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Sudden Drop in Oil Pressure

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Sudden Drop in Oil Pressure
#1
zman4011 Avatar
zman4011 Adam Z
San Francisco, CA, USA   USA
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Took the car out for a spin this morning. It was mostly warmed up when I got it on the highway (170ish). Was cruising for about 4 minutes when there was a noticeable drop in power....almost like my foot slipped off the pedal. It hesitated a bit and I backed off the accelerator immediately. I took the next exit (which was my exit anyways) and cruised down the 1/4 mile exit in 4th gear to my destination. The car started back up with no problems 30 minutes later and it drove home with no noticeable difference with the exception of having about 9 psi less of oil pressure than I usually do. Any thoughts?


Don't Have 21st century expectations from a 20th century car

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Re: Sudden Drop in Oil Pressure
#2
Basil Adams Avatar
Basil Adams Platinum Member
About 12 miles from Sears Point, CA, USA   USA
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Adam, It could be a lot of things but a drop in oil pressure and loss of power at the same time indicates the need for a compression test, cooling system pressure test (for head gasket) and maybe a leak down test. Drain the oil and see if there's any metal in it (probably not.) And just for the heck of it, see if you have spark at all 4 plugs. I'd also take the rocker cover off and check valve clearances too. Let me know how I can help. Basil 707.762.0974


Basil C. Adams
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Re: Sudden Drop in Oil Pressure
#3
ghnl Avatar
ghnl Eric Russell
Mebane, NC, USA   USA
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1961 MG MGA "Calvin"
Since we're allowed wild guesses (chanelling Tom Magliozzi's 'unencumbered by the thought process'), might a carb float have stuck, flooded the engine & raw gas diluted the oil?

Certainly the first thing to do is drain the oil and inspect it closely. If it were diluted with gas you should be able to smell that.


Eric Russell ~ Mebane, NC
1961 MGA #61, 1981 Alfa Romeo GTV6, 1984 Alfa Romeo Spider, 1991 Honda ST1100

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Re: Sudden Drop in Oil Pressure
#4
zman4011 Avatar
zman4011 Adam Z
San Francisco, CA, USA   USA
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Drained the oil.....no metal flakes or shimmer. No metal on the magnetic plug either. The oil didn't smell of gas.

Compression test yielded 143, 135, 135, 138 . Valve clearances all checked out. Not sure how to check the coolant system pressure (Autozone has a tester but I doubt it will fit this radiator).

I'll test the gauge itself tomorrow. Should I pull the oil pressure relief valve?

Secondary Question:
This is the first compression test I've done since rebuilding the engine 3000 miles ago. After the intial break in, the compression readings were 148, 145, 142, 142 . I figured you'd lose some compression as it wore in. Do the new readings seem right?


Don't Have 21st century expectations from a 20th century car

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Re: Sudden Drop in Oil Pressure
#5
ghnl Avatar
ghnl Eric Russell
Mebane, NC, USA   USA
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1961 MG MGA "Calvin"
Compression test readings will vary depending on things such as battery charge, engine temp, throttle opening, valve clearance, gauge differences, etc. Most important is consistency between cylinders (trying to limit all the other possible variables).

I had an oil pressure relief spring go bad rather suddenly. If you don't find any other 'smoking gun' that'd be the next thing to check.


Eric Russell ~ Mebane, NC
1961 MGA #61, 1981 Alfa Romeo GTV6, 1984 Alfa Romeo Spider, 1991 Honda ST1100

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Re: Sudden Drop in Oil Pressure
#6
KHP Avatar
KHP Karl Henning
IL, Burr Ridge, USA   USA
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1959 MG MGA 1500
Adam
I had a valve that would ocassionaly stick open and caused a power loss. This was after a rebuid on the head. The guides were left too tight. It had done it about six times over a couple of weeks. I found it by pulling the valve cover imediately when it happened. After it cooled a little it would be fine. That would not explain a loss of oil pressure though.

Karl

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Re: Sudden Drop in Oil Pressure
#7
bobs77vet Avatar
bobs77vet bob K.
northern Va, VA, USA   USA
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why don't we think this is a fuel related problem?......that's my first guess something blocking the flow of fuel ......fuel pump, filter, stuck float,

and the oil pressure drops as the RPMs stutter

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Re: Sudden Drop in Oil Pressure
#8
ghnl Avatar
ghnl Eric Russell
Mebane, NC, USA   USA
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1961 MG MGA "Calvin"
In reply to # 2859781 by bobs77vet why don't we think this is a fuel related problem?

and the oil pressure drops as the RPMs stutter

Except he said it then drove OK except for the lower then usual oil pressure.

In reply to # 2857363 by zman4011 The car started back up with no problems 30 minutes later and it drove home with no noticeable difference with the exception of having about 9 psi less of oil pressure than I usually do.


Eric Russell ~ Mebane, NC
1961 MGA #61, 1981 Alfa Romeo GTV6, 1984 Alfa Romeo Spider, 1991 Honda ST1100

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