Oil Pressure

[ak46champ]

Any suggestions?

My 6.5 Suburban has low oil pressure (about 10psi) at idle when the engine is warm. But when the engine is cold or when at highway speeds or around town oil pressure is fine. Up around 50 or so. Turbo now only puts out a max of 4 psi. Thinking of main bearings going bad or oil pump.

Thanks!

[simon]

To start,take a reading with a manual gauge to establish real oil pressure. this is a good time to bring the ops out of its hiding place anyway. what oil are you using? do a oil change too. The later 506 blocks do have lower press at idle hot. how is your coolant temp?

[Robyn]

The dash gauge and senders in these things are notoriously lousy.

As has been mentioned, do a check with a manual gauge to establish a real world baseline.

40lbs running hot is fine. idle at 20 is normal but a hinky sender will definately cause the gauge to get goofy.

Check your turbo to see if its getting loose.

Just undo the inlet boot and check the turbine shaft for slop.
With the engine off and no oil flowing the shaft should have a slight bit of wiggle radially but none in and out.

If you find things getting sloppy it may be time for a fresh turbo.

15-40 oil is the ticket for these little creatures. 10-30 is just too thin.

Give things a check and let us know.

Best

Robyn

[ak46champ]

Havent checked the oil pressure yet but we use Delo 400 and I religiously change the oil and filter at 3000 miles. It has 155000 miles.

Thanks

[simon]

Havent checked the oil pressure yet but we use Delo 400 and I religiously change the oil and filter at 3000 miles. It has 155000 miles.

Thanksi am not familiar with that brand? is it 15w40?

[DmaxMaverick]

i am not familiar with that brand? is it 15w40?

Delo (400, et el) is Chevron's Diesel engine oil. It is available in 15w-40, among other grades, but 15w-40 is most common. Probably the most popular, most widely used Diesel engine oil of all time. Good stuff, for dino oil.

[ak46champ]

Well still haven't checked the oil pressure with another gauge. But I did notice the waste gate wasn't closing. So I checked the vacuum and it was poor. I wired the wast gate open and boost was a little better. I actually made 6psi. So I think the Turbo is Toast!!

[AKMark]

That might explain your other problem.

[rhsub]

Minimum oil pressure hot at idle with mechanical guage 6 psi
Minimum at 2000 rpm 30-43 psi

Turbo charger is a very simple but precision machine, if it checks out as per Robyns post its likely something else 'ie' restricked intake or exhaust, vacuum or wastegate problem. My sub only puts out 7 psi max and it only does that a certian rpm and load conditions, check your vacuum pump, lines and solenoid valve first
Good luck
Ron

[ak46champ]

Thanks, I am trying to acquire a mechanical gage that will fit in the hole. My other truck will put out 20+ psi boost with the stock turbo charger. That is why I think there is a problem with this one. I checked the play in the turbo charger and it seemed ok, not loose.

[Hubert]

I looked it up for reference my Helm Manual for my '97.... (pg 6A-258 Engine Mechanical Specifications). It doesn't explicitly say but its 15w-40 oil and hot is operating temp approximately 180-200F.

oil pressure - hot

10 psi @ idle
40-45 psi @ 2000 rpm

69 Kpa @ idle
275-310 Kpa @2000 rpm

Low oil pressure could be any loose clearances of bearings or a "leak" in the oil delivery. The crank and cam bearings have most influence. Turbo could contribute too though if it were really bad. But intake or exhaust would probably show some signs and/or you probably would be loosing some oil.

IF mechanical guage shows low oil pressure I am going to guess being an Alaskan truck and severe cold weather its higher bearing wear due to cold start issues???

[DmaxMaverick]

Yes. Do verify your pressure with a known good mechanical gage. The OEM instrument panel gages are notoriously inaccurate. Any degraded wire insulation or poor connection/ground can also effect the reading.

I think the turbo isn't part of your problem. 6 PSI boost is in the ballpark for stock. Perhaps a bit higher under full, WOT load. Hard to do w/o having a load on going up a grade. Higher elevations will also skew your results. If you are building boost during a brake stand, or doing WOT starts with an empty truck, you may not see your max boost. Low vacuum will also limit boost (doesn't apply with the WG wired closed). Wiring your wastegate CLOSED will prevent exhaust gas bypass, giving the max boost at the fueling volume and dynamic load. Wiring it OPEN will prevent any and all boost, as the exhaust gas just goes around the turbine. Still, 6 PSI isn't far off the mark, and normal for many stock trucks. I don't know how you are able to get 20 PSI on an OEM equipped engine. Even with aggressive programming, the GM-8 turbo is capable of only so much, and will be operating well beyond its efficiency range at that boost. You either have some "other" mods involved, or the boost measuring method is inaccurate. If you are making 20 PSIG (NOT PSIA) on a stock engine, it won't do it long before you'll be starting another thread about your need for a dust pan and broom on the highway. Even quicker w/o an intercooler.

The turbo oil supply won't cause a drop in oil pressure w/o showing some serious signs you won't miss. Among them are: compressor wheel contacting the housing; very poor boost; external oil leak (large); very messy intake (oil soaked); and lastly, the engine won't shut off, or run away 'til it grenades (that much oil is fuel in a Diesel engine).

[Robyn]

Definately get a manual gauge hooked up, at least temporarily to see the real deal with the oil pressure.

My 94 had a very slow unresponsive dash gauge that read poorly and just the change of the sender unit put it back where it should be.

Most of the 6.5's I have seen will still produce good oil pressure even with 200K on them unless there has been serious issues.

The cam bearings on my 94 were still great at 230K and I elected to to leave them alone during the rebuild and just replace the crank bearings.

Turbo was the factory unit with the same miles, and a quick disassembly and clean out of the little beast was all it needed.

The bushings were still nice and tight and the seals were in fine shape too.

Stuffed the little beast back together and its off and running for another Gazillion revs.


***Just a note on oils***
The Delo 400 as Maverick mentioned is Standard Oil co's offering for diesel engine lubricants.
I have used this stuff in my GM diesels as well as the Big Cat in the Star.
I prefer Shell Rotella T in the Cat as it will use less of it between oil changes.

The Cat will use a Gallon of Delo in 5000 miles and with Rotella only about half as much,if that.

As long as the oil you are using is Diesel rated and a 15-40 it will be ok.

Most manufactures offer such a product. I personally would stay away from the trick synthetic stuff or the blends.

Stuff like Amzoil is great and I have seen a 6.5 apart after 300K using the stuff since new and the engine looked wonderful inside. ( was down for a blown head gasket)

My issue is the cost and the availability when traveling. (if you dont mind carrying a gallon its fine)




Good luck with the oil pressure

[ak46champ]

Thanks for the info.

My other truck has the JK TD max boost controller with the large exhaust and performance computer. I installed the x-monitor gage set. I can tell you that my boost will get over 20 psi indicated if I push it. I don't though I saw it once and limit my self to about 17-18psi. The engine is all stock. I took it to a chev dealer to adjust the timing to -1.9 and he was impressed that that turbo could put it out too. He had his scanner hooked up so it wasn't my gage.