low oil pressure
Thread Starter
Junior Member
Joined: Feb 2005
Posts: 60
Likes: 0
From: Paducah, KY
Car: 89 Trans AM GTA, 99 Olds Alero GLS
Engine: TPI 350 L98
Transmission: 700r4
Axle/Gears: Borg Warner 3.27
low oil pressure
I need to find out what is the problem with my 89 Trans Am GTA. When I crank up and the engine is cold the oil pressure reads about 35 or 40 lbs. After it gets hot, it drops all the way to about 8-10 at a stop light and about 25-30 at driving speed. Also when the motor is hot, it sounds like the lifters are knocking. They dont act up till the engine is hot and I am driving down the road. The sound gets louder as I get into higher RPMs and stops again when it the RPMs get lower 
. Someone told me bad main bareings probably. It supposedly has a high volume oil pump from about 3 yrs back when a guy, that I found out after I had him do it that he drinks allllll the time
, rebuilt my engine; so I dont know what he really did to my engine if anything. Any help would be great! If I do have to change the main bareings, how hard is that?
. Someone told me bad main bareings probably. It supposedly has a high volume oil pump from about 3 yrs back when a guy, that I found out after I had him do it that he drinks allllll the time , rebuilt my engine; so I dont know what he really did to my engine if anything. Any help would be great! If I do have to change the main bareings, how hard is that? 
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iTrader: (1)
Joined: Dec 2004
Posts: 2,492
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From: Arcadia ,Ca
Car: 82 firebird s/e 83 Trans Am
Engine: 5.0L 305ci 4b carb.....CFI
Transmission: TH200C....700R4
When was the last time you changed your oil?Maybe its just due for an oil change?
Supreme Member
iTrader: (1)
Joined: Dec 2004
Posts: 2,492
Likes: 0
From: Arcadia ,Ca
Car: 82 firebird s/e 83 Trans Am
Engine: 5.0L 305ci 4b carb.....CFI
Transmission: TH200C....700R4
maybe this will help..........
Diagnostic Tips
A good place to start your diagnosis of a low pressure condition is at the dipstick. Check the oil to see that it's at the proper level (not low nor overfilled). If low, the engine may be burning or leaking oil. Adding oil may temporarily remedy the low pressure condition, but unless the level is properly maintained, the problem may recur.
If the engine is leaking oil, try new gaskets or seals to fix the leak. If the engine is burning oil, the valve guides and seals are most likely worn, but the rings and cylinders might be bad, too. A wet compression test and/or leakdown test will tell you if it's the valve guides or rings and cylinders that are worn.
The least expensive fix in the case of worn guides is to install new valve guide seals (if possible) without pulling the head.
The best fix is to pull the heads and have the guides lined, knurled, replaced or reamed for oversized valve stems. Worn rings and cylinders would call for a complete overhaul.
Also note the condition of the oil and make sure it's the correct viscosity for your car and climate.
Heavier viscosities, such as 20W-50, straight 30W or 40W, may help maintain good pressure in hot weather but are too thick for cold weather driving and may cause start-up lubrication problems - especially in overhead cam engines.
Light viscosities, on the other hand, such as straight 10W or 5W-20, may improve cold weather starting and lubrication but may be too thin in hot weather driving to maintain good pressure.
That's why most car and OE parts manufacturers recommend 5W-30 in modern engines for year-round driving.
If the level is okay, the next thing to check would probably be the pressure sending unit. Disconnect the unit and check the warning lamp or gauge reading.
If the warning light remains on with the sending unit disconnected, there's probably a short to ground in the warning lamp circuit. Likewise, if there's no change in a gauge reading, the problem is in the instrumentation, not the engine.
Bad sending units are quite common, so many mechanics replace the unit without checking anything else to see if that cures the problem. This approach might save time, but it's risky because unless you measure pressure directly with a gauge attached to the engine, you have no way of knowing if pressure is within specifications or not.
Most warning lamps won't come on until pressure is dangerously low (less than four or five pounds). So don't assume the absence of a warning lamp means pressure is okay, especially if the engine is making any valve or bearing noise.
If a check of pressure reveals unusually low readings, check the filter. It's possible the filter might be plugged with gunk. Replace the filter and see if that makes a difference.
The next step is to drop the oil pan and check the oil pump pickup screen. If the screen is clogged with debris, you've found the problem. Also, check to see that the pickup tube is properly mounted and positioned, is firmly attached to the pump (no leaks) and is not obstructed.
If the pump is mounted inside the crankcase, the next step might be to remove and inspect the pump. Open the pump cover and measure clearances. Also, check for scoring or other damage. A broken pump drive would tell you something entered and jammed the pump. If the pump is worn or damaged, replacement is your only option.
If the pump appears to be okay, the next step is to measure the rod and main bearing clearances. Check the clearances on the main bearing closest to the pump (this has the greatest effect on pressure) and clearances on the furthest rod bearing (this will show the greatest wear).
If the bearings are worn, they need to be replaced. But before you do so, carefully inspect and measure the crankshaft journals to check for wear, scoring, out-of-round and taper. If the journals need attention, the crank will also have to be reground or replaced.
Other diagnostic checks might include camshaft end play and/or pulling a valve cover or the intake manifold to check the cam bearings and lifters.
Remember, excessive clearances or leaks anywhere in the engine's oil supply system can contribute to low pressure.
Once you've identified and repaired discovered problems, your final check is to start the engine and make sure pressure is within your car's specifications. Use a mechanical pressure gauge and don't rely on the dash gauge or the warning light to verify that the repairs you've made have eliminated your problem.
One Final Warning
If you insist on driving blind and deaf to the obvious warnings coming from under your car's hood, the next sound you hear may be a rapping or knock noise from the rod bearings - which will eventually be followed by dead silence as your engine seizes and your car coasts to a dead stop.
Diagnostic Tips
A good place to start your diagnosis of a low pressure condition is at the dipstick. Check the oil to see that it's at the proper level (not low nor overfilled). If low, the engine may be burning or leaking oil. Adding oil may temporarily remedy the low pressure condition, but unless the level is properly maintained, the problem may recur.
If the engine is leaking oil, try new gaskets or seals to fix the leak. If the engine is burning oil, the valve guides and seals are most likely worn, but the rings and cylinders might be bad, too. A wet compression test and/or leakdown test will tell you if it's the valve guides or rings and cylinders that are worn.
The least expensive fix in the case of worn guides is to install new valve guide seals (if possible) without pulling the head.
The best fix is to pull the heads and have the guides lined, knurled, replaced or reamed for oversized valve stems. Worn rings and cylinders would call for a complete overhaul.
Also note the condition of the oil and make sure it's the correct viscosity for your car and climate.
Heavier viscosities, such as 20W-50, straight 30W or 40W, may help maintain good pressure in hot weather but are too thick for cold weather driving and may cause start-up lubrication problems - especially in overhead cam engines.
Light viscosities, on the other hand, such as straight 10W or 5W-20, may improve cold weather starting and lubrication but may be too thin in hot weather driving to maintain good pressure.
That's why most car and OE parts manufacturers recommend 5W-30 in modern engines for year-round driving.
If the level is okay, the next thing to check would probably be the pressure sending unit. Disconnect the unit and check the warning lamp or gauge reading.
If the warning light remains on with the sending unit disconnected, there's probably a short to ground in the warning lamp circuit. Likewise, if there's no change in a gauge reading, the problem is in the instrumentation, not the engine.
Bad sending units are quite common, so many mechanics replace the unit without checking anything else to see if that cures the problem. This approach might save time, but it's risky because unless you measure pressure directly with a gauge attached to the engine, you have no way of knowing if pressure is within specifications or not.
Most warning lamps won't come on until pressure is dangerously low (less than four or five pounds). So don't assume the absence of a warning lamp means pressure is okay, especially if the engine is making any valve or bearing noise.
If a check of pressure reveals unusually low readings, check the filter. It's possible the filter might be plugged with gunk. Replace the filter and see if that makes a difference.
The next step is to drop the oil pan and check the oil pump pickup screen. If the screen is clogged with debris, you've found the problem. Also, check to see that the pickup tube is properly mounted and positioned, is firmly attached to the pump (no leaks) and is not obstructed.
If the pump is mounted inside the crankcase, the next step might be to remove and inspect the pump. Open the pump cover and measure clearances. Also, check for scoring or other damage. A broken pump drive would tell you something entered and jammed the pump. If the pump is worn or damaged, replacement is your only option.
If the pump appears to be okay, the next step is to measure the rod and main bearing clearances. Check the clearances on the main bearing closest to the pump (this has the greatest effect on pressure) and clearances on the furthest rod bearing (this will show the greatest wear).
If the bearings are worn, they need to be replaced. But before you do so, carefully inspect and measure the crankshaft journals to check for wear, scoring, out-of-round and taper. If the journals need attention, the crank will also have to be reground or replaced.
Other diagnostic checks might include camshaft end play and/or pulling a valve cover or the intake manifold to check the cam bearings and lifters.
Remember, excessive clearances or leaks anywhere in the engine's oil supply system can contribute to low pressure.
Once you've identified and repaired discovered problems, your final check is to start the engine and make sure pressure is within your car's specifications. Use a mechanical pressure gauge and don't rely on the dash gauge or the warning light to verify that the repairs you've made have eliminated your problem.
One Final Warning
If you insist on driving blind and deaf to the obvious warnings coming from under your car's hood, the next sound you hear may be a rapping or knock noise from the rod bearings - which will eventually be followed by dead silence as your engine seizes and your car coasts to a dead stop.
Supreme Member
Joined: Jul 2004
Posts: 1,840
Likes: 1
From: Tigard, Oregon
Car: '86 Berlinetta
Engine: 350
Transmission: 700R4
Originally posted by 82knightrider
maybe this will help..........
Diagnostic Tips
A good place to start your diagnosis of a low pressure condition is at the dipstick. Check the oil to see that it's at the proper level (not low nor overfilled). If low, the engine may be burning or leaking oil. Adding oil may temporarily remedy the low pressure condition, but unless the level is properly maintained, the problem may recur.
If the engine is leaking oil, try new gaskets or seals to fix the leak. If the engine is burning oil, the valve guides and seals are most likely worn, but the rings and cylinders might be bad, too. A wet compression test and/or leakdown test will tell you if it's the valve guides or rings and cylinders that are worn.
The least expensive fix in the case of worn guides is to install new valve guide seals (if possible) without pulling the head.
The best fix is to pull the heads and have the guides lined, knurled, replaced or reamed for oversized valve stems. Worn rings and cylinders would call for a complete overhaul.
Also note the condition of the oil and make sure it's the correct viscosity for your car and climate.
Heavier viscosities, such as 20W-50, straight 30W or 40W, may help maintain good pressure in hot weather but are too thick for cold weather driving and may cause start-up lubrication problems - especially in overhead cam engines.
Light viscosities, on the other hand, such as straight 10W or 5W-20, may improve cold weather starting and lubrication but may be too thin in hot weather driving to maintain good pressure.
That's why most car and OE parts manufacturers recommend 5W-30 in modern engines for year-round driving.
If the level is okay, the next thing to check would probably be the pressure sending unit. Disconnect the unit and check the warning lamp or gauge reading.
If the warning light remains on with the sending unit disconnected, there's probably a short to ground in the warning lamp circuit. Likewise, if there's no change in a gauge reading, the problem is in the instrumentation, not the engine.
Bad sending units are quite common, so many mechanics replace the unit without checking anything else to see if that cures the problem. This approach might save time, but it's risky because unless you measure pressure directly with a gauge attached to the engine, you have no way of knowing if pressure is within specifications or not.
Most warning lamps won't come on until pressure is dangerously low (less than four or five pounds). So don't assume the absence of a warning lamp means pressure is okay, especially if the engine is making any valve or bearing noise.
If a check of pressure reveals unusually low readings, check the filter. It's possible the filter might be plugged with gunk. Replace the filter and see if that makes a difference.
The next step is to drop the oil pan and check the oil pump pickup screen. If the screen is clogged with debris, you've found the problem. Also, check to see that the pickup tube is properly mounted and positioned, is firmly attached to the pump (no leaks) and is not obstructed.
If the pump is mounted inside the crankcase, the next step might be to remove and inspect the pump. Open the pump cover and measure clearances. Also, check for scoring or other damage. A broken pump drive would tell you something entered and jammed the pump. If the pump is worn or damaged, replacement is your only option.
If the pump appears to be okay, the next step is to measure the rod and main bearing clearances. Check the clearances on the main bearing closest to the pump (this has the greatest effect on pressure) and clearances on the furthest rod bearing (this will show the greatest wear).
If the bearings are worn, they need to be replaced. But before you do so, carefully inspect and measure the crankshaft journals to check for wear, scoring, out-of-round and taper. If the journals need attention, the crank will also have to be reground or replaced.
Other diagnostic checks might include camshaft end play and/or pulling a valve cover or the intake manifold to check the cam bearings and lifters.
Remember, excessive clearances or leaks anywhere in the engine's oil supply system can contribute to low pressure.
Once you've identified and repaired discovered problems, your final check is to start the engine and make sure pressure is within your car's specifications. Use a mechanical pressure gauge and don't rely on the dash gauge or the warning light to verify that the repairs you've made have eliminated your problem.
One Final Warning
If you insist on driving blind and deaf to the obvious warnings coming from under your car's hood, the next sound you hear may be a rapping or knock noise from the rod bearings - which will eventually be followed by dead silence as your engine seizes and your car coasts to a dead stop.
maybe this will help..........
Diagnostic Tips
A good place to start your diagnosis of a low pressure condition is at the dipstick. Check the oil to see that it's at the proper level (not low nor overfilled). If low, the engine may be burning or leaking oil. Adding oil may temporarily remedy the low pressure condition, but unless the level is properly maintained, the problem may recur.
If the engine is leaking oil, try new gaskets or seals to fix the leak. If the engine is burning oil, the valve guides and seals are most likely worn, but the rings and cylinders might be bad, too. A wet compression test and/or leakdown test will tell you if it's the valve guides or rings and cylinders that are worn.
The least expensive fix in the case of worn guides is to install new valve guide seals (if possible) without pulling the head.
The best fix is to pull the heads and have the guides lined, knurled, replaced or reamed for oversized valve stems. Worn rings and cylinders would call for a complete overhaul.
Also note the condition of the oil and make sure it's the correct viscosity for your car and climate.
Heavier viscosities, such as 20W-50, straight 30W or 40W, may help maintain good pressure in hot weather but are too thick for cold weather driving and may cause start-up lubrication problems - especially in overhead cam engines.
Light viscosities, on the other hand, such as straight 10W or 5W-20, may improve cold weather starting and lubrication but may be too thin in hot weather driving to maintain good pressure.
That's why most car and OE parts manufacturers recommend 5W-30 in modern engines for year-round driving.
If the level is okay, the next thing to check would probably be the pressure sending unit. Disconnect the unit and check the warning lamp or gauge reading.
If the warning light remains on with the sending unit disconnected, there's probably a short to ground in the warning lamp circuit. Likewise, if there's no change in a gauge reading, the problem is in the instrumentation, not the engine.
Bad sending units are quite common, so many mechanics replace the unit without checking anything else to see if that cures the problem. This approach might save time, but it's risky because unless you measure pressure directly with a gauge attached to the engine, you have no way of knowing if pressure is within specifications or not.
Most warning lamps won't come on until pressure is dangerously low (less than four or five pounds). So don't assume the absence of a warning lamp means pressure is okay, especially if the engine is making any valve or bearing noise.
If a check of pressure reveals unusually low readings, check the filter. It's possible the filter might be plugged with gunk. Replace the filter and see if that makes a difference.
The next step is to drop the oil pan and check the oil pump pickup screen. If the screen is clogged with debris, you've found the problem. Also, check to see that the pickup tube is properly mounted and positioned, is firmly attached to the pump (no leaks) and is not obstructed.
If the pump is mounted inside the crankcase, the next step might be to remove and inspect the pump. Open the pump cover and measure clearances. Also, check for scoring or other damage. A broken pump drive would tell you something entered and jammed the pump. If the pump is worn or damaged, replacement is your only option.
If the pump appears to be okay, the next step is to measure the rod and main bearing clearances. Check the clearances on the main bearing closest to the pump (this has the greatest effect on pressure) and clearances on the furthest rod bearing (this will show the greatest wear).
If the bearings are worn, they need to be replaced. But before you do so, carefully inspect and measure the crankshaft journals to check for wear, scoring, out-of-round and taper. If the journals need attention, the crank will also have to be reground or replaced.
Other diagnostic checks might include camshaft end play and/or pulling a valve cover or the intake manifold to check the cam bearings and lifters.
Remember, excessive clearances or leaks anywhere in the engine's oil supply system can contribute to low pressure.
Once you've identified and repaired discovered problems, your final check is to start the engine and make sure pressure is within your car's specifications. Use a mechanical pressure gauge and don't rely on the dash gauge or the warning light to verify that the repairs you've made have eliminated your problem.
One Final Warning
If you insist on driving blind and deaf to the obvious warnings coming from under your car's hood, the next sound you hear may be a rapping or knock noise from the rod bearings - which will eventually be followed by dead silence as your engine seizes and your car coasts to a dead stop.
Damn man, you covered all the bases lol. Nice write up
.By the sounds of it, you've got ROD knock. spun mains would go away after 2000RPM or so.... while rod knock gets continually worse upon the RPMs. Either way, you're looking at a rebuild :-(. Or at the very least having everything hot tanked, replace the bearings and freeze plugs, and oil pump while you're at it.
Supreme Member
iTrader: (1)
Joined: Dec 2004
Posts: 2,492
Likes: 0
From: Arcadia ,Ca
Car: 82 firebird s/e 83 Trans Am
Engine: 5.0L 305ci 4b carb.....CFI
Transmission: TH200C....700R4
Originally posted by sellmanb
Damn man, you covered all the bases lol. Nice write up .
By the sounds of it, you've got ROD knock. spun mains would go away after 2000RPM or so.... while rod knock gets continually worse upon the RPMs. Either way, you're looking at a rebuild :-(. Or at the very least having everything hot tanked, replace the bearings and freeze plugs, and oil pump while you're at it.
Damn man, you covered all the bases lol. Nice write up
.By the sounds of it, you've got ROD knock. spun mains would go away after 2000RPM or so.... while rod knock gets continually worse upon the RPMs. Either way, you're looking at a rebuild :-(. Or at the very least having everything hot tanked, replace the bearings and freeze plugs, and oil pump while you're at it.
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Thread Starter
Junior Member
Joined: Feb 2005
Posts: 60
Likes: 0
From: Paducah, KY
Car: 89 Trans AM GTA, 99 Olds Alero GLS
Engine: TPI 350 L98
Transmission: 700r4
Axle/Gears: Borg Warner 3.27
Thank you very much Knightrider for that hugh piece you found. I dont want to rebuild that engine again! Well, I guess my big plans are gone again till I can get enough money to have the motor redone...I might as well go and try to do my 383 I wanted now. Thanks to everyone too for the help.
Well, I guess my big plans are gone again till I can get enough money to have the motor redone...I might as well go and try to do my 383 I wanted now. Thanks to everyone too for the help. Supreme Member
Joined: Jul 2004
Posts: 1,840
Likes: 1
From: Tigard, Oregon
Car: '86 Berlinetta
Engine: 350
Transmission: 700R4
try some higher weight oil in your car to hide the knock until you can afford a new engine/engine rebuild. You just wont be able to rev very high w/o doing even more damage.... but it's better than being w/o a car.
Thread Starter
Junior Member
Joined: Feb 2005
Posts: 60
Likes: 0
From: Paducah, KY
Car: 89 Trans AM GTA, 99 Olds Alero GLS
Engine: TPI 350 L98
Transmission: 700r4
Axle/Gears: Borg Warner 3.27
I think I found out about the knocking sound 
. It seemed to be my timing that was off. I have been playing with it today and I had it set to high and thats why it did that. Just wierd that it only made that sound when it got hot, but oh well if that cured it I am happy. The engine has a different cam in it (dont know the specs, the guy wrote it down on a torn off piece of paper). I marked the spot now. Also, my timing jumps on me so I can never get it set just right. I used to have it higher since it had better take offs. Now it is a little sluggish but it doesnt knock at all...I drove it for like 45 mins straight and it sounded great! The oil pressure is still low though. Maybe things isnt as bad as I first thought they was
I kinda wonder about the sending unit. I am going to drive it like this for a little while to see if the knocking comes back and if it doesnt I can start on my cam and headers! Hopefully I can get it where it wont be as sluggish anymore. I used to run 50w oil in it before it got the rebuild but it held oil pressure good after the build so I stopped. I guess I should go back to the racing oil again if I can not find out the problem.
. It seemed to be my timing that was off. I have been playing with it today and I had it set to high and thats why it did that. Just wierd that it only made that sound when it got hot, but oh well if that cured it I am happy. The engine has a different cam in it (dont know the specs, the guy wrote it down on a torn off piece of paper). I marked the spot now. Also, my timing jumps on me so I can never get it set just right. I used to have it higher since it had better take offs. Now it is a little sluggish but it doesnt knock at all...I drove it for like 45 mins straight and it sounded great! The oil pressure is still low though. Maybe things isnt as bad as I first thought they was I kinda wonder about the sending unit. I am going to drive it like this for a little while to see if the knocking comes back and if it doesnt I can start on my cam and headers! Hopefully I can get it where it wont be as sluggish anymore. I used to run 50w oil in it before it got the rebuild but it held oil pressure good after the build so I stopped. I guess I should go back to the racing oil again if I can not find out the problem. 
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