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  #1  
Old 07-16-2013, 07:04 PM
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Join Date: Jan 2013
Posts: 93
W114 oil pressure and A/C

Hi,
I took this video of the car after being driven for an hour and with the a/c on.
As you can see the oil pressure sits at 15 and with the a/c on drops even lower and almost stalls.
I can always increase the idle speed but it doesn't affect the oil pressure (at least not by a lot).

I don't know if you can hear but when I rev the engine you can also hear the knocking which I was told it's crankshaft bearings.
Cold start has full oil pressure to the top and as it gets warmer it just keeps dropping.
My question is:
Can worn crankshaft bearings affect the oil pressure this much and if not what else can be the reason for such a low oil pressure?

Thank you.

M130 with a/c on - YouTube

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  #2  
Old 07-16-2013, 07:39 PM
Pooka
 
Join Date: Sep 2005
Posts: 664
Worn crankshaft bearings are the number one cause of low oil pressure in an engine.

Of course, you can also have: A worn oil pump, a faulty oil pressure relief valve or low oil levels.

One quick and easy way to determine if it is worn bearings is to pour a bottle of Lucas Engine Treatment in and see if your pressure goes up. Make sure you don't exceed the normal level of oil when doing this as this can lead to real oil pressure problems.

Anyway... After you have added this to your oil (or any other brand, I just like the Lucas products) you can watch your oil psi and see if it goes up. If it is worn crank bearings this treatment will increase your oil psi. This will not stop the knocking noise unless it is very slight, so don't depend on this to cure all your problems.

But since the A/C seems to be bogging down the rpm I would suspect that you might have a restriction in your ac system which is causing your ac pressure to be high. Or it could be the clutch is worn to the point that it is dragging.

Try treating the oil and running with the ac off and see what the oil psi does.
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  #3  
Old 07-16-2013, 11:31 PM
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Join Date: Jan 2013
Posts: 93
Thank you.
I will try the engine oil treatmant and advise on the changes.
Oil level is good, so that leaves me with the bearings which are number one suspect due to the knocking sound but not sure how to check if the pump is working properly or if the release valve is working (if that is even possible to check)

As for the a/c the compressor is making funny noises in my opinion and it does look like the clutch is slipping.

I will take a video of the noise and the clutch and post in another thread.
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  #4  
Old 07-17-2013, 08:49 PM
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Join Date: Jan 2013
Posts: 93
Quote:
Originally Posted by Pooka View Post
Worn crankshaft bearings are the number one cause of low oil pressure in an engine.

Of course, you can also have: A worn oil pump, a faulty oil pressure relief valve or low oil levels.

One quick and easy way to determine if it is worn bearings is to pour a bottle of Lucas Engine Treatment in and see if your pressure goes up. Make sure you don't exceed the normal level of oil when doing this as this can lead to real oil pressure problems.

Anyway... After you have added this to your oil (or any other brand, I just like the Lucas products) you can watch your oil psi and see if it goes up. If it is worn crank bearings this treatment will increase your oil psi. This will not stop the knocking noise unless it is very slight, so don't depend on this to cure all your problems.

But since the A/C seems to be bogging down the rpm I would suspect that you might have a restriction in your ac system which is causing your ac pressure to be high. Or it could be the clutch is worn to the point that it is dragging.

Try treating the oil and running with the ac off and see what the oil psi does.
I used Lucas oil treatment and there was no significant oil pressure increase but the knocking was reduced
I used rotella 15w 40
Should I try different oil?
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  #5  
Old 07-17-2013, 10:26 PM
79Mercy's Avatar
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Join Date: Mar 2008
Location: Florida
Posts: 4,131
try valvoline VR1 racing oil 20W-50, has lots of Zinc in the oil to help protect cams. Its a bit thicker than 15W-40

Depending on your climate, you may try the VR1 50WT oil since it appears your engine isnt very tight. However i would not recommend using this thick of an oil in a tight engine.
__________________
1985 300TD Turbo Euro-wagon
1979 280CE 225,200 miles
1985 300D Turbo 264,000 miles
1976 240D 190,000 miles
1979 300TD 220,000

GONE but not forgotten
1976 300D 195,300 miles
1983 300D Turbo 175,000 miles

http://i42.photobucket.com/albums/e3...e485-1-2-1.jpg
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  #6  
Old 07-17-2013, 10:29 PM
79Mercy's Avatar
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Join Date: Mar 2008
Location: Florida
Posts: 4,131
Also, i cannot remember if you model has the electric switchover valve that supply's vacuum to the advance side of the dizzy to advance timing(race engine) when the compressor comes on, but if you do make sure that it is functioning properly. When you switch on the compressor the engine speed should actually increase slightly.

__________________
1985 300TD Turbo Euro-wagon
1979 280CE 225,200 miles
1985 300D Turbo 264,000 miles
1976 240D 190,000 miles
1979 300TD 220,000

GONE but not forgotten
1976 300D 195,300 miles
1983 300D Turbo 175,000 miles

http://i42.photobucket.com/albums/e3...e485-1-2-1.jpg
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