want to do/learn to do yourself would probably dictate the path you want to take.


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Re: Oil Pressure Specs

Postby AveryStella [OP] » December 22nd 2020, 5:41pm

Thanks Will, we have two goldens that come on all our camping trips, best dogs ever. Lots of pictures of the Tiger on Insta @thelochnessvan.
Ugh. Back when I got this thing and did the suspension lift myself I changed out the water pump, fan clutch, idlers, etc., etc. Kills me that that was wasted work now and that I need a new engine. I don't have the skills or setup to do a rebuild or replacement myself although maybe I can try Chevymaher's trick with the different pressure relief spring in the oil pump. Can anyone recommend a mechanic for engine swaps near the Bay Area in Northern California?
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Re: Oil Pressure Specs

Postby Mmusicman » December 22nd 2020, 6:11pm

Well I'd certainly pull the pan and do an inspection before I decide for sure the engine is bad.
While I'm in there... I'd likely also replace the pump just to be additionally sure.
(I believe the spring regulates maximum pressures.. not minimum)
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Re: Oil Pressure Specs

Postby AstroWill » December 23rd 2020, 11:17pm

AveryStella wrote:Ugh. Back when I got this thing and did the suspension lift myself I changed out the water pump, fan clutch, idlers, etc., etc. Kills me that that was wasted work now and that I need a new engine. I don't have the skills or setup to do a rebuild or replacement myself although maybe I can try Chevymaher's trick with the different pressure relief spring in the oil pump.


Well it may not really be wasted. With an engine hoist(less than $200 and you can sell it after) and some hand tools, it's quite easy to swap out an engine if you have a place to work on it. I did my Tiger's first swap(before the v8) in the street because it was flatter than the driveway.

Of course it might last a while longer, and is definitely worth dropping the pan and seeing what is what.

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Re: Oil Pressure Specs

Postby AveryStella [OP] » December 27th 2020, 2:42am

Thanks again, everyone. Would love to be able to do some of this myself but just don't have the right workspace or setup for this project. I'm taking it in to have the pan dropped on the 4th and will keep you posted.
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Re: Oil Pressure Specs

Postby MechBob » December 27th 2020, 3:02am

Best of luck.As you never reported any horrible engine noises,just intermittent lifter tic, you very well might be able to have the rod and main bearings replaced,and make it live longer.We used to do that a lot,in the old days.Same as we used to re ring lots of jap cars.
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Re: Oil Pressure Specs

Postby AstroWill » December 27th 2020, 7:54am

AveryStella wrote:Thanks again, everyone. Would love to be able to do some of this myself but just don't have the right workspace or setup for this project. I'm taking it in to have the pan dropped on the 4th and will keep you posted.

I hear that, I always encourage those that can to do their own as it's not difficult. Unfortunately if you don't have the space to do it, you don't have the space to do it. Good luck with everything!

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Re: Oil Pressure Specs

Postby Mmusicman » December 27th 2020, 1:57pm

MechBob wrote:you very well might be able to have the rod and main bearings replaced,and make it live longer.

Correct.. and this would certainly be the time to do it.. and not terribly difficult.
Otherwise, with worn bearings your engine may likely be headed for certain premature death.

Worn cam bearings are another issue too, however not easily repairable.
They may additionally add somewhat to lower pressure readings.. but they won't break your engine.

AveryStella wrote:I'm taking it in to have the pan dropped on the 4th and will keep you posted.

Hopefully this "inspection" also has a contingency plan... what to do with what is discovered.

At the very least, I'd change the pump while pan is off... if nothing else is done.
Inspection won't show old pump good or bad.
They are not expensive or hard to do.
My guess however, is this would not likely fix your issue, but maybe might improve it slightly.
If problem still exists, then you know for sure it's not the pump, but something more serious and involved.
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