# loose oil pressure at low rpm??



## skapegoat (Nov 5, 2008)

I have a 74 455 with 6x-4 heads. When the engine is cold the oil pressure stays where it is supposed to be. But when it gets up to temp I loose all oil pressure at idle. I even put a couple quarts of 50 weight race oil with zinc, helped but still has the problem. Anyone have any ideas?


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## pontiac (Mar 6, 2011)

what do you mean by all oil pressure, does the idiot light come on? If gauges, where is your sender located?


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## skapegoat (Nov 5, 2008)

The engine had a light sensor when I got the car but the car has gauges so I changed the sensor to a gauges sensor. Now the gauge says it has good oil pressure when the oil is cold and the engine is above 1000 rpm, but when it is at idol the gauge says there is no oil pressure. But the engine dosent sound like it has lost oil pressure. Running out of ideas why it would loose pressure like that.


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## Eric Animal (Oct 28, 2007)

VERIFY gauge accuracy with another gauge and sender. If it is a mechanical gauge, the line could be clogged. Change the oil filter also......Are the lifters clicking at idle? Look in the oil filler on the valve cover and see if the engine is pumping oil up to the rocker arms at idle. Report back with results. GL, Eric


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## geeteeohguy (Feb 2, 2008)

I agree with Eric. Verify that there is actually little or no oil pressure. Normally, you'd have lifters clacking away and other bad noises going on. If it truly has no oil pressure at idle when hot, it could be oil pump issues, or worn bearings.


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## 646904GTO (Feb 10, 2008)

Yep just look under the filler cap when it is running and you will see oil running along the head. If the gauge travel is only 20 degrees or less I would consider a better quality gauge like Stewart-Warner 0-80 that reads 300 degrees travel. You will probably have 25-35 at hot low idle and a touch of the throttle it will jump over 60 at least...IF you are running a high pressure pump. My Pontiac oil senders come off the oil filter adapter and I have seen the tube plugged up in the past.


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## skapegoat (Nov 5, 2008)

The engine has maybe 6000 miles on it so the bearings should be good. Earlier this summer I noticed the rockers were clacking so I changed the oem nuts with the kind that have the allen head locking screw. When I was doing that I had to start the engine a few times without the valve covers and oil was pumping good enough to splatter the wall 3' away at idol. The sensor is probably a couple months old and the previous one was for oil light which is why I changed it in the first place. Usually when an engine looses pressure you can hear the bearings scraping but when this one looses it there is no obvious sound of scraping bearings. Could the new sensor from advanced not be reading right at low rpms? Its an automatic shouldn't the pressure be a constant number and not fluctuate as much as a manual?


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## Eric Animal (Oct 28, 2007)

I would suspect the sensor (new: chinese) usually. BUT, ya gotta be sure!


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## markdavid (Nov 29, 2009)

You state the engine has only 6000 mileson it since built.Was this just a refresh by yourself in the garage or built in a machine shop ? Any line boaring on the mains , crankshaft turned , rods resized , cam bearings installed ,etc. Incorrect clearances will cause exactly the problem you state just as in an old engine with alot of miles. Oil pressure is always more on any car when cold ,well,because it is cold.That is why some manufacturers(chevy)put oil pressure relief valves at the filters as well ,but if they are faulty it will cause loss of pressure as well.Several companies make a billet oil filter adapter without the valves in it to erase this problem,but i don`t think pontiac has but one valve ,and it is in the oil pump itself.You got to love it,but if the oil pressure guage doesn`t seem to solve your problem ,pull it! Good Luck .


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## skapegoat (Nov 5, 2008)

I bought this car as a shell with a new engine. Supposedly the engine was professionally built for drag racing. I think the sensor probably is the problem but what part store sells a good quality sensor?


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## Rukee (Feb 8, 2007)

I have a mechanical gauge just for instances like this, I would install and read the actual pressure.


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