351 lost oil pressure
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Elder User
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From: Baltimore
351 lost oil pressure
I have a 1991 Bronco with a 5.8L engine. This engine has 185K miles on it and it was running great. Then, one day the valves started making a bunch of noise and I noticed the oil pressure gauge was showing no pressure. I shut it down and after about 1/2 hour, I started it and the oil pressure gauge was showing normal pressure but the valves were still making a lot of tapping racket. Then, the gauge again dropped to 0.
What is the more common problem with these engines? Is it the oil pressure sending unit going bad or is it the oil pump? If I could be reasonable sure that a new oil pump would fix the problem, I would put a new one in.
That leads me to the next question. Is it possible to drop the pan on this engine while the engine is still in the Bronco?
Thanks,
ron
What is the more common problem with these engines? Is it the oil pressure sending unit going bad or is it the oil pump? If I could be reasonable sure that a new oil pump would fix the problem, I would put a new one in.
That leads me to the next question. Is it possible to drop the pan on this engine while the engine is still in the Bronco?
Thanks,
ron
Lead Driver
Joined: Feb 2003
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From: Oak Harbor, OH
Okay, with the engine makin noise you've already ruled out the sending unit.... And running any engine without oil pressure is very bad for it.. If you're luck you DIDN'T spin a bearing. It will now require a new oil pump, and bearings. Get the standard bearings, a haynes manual, and some plasti-gauge. Check the bearing clearanced with the NEW bearings. You can change it with the engine in the truck, but it's a whole lot easier to do it out.
Elder User
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oil pumps don't fail all at once unless the shaft breaks or the pressure relief gets crud in it and wont close. they run in oil and usually will outlast most other components in the engine, try changing the filter, it may be faulty. You definitely lost most of your pressure but not all or the engine wouldn't run for 30 min.. Also get a mechanical gauge and put it on as fords gauges are basically idiot lights and don't actually give a reading ( if you have over 7-8 lbs they read somewhere on the scale if less they don't read).
Senior User
Joined: Jun 2004
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From: Mid-Missouri
I agree, get a mechanical pressure gauge.
Also, I think you may already be looking at a rebuild. Cam and main bearings wear quickly with little or no oil pressure. After they are worn, it becomes even more likely because the pump won't be able to put out the volume of oil neccessary to take up the additional clearence created by the worn bearing. It is an endless cycle.
Also, I think you may already be looking at a rebuild. Cam and main bearings wear quickly with little or no oil pressure. After they are worn, it becomes even more likely because the pump won't be able to put out the volume of oil neccessary to take up the additional clearence created by the worn bearing. It is an endless cycle.
Junior User
Joined: Jun 2001
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From: Florida
My 1988 5.8L Bronco had same problem, complete loss of oil pressure on the gauge, causing very noisy lifters. Mistake was driving truck 35 miles back home, instead of just having it towed. Oil pressure problem, was a 90 % clogged oil screen [silicone and hard gasket material remnants] in the pickup tube at bottom of oil pan. Replacing oil pump and pickup tube was a three day back breaking job, [engine inside the truck] ... helps to be part magician! At 149K, the 5.8L engine still runs great and doesn't burn oil, but now appears to have a mild knock when it gets hot ... will not chance 100+ mile trips anymore, without a rebuild first.
Oh, had to remove upper intake manifold and motor mount bolts ... then lift front of engine with a shop crane. Removed oil pan bolts, lower pan some to get clearance ... removed two oil pump bolts, one pickup tube support bolt. Once the complete unit is disconnected, oil pan and oil pump assembly can then be removed together from the vehicle. Getting everything back together is even more frustrating. Hope this info helps ... John
Oh, had to remove upper intake manifold and motor mount bolts ... then lift front of engine with a shop crane. Removed oil pan bolts, lower pan some to get clearance ... removed two oil pump bolts, one pickup tube support bolt. Once the complete unit is disconnected, oil pan and oil pump assembly can then be removed together from the vehicle. Getting everything back together is even more frustrating. Hope this info helps ... John
Lead Driver
Joined: Feb 2003
Posts: 8,140
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From: Oak Harbor, OH
FS88, where is the knock coming from? It may just be bearing knock... It is very possible that you could get another 25 to 50k out of that engine by just replacing the rod and main bearings.
Lead Driver
Joined: Feb 2003
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From: Oak Harbor, OH
fords gauges are basically idiot lights and don't actually give a reading ( if you have over 7-8 lbs they read somewhere on the scale if less they don't read).
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Elder User
Joined: Apr 2004
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From: Ocala, Florida
You should be able to drop the oil pan with the engine in the truck. Get a Chilton's book from your local library. I beleive that your bearings are bad. First, check with a manual oil pressure guage and make sure the pressure is dropping.
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Junior User
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From: Florida
Knock sound appears to be at lower rear on the passenger side, but my hearing is not keen. Went to using straight 40W Castrol ... made little difference.
Believe the oil gauge in my "88 Bronco is an idiot light ... if I remove and "ground" oil switch connector wire, [with key in on position] the gauge will read normal on dash, even when engine is not running. Have read posts which say if oil pressure drops below 7 psi, this type gauge will drop to zero. With a 90% blockage in my oil screen at the time, the above theory sounds logical.
Yes, the oil pan can be removed with engine in truck and crankshaft bearings are accessible. However, in the next couple of months I will pull the engine and have it rebuilt at local shop. Was quoted $900 to rebuild the 5.8L, last March, when I had a four banger rebuild there for ladyfriends vehicle. Must bring engine and pickup at that price, but shop does a good rebuild. I need a reliable truck; one 2,500 mile round trip and several shorter trips each year, towing a camper. Also have a second vehicle to drive, but love the Bronco!
Believe the oil gauge in my "88 Bronco is an idiot light ... if I remove and "ground" oil switch connector wire, [with key in on position] the gauge will read normal on dash, even when engine is not running. Have read posts which say if oil pressure drops below 7 psi, this type gauge will drop to zero. With a 90% blockage in my oil screen at the time, the above theory sounds logical.
Yes, the oil pan can be removed with engine in truck and crankshaft bearings are accessible. However, in the next couple of months I will pull the engine and have it rebuilt at local shop. Was quoted $900 to rebuild the 5.8L, last March, when I had a four banger rebuild there for ladyfriends vehicle. Must bring engine and pickup at that price, but shop does a good rebuild. I need a reliable truck; one 2,500 mile round trip and several shorter trips each year, towing a camper. Also have a second vehicle to drive, but love the Bronco!
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