I build stand alone LS swap packages. Most of the donors are from insurance wrecks so very little history if any is available and many are not able to be run before dismantling. All of my packages are put together and test run on a stand to check them over before they go out and the customer can see/hear them run. I just put together a LQ4 for a fellow and was running it on the stand when I noticed that the oil pressure would continue to climb as I revved up the engine. When warm it sits at about 40 psi at idle but will hit 100 - 110 psi at 4500 rpm and I did not push it past that. I'm sure the oil filter was close to letting go at that.

My first thought was the pressure relief valve in the oil pump was stuck. Installed a new Melling pump with no better results. The engine was middle of the road for sludge inside. I have seen better but have seen far worse that ran fine.
My next thought is a plugged lifter or two but there is no lifter noise at all. In fact this thing runs perfectly with no smoke, ticks, rattles, etc.
The oil pressure gauge is mechanical and I even swapped it with a new on just to be sure that wasn't the problem.
I did do a search but could not come up with much more than what I tried. Some fellows were suggesting a plugged oil filter or oil passage. I cant see how that could cause the issue when the pressure relief valve is in the pump which is before any of the oil passages and filter.

Any thoughts on this one would be appreciated.

 

Maybe drop the pan and use an external preluber and see if oil is flowing, but I’m confused if it isn’t making any noise or anything.

 

maybe try a different guage

 

He did...

 

Did you change the oil filter?

 

I'm quite confident that the oil is flowing. I pulled the valve covers and each of the rockers has puddles of oil in the recesses as well as the heads. I always pull the covers before I fire these things up to do a visual inspection as I have had the odd one with a bad rocker. It was quite dry under the covers before the start up as this one was from a theft recovery that had sat around for quite some time.
I'll probably end up putting a set of lifters in it as it is not a huge deal when the engine is sitting on a test stand. I just thought that I would throw it out there to see if anyone else had ever run into this or had another idea what could be the cause. It's not the expense so much so long as it fixes the problem... I just hate wasting a bunch of shop time if it still doesn't cure the problem and I end up having to rebuild it anyway.

 

Yes I did.... twice. I always drop the oil and change the filter before the initial start up. The filters I use are AC Delco's. As I mentioned, I did a a bunch of searching prior to posting and a few fellows claimed that a bad filter could cause this issue.
Although I could not see how that could cause the issue when the filter is downstream from the pressure relief valve, I replaced the new oil filter with another one... just to be sure and try the easy stuff first.

I have given this issue some considerable thought through the night... my version of counting sheep. I think what is happening is one or more lifters are clogged and are back feeding the oil passages. The backflow valve in the oil filter is preventing the pressure relief valve from doing its job and because the port for the oil pressure gauge is between the oil filter and the valve train it is registering the pressure of the clogged lifter(s) back feeding the oil passages.
The offending lifter(s) are continually pressured up and at 50 - 100+ psi oil pressure there will be all kinds of oil spraying around under the valve cover to lube the rocker(s) that are not getting oil from the clogged lifter, so, no strange noises.
But just a theory at this point.

 

"Installed a new Melling pump with no better results. "

Interesting issue. Remember NEW = never even worked. i.e. unless verified, we're hopeful with new parts. Since max oil pressure is dictated by the oil pump relief valve spring, verify oil pump relief valve and make sure there is no restriction in the relief port to pan. Where are you measuring pressure?

 

Thanks for all of the replies.... great forum. It has been a great resource over the past 5 years.

I have gotten to the bottom of the problem. It was indeed the lifters... not just one or two but all 16 of them. Couldn't mess around any longer as I had a customer wondering where his engine was so I pulled the heads.
When I pulled the lifters every one of them had the plungers stuck partially down so the small washer in there was free floating between the retaining clip and the stuck plunger. This area would fill up with oil and when the cam opened the valve this oil was back fed into the oil passage by the washer being forced back down to the plunger... x 16! Little wonder that oil pressure was hitting over 100 psi.

The excess oil could not bleed off at the pressure relief valve because of the backflow valve in the filter and I was picking up the oil pressure at the sending unit port which is in the oil passage between the valve train and the oil filter.
I believe what happened to the lifters to be the fact that this engine sat for quite some time. The dark brown film that is on the internal parts of lots of these engines dried out and became non viscous causing the plungers to hang up. The force of the valve spring was enough to push the plunger down but the internal spring and oil pressure could not push it back up.
There was no valve noise because of the cushion of oil between the plunger and washer. Because nothing was actually clogged, lots of oil at the rockers.

Set of lifters and oil pressure is normal... 45 years turning wrenches and still learning.

 

Thanks for the update

 

No problem.... it's the least I could do. As mentioned I have found this forum a very valuable tool over the years, especially the first couple of years starting into the LS world. I always find it a little frustrating following a thread and coming to the end with no solution or outcome. If my follow up helps even one other person, it was worth the effort.