I am pretty sure I know the answer to my problem, just wondering if there were any other ideas or thoughts. Long story short 4.3 engine overheated so I changed the head gaskets, after I put the blazer back together the engine runs great but I'm sure I have a rod knocking. There was not any water in the oil that I ever noticed and I was careful when changing the gaskets. I have about 50 lbs of oil pressure at idle and 60 while driving down the road. I didn't notice any knocking before changing the head gaskets. Anyone else have this happen and what would make the bearings go bad except for water?

 

Did you change your oil after putting the new head gaskets on .

 

Yeah twice actually, 2nd time went with 20w-50.

 

That is some heavy oil for that engine, 5w30 is recommened...what year???

To see if you have a rod knocking...you can remove the plug wires from each spark plug one at a time until the noise subsides, that will give you an idea of where the problem might be.

But, with that heavy of oil it might be preventing the engine from getting sufficient lube to the bearings.

 

How loud and what does the knocking rod sound like? I'm just wondering if it could be a collapsed lifter instead of a rod. I'm not saying you don't know what your talking about but just that if it wasn't there before and you really didn't do anything that should affect a rod bearing; however you did with lifters that it could be a possibility.

 

My 97 has a knock that it has had for almost 80,000 miles now. I run 20-50 oil & have in my engine for 80,000 miles. I'm not sure what the knock is but it starts at about 1500 RPMs no load about 3000 RPMs under load.
I read something about a balance on the crank could be the problem. But after almost 80,000 miles I'm not to worried about it. My Blazer has 157,000 miles on it now.

 

20w50???? Seriously??? I have 242K of beaten, hard earned miles on an all original 1998 motor and trans. I ran 10w30 since about 140K miles and started adding a few squirts of lucas mucus to the mix around 200K. That kept the pressure about 40psi all the time. I recently changed the oil pump to a melling high volume pump and now I am back down to 5w30 and it keeps ~50 psi at idle and ~70 psi at speed without any additives.

The concern about lube reaching the bearings with 20w50 is only one part of the problem running oil that heavy. The lifters may not be able to fully pump up. That would cause a loud knocking or clicking in the valve train. Try Frog's suggestion and see if the noise is reduced. If not, it is probably valves. Also, flow through the filter will be heavily restricted with 20w50. I have no idea if the oil pressure sensor is before or after the filter, but if the pressure drop across the filter exceeds 10psi, there is a bypass valve that opens up and essentially your oil goes through UNFILTERED. If you are running a stock filter with that heavy oil, chances are that it is not getting filtered and any carbon particles have been eroding the bearing surfaces for however long you have been running 20w50.

In general I would expect that running oil that far out of spec for any engine would ruin it completely within 50K miles. That is of course if it did not already have a rod knock that you were trying to shut up.

Good luck,
-William

 

i thought once heated to operating temp all oils had the same viscosity?

 

not a chance. http://www.upmpg.com/tech_articles/motoroil_viscosity/

 

well thought i read something like that in a davetheoilguy article, he recommends running 0w-30 and that 90% of engine wear is done at start-up