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1999 Blazer 4x4 dropping oil pressure
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dmangrum
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Oct 18, 2011, 5:23 PM
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1999 Blazer 4x4 dropping oil pressure
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I have a 99 S10 Blazer with the 4.3 Vortec V6 that has 159,000 miles. It runs great on start up with 60lbs of oil pressure. When it warms up the oil pressure drops to about 15 to 20 when at a red light, on acceleration the pressure goes up to about 45 to 50 with a lot of valve clatter and that is with a new Meling High Volume pump with the recommended pump drive shaft. I'm thinking the rod,main and maybe even the cam bearings are bad.My question is could it be anything else and if it is the bearings how can I tell short of pulling the engine and doing a complete tear down. Can anybody help me?
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Hammer Time
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Oct 18, 2011, 5:42 PM
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Re: 1999 Blazer 4x4 dropping oil pressure
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I don't know why you are asking. Those readings sound completely normal and shouldn't present a problem.
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Discretesignals
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Oct 18, 2011, 6:21 PM
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Re: 1999 Blazer 4x4 dropping oil pressure
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Why did you replace the oil pump?
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
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dmangrum
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Oct 19, 2011, 2:13 AM
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Re: 1999 Blazer 4x4 dropping oil pressure
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Extremely low oil pressure combined with excessive over heating. Installed new radiator, thermostat, water pump and fan clutch with no improvement.
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Hammer Time
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Oct 19, 2011, 3:11 AM
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That's because you don't have "extremely low oil pressure"
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dmangrum
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Oct 21, 2011, 8:12 AM
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Re: 1999 Blazer 4x4 dropping oil pressure
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Well here is a brief history of my problem. Bought the Blazer almost a year ago (was late winter) with no known problems. Started using the AC when summer set in. Was driving home from work on a hot Friday afternoon. Suddenly had steam coming from under the hood. Was a busted heater hose. Replaced hose. Drove less than one day over heat again. This time replaced thermostat. Still over heated. This time flushed and refilled cooling system, including back flushing the heater core. Still over heated. Then noticed that upon a cold start oil pressure was 40.As it warmed up the oil pressure would drop to around 15 and the coolant temp would rise to the point of over heating. Reving the engine would get the pressure back up to around 40 but as soon as you would let off the gas would drop back down to around 15. So I figured the oil pump was weak so i replaced it.
Now on a cold start it shows 60lbs of pressure and as it warms up to normal operating temp the oil pressure slowly drops back down to around 15lbs and temp slowly rises to above normal and now I have what sounds like lifter and/or valve clatter. Which only increases upon acceleration and only goes away with an over night cool down.Start engine the next day and the process repeats it self. So that is my reasoning for the bad rod, main and possibly cam bearing.
Plus have 1998 full size GMC C-1500 pickup with same engine can drive under the same conditions and oil pressure never and I repeat never falls below 40lbs.and has never over heated. So help me here is my hunch right?
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Tom Greenleaf
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Oct 21, 2011, 8:26 AM
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Re: 1999 Blazer 4x4 dropping oil pressure
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IMO that engine is hurt. If not to fix everything in it for low oil pressure use a higher viscosity synthetic oil and it might stop the clattering and raise oil pressure when warmed up.
15 to 20- 50 grade oil. If real cold it will be hard to start so use a block heater of choice. IMO if the 15 PSI is real that too low and you should be getting a warning light on dash. Check by real gauge not just the dash one but the noise is a good clue alone that it's too low. Bearings will wear fast and leak down too fast to get to lifters which is what you are hearing I think,
T
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dmangrum
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Oct 21, 2011, 8:49 AM
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Re: 1999 Blazer 4x4 dropping oil pressure
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Tried using 20w50 not much improvement. Wild shot here could it be a cracked head or blown head gasket?
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Tom Greenleaf
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Oct 21, 2011, 10:18 AM
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My guess is oil pressure is leaking down faster than the pump can pump due to worn bearings. Could it be something strange as mentioned? Maybe but would think it would be leaking or smoking out tailpipe.
This engine may have had it!
T
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Hammer Time
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Oct 21, 2011, 12:13 PM
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I don't know how many times I have to explain this trio you. You do not have low oil pressure. That engine doesn't even trigger the oil light until it goes under 5 PSI. You have more oil pressure than most others. Now, putting 20W50 in that engine can ruin the engine. These later odel engines are designed with much smaller oil clearances for better fuel mileage and you HAVE to run light oil in them. If you put that heavy oil in them, you will get dry "cold starts" meaning the parts will not get lubricated fast enough and that can lead to just what happened to you. Leave the oil and oil pressure alone. There is nothing wrong with it. You probably blew a head gasket the first time you overheated it from the bad hose.
Apparently you don't believe me so here are the factory specs on your engine
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
(This post was edited by Hammer Time on Oct 21, 2011, 12:17 PM)
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dmangrum
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Oct 21, 2011, 5:02 PM
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Re: 1999 Blazer 4x4 dropping oil pressure
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Well I only ran it for a couple of hours grand total so hopefully I didn't do any damage.Will change back to what is recommended 5w30. A blown head gasket had crossed my mind. Is there a way I can tell if that is the culprit without taking it to a shop? I can do all the heavy work my self if I know this for sure.
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Hammer Time
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Oct 21, 2011, 5:05 PM
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Re: 1999 Blazer 4x4 dropping oil pressure
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Watch this video
http://www.youtube.com/watch?v=oYQHkWVULn8
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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Discretesignals
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Oct 21, 2011, 5:11 PM
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So the real problem isn't so much the oil pressure. It is the overheating problem you can't figure out?
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
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dmangrum
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Oct 22, 2011, 10:47 AM
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If it is a blown head gasket would that contribute to the over heating problem?
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dmangrum
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Oct 22, 2011, 1:30 PM
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Update:Changed back to recommended oil (5w30) most of the valve/lifter noise seems to be gone. Oil pressure is acceptable,still fluctuates but not quite as bad. Think I may now have a frozen lifter or two. Will drive this week to see what happens,hope its not a rod knocking. Sounds more like a tap than a knock,but we'll see.
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Hammer Time
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Oct 22, 2011, 5:52 PM
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You need to get an accurate diagnosis on what that noise might be before anybody can tell you what to do about it.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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