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ironmike
ironmike, ASE Master tech
Category: Chevy
Satisfied Customers: 3300
Experience:  30 years ASE Master L1 GM certified
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I have a 2004 5.3 silverado and I am getting a low oil pressure

Customer Question

I have a 2004 5.3 silverado and I am getting a low oil pressure reading after I replaced the cylinder heads myself. what could be the problem.
Submitted: 4 years ago.
Category: Chevy
Expert:  KMP1171 replied 4 years ago.
what is the pressure reading?
Customer: replied 4 years ago.
20 to 25 at idle and 40 at 3500 rps. Before I replaced the heads it was in the 40 range at idle.
Expert:  KMP1171 replied 4 years ago.

Testing

  1. Check the oil level and correct as necessary. Turn the ignition switch on, but do not start the engine.

  2. Disconnect the sensor lead at the sensor. The gauge should read full scale.

  3. Ground the connector. The gauge should read at the bottom of the scale.

  4. If the gauge functions properly, replace the sensor.

Customer: replied 4 years ago.
what do you mean if it fuctions properly.
Expert:  KMP1171 replied 4 years ago.
do you have a oil pressure gage ? If yes install it in place of the sensor and check reading. But 20 psi at idle is more than sufficient. GM spec says engine warm at idle above 8psi is ok.
Customer: replied 4 years ago.
Like I said the oil pressure was always in the 40 range before. Now it drops and i get the low pressure warning in the dashboard. The reason i said might be a clogged strainer or bad pump is because the old heads had a lot of sludge, mud. Also when I removed the oil filter it was clogged. it seem like mud was coming out it.
Expert:  KMP1171 replied 4 years ago.
How long did you drive it with the coolant in the oil? Also it is possible that the sensor might be partially plugged. Did you just change oil or did you flush engine ?
Customer: replied 4 years ago.

I drove it for approximately 8 months or so before I noticed something was wrong. During this time I was losing about a gallons every two months, but i did not know what was th problem. Untill I found out about this problem with the castech heads. During this time I changed the oil regularly through(full synthetic. After I replaced the heads I just change the oil. I did not flush the engine.

Customer: replied 4 years ago.
when would I get a respond. I been waiting for 48 hours now.
Expert:  ironmike replied 4 years ago.

greetings,

what did you use to clean the block?

 

Customer: replied 4 years ago.

I just cleaned the top end with rags and gasoline. washed the rocket arms, push rods, lifter and valve covers with gas. then I just drained the oil. I have not ran the truck since I noticed the low pressure. After I installed the heads I ran the truck for a few hours only. Then I got the low pressure warning and at the same time the lifter also begun knocking. If I start the truck know it runs great. there is no knocking, but real low oil pressure.

Expert:  ironmike replied 4 years ago.
you sound like you know what you are doing. Most oil pressure issues after major repairs are due to contamination(coolant can take out bearings). You know the only way for sure to know if it is a bearing issue or oil pump is to tear it down. I agree that 20 is too low, I have done oil pans,rear mains on 250k plus and after the repair they would start up with 60-80 and hold 40 warm at idle. It would be worth it to at least pull the oil sender and clean it.
Customer: replied 4 years ago.

Theonly reason I believe it could be the oil pump is because before I replaced the heads the pressure was ok. When i found out about the problem with the heads I parked the truck for about 3 months before I work on it and i did not drain the oil. After i installed the heads I changed the oil and the oil filter was clugged. Real heavy gelly sludge came out it. Thats why I am incline to belive is a pump issue. If the sender is falsing then why the lifters start knocking when I get the low pressure warning.

Expert:  ironmike replied 4 years ago.
That does sound right. I have seen pumps cure oil pressure issues, not on this engine. I don't see any bulletins on these pumps or for this issue with these engines. I did run into a bad o ring once in the pick up. But the oil pressure was lower and it was after a pan gasket. If you do the oil pump you will change that. Lifter noise does indicate pressure issue. I would try the oil pump if it were my truck. If it were a customer I would advise him of the chance of bad bearings.
Customer: replied 4 years ago.
Ok thanks a few more questions. Do you belive the pump strainer might be clugged or have you seen a clugged strainer causing this problem. The bearing you are talking about that might be bad are the camshaft bearings.
Expert:  ironmike replied 4 years ago.

I would think crankshaft bearings. Yes If the sludge was as bad as you said the pick-up strainer could be restricted. Just had advice that agreed the pick up needs to be cleaned. Good idea to drop the pan and clean down there also. If you drop the pan you could drop a cap and plasti gauge the bearings to see if the wear is excessive.

good luck



Edited by ironmike on 2/16/2010 at 2:23 AM EST
Customer: replied 4 years ago.
well thanks ironmike you might be right. I just cold started the truck and it read 40 upon starting and then begun dropping untill it reached 20. But I will replace the pump anyways hopefully it will aliviate the problem. If not i will check the bearing. I was hopeping that could be something else more simple.
Expert:  ironmike replied 4 years ago.
yep, I hope it is the pump and no more than the pick up.
Customer: replied 4 years ago.

ok do you know thaw is an acceptable plastic guage reading there fo the bearings

 

Expert:  ironmike replied 4 years ago.

this is the main bearing clearance 0.02-0.052 mm (0.0008-0.0021 inch)

Expert:  KMP1171 replied 4 years ago.
I am sorry for not responding sooner . I had a computer meltdown. I see you are being helped by ironmike. Good luck with vehicle.
Customer: replied 4 years ago.

Yea ironmike gave me some good info. I will replace the oil pump but I dont know if the oil pan will come out without getting the engine out.

Expert:  ironmike replied 4 years ago.
you can remove the oil pan without pulling the engine. If this is 4x4 you will have to drop the differential. The pan comes straight down, there is a baffle and a small hole that the pick up goes into. Make sure you clean the pick up and change the o ring to the pump.
Customer: replied 4 years ago.

Thanks ironmike your saved me a lot of work. My truck is 4x4 with 6"

lift kit. Do you think this makes a difference to remove the pan.

 

 

Customer: replied 4 years ago.

Thanks ironmike your saved me a lot of work. My truck is 4x4 with 6"

lift kit. Do you think this makes a difference to remove the pan. The lift kit makes easier or more difficult

Customer: replied 4 years ago.

Thanks ironmike your saved me a lot of work. My truck is 4x4 with 6"

lift kit. Do you think this makes a difference to remove the pan. The lift kit makes easier or more difficult.

Expert:  ironmike replied 4 years ago.
you may have enough room for the pan to clear when you drop it if it is a suspension lift. I had a truck that had a 6 inch suspension and 3 inch body lift and it made it easier to work on the engine.
ironmike, ASE Master tech
Category: Chevy
Satisfied Customers: 3300
Experience: 30 years ASE Master L1 GM certified
ironmike and 7 other Chevy Specialists are ready to help you
Customer: replied 4 years ago.
well ironmike thanks for all your help. You are a real good and knowledge man. i will accept your answer and sorry for asking you so much questions.
Expert:  ironmike replied 4 years ago.
that is ok, that is what we are here for. Feel free to ask more. I hope to hear you finish the job and have great oil pressure.
Customer: replied 4 years ago.

This message is for IRONMIKE . Mike, I resolve the problem. It was the oil pick up tube and the strainer that were clogged. The strainer was completed clogged and at the bottom of the oil pan were strainer sits there was more that a quart of a real heavy sludge, gelly, muddy, looking oil. I cleaned everthing up and now it runs great. Now, it always runs above 40 psi even at idle. I did not not repalce the oil pump through. I just replaced the o-ring. Mike thanks for you assistance. Let me tell you though it was quit a challange to drop the oil pan because of the suspensin lift.

Expert:  ironmike replied 4 years ago.

thanks for the info. I knew these motors were tough and though as you 20 psi is not enough. I am glad you did not change the pump, more daring than I. I would have cleaned the pick-up and changed the pump to cover myself.

hope you get many more miles

thank you again

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