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MGB Oil pressure fluctuating

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PAUL161

PAUL161

Great Pumpkin
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On a run the other day, I noticed if I'm running between 60 & 65 the oil pressure is steady at 65 lbs, when I step on it for a bit to run it up a little, the oil pressure gauge needle fluctuates very rapidly, as soon as I let off it and return to a steady speed, it stops and holds at 65 lbs. Kinda crazy as I've never experienced this before. Any clues?? PJ
 
Interesting.

You might want to find another gauge to compare.
 
PAUL161 said:
On a run the other day, I noticed if I'm running between 60 & 65 the oil pressure is steady at 65 lbs, when I step on it for a bit to run it up a little, the oil pressure gauge needle fluctuates very rapidly, as soon as I let off it and return to a steady speed, it stops and holds at 65 lbs. Kinda crazy as I've never experienced this before. Any clues?? PJ
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Mechanical or electrical guage? How many miles on the engine?
 
Oil pressure relief spring and valve ? I have seen what you are describing before. I would think its just the valve releasing excess pressure then closing , opening etc rapidly. I think everything is fine. Did you change oil recently or have a carb needle and seat stick and dilute the oil?
 
bob67bgt said:
Oil pressure relief spring and valve ? I have seen what you are describing before. I would think its just the valve releasing excess pressure then closing , opening etc rapidly. I think everything is fine. Did you change oil recently or have a carb needle and seat stick and dilute the oil?
Click to expand...

Most likely the relief valve. I've seen the valve seat/mating surface in several instances worn to an ovoid shape. Makes for a less positive seating and a "fluttering" at threshold pressure. On rebuilding I usually hand lap the seat with valve lapping compound and replace the little piston and spring.
 
Brinkerhoff said:
Mechanical or electrical guage? How many miles on the engine?
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Brinkerhoff, Mechanical gauge, 700 miles on totally rebuilt engine!
No miles on oil change. 20/50 oil.

Mickey, being a mechanical gauge, I don't think that's the problem, but possible, funny things do happen.

Bob, I think your right on the valve. Oil changed just before this run. Actually the carbs are a tad lean.

Doc, Very possible the relief valve wasn't changed at rebuild and original parts were put back in. That's the 64 dollar question. I think your right about the relief valve popping off and on, It's the only thing I could think of also. It has never done this before and was quite an attention getter! 65 lbs of pressure is as high as I've ever seen the gauge go when the oil was hot, a couple pounds more when cold. So I'm guessing that the relief pressure is in the 65/66 lb range.

Thanks for all the input guys, very much appreciated. PJ
 
Are you using an oil filter with relief valve too? Can react to the mechanical valve in the oil housing assembly.
 
LarryK said:
Are you using an oil filter with relief valve too? Can react to the mechanical valve in the oil housing assembly.
Click to expand...

You know Larry, you might have a point there! I just changed the oil and filter, but the filter came from NAPPA, where I always get my filters. Oops, I'm wrong, the new filter is a Fram, one I had on the shelf. I don't know if it has a check valve or not. I'm not against pulling the Fram off and replacing it with a NAPPA/Wicks! I've never had problems with them. Soon as I get a chance I'll change it. Thanks for the suggestion. PJ
 
We want to know how this turns out, Paul.
 
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