I have a 6.2 diesel that a rebuilt and when i start it up i have 40 psi of oil then when the oil gets hot it drops low and sometimes to no oil pressure. I pulled the pan to replace oil pump and see if there is anything else is wrong. Well here is a picture of the rear main cap with the oil pump removed. We the red arrow is pointing is a hole that has no treads in it and i never removed anything from it during the rebuild. YOu can see the main bearing and oil holes through this hole. My question is that this looks like a place where oil is bypasing the system and dumping in the pan, should there be a plug there?

http://www.texasoffroad.net/albums/lonestar/album453/62main.gif

What are your bearing clearances? Did you replace the cam bearings? Low oil pressure could be from a bad cam bearing. Did you double check your oil pressure with a mechanical gauge?:rolleyes:

I don't remember seeing a hole in my 6.2L cap. The hole looks very clean as if maybe a plug does go in the hole. Did you find a plug in the oil pan? Go to a Chevy dealer to see if a plug does exist.

Another thing about your overhaul, did you replace the main bearings. My 1984 engine has select fit bearings (different sizes) so unless the crank was ground then you need to replace the bearings with identical bearings. Since it has been overhauled then the crank would have to be removed so each journal could be measured.

If you had your block hot tanked then the camshaft bearings would have been destroyed so they would have to be replaced (and the camshaft re-ground.

Do you still have an oil pressure relief valve in the engine? You might get 40 PSI at startup with cold oil, but it would start dropping fast as the oil warmed up.

Let us know the end of the story.

I replaced the main bearings when i rebuilt it and i didnt reground the crank and used standard bearings. I talked to several mechanics and eventhough they couldnt give me a stright answer they agreed that you shouldnt beable to see the bearing like that. I fabed a plug to go into it and im waiting on an oil pump that will arive monday. We will see if thats my problem after that. The 6.2 wasnt hot tanked. I pressured washed it, btu didnt replaced the bearings.


Kyle

You may have some excess clearances in your main bearings since the early 6.2's came with different size bearings, but the pressure probably would not go to zero. I would still check with a Chevy dealer parts dept. to checkout that hole. I do not remember seeing a hole in that cap!!!

Get the hole cleaned out good with Brake Cleaner and then install the plug (hopefully a Chev. plug) with J-B Weld. That stuff is amazing!!!! From my experience with J-B Weld, the only way to get the plug out (if the hole is clean of oil) would be to drill it out.

The hole is normal, don't mess with it. Stock bearing sizes are stamped on the back side of the bearing. Most stock 6.2's have one half of the bearing that is standard and the other half is .001 undersize which yields .0005 undersize. I usually replace the bearing with standards if the crank is in good condition and have never had an issue with oil pressure. Cam bearings on the other hand could be the culprit, especially if one is loose in it's bore.:eek: Inspect your main bearings first and see what the wear pattern is. They should be smooth and very evenly polished.:grd:

well im done with the fix and all i have to say it worked.

On the rear main bearing cap, there is three groves: one for the main seal, one for the oil ring on the crank, and one for the oil grove for the main bearing. YOu can tell from the cap and imagining the way it was made that the milling process made the groves and the hole was driled to make a passage from the oil ring grove and the oil grove on the bearing. This needs to be caped so that oil from the crank flows into the grove of the oil ring and the oil ring inturns oils the main seals. The oil then escapes through a grove that is milled between the cap and the block. when i took the main cap off the rear main seal was destroyed from the lack of oil. Now with my motor warm and driving in 103 degree temps here in Texas with the AC full blast, i have about 30 psi on driving rpms and 10 psi on idle, right were the book says the psi should be.

That still sounds low to me. I pulled a pan on an '03 6.5 last night and it had that hole in the main cap just as the picture shows.

My oil pressures run 25-32# @ idle and 50+ running down the road with no mods to the oil pump/system. Engines both have lots of miles on them.

I built a 6.2 once that had low oil pressure (about 4000 miles after rebuild). After tear-down, I found the rear cam bearing spun in the block and a crack in the journal between the cam bearing and the vacuum pump drive (post hole). Had to start over with a different block, machine it up and install all the parts from the cracked block.

My 1984 6.2 started out new at 37 PSI at highway speeds winter or summer and 20+ at idle depending on temperature. It has 35 PSI after 225K miles. I have never had the oil pressure valve out, but I have wondered sometimes if it is not passing oil. When I replaced the rear main seal two years ago I checked the main bearings and they were half way between min. and max so I didn't change them since they were the selective fit bearings. I have a good mechanical pressure gauge, but it is possible that it reads low.

I know about electric guages, the factory guage in the old pickup reads dead center (40#) at idle and on decel. If you touch the throttle, it jumps immediately to the peg (80#) and won't move again until you let completely off the throttle. It only has two positions, 40 and 80 when the truck is running. The manual guage, Stewart Warner, 0-80#, shows the numbers I quoted in the reply above. I tend to believe it more than any electronic gadget.

The guage in my Suburban seems to read normally, like a manual would. It's signal is analog and variable like it's supposed to be. It runs a little below what the pickup guage says but is still 50# on the highway and between 28 and 30# at idle.

Somewhere, someone probably changed the sending unit in the truck to something the local auto parts store said "Try this, maybe it'll work!?"

What is the cause of erratic oil pressure gauge readings? The gauge will peg and then suddenly go to normal pressure. It it is pegged at idle it will go to normal pressure if the engine is shut down and immediately restarted. Engine temp doesn't make a lot of difference except the gauge is usually pegged when cold.

'89 6.2 J
230,000 miles

Jim, Could be the guage, sending unit or the printed circuit connections. I've had the printed circuits make and break connections after they get old. This will cause erratic readings.

Ground problems to the printed circuit will also create nightmares trying to diagnose and repair. The dash in my vehicles is plastic, so grounds are external and rely on good chassis grounds. The printed circuit is grounded through the main instrument panel plug and associated wiring. GM refers to it as "the black 150 circuit".

Some temp guages go to "Cold" when you ground the sending unit wire and some peg the guage at the "Hot" side. It depends on the truck and which style of guage it has. Most of the stuff used up until '87 had the one that went to "Cold" when grounded.

Try checking the readings with the guage both "open circuit" and grounded. I.e., take the wire off the sending unit, turn the ign on and read the guage. Then try grounding the wire to the sender, turn ign on and read guage again. The guage should read "cold" in one test and "hot" in the other. This will tell you if the guage is capable of reading in both directions. It doesn't mean the guage is surefire guaranteed good, but it gives the indication that it can work.