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Oil Pressure on rebuilt 350 HELP!

W

wed68

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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
 
oil pump? did you replace that with the rebuild? not even sure you can replace, just taking a stab
 
did you tack weld, or use the bracket that holds the Oil pump pickup tube, in the pump?

are you using the stock GM oil pressure gauge? Is it the electrical style, or the tubing style?
 
might wanna throw a cheap mechanical on it to confirm your readings...
 
Yes I changed the oil pump with the rebuild! I am going to put a mechanical on it soon to check it, no I did not tack weld it or use a bracket could it have came off?



Bill
 
it could have, i dunno how likely it is though as it sounds like you have not ran it much... Check it with an aftermarket gauge first... If it still persists then drop the pan and check the pickup... if that checks out ok, then i dunno what else to do but start taking **** apart hehe.. Good luck
 
This very same thing happened to me. The fix: I put in 10W 40. My engine hates 10W 30. At idle and going down the road I would lose all oil pressure. When I would kick the 4 barrel in my oil pressure would go way up then come right back to 0. This may be your problem this may bot be your problem. But if I was you I would check it out.
Thanks
Adam
 
if you lose oil pressure as it gets hot your main bearing clearances might be too big. i
ve been told this is the #1 reason for loss of pressure at running temps. i had this problem before with new rebuilds. but in my case it was on an oddball 340 buick thats needs super tight bearing specs. the rebuilder set it up to 350 buick specs, which is double the gap that i needed. pretty unlikely with a 350 since they are so common. but if you did it yourself that might be what to look for.

you can bandaid fix it by installing a high volume(not high pressure) oil pump, if it isnt in there already.
 
I may have to try the high volume oil pump if I can not find the problem! The machinsts at the shop that did my heads and bore job, miked the crank and they were still in standard specs so I went back with new standard bearings. The oil pressure was good on the first few starts, now it is 0 at start up when cold!



Bill
 
wed68 said:
I may have to try the high volume oil pump if I can not find the problem! The machinsts at the shop that did my heads and bore job, miked the crank and they were still in standard specs so I went back with new standard bearings. The oil pressure was good on the first few starts, now it is 0 at start up when cold!



Bill
Click to expand...
if its zero when cold you may have a problem w/ oil pressure sending unit. either that of something serious inside. a high volume pump will only work if it loses pressure when hot, but has good pressure cold.
 
do you have the stock oil pan, and is the pickup also stock?


sometimes the oil pump comes with a gasket and it prevents the pump from sucking in air.

Double check your oil filter, see if your getting oil in there. Maybe it got clogged.


Did you get a chance to plastigate the bearings?
 
Check the oil for gas or coolant....I had a fuel pump diaphram let go once, and it pumped gas into the oil. An oil pressure gauge saved that motor....


You must measure those bearing clearances....
 
Sounds like a Main or Cam bearing problem. Did you put a performance cam in it? If you did. Did you check for coil bind? if
 
I would also recommend the mechanical gauge. I was told by my engine builder that they have customers with electric oil pressure gauges coming back freakin' out about a lack of oil pressure, and they tell them to get a mechanical. Then with the mechanical gauge oil pressure is just fine.


The fact that the engine gets hot is suspicious. Does oil pressure drop before or after the engine gets hot?
 
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
 
Drop the oil pan, pull the main caps and maybe a rod cap or 2, and take a look. That's what I would do. HTH
 
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
 
Dude that sucks. Keep us up to date on what is going on.
Thanks
Adam

wed68 said:
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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