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Old 08-08-2015, 05:17 PM   #1
driveitforlife
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1993 SL1
Default Oil light + knocking. Oil level full, new sending unit

'93 SL1, 275K miles, problem started July 2015

Light came on (initially only at stoplights). I changed oil ( it was several months overdue) and oil (Fram PH 3614 - same as always) but light kept coming on. I replaced sending unit/oil pressure switch. Light kept coming on. Then engine started knocking. I took the car off the road and researched the problem. I gather these are the possible causes of what I'm pretty sure is an low oil pressure problem:

1.) "There is a check valve in the timing cover. If you have a manual oil pressure gauge this could be useful. Disable ignition loosen filter spin engine and see if oil leaks from filter, if no leak then the check valve in the timing cover is bad"

2.) Bad oil pickup tube - seems plausible because there is a big dent in the pan from hitting something - perhaps it jarred the pickup tube? But dropping the pan entails (among other things) unbolting the exhaust from the manifold (risking breaking the old bolts).

3.)Bad oil pump - I bought a repair kit but that looks like a major job, too.

Am I missing anything? Should I try test #1 first because it's easiest?

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Old 08-08-2015, 05:22 PM   #2
robb_sc2
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1999 SC2
Default Re: Oil light + knocking. Oil level full, new sending unit

Quote:
Originally Posted by driveitforlife View Post
'93 SL1, 275K miles, problem started July 2015

Light came on (initially only at stoplights). I changed oil ( it was several months overdue) and oil (Fram PH 3614 - same as always) but light kept coming on. I replaced sending unit/oil pressure switch. Light kept coming on. Then engine started knocking. I took the car off the road and researched the problem. I gather these are the possible causes of what I'm pretty sure is an low oil pressure problem:

1.) "There is a check valve in the timing cover. If you have a manual oil pressure gauge this could be useful. Disable ignition loosen filter spin engine and see if oil leaks from filter, if no leak then the check valve in the timing cover is bad"

2.) Bad oil pickup tube - seems plausible because there is a big dent in the pan from hitting something - perhaps it jarred the pickup tube? But dropping the pan entails (among other things) unbolting the exhaust from the manifold (risking breaking the old bolts).

3.)Bad oil pump - I bought a repair kit but that looks like a major job, too.

Am I missing anything? Should I try test #1 first because it's easiest?
wouldn't problem #2 lead to problem #1 because if no oil is picked up, doesn't matter what the check valve is doing, and there won't be oil in the filter. I could be wrong, too just what comes to mind.

When I was replacing my oil pan, I was surprised how low the pickup tube comes down, but I don't recall the exact location of the pickup, so no idea if the dent in your pan is affecting that.

...
Gold 1999 SC2 ~385k Kms

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Old 08-08-2015, 05:41 PM   #3
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Default Re: Oil light + knocking. Oil level full, new sending unit

Instead of removing the timing cover, did you try connecting an oil pressure gauge to the oil fitting where you replaced the oil sending unit? This is the only place to connect an opg (adapters needed) and observe actual pressures. By the time you remove the timing cover, you might as well replace the oil pump gear as the one way check valve is mechanically spring loaded and not likely to fail for the life of engines. The only way this check valve can fail is if the oil pick up tube is running without a screen and solid crap is sucked up into the oil system where it may cause oil pump damage. If the check valve opens from excessive pressure or crap lodges into the opening preventing the valve from closing, losing oil pressure may be the least of your problems with crap being pumped into (and lodging) in every oil passage................ The reason to try connecting an opg before an over active imagination becomes true.

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Old 08-08-2015, 10:36 PM   #4
driveitforlife
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Default Re: Oil light + knocking. Oil level full, new sending unit

Thank you both for your responses. Fdryer, I considered getting an oil pressure gauge to get a reading, but I figured that the knocking sound and the illumination of the low oil pressure warning light even after I installed a new oil pressure sending unit gave me sufficient confirmation that no oil was reaching the engine - therefore indicating low or no oil pressure.
With the knocking, I'm a little scared I'll damage the engine if I run it now to try to get an oil pressure reading on a gauge. Any further thoughts on this? Thanks.

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Old 08-08-2015, 10:53 PM   #5
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2003 L-Series 3.0L Sedan
Default Re: Oil light + knocking. Oil level full, new sending unit

Why guess since the engine's already knocking? Connecting an opg takes a few minutes unless adapters are difficult to find. Removing all doubt is better than going on hunches yet to be proven despite evidence supporting your hunches. Some more minutes of idling to assess actual oil pressure will tell you whether its a failed oil pump, oil pressure check valve, crap blocking lifters from filling with oil or anything else that comes to mind. Speculating is great for the world's armchair quarterbacks not paid to be one. The rest of us not familiar with your car can guess too. Me, I use all tools and equipment needed to assess a problem to come to a conclusion, not guess. Its a little more time consuming testing and diagnosing but since engines are mechanical by design and controlled/managed by the EFI system, mechanical problems like suspected lost oil pressure are simply tested the old school way - connecting an opg to confirm or dispel oil pressure. Its really your choice to decide which method to diagnose a possible low oil pressure problem. At 275k miles, its already a foregone conclusion that this engine is well broken in and either nearing a point of rebuilding or diagnosing specific problems without having to take apart the engine. I suggest the easiest way without taking apart anything more than removing the oil sending unit.

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Old 08-09-2015, 05:00 AM   #6
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Default Re: Oil light + knocking. Oil level full, new sending unit

Quote:
Originally Posted by driveitforlife View Post
Thank you both for your responses. Fdryer, I considered getting an oil pressure gauge to get a reading, but I figured that the knocking sound and the illumination of the low oil pressure warning light even after I installed a new oil pressure sending unit gave me sufficient confirmation that no oil was reaching the engine - therefore indicating low or no oil pressure.
With the knocking, I'm a little scared I'll damage the engine if I run it now to try to get an oil pressure reading on a gauge. Any further thoughts on this? Thanks.
You've already damaged the engine since it's knocking. In the future, when confronted by an oil pressure light blinking, it would be advisable to immediately pop out the pressure switch and use an actual gauge to get the oil pressure at idle to confirm/deny that you've got poor oil pressure. Then and only then do you start throwing parts at the problem.

...
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