Last week, my 1997 4wd 4.3 vortex blazer started to overheat. Had the intake replaced. Got it back and now the oil pressure gague is very erratic, jumping all over the place. Also noticed that when you hit the gas hard, hitting higher RPM's, there is a knocking noise in the engine. You can almost feel it on your feet. Anyone have any clue? Did something fry when it got too hot? Any help would be appreciated

 

You should check your oil to see if there is coolant in it. Could have cracked the head gasket when it overheated.

 

oil looks brand new and clean

 

You have bearing damage caused by coolant in your oil system. I assume you had your oil and filter changed, Now do this.

Shop around for best price for Mobil 1 20w 50 weight oil. Change your oil and filter and use that.
You run the risk of spinning a bearing and here's how that happens.
The bearings have eroded and there are sharp ridges remaining which score your bearing journal but more important overheat and bake the oil coming in contact. this create a carbon deposit next to the ridges which in turn insulates them from the cooling effect of the oil in turn heating and baking the oil next to it. After a while the carbon will build until the point it breaks free.
Then it slides around to a high point on the bearing and wedges, the bearing spins until it wedges and may either lock up the crank or break a piston rod.

Mobil 1 has a significantly higher ash point {temp at which it creates carbon deposit} than dino oil. The heavier weight will also build a thicker cushion in the bearing to journal and you wont hear the knock.. or as much.
If you still do, add Lucas engine treatment.

If you do what I suggest above you may get the rest of your vehicle's normal life out of your engine, without rebuilding it.

If you don't do that and insist on following what pro's {and others who never tried it but go on conventional wisdom} tell you you need your engine rebuilt.
If I am wrong, you will need your engine rebuilt.

I ran an engine that sounded like a kettle drum chorus with standard weight oil, for over 75,000 miles doing that. Up to the point the car was wrecked. Never opened it up or had an annoying knock except sometimes on startup, till pressure went up.

Do not under any circumstance try to get by just adding something to regular oil. That is not a compromise, you will still spin a bearing if it's going to happen because that dino oil WILL 'coke'
Your choice.

 

With a knocking engine if the heavier oil reduces the knocking that has to be a good thing. These 4.3 engines do not have to turn 5000 RPM to put out a lot of power. An engine on its last leg that has good oil in it and is not pushed over 2500 RPM often can last a long time.

If you try a high end 20W-50 share the results with us please. To a point the higher the oil pressure the better the oil film thickness sould be in a worn bearing surface.

It is only when metal makes contact that massive wear occurs.

 

I'll make it clear as I can... not just high end oil.. Synthetic as you can actually test the carbonizing temp on any stove. Not synth blend.. not Dollar General synthetic.

It's carbon formed in the bearings that causes bearings to spin. Since Mobil 1 used to make a point of it and I used it successfully, that's what I recommend.

 

While I have standardized on 5W-40 Rotella Syn because I have both gas and diesel engines and could not find higher zinc. the Youtube of the tear down after running it on Mobil One for four years was impressive. It was a BMW i think.

 

been told it is my bearings....possible rods. Is this fixable or is it not worth it? New motor?

 

The 1998 S10 project truck with 1/2 million miles that we picked up last month had a sticking valve then it stuck open and got bent so I blew it up running it on put ATF in the crank case after a 5 minute running flush of pure diesel. But it took a whole lot of abuse to blow it.

We had found an awesome 1998 119K mile engine before I blew up the old one for $450 but the going rate is more around $700 in these parts. I got a friend to do the swap in his home shop while he was off over New Years so my labor costs was lower. It would have been $1000 in the shop I use in town. Where you pull and go with new rod bearings or get a used engine you need to strip it down to a long block and come back out with new gaskets if you want a dry engine for a while.

I would consider a used engine that you or someone you trust has heard it run preferably but if your crank is fine you could save the price of a used engine and just be out some parts.

IF you knew you did not want to rebuild your current engine the 20W-50 oil mentioned could be a good option. If it is your only wheels and a daily driver then you may want to get it fixed for the long haul. I can tell you after all of the abuse (improper oil film) our crank still did not look at bad when my son took the engine totally apart for the heck of it.

Last weekend we put 550 miles on our 'new' engine in 13 hours and it ran fine and did not lower the oil.

Again there is no perfect call when it comes to fixing/ditching vehicles.

 

yeah, it's kindo of our main vehicle...thinking about a used engine or a new one out of the crate...don't have much tied into this vehicle at all so $1000 new engine may be worth it since the body is still in awsome shape.

I have been told it is possible to replace the bearings, as they don't cost much, but it is a lot of work. Also told that the new bearings could last 50,000 miles or 100 miles, you never know

Anyone know if this is true or not? Or should I just junk the motor? Sucks because just put money into the intake.