BBC 454 Oil Pressure
Thread Starter
Teching In
Joined: Dec 2006
Posts: 7
Likes: 0
From: AZ
BBC 454 Oil Pressure Hello to All,
I have been a long time follower, but dorment for a while.
Happy New Year!
I have an issue with low oil pressure on my 1982 454 C20. The engine has 277,000 miles on it. I know most of you will say just rebuild the engine, but that is not in the cards right now. The engine runs just fine, it is stock but for a mild hydralic cam. I have tuned it to pass emissions with flying colors. It starts right up and never makes any knocking or tapping sounds.
When I fire it up cold (even on 110 deg AZ days) it has 60 + PSI oil pressure.
As it warms up, the oil pressure always gradually goes down. It never goes past 1/4 (25%) on the water temp guage. But when fully warm, at idle (700 rpm) oil pressure will go down to about 7 PSI. Yes 7. at cruise it is about 20. As I said, even at idle there is no knocking or tapping from the engine. I have replaced the oil pressure sensor many times, not because of this but because the oil pressure sensors fail over time. I have used old NOS GM, new GM (Chinese junk) and quality aftermarket, all read the same on the guage.
So obviously, something in the engine, some clearance somewhere, is opening up as the engine warms (don't forget, always 60 + PSI when cold).
Now, I know many will say just rebuild the engine.
But my question is, does anyone have any idea what part of the engine might be expanding enough to do this? What is most likely? More likely than others. For example, the main bearings, the rod bearings come immediately to mind, but what about the oil pump? Any other ideas? Since it is a truck, pulling the oil pan is not that bad. So, if there is a chance its the oil pump, I could make that attempt.
Any ideas?
Thanks.
DAP
I have been a long time follower, but dorment for a while.
Happy New Year!
I have an issue with low oil pressure on my 1982 454 C20. The engine has 277,000 miles on it. I know most of you will say just rebuild the engine, but that is not in the cards right now. The engine runs just fine, it is stock but for a mild hydralic cam. I have tuned it to pass emissions with flying colors. It starts right up and never makes any knocking or tapping sounds.
When I fire it up cold (even on 110 deg AZ days) it has 60 + PSI oil pressure.
As it warms up, the oil pressure always gradually goes down. It never goes past 1/4 (25%) on the water temp guage. But when fully warm, at idle (700 rpm) oil pressure will go down to about 7 PSI. Yes 7. at cruise it is about 20. As I said, even at idle there is no knocking or tapping from the engine. I have replaced the oil pressure sensor many times, not because of this but because the oil pressure sensors fail over time. I have used old NOS GM, new GM (Chinese junk) and quality aftermarket, all read the same on the guage.
So obviously, something in the engine, some clearance somewhere, is opening up as the engine warms (don't forget, always 60 + PSI when cold).
Now, I know many will say just rebuild the engine.
But my question is, does anyone have any idea what part of the engine might be expanding enough to do this? What is most likely? More likely than others. For example, the main bearings, the rod bearings come immediately to mind, but what about the oil pump? Any other ideas? Since it is a truck, pulling the oil pan is not that bad. So, if there is a chance its the oil pump, I could make that attempt.
Any ideas?
Thanks.
DAP
higher oil pressure is the result of when the oil is cold (below ~150°) and it having higher viscosity. as the engine gets to around 180° coolant temp your oil temp can be anywhere between 160-200° and higher depending on what you are doing. and if you're in AZ you said 110° outside temperature then most likely you're running hotter oil temperatures.
the first rule in any machinery lubrication is to use an oil of the correct viscosity for the operating temperature. if the operating temperature is high, then you either need a higher viscosity oil or an oil cooler, or somehow get operating temperature within respectable limits. ideal oil temperature is between 160-200°F. if you're running 5w30 oil then that is mostly the cause of your low oil pressure, in AZ in those temps your best choice is a 20w-50 oil.
also realize at idle if it's 700 rpm that the oil pump puts out much less oil than at say 1400 rpm. do you notice your oil pressure rise immediately going from idle up to say 100 rpm? if so the motor is healthy and your experiencing low viscosity oil because of high operating temperature, and 700 rpm compared to 1400 rpm is 50% so the oil pump is putting out half the oil volume at idle compared to 1400 rpm so naturally there will be a reduction in oil pressure, perfectly normal to experience lower oil pressure. the solution to that is to install a higher volume oil pump.
if you can easily drop the pan and replace the oil pump, i would consider doing that and use at least a 15w-40 in AZ. as to what's possibly worn out i would think the rod bearings like said and also the cam bearings. but i wouldn't touch them, at 277k miles if it's running fine with no noises i wouldn't mess it, not until it does start making noise.
the first rule in any machinery lubrication is to use an oil of the correct viscosity for the operating temperature. if the operating temperature is high, then you either need a higher viscosity oil or an oil cooler, or somehow get operating temperature within respectable limits. ideal oil temperature is between 160-200°F. if you're running 5w30 oil then that is mostly the cause of your low oil pressure, in AZ in those temps your best choice is a 20w-50 oil.
also realize at idle if it's 700 rpm that the oil pump puts out much less oil than at say 1400 rpm. do you notice your oil pressure rise immediately going from idle up to say 100 rpm? if so the motor is healthy and your experiencing low viscosity oil because of high operating temperature, and 700 rpm compared to 1400 rpm is 50% so the oil pump is putting out half the oil volume at idle compared to 1400 rpm so naturally there will be a reduction in oil pressure, perfectly normal to experience lower oil pressure. the solution to that is to install a higher volume oil pump.
if you can easily drop the pan and replace the oil pump, i would consider doing that and use at least a 15w-40 in AZ. as to what's possibly worn out i would think the rod bearings like said and also the cam bearings. but i wouldn't touch them, at 277k miles if it's running fine with no noises i wouldn't mess it, not until it does start making noise.
Thread Starter
Teching In
Joined: Dec 2006
Posts: 7
Likes: 0
From: AZ
Thanks for the comments and suggestions so far. Just to clarify a couple of facts:
Any other suggestions are welcomed.
Thanks
DAP
- I run 20W50 oil exclusively all year round.
- The vehicle does not run hot, in fact it runs very cool. It has a new aluminum radiator of greater capacity than original. It never goes above 25% on the water temperature.
- It doesen't make any difference what the ambient temperature is, the oil pressure is the same whether it is 107 deg in the summer or 38 deg in the winter.
- This engine idles at 700 +/- 50 RPM.
I have another vehicle almost exactly the same as this one. A 1981 454 K30 with 48k original miles. This one has 60 PSI oil pressure all the time. Hot or cold, idle or cruise. And this one runs much hotter, water temperature is at 50% guage when warmed up.
Any other suggestions are welcomed.
Thanks
DAP
