So when I got my 1998 blazer the service engine soon light came on took it to auto zone and got the code read and it had to do witht the egr valve gasket. Light went off didn't think of anything. My question is that 1. Is it normal for when my blazer is warmed up, half way on the temp gauge, to lose oil pressure, and 2. When I lose oil pressure there is a weird knock noise that sounds like its just under the dash where the radio is on the floor board. My light came on today I need to get the code read after work. Has anyone else had this problem before or know what's going on ?

 

No that is definitely not normal to lose oil pressure, and the knock definitely isnt good either. when your truck is warmed up the oil pressure when idling should be at about 20 PSI. 10 PSI is alright but 20 is better. then for every 1000 RPM it should go up by about 10 PSI. (when im cruising my PSI is generally at about 50) Because you are hearing a knock that tells me that its not a problem with the gauge, so the knock could be a lot of things, a rod, a valve, a lifter, etc... I would recommend NOT driving the truck until we can help you figure out the problem because damage WILL be caused to the engine.

So a few questions.. What is the oil pressure when you first start it cold? does it only lose oil pressure at half temp? does it regain pressure at operating temp? what oil are you using? If you could answer these questions it will help us tell you what the problem could be. Hopefully this will help.

Edit: oh and let us know what the code is when you get it read.

 

When I first start it up it runs at like 60 psi, but then like I said when its heated it'll drop to like 15 ish giver or take when its idle and that's when it will knock. But like I said only when I'm idleing. Ill be leaving work in like 2 hours.

 

And yes it does go back up to about 60 when crusing.it does not hesitate make sounds nothing. It sounds clean and crisp like a champ. And I'm not sure what oil. It was done at walmart there 24 dollar special lol. I think its quaker that's all I know.

 

ahh.. here we go again.

you have unusual bearing wear. If your bearings were in good shape it would idle at more than 15 lbs. My truck has 110,000 miles and idles at over 40 warm with 10w 30 in it. The guage is correct because it shows 57 lbs at 1000 rpm and never higher when warm.
Further you hear knocking at idle warm. you forgot to mention you also hear it for a second when you start it after overnight in warm weather.
Your knocking unlike many on here complaining of cold start piston slap is NOT relatively harmless. It is making the bearing wear worse.

If your typical drive cycle has the engine warm for more than half the trip.. Or if you drive one trip a week of 40 miles or more, put in mobil 1 oil of 3 parts 20w 50 and 2 parts 10w 30.
Or you can reverse that to see if it works. Used to be the heavier oil was the same price, now Walmart has jugs of 10w 30 cheap.

You'll make the cost up by only changing every 10-15000 miles after the first time. Do suggest changing filter at first 1000 miles and again at first 3000. After that.. about 6 or 8k. Because the M1 will be cleaning all the dino oil crap from inside.

Been there had that. Know what I'm taking about.

 

Well it honestly hasn't been warm sense I have had it so I can't confirm or deny what happens then. To further answer your question I will be leaving work in a hour or so, and I will let you know exactly what it starts up at, and what it runs warm, and what it runs when I'm idleing. In about an hour I will be leaving so be prepared for a response then I will be at autozone

 

It's not a question, Kyle. You have classic bearing wear symptoms. I told you what I did for an engine that sounded like a kettle drum chorus, and would do if I were you.

It would be great if you did it and came back and said.. "HEy that worked." But since it has worked for me several times, I dont need it.
look at it this way... "I am your Yoda."

 

Ok starting it is at 58 ill keep posted

 

Damnit well my service engine soon light went off. It dropped to about 25 for an idle while driving it runs about 55

 

Damnit well my service engine soon light went off. It dropped to about 25 for an idle while driving it runs about 55