Oil pump operation

[Gunslinger]

Gents,
As you know Triple X is getting a heart transplant becuase the number one rod bearing went out on her last month, I've had a difficult time understanding the problem, here it is.  When I drive it the temperature would slowly climg to 210 and then stabilze.  Oil pressure would start at 50 psi ( NOS pump from an M38), and then it would slowly drop to about 15-20 psi after about 1/2 hour of driving, stop for a while and get some lunch and the OP would be back to 50 and we start over.  Eventually I lost the number one rod bearing when the OP dropped way low.  Lots of confusion on this issue so let me try a scenario and you tell me if it makes sense.

Suppose the radiator is partially plugged, so marginal cooling causes the temp to run at 200F, the pressure relief on the OP sticks at a significantly open position where I have plenty of pressure with cold oil ( Rotlella 10-40 zinc added) but as ther temp climbs the oil gets thinner and the relief dumps more oil back to sump rather than through the gally, thus starving number 1 rod.  My understanding is that if there is a weak spot in the lube system its at the number 1 bearing.  Does this make sense to you guys?

[Carls_jeep]

A 10-40 wt oil is supposed to get thicker as the temp rises. That is, it should start at 10wt cold and then as the oil temp rises the oil will thicken to keep the thickness relative to the 10wt starting point.

In the days of straight weight oil a 30 wt oil will start at 30 wt at a given spec temp and thin as the temp rises. It will also be thicker than 30 wt when at winter temps.

Since your using a 10-40 wt oil I don't think the thickness of the oil will have a lot of effect because it should be fairly constant.

I have a 180 thermostat in my Jeep and it seldom gets above 190. The only time I have seen it near 200 was on Blue Mountain above 8000 ft in Utah at Calvins.

You may need to have your radiator cleaned and the block flushed. Since your going to rebuild it I suggest boiling the block out and having it line bored and all the oil galleys brushed out. It would be a good idea to check the oil pump and relief valve and everything else to do with the lube system.

I would replace the rod also. I assume you will be grinding the crank.

[Bob W]

210 degrees F is higher than normal for one of these old engines but it is not too hot. 10psi of oil pressure per 1000rpm is adequate. Did the pressure go below this spec? What type of oil filter do you have?

[Gunslinger]

Hey Bob,
I've got what I believe is a Fram oil filter housing, it uses a Napa 1010 cartridge filter.  That is what is so confusing about this problem, the pressure did go below the spec rate, but only about 1/2 hour into use, then, if I let it sit for a bit, it would go back up to the 50 psi range, I don't know where to look for the cause of this problem it just don' t doesn't make good sense in my head.

[Bob W]

The front main journal and therefore the #1 rod share their oil with the oil filter and timing gears so if the oil pressure goes too low they could be the first to fail. Low pressure was probably caused by a "leak" somewhere. Too much clearance is usually the reason but there are many other things too. An oil filter housing without an orifice is another potential leak as is a stuck bypass valve in the oil pump.

[Gunslinger]

Tell me more about the oil filter housing orifice, I'm not up to speed on that one.  I get the orifice on the gear drive, I need to check that and make sure its the right size, but where would I look for an orifice on the oil filter?  and what size would it be?

[Bob W]

The orfice is near the top of the center stand pipe. It looks about the same size as a 1/16" drill bit. For any oil to leave the filter it must pass through this orifice to go down the pipe and out to the timing cover.

[Gunslinger]

I'm going to try and get a picture of the inside of my oil filter canister, would you be able to look at it and see if its correct?

[Bob W]

I'm going to try and get a picture of the inside of my oil filter canister, would you be able to look at it and see if its correct?

Perhaps. It will be difficult to see if there is only one small hole in the stand pipe from a photo.

[Gunslinger]

Hey guys
Found out something new on the sick motor, my guy is taking it apart and diagnosing stuff, it turns out the rods are tighter than the minimim spec. at the bearing surface, meaning they are tighter than they should be at specified touque.  Anybody ever hear of that?  Might be the reason why my rod bearing went out afeter just a couple hundred miles.