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Blazer: i have rebuilt the engine and it runs great but i…

i have a 98 4.3...
i have a 98 4.3 blazer. i have rebuilt the engine and it runs great but i have a problem. the oil pressure is around 40 when i crank it up but when it heats up the pressure drops to near nothing. i understand that it only requires 6 psi at 550 rpm but im really worried about it causing engine problems because the 6 psi mark is so close to nothing ....and hard to tell want any and all troubleshooting ideas or maybe ways around this problem. no oil leaks. im using 10w 30 oil and someone suggested i use 5w 30 but need more info
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Answered in 13 minutes by:
6/27/2010
Eric
Eric, Master Technician/shop foreman
Category: Chevy
Satisfied Customers: 846
Experience: ASE Master Technician, 25 years experience, Over400 General Motors certifications
Verified
Hi, when you say the engine is rebuilt, what exactly do you mean? Was it a complete overhaul, new rod and main bearings, etc, Let me know. Thanks Eric
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Customer reply replied 8 years ago

the engine was tore down, honed, and the cam and main bearing replaced and freeze plugs. the rest were the original parts.

Okay, its possible that the main bearings, or even the rod bearings have too much clearance when the engine is warmed up. This will cause a drop in oil pressure because the pump has a hard time with the excessive bearing clearance. Now im not for sure thats your probem yet, does the engine tap when the pressure reads low? Thanks, ERic
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Customer reply replied 8 years ago

no the engine purrs like a kitten lol sounds really good just a drop in oil pressure. i used standard bearings but that is a good idea to consider. the oil sending unit is new too. what other possiblilties could it be

Okay, if its quiet then enough oil is getting to the valve train. Well is your oil sender have 2 wires or 3? Im thinkin of a quick way to check the gauge itself. The only other thing that comes to mind is the pump itself. It may have a bad relief valve. I would also remove the sensor and check with a mechanical gauge to verify that the pressure is really dropping that low. There should be a tap also on the side of block and one behind distributor. Ill keep thinking let me know. Thanks, Eric
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Customer reply replied 8 years ago
it has three wires and the one on the side has two. i wish i could fine a guage to measure that. ive tried alot of different parts stores. what exactly does the one on the side of the block do
The one on the side of the block is a tap off the oil galley. Its pump pressure there. Then there is another tap behind the distributor for the sensor.
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Customer reply replied 8 years ago
would you say maybe that sensor on the side of the block might be faulty and needs to be relplaced cuz i didnt replace that one or that wouldnt cause the drop
You have a sensor on the side of the block? by the oil filter housing? Usually the oil sender is behind the distributor, but occasionaly its near the oil filter housing also. If it doesnt have a sensor there it will just have a plug screwed in. Thats why it would be nice to know the actual oil pressure at those ports.
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Customer reply replied 8 years ago
ohhhhh i got you no the oil sending unit is behind the distributer. there was another sensor right above the third cylinder spark plug. ya ive tried to find a pressure gauge but have no luck and so far with this build ive spend alot more on tools than parts lol. so it could be oversized bearing, bad pump, missreading from the sending unit, or anything else you could think of. is there something simple that i might be able to try without a guage without a chance of messing up the engine
Try unplugging the sending unit and grounding one of the wires. With key on, i believe one wire is for the gauge reading. With it grounded it should go the opposite way it is when you unplug it. Remember key on. Try that and maybe we can eliminate the gauge. The wire i believe is tan/white.
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Customer reply replied 8 years ago
just key on or engine on
Key in run position.Engine not running.
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Customer reply replied 8 years ago
ok ya gauge went all the way past 80 and when i grounded it it went to 20 so it went the opposite way im cranking it right now and when the engine is at running temp the pressure drops from 40 to the first notch above 0 which is about 6. how far will the gauge drop is there is no pressure. will it go to the 0 or just stay in the red. and also the pressure does go up as the rpms go up so no its not the guage. it goes up to about 50 psi
Okay, then im gonna say you either have a problem with the pump or clearance is the problem. If you reused the original crankshaft and just put standard bearings in then most likely that is where the problem lies.
Eric
Eric, Master Technician/shop foreman
Category: Chevy
Satisfied Customers: 846
Experience: ASE Master Technician, 25 years experience, Over400 General Motors certifications
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Customer reply replied 8 years ago
well dern you might be right well i appreciate the help. thanks for all the info
Thanks and hope you get it figured out. Take Care, Eric
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