I have a 455 Pontiac with 2300 miles since the rebuild. Well the other day oil pressure dropped. It gets about 5 and idle and 20 down the hwy. It used to get 40 to 60. No knocking no funny noises. I changed the oil for the 3rd time since the rebuild, it was dirty but no metal shavings that i can see. Bad oil pump? Stuck check valve? Spun cam bearing? Just wanting opinons before I pull the engine out again
I know it's getting down to 5 pounds at times because I have the fuel pump wired into a sending unit and it shuts off the Holley blue fuel pump. it's a Stewart Warner green line mechanical gauge. I may go buy a new gauge to see if it's any different
I'll bet that one of the oil galley plugs behind the timing chain popped out, seen it happen before, and causes a big oil pressure loss.
Third oil change w/2300 miles and the oil is dirty? Who rebuilt the engine a reputable engine shop or you? After the obvious, oil gauge,sender, etc, you need to cut open the filter and look for particles, not just the drained oil. What brand oil filter? What brand oil, and did you use a ZDDP additive if needed? What was mentioned above about the popped galley plug is a definate possibility.
If the plug popped out, wouldn't there be oil all over the place? There was no mention of oil on the ground.
The plugs are be behind the timing chain cover so it wouldn't leak oil out on the ground. I had this exact same experience once, now I tap them out for NPT (screw in) plugs on every engine I build.
It has the tapped in plugs. Calvert engines in Denton Texas did the machine work. He is well known in the Dallas area for building Pontiacs. had another shop put the bottom end together. I use wix filters and Rotella oil. Havent cut the filter open yet. Has anyone sent an oil sample to Blackstone labs for analysis? I'm gonna do that to see what they say
Sin, I would save my money on the analysis, and start to diagnose/tear down and look for a direct mechanical reason for the pressure drop. Just saying from decades of dyno experience, cut open the filter, if nothing there is significant, drop the pan next. Also, forget the Rotella oil for the future, do a search on here and you will find oils that will do everything you need even without adding any additives, loose the Rotella!
The lab test won't really tell you was the exact cause of low oil pressure. If it were me I'd change the oil filter first, even though you have a Wix filter dosn't mean that it can't be the cause, then try another mechanical guage. Never assume that a pro engine shop can't make a mistake, or forget something.
Had the same issue with my 348" and there was absolutly no knocking or any other funny sound in it. After I tried with new gauges and senders I finaly pulled the pan and what a chock. On the bottom was all the babbit from the bearings and I could wiggle the rodend back and forth on the crank so there was a clicking sound and there was no knocking att all when it was running. Sounds to me that you have the same problem. Not fun to here but I would have pulled the pan and check. I too had a machineshop to do the job but they didn´t take it on a warranty. Had to regrind all bearingtaps on the crank and put new bearings in it and after that was done it works just fine.
# 15 sounds like my experience with 10 k on a 351 W build.....Oil pres went way down, I dropped the pan and the mains were wiped,....Slipped in some new inserts, and it's still running strong. I guess there's bad bearing material out there..... I was lucky, the crank was still ok. 4TTRUK
new sender, old mechanical gauge. Gonna try a new gauge. I have changed the oil and put a new filter on it. Its about 10 psi at idle till it warms up then drops to below 5. Guess the engine is coming out again. Thinking of going roller cam this time. Since its coming apart. Then I dont have to worry so much about ZDDP
Isnt that what a mechanical gauge is? Live oil line to the gauge. I have never ran an electrical gauge in any of my cars
In the old days of nylon timing gears, Pontiacs were known for sucking the pieces into the oil pump and either sticking the relief valve open or closed. If it stuck closed it would blow the filter off or blow an oil galley plug out. If it sticks open, the oil pressure is low at idle. I never understood why they had that hole in the suction screen.
Oil report from Blackstone Labs. Got this back today on the 64 Tempest. Sounds like a bearing problem to me. Dont know about the coolant deal though. Soon as I get some free time I'll get it apart. I attached the pdf file if anyone wants to see it Wear metals are a little on the high side, but the engine is still fairly new so some of the metal could be residual wear-in. Unfortunately, potassium, silicon, and sodium may show a little coolant in the oil. Sodium could also be residual oil additive, though with the bearing wear that's showing up, we're leaning toward it being antifreeze. Check the cooling system if you can. The elevated viscosity could be the result of antifreeze.
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