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Heavy drop in oil pressure after warm up......anything to check before pulling the pan......

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BanditRX

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Discussion starter · #1 ·
Okay Guys, not happy news in breaking in a rebuilt 396. I put in Lucas 30 sae high zinc oil break in oil for first run of a flat tappet hydraulic cam engine. At first fire, oil pressure on a mechanical gauge was at 60 pounds. After getting carb set to hold 2300 rpm I began to notice oil pressure dropping . After several start and stops tightening up water and gas leaks I noticed oil pressure would start out high and began to drop as motor heated up. As I finished about a 30 minute break in run and began to cut back on rpms , oil pressure sank to about ten pounds. I shut it off and installed another mechanical gauge in the side oil gallery up front and ran the engine again.....and it also showed a drop in pressure to ten pounds.
Is there any thing else to check or do before pulling the oil pan? The engine was built several years ago and I am not sure what oil pump was used, new or used. I do know that it was not a high volume pump. Im now thinking maybe some kind of pick up blockage, pick up fell out , or by pass stuck open problem, any opinions.....thanks.....
 
#2 ·
You may want to try a separate oil press gauge just to make sure its not the issue. Think you could get one that threads right into the block.

If you are going to need to get at the pump you will have to pull the engine.
 
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#5 ·
BanditRX said:
Okay Guys, not happy news in breaking in a rebuilt 396. I put in Lucas 30 sae high zinc oil break in oil for first run of a flat tappet hydraulic cam engine. At first fire, oil pressure on a mechanical gauge was at 60 pounds. After getting carb set to hold 2300 rpm I began to notice oil pressure dropping . After several start and stops tightening up water and gas leaks I noticed oil pressure would start out high and began to drop as motor heated up. As I finished about a 30 minute break in run and began to cut back on rpms , oil pressure sank to about ten pounds. I shut it off and installed another mechanical gauge in the side oil gallery up front and ran the engine again.....and it also showed a drop in pressure to ten pounds.
Is there any thing else to check or do before pulling the oil pan? The engine was built several years ago and I am not sure what oil pump was used, new or used. I do know that it was not a high volume pump. Im now thinking maybe some kind of pick up blockage, pick up fell out , or by pass stuck open problem, any opinions.....thanks.....
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Maybe the bearing clearances are incorrect? Excessive clearances will result in the oil pressure dropping away as the engine warms up. If extreme you will also get some rumbling sounds coming from the mains. I had that happen to me and it turned out that the builder didn't check that the bearings matched what was stamped on them...
 
Discussion starter · #7 ·
Did not think to change the oil filter, and that I will do first. Like I said, the engine was built for another car several years ago, but was not used then . After the rebuild, I pre oiled the system as I always do, and ensured all the rockers were getting oiled. And that is the same filter on it as it was first fired today. Could very well be a problem, thanks guys...
 
Discussion starter · #8 ·
Installed new oil filter and fired up the new engine and had same results, 60 psi of oil pressure at start up and would fall down to about 10 pounds. Shut her down and pulled the pan. MASSIVE OPERATOR ERROR found quickly . Engine rebuilder, me, FAILED to tighten the oil pump bolt. Screwed it right out with my fingers. Brand new Melling pump and pick up, and all looked pretty clean. Just was surprised how "dirty" looking that Lucas break in oil looked with only 45 minutes run time. Guess washing off all that cam/lifter break in paste really dirty s it all up.
Good news is I had the engine on a break in stand, found the problem, and was able to pull it down on the run stand. Mark Worman of Graveyard Kars said they will never install a new engine in a car before running it on the engine stand and that seems to be good advice , at least for the engines I build. While I have had my share of engine building problems , that is the first time I ever pulled a bone head move like this, but like most things, time, effort and money can solve most problems. thanks guys.
 
#10 ·
I'm glad you found the problem! We've all had bone head moves, lol. I'll share mine: I built a 350 out of used parts for my Nova. While breaking in the cam I too noticed the oil pressure going away. I had used a used oil pump, so pulled engine and put new pump in. installed engine and same problem. Even drove it. After drive I heard slight bearing knock. Doh! pulled engine again and checked crank. Yep, put standard bearings on a .010" under crank! That was a valuable and almost catastrophic lesson I learned. After the correct bearings were installed it ran like a champ with great oil pressure.
 
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