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Chevy 350 rebuild....LOST oil pressure

7K views 24 replies 13 participants last post by  edge 
#1 ·
I started a rebuilt 350 a few days ago, broke it in proper, it had great oil pressure the entire break in and the first few test drives. Today I took it out for a little 20 minute drive at about 55mph and it seemed to gradually lose oil pressure eventually getting hot and losing power. I got it home ok but now it has no oil pressure at idle but the pressure will come up as the engine revs.

Any ideas on where to start looking? It never knocked or ticked like a rod bearing spun! It starts fine just has no pressure at idle.

Bill
 
#2 ·
Oil and Filter

wed68 said:
I started a rebuilt 350 a few days ago, broke it in proper, it had great oil pressure the entire break in and the first few test drives. Today I took it out for a little 20 minute drive at about 55mph and it seemed to gradually lose oil pressure eventually getting hot and losing power. I got it home ok but now it has no oil pressure at idle but the pressure will come up as the engine revs.

Any ideas on where to start looking? It never knocked or ticked like a rod bearing spun! It starts fine just has no pressure at idle.

Bill
Did you change the oil and filter after the break-in period? Avoid Fram filters (IMO), use an AC or Wix (Napa or Carquest). Ed
 
#4 ·
yes I did change the oil after the break in and yes there is an orange filter under the block, could that be it the filter came apart?

The gauge is the stock electric gauge! and the oil pressure at idle reads 0 at 1000 or so it reads about 20 and it contiues to climb as the rpms do but when the rpms level off at any point the oil pressure falls off to 0?

Could the pick up have come loose, screen plugged, filter came apart? why pressure for two days now none?

I will drop the pan tomorrow and look! I just needed some incouragement!

Bill
 
#12 ·
Pick up a good mechanical oil pressure gauge. You can hook it up and not make a permanent fixture in your car if you need to. You could hook it and mount it under hood to check what it is at idle and with the engine running thru the RPM band. Good mechanical gauges are not expensive and are a direct piece that will read regardless of whether there is a circuit problem going to the electric. Your sender pulls a signal from there it sends it to the circuit board in your dash panel.
 
#14 ·
Update! I change the oil today to 10w40 but no change. I did find pieces of what looked like bearings in the oil filter. When I started it cold it had good pressure. I then found an oil leak on my sender unit, I changed it but the same thing little pressure at idle but about 30 psi while driving!



Bearing spun?

Oil pump came apart?





Bill
 
#17 ·
Have you made sure that your oil pickup tube in the oil pan is not sucking itself to the bottom of the oil pan??? It would not get oil then and my brother has had that happen before, just a thought! The easy way to tell that is take a valve cover off (either side) and if it's not spitting oil into the head and it's not the sending unit then chances are it's probebly the pickup tube in the pan... Just my worthless two cents :)

*Edit* - Sorry, didn't see your post right above this one, if you're going to drop the pan, go ahead and check it when you drop the pan, you might be surprised at what could be going on...
 
#18 ·
A while back someone wrote in an interesting way to check main shaft bearing pressure. I'm not sure if it's even valid but most people that read it seemed impressed by the logic. Basically, you pick an rpm, say 2000, then you do a standing brake rev, bringing the rpm's to 2000 . Don't let the wheels spin. Note the oil pressure at 2000 rpm. Next, put the car in neutral, bring the rpm's to 2000, again noting the oil pressure. Supposedly, if your oil pressure is higher in neutral at 2000 rpm than under brake rev pressure at 2000 rpm , then your bearings are losing pressure. The lower the pressure when brake revving, the worse the bearings are. Sounds feasible. I guess normal would be when both readings are the same. Maybe there is someone out there with knowledge of this theory that could corroborate or dispel it. Rick
 
#19 ·
If you've ruled out the gauge.Drain the oil and examine it for metal particals.Then stick a coat hanger in the drain hole to see if the pickup is laying in the bottom of the pan.I had that happen on a new motor w/ 10k. Had like 45psi moving and 4psi idling.If thats the problem you'll have to drop the pan and put the pickup back in and have it tacked to the pump.Also should prolly pull a few caps and check for wear if thats the case.
 
#23 ·
NAIRB said:
If you have metal in the filter and you have no oil pressure at idle, you have an internal problem. There is no quick fix, so I would stop starting the engine, as you are going to tear something up even worse by doing so.

Pull the engine and start over.
I'll second that. I'll add that just becuase the machine shop cleaned the block doesn't mean that you can call it clean and put it together. Some machine shops will hand wash the block with hot soapy water and rifle brush the galleys but they often charge extra for that on top of the normal block cleaning charge.
 
#24 ·
Bad news but bad as well!

I dropped the pan and found what I had been expecting, all bearings rod and main were scarred bad! I will pull the engine and start over, new crank and such!

What could have caused this, I believe that due to the fact that all bearings were scarred that I must have started the engine with trach still in it, I pulled the ultimate f>>> up I did not clean the oil gallerys before assembly, I thought the vat was enough!

I will keep yall posted!

Thanks for the Help!

Bill
 
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