Ok, so I have a 92 z28 5.7 I just got it back from getting the engine rebuild. Before the engine rebuild when engine was hot or at normal engine temperature, i would shift from drive to reverse or vice versa the oil gauge needle would drop to the red zone and car would shut off. Now after the engine rebuild with new oil pump, pistons, and all new internal parts. The car is still shutting off, showing low oil pressure when hot or at normal engine temperature (also has new oil pressure sensor). Not sure what's wrong or bad. No check engine light. Need help!

 

Since you're reading oil pressure when it's cold, you can assume the sending unit, wiring and gauge are working properly.

Generally low oil pressure when hot means there's a bad internal leak somewhere. Since it was just rebuilt, it could be anywhere. I've seen this happen the most when a cam bearing fails.

Since this was happening before and after a rebuild, and not knowing who rebuilt it or what exactly was done for a rebuild, I would still put my money on cam bearings.

 

An engine shop about 40 minutes from where I live did the whole rebuild. I really wanted to keep the original engine block so I asked them put sleeves in the cylinders. This engine block had been bore out .60 over some time. The guy i bought the car from didn't know if the engine had been rebuild before.

the engine shop cleaned and polish the cam too, they said it was still in good shape. Not sure about cam bearings I don't see anything about cam bearings in the paper work.

 

Uhhhhh..... a rebuild must include cam bearings. That's not a rebuild if you don't replace them. That's concerning - not only because that's a very common reason for low oil pressure, but also they must be removed to properly clean the block prior to reassembly. Just like the casting plugs and oil passage plugs need to be removed. You can't properly clean it with the cam bearings in place.

GD

 

The cost for sleeving 8 cylinders would come to more than the entire engine is worth. Someone is pissing on your leg and telling you it's raining.

 

[QUOTE=GeneralDisorder;6293662]Uhhhhh..... a rebuild must include cam bearings. That's not a rebuild if you don't replace them. That's concerning - not only because that's a very common reason for low oil pressure, but also they must be removed to properly clean the block prior to reassembly. Just like the casting plugs and oil passage plugs need to be removed. You can't properly clean it with the cam bearings in place.

So I called the shop today. They told me they put new cam bearings and all the oil passage plugs where taken out and completely cleaned the engine block. Also, they said I'm having low oil pressure because of a bad oil cooler (original oil cooler) where the oil filter is attached to.

 

I was charged about $480 for the sleeves

 

NOBODY in their right mind would EVER sleeve more than 1 cylinder in a common 305 block. You just get another block.
The only way someone would sleeve all 8 cylinders in any block is if it was SUPER RARE and desirable.

 

8 sleeves in an OEM block is a waste of money. Trying to keep it numbers matching won't help because the deck will need to be machined after the sleeves are install and milling the deck will shave off the original stamped numbers. Probably would have been a lot cheaper to just buy a stock replacement engine and doing a cam swap.

Now my Dart block is work over $2000. The cost of 8 sleeves and machine work is minimal to replacing the block but I've already had to replace a Dart block when I cracked the webbing under one of the main bearings.

Bad oil cooler? Is it plugged? If the machine shop says there's something wrong with it then spend the money and replace it to see if oil pressure gets better when the engine is at operating temps.

 

Throw the oil cooler in the nearest dumpster. With modern synthetics you don't need it.

And yeah - sleeves in that block is ridiculous. You can get good condition Vortec blocks for about $200 or less if you have a look around. Mine had perfect stock sized cylinder walls at 177k.

GD

 

I was told that a high performance torque converter with a stock motor can cause slightly low rpm's when shifting to gear, Therefore causing low oil pressure for a brief second. Is this true? The car does "jerk" a bit when I shift to drive or reverse. I just don't want to spend more money if i don't need to. Just like rebuilding the engine, since it didn't fix low oil pressure when hot. As far as I can tell everything is stock on this car.

Thank guy's for your help and response.

 

Verify the actual oil pressure with a shop gauge. The dash "gauge" is not sufficiently accurate to be relied on.

GD

 

I agree. I've had personal experience with knockoff senders giving increasingly incorrect readings at the low end of the scale, while being reasonably accurate at the higher end. I had the same problem with 3 of them in a row. Mechanical gauge showed they were wrong. No number of warranty replacements would fix it, they were just faulty by design. ACDelco was better.
Verify pressure with a mechanical gauge before worrying. If you find it's a faulty reading and want to replace the sender, get an ACDelco. But that's still not a substitute for measuring with a mechanical gauge.

It also sounds like you have a bad fuel pump relay, otherwise the engine shouldn't be stalling when the oil pressure gauge drops. You might prefer to leave it this way, but there's a chance that powering the fuel pump entirely through the oil pressure sender could undervolt the pump and help it to burn out.

 

Don't panic until you try a mechanical oil pressure gauge....which eliminates a flaky sender from the equation. I've had a "pucker moment" seeing low pressure a couple times before and it's been the sender both times.

-Rich

 

I highly doubt the oil cooler has anything to do with low oil psi. It would have to be so badly neglected it's not funny.

What oil filters are you running?