Oil system problem/question
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Junior Member
Joined: Dec 2000
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Oil system problem/question
1990 F-150, 4.9L, 110K mi, normal wear & maint, original owner.
Here's the symptoms:
Oil pressure at idle RPM is satisfactory, but when engine speed increases (even modestly) the oil pressure drops off completely. When backed off to idle speed, the pressure comes back to normal. Oil level & color just fine. I do believe the pressure indicator is working properly.
I've read some of of the previous topics dealing with oil pressure problems, but mine seems just opposite of what I've seen from others.
I don't relish the thought of replacing the oil pump in mid-winter and would like to try other methods or ideas first... Anyone have a suggestion? Any ideas other than a faulty oil pump? Maybe a clogged strainer? Is there a good clean & flush product out there anyone has experience with?
Here's the symptoms:
Oil pressure at idle RPM is satisfactory, but when engine speed increases (even modestly) the oil pressure drops off completely. When backed off to idle speed, the pressure comes back to normal. Oil level & color just fine. I do believe the pressure indicator is working properly.
I've read some of of the previous topics dealing with oil pressure problems, but mine seems just opposite of what I've seen from others.
I don't relish the thought of replacing the oil pump in mid-winter and would like to try other methods or ideas first... Anyone have a suggestion? Any ideas other than a faulty oil pump? Maybe a clogged strainer? Is there a good clean & flush product out there anyone has experience with?
Former Sponsor
Joined: Mar 1998
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From: Virginia
Hi Roger,
Welcome to F-150 Online!
Those 4.9's are infamous for clogged oil pickup screens and accumulating sludge if the oil isn't changed every 3000 miles like clockwork, this is very common on these motors.
What I would suggest is to drop the pan, and clean the pickup screen, I don't think you're going to be able to clean it enough with any chemicals. It may or may not be the oil pump itself, it's usually sludge in these cases from the feedback we get from our 4.9 customers.
Once you've got the screen & pickup tube clean, see if that takes care of the problem, and if so, then I would suggest using 1 quart of automatic transmission fluid in place of 1 quart of oil for the next couple of oil changes (meaning 1 qt. tranny fluid with 4 qts. oil if it takes 5 qts. normally), and reduce the oil change interval while you're doing that down to just 1000 miles, or maybe even just 500 miles. Automatic transmission fluid is highly detergent, so it does a good job of cleaning some of the sludge, etc. (it won't get it all of course), it's worth a try. This will hopefully also help to clean the oil passages and galleries from buildup of sludge, so that the oil will flow more freely throughout the oiling system.
Good luck & let us know what happens!
------------------
Mike Troyer
Performance Products, Inc.
National Distributor of Superchips
(540) 862-9515
Email: mtroyer@compuserve.com
Performance Products F150Online Superchip ordering system: F150Online Superchip Ordering System
First National F-150 Online Rally Event Organizer
Welcome to F-150 Online!
Those 4.9's are infamous for clogged oil pickup screens and accumulating sludge if the oil isn't changed every 3000 miles like clockwork, this is very common on these motors.
What I would suggest is to drop the pan, and clean the pickup screen, I don't think you're going to be able to clean it enough with any chemicals. It may or may not be the oil pump itself, it's usually sludge in these cases from the feedback we get from our 4.9 customers.
Once you've got the screen & pickup tube clean, see if that takes care of the problem, and if so, then I would suggest using 1 quart of automatic transmission fluid in place of 1 quart of oil for the next couple of oil changes (meaning 1 qt. tranny fluid with 4 qts. oil if it takes 5 qts. normally), and reduce the oil change interval while you're doing that down to just 1000 miles, or maybe even just 500 miles. Automatic transmission fluid is highly detergent, so it does a good job of cleaning some of the sludge, etc. (it won't get it all of course), it's worth a try. This will hopefully also help to clean the oil passages and galleries from buildup of sludge, so that the oil will flow more freely throughout the oiling system.
Good luck & let us know what happens!
------------------
Mike Troyer
Performance Products, Inc.
National Distributor of Superchips
(540) 862-9515
Email: mtroyer@compuserve.com
Performance Products F150Online Superchip ordering system: F150Online Superchip Ordering System
First National F-150 Online Rally Event Organizer
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Junior Member
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Hey, thanks for the quick replies.
Hmmm, I like the oil filter change idea and will try that - even though it seems unlikely to me, it's just too simple to pass up though... I'll let you know if it works.
I'm going to try some sort of commercial sludge-out product (or two) before I drop the pan, but I suspect S_D is right and it won't do me any good. I'll definately try the ATF in the oil afterward though, that sounds like a good tip. I'm just not ready to shovel the snow out from under that shadetree and get serious until I've exhausted all other options.
Hmmm, I like the oil filter change idea and will try that - even though it seems unlikely to me, it's just too simple to pass up though... I'll let you know if it works.
I'm going to try some sort of commercial sludge-out product (or two) before I drop the pan, but I suspect S_D is right and it won't do me any good. I'll definately try the ATF in the oil afterward though, that sounds like a good tip. I'm just not ready to shovel the snow out from under that shadetree and get serious until I've exhausted all other options.
Senior Member
Joined: Sep 2000
Posts: 136
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From: Glenwood, IA
On an older six, you may have the starts of the fiber cam drive gear going t!ts up too. You need to pull the pan and se exactly what it is that is blocking the pickup. If it is sludge, it may need the cleaning that was spoken of before, if it is fiberous, you need gears too.
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redlariet hit the problem. Clogged oil filter. How it got so clogged, I dunno. Changed it back in September, with the last oil change about 1700 miles ago. Last thing I would have ever thought of, though now it seems obvious.
I slapped in a new filter and the problem (or at least the symptom) was gone. Once I got it home, I went ahead and flushed the motor with Gunk and changed the oil again. Runs beautiful again.
I still plan to drop the oil pan and check the pump, screen, and clean out whatever goo is building up in there. Now I think I can wait to do it in the Spring though. I was sure dreading the idea of a sub-zero evolution in the driveway and I can't stand to just let it sit (and the thought of letting someone else touch my truck is revolting
).
Anyway, thanks for the help! Now lets see if I can return the favor and be of assistance to someone else.
I slapped in a new filter and the problem (or at least the symptom) was gone. Once I got it home, I went ahead and flushed the motor with Gunk and changed the oil again. Runs beautiful again.
I still plan to drop the oil pan and check the pump, screen, and clean out whatever goo is building up in there. Now I think I can wait to do it in the Spring though. I was sure dreading the idea of a sub-zero evolution in the driveway and I can't stand to just let it sit (and the thought of letting someone else touch my truck is revolting
). Anyway, thanks for the help! Now lets see if I can return the favor and be of assistance to someone else.