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Discussion Starter · #1 · (Edited)
First about the car
2001 mercury sable Duratec engine 130000miles.
Bought this car in 2006 from the original owner with 51000miles on the clock.
The owner provided all maintenance records,the car had been serviced in the dealership only.After buying it I continued to use motorcraft 5W20 until about 85000 miles changing the oil every 5000m.After that I switched to Mobil1 Synthetic 5W30 increasing the oil change interval to 8000m.

At about 95000 replaced leaking oil pan gasket and found a lot of sludge(heavy dark oil) on the bottom of the oil pan took me a while to clean it.

Now about the issue at about 120 000 my wife complained that she gets flickering oil light at hot idle after driving about 20-25 minutes on the interstate.Drove the car couldn't see the light.Changed the oil and the filter -no more complains for the next 3000 before my wife said it is doing it again.Changed the oil again and it was OK for few thousand miles and was told that is doing it again.Finlay i decided to drop the oil pan again and check the oil pump screen.The oil pan was this time very clean the oil pump pick up screen didn't look to bad either except for a few hard pieces of RTV from my previous oil pan gasket change.Took the front valve cover and found out terrible sludge build up -something like 1/4 inch thick sludge covering everything!!! I couldn't believe how that was possible with the regular oil changes.I cleaned the valve cover and reinstalled it.I was hoping that the RTV pieces on the oil pick up screen were the problem.Put new oil and filter and it was OK for about 1500 miles before i was told again that the oil light is flickering again at hot idle.Change the oil again this time I put dino 5w30 drove the car on interstate for about 20 minutes after that did some city driving and at first traffic light the oil light came on, this time it was solid not flickering. Next day did some test city only driving for about 15 minutes the light never came on.
Decided to check the actual oil pressure connected mechanical gauge and found out that the pressure is fluctuating very rapidly 10-15psi.For example at hot idle it fluctuates between 10 and 20 psi and at 1500 rpm 30-45psi.It fluctuates so fast.The spec. for gen4 duratec is minimum 11psi at 1500 rpm .
I don't think that the oil switch is bad.Probably after interstate driving the pressure drops and fluctuates between 5 and 15 psi or something similar.

My questions are what can cause that rapid fluctuation in oil pressure-rod bearings ,oil pump or sludge.
 

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Discussion Starter · #2 ·
I forgot to mention when I cleaned the oil pump pick up screen I didn't replace the o-ring but I do not think leaky o-ring can cause that kind of fluctuation in the oil pressure.
 

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Discussion Starter · #3 ·
I just found that-"The rapidly fluctuating levels must mean the oil quality has been poor enough in the past to obstruct the drain-back passages from the heads to the crankcase."
May be my problem is sludge related.
 

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Your oil change intervals seem fine for the quality of oil used. Does the engine run cold (where does the temp gauge needle sit when fully warmed up)?
 

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Discussion Starter · #5 ·
Your oil change intervals seem fine for the quality of oil used. Does the engine run cold (where does the temp gauge needle sit when fully warmed up)?
I know that my oil change intervals are fine ,i put them just to avoid replies like "you needed to change your oil more often " and "what kind of oil you are using" and so on.I know that this car was well taken care for and that is why i cannot explain to myself the sludge build up.

About running cold,it had never ran cold.The cooling system is in perfect shape.
 

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my 00 duratec did the same thing... at first it was just a flicker then solid towards the end it would stay solid all the way up to about 2k rpm. now my oil pressure sending unit was bad but i replaced it and still got the light i checked with a mechanical gauge and got very similar results as yours. i ended up not being able to figure it out completely i have not torn down the old engine yet to see whats up. though the 04 engine i put in is running great! i decided on a new engine because i plan on keeping the car for a very long time it was cheaper in the long run 1000 for a new engine (20k miles) or who knows how much to fix the one with 120k on it. this spring i am going to tear it down and see what was wrong... i did not have a sludge issue though i had the valve cover off a couple weeks ago
 

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Discussion Starter · #7 ·
I have seen a lot of threads about flickering oil light at idle after highway driving on this forum.But nobody have found the reason for that.Probably there are different reasons.Bearings,Cam sync. for vulcan engines,there was one person who suggested his problem was sludge and he said he fixed it after engine flush. Another person switched to 10W40 and temporarily fixed his oil light problem(that is indicator for bad bearings).I was thinking to do the rod bearings first and see what will happen but the fluctuating oil pressure and the huge amount of sludge under the valve covers changed my mind.
I am going to do engine flush first (gunk in cold engine and idle for 5 min.)I know i hate to use this stuff but i have no choice. If that do not fix the problem I'm switching to 10W40 to find out do i have bearing problem.
Also I'm interested to know is the sludge common problem for high mileage Duratecs.I didn't find anything about that on this forum.
 

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Also I'm interested to know is the sludge common problem for high mileage Duratecs.I didn't find anything about that on this forum.
I've never heard of it. Very, very unusual. Does the car get out on the highway enough? If the motor doesn't have cold spots breaking fown the oil prematurely, then my other guess is too much short-trip driving in between changes. That will break down and acidify oil much faster than cruising mileage.
 

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Discussion Starter · #9 ·
Since I have the car it has been mostly(or at least 60-70%) interstate driving 75+MPH.I don't know about the original owner.He is local older person.The car originally had been bought from the city Lincoln-mercury dealer and serviced there.Knowing that it is possible he had done mostly city driving but an other hand he had done 51000m. for 5 years that is 10000 per year and also getting this kind of sludge for only 51000m. with regular oil changes seems highly unlikely to me.
 

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Discussion Starter · #10 ·
OK I flushed it today with gunk(this thing is probably straight kerosene).Followed the direction on the back of the bottle(cold engine ,pour the bottle and let the engine idle for 5 min.,replace oil and filter)) Well this thing didn't flush anything, just wasted the oil.Probably to make this thing to work you have to drive with it but in that case your engine will be done.
Also did some tests on the mechanical oil pressure gauge.Connected it to my air compressor and verified that the gauge shows steady pressure and it was showing the same pressure as the gauge on the compressor. So that means my car really has fluctuating oil pressure .
After all that did some test driving and after 15-20min. the flickering oil light came back at idle.
Tomorrow morning I am putting 10W40 .
 

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Discussion Starter · #14 ·
I changed to 10W40 and will go to test drive.
After one day driving with 10W40 I didn't get the oil light to come on, so it sounds like bearings.I hope that only the rod bearings are bad not the main ones.

Next step will be to attach the mechanical pressure gauge again and to see is the oil pressure stable or it is still fluctuating (attaching mechanical oil gauge to Duratec is not fun believe me)
 

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After one day driving with 10W40 I didn't get the oil light to come on, so it sounds like bearings.I hope that only the rod bearings are bad not the main ones.

Next step will be to attach the mechanical pressure gauge again and to see is the oil pressure stable or it is still fluctuating (attaching mechanical oil gauge to Duratec is not fun believe me)
Baby it and she'll go for awhile. It's very rare on Duratecs from what I know. It's pretty common on Vulcans, but it's usually caused by a few certain issues.
 

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Discussion Starter · #18 ·
I checked the oil pressure(10W40). It is higher (as expected) compared to 10W30 but it is doing the same thing -fluctuating very rapidly.
I was thinking about replacing the bearings but in my personal experience , worn bearings means low pressure , not fluctuating.
Tried to do some research on internet but couldn't find many similar cases. Actually I found some but the owners couldn't find what was wrong.And I found something very interesting(the topic was for a piston aircraft engine) They were saying that RAPIDLY FLUCTUATING oil pressure is caused by the oil pump sucking air, through worn/broken pickup tube o-ring or through the oil pump casting.

As I said in my previous posts I removed the oil pickup tube to clean it and didn't replace the O-ring ( 3-local dealerships didn't have it in stock ), anyway the old o-ring was looking fine but it is possible that i damage it by over tightening the pickup tube to oil pump bolts.
I do not have to much hopes that my oil problem can be so simple to fix, but it is worth to try.
I already received the new pickup tube(it is coming with new o-ring ) and will replace it on Tuesday.

 

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A sticking oil pressure relief valve will make the pressure fluctuate. Most are just spring loaded plungers controlling bleed off from the pump.
My sister had a Camry 4 cyl. that was sludged up ( she was 2nd owner) and it blew out the front cover gasket by the pressure relief valve. I found this out after disassm. to fix a bad oil leak.
Loose bearings would be a constant pressure loss, IE low oil pressure consistently
 
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